Can the MAF fail only when hot? (SL500)

[powerofgreen]

(Admin edit: Copied post below from previous thread at this link.)

I have a strange behaviour from my [M119.972 / SL500] engine, when it's hot the idle is veeery rough and poor; the engine shakes badly and the car takes off without power, but no hesitation. The Only thing I noticed in this case is that when I start the engine it starts right up as if the starter didn't spin at all! But the idle is so poor you almost don't hear the engine running!

Long story short, after checking the fuel system and replacing the fuel pumps the only thing that seems to be the culprit is the MAF. Because when I disconnect it and drive the car for almost 2 hours, nothing wrong with the idle... Unfortunately without codes I cannot confirm.

So my question is: can a MAF go wrong ONLY when hot??

Thanks in advance ... I'm really lost!

 

[gsxr]

Re: Can the MAF fail only when hot?

I suppose the MAF could act up when hot, but you could confirm this by viewing live data from the SDS and compare cold readings vs hot. The fact that hot idle is smooth with the MAF disconnected does seem to point towards the MAF, but doesn't automatically condemn it. You also may not find any codes for the MAF, as codes may only be triggered if there is a wiring short circuit or open circuit. (?)

That said, most misfiring issues tend to be ignition related. How old are all the secondary ignition components (caps, rotors, insulators, wires, non-resistor plugs, coils) and when was the last time you checked them?

 

[powerofgreen]

Re: Can the MAF fail only when hot?

I suppose the MAF could act up when hot, but you could confirm this by viewing live data from the SDS and compare cold readings vs hot. The fact that hot idle is smooth with the MAF disconnected does seem to point towards the MAF, but doesn't automatically condemn it. You also may not find any codes for the MAF, as codes may only be triggered if there is a wiring short circuit or open circuit. (?)

That said, most misfiring issues tend to be ignition related. How old are all the secondary ignition components (caps, rotors, insulators, wires, non-resistor plugs, coils) and when was the last time you checked them?

Dave, I'm sorry I didn't notice the post has been moved!
Well, to answer your questions: I assure you the ignition system is in tip top condition!
From the battery to the plugs!
Small inventory:
Brand new Bosch battery S5 013 (830A), installed 16 months ago and tested 12.85 V .
Good used and tested Bosch alternator 150A.
Brand new Bosch CPS.
Good used and tested Siemens EZL.
Brand new Bosch coils(×2)
Brand new Bremi plug wires set.
Brand new Bremi distributor caps and rotors; checked and still ok: no moisture at all, just few condensation but absolutely normal.
>>> all above items are less than 2 years old and ok.
Brand new original MB plugs(installed 3000 km earlier).
The current MAF I bought last year is a Bosch reman unit not used: sealed box.
Now, since yesterday I was driving with the MAF disconnected, and the idle is veery steady: no hiccup or shaking whatsoever!
I also noticed that even with the AC on and under load, the engine temp is absolutely normal; whereas in the last 3 months it was climbing fast around 95/100 under load! Also the exhaust was slightly more hot than before...
I wasn't suspecting the MAF because it was brand new; but who knows? May be the reman units don't last as long as the brand new unused ones!! I think I did around 30000 km with this MAF, and to tell you, I will never buy reman units anymore!
Only original units...

To repeat: all ignition components are ok. I even swapped another EZL to see if there is any change, but no change occured: the engine started and ran exactly as before.
All other parts were checked twice and everything looks ok.
Cam sensor is also fine.
No vacuum leaks: the intake was removed; cleaned thoroughly; re-installed with new Elring gaskets and mid intake ring seals. EGR checked meanwhile and cleaned.
All rubber elbows refreshed as well as breather hoses. Original parts installed when available. Rubber boot between MAF and ETA replaced with an original one. ETA replaced with used but good working unit manufactured in 1997(wires checked: no junk). ETA gasket to intake replaced with original one also.
To tell you...
Only items I still didn't replaced are O2 sensors, but will do in short time...
But I doubt they are the culprit.
To answer your second question regarding the codes, well: no codes! One regarding the previous MAF was "stored code". We erased it.
What do you think guys??

 

[powerofgreen]

Re: Can the MAF fail only when hot?

...
Still driving with MAF disconnected...
Apart from a small lack of power when take off and at WOT, everything is fine: start up fine; perfect idle; engine temp within specs...
Dave, where are you??

 

[195910]

Re: Can the MAF fail only when hot?

Engine Wiring harness?
Check the separate ground wire for the MAF.

 

[powerofgreen]

Re: Can the MAF fail only when hot?

Engine Wiring harness?
Check the separate ground wire for the MAF.

The wiring harness has been already replaced by the previous owner and looks very clean.
The ground is ok..

 

[powerofgreen]

Re: Can the MAF fail only when hot?

Update...
I'm driving for about an hour with the MAF still unplugged. All seems fine... until I stopped, shut down the engine 15 min and restarted, and surprise: the same poor idle began!!!
Man... I'm going crazy right now!
What the hell is going on with this engine???
It goes like this: you turn the ignition on and it starts right away! The starter doesn't even spin! Then the rpm goes straight to 600/700 and back to 250.. then the engine starts to shake so badly that the whole car starts bouncing from front to tale! You feel it in the exhaust also... the rpm is now at 250 with small fluctuations.
It seems struggling to stay on, but it's not like fuel starvation. When you press on the gas pedal you feel the power is there, but the idle is so poor and rough you don't know why it is happening like that!!
It's not normal at all. When you drive after a while you don't feel anything unusual but when you stop and restart; the same scenario once again!
If it was stalling I would expect the CPS to be faulty; but it doesn't.
The fuel is ok.
What to suspect??
The MAF again?? if ever the E gas module now is applying the last parameters as when the MAF was plugged in???
Please guys help me on this one...

 

[sheward]

Re: M119.975 oil pan gasket change.

I have not read the entire thread but noticed you did not mention the insulators behind the rotors. Have they been checked/replaced?

drew

 

[gsxr]

Re: M119.975 oil pan gasket change.

I have not read the entire thread but noticed you did not mention the insulators behind the rotors. Have they been checked/replaced?

I'm just catching up on this thread, and was thinking the same thing as Drew. More specifically, the insulators behind the rotors have to be REMOVED, and the back side inspected. If these haven't been removed yet, that is top of the list... what you describe sounds very much like the insulator issue. Again, you can't inspect the front side only, the rotor and rotor bracket must be removed to get the insulator out.

 

[powerofgreen]

Re: Can the MAF fail only when hot?

Alright. I will remove them when the engine is cold. Now I'm still on the road back home...
I made some halts on the freeway and when restarting, the same thing happened again each time(this time I re-connected the MAF). So you start the engine; whether it starts right away and the idle is poor/whether it cranks a few times and starts veeery rough with the same poor and shaking idle!
The last time was about 10 min ago and it started after cranking 6/7 times and I noticed that the battery warning lamp blinked shortly after starting the engine...
The crazy thing is that when driving there is no heditation or misfire...
I will inspect the insulators and get back to you soon...
Thannnnnxxxxx

 

[powerofgreen]

Re: Can the MAF fail only when hot?

I forgot to say that I had issues with the coolant temp sensor 3 months ago(I mean the one with only 1 pin; not the 4 pin sensor; There are 3 sensors on the intake: the 1 pin/4pin/and a small sensor for the temp gauge); and I replaced it but with a used one.. I thought it was ok. Well I don't know if it is working perfectly but who knows indeed??
Could a "weak" temp sensor create troubles like I'm experiencing right now??

 

[gsxr]

Re: Can the MAF fail only when hot?

1-pin sensor = dash temp gauge
2-pin sensor = HVAC system
4-pin sensor = engine computers (fuel + ignition)
Each of the 3 are completely separate and have no interaction with each other.

If the 4-pin sensor is bad, it will normally trigger an error code on the LH or EZL for "implausible signal". Alternately you view the live data on a digital scanner which shows the engine temp from the 4-pin sensor. And, you can use an ohm meter (a good one, not Harbor Freight freebie) to measure resistance at the 4-pin sensor and compare to the FSM specs. It's extremely unlikely the temp sensor would cause significant misfiring as you describe though.

 

[powerofgreen]

Re: Can the MAF fail only when hot?

1-pin sensor = dash temp gauge

Well, I'm glad to know that it's not the culprit(one doubt cleared!)
I'm home right now and before that I made a stop at a gas station and was having a coffee with a friend of mine; and I let the engine running; on purpose, for about 15 min(with AC on). After that I drove home with no problem whatsoever! The idle was again fine and the power good enough..!
As if nothing happened.....

 

[gerryvz]

Re: M119.975 oil pan gasket change.

Definitely sounds ignition to me.

 

[powerofgreen]

Re: Can the MAF fail only when hot?

Well, back again..
I removed the caps&rotors this morning and found a deep crack in the left rotor! Don't know how the indy didn't notice it before...
The cap itself seems on its way out...
The right side cap is also bad but not too much. Its rotor had a very small crack too...
The rotor arms look fine..
Now, the famous insulators....
Well, honnestly they are absolutely fine!
No crack, no condenation, no oil, no moisture...
I just cleaned them with contact cleaner and they look almost new! I have already replaced the right side insulator 2 year ago(the same time I have replaced the current caps & rotors) because I saw some black Spots on the front side of the old orange insulator. I replaced it with a black Beru original one.
The cam seals are fine since I've replaced them too; 2 years ago...
So, I re-installed the insulators and the rotor arms after wiping everything off.

I replaced both caps&rotors with a used but very clean set(momentary) I have. And then started the car to see if there were any improvement...
Indeed, the car started a little bit better than yesterday, and drove fine.
30 min later I made a stop at a supermarket and re-started again 30 min later... surprise! It started rough again!
Not as bad as yesterday, but the idle dropped a little bit and the power seemed down!
I stepped on the gas pedal and then took off.
Then I stopped again 15 min later and let the car idle for 5 min. Seems the idle is a little poor but the car isn't shaking as before...
I shut down the engine and restarted a minute later.. it starts fine but again the idle seems a little bit poor; as if the power is dropping down progressively!
I don't know how to explain it other than that...
It seems fine when it starts but 5 seconds later it drops a little bit and the rpm stays at 250...
I know the caps aren't brand new but believe me they are very clean... I will go shopping for a new set anyway; but now I don't think they are the main cause of the trouble...

 

[gsxr]

Re: Can the MAF fail only when hot?

On TFTSNBN (The Forum That Shall Not Be Named), there was a long thread where someone was chasing an ignition misfire issue and replacing almost every possibly part... and had swapped in used caps/rotors, which did not change the problem. Long story short, he eventually caved in and bought new caps/rotors, and the problem was solved. If it were my car, I'd try that next. Bosch, Beru, or OE caps; Beru or OE rotors. I'm not crazy about Bremi as they were never OEM for any M119 ignition components.

If you still have issues with new caps/rotors, I'd check resistance on all 10 of the plug wires. What do the plugs look like, btw? Do all 8 look similar, or are 4 different?

Last item is that rebuilt MAF you installed, but you can't test that without a digital scanner to view airflow readings, as mentioned back in post #2.

 

[powerofgreen]

Re: Can the MAF fail only when hot?

I have the intention to replace the caps and rotors with a new set; but I couldn't find anything else but this Bremi brand...
Even the dealer doesn't have them in stock...
Talking about the plugs; I had an original set F8dc4 that I replaced a month ago with another new original set that was made by Beru(non resistor plugs); even though the previous plugs still looked ok.
I'm tempted to say it's may be the coils(replaced 2 years ago when I replaced my old EZL). Not that the original coils were dead but as everyone is advising to renew the coils once the EZL has been replaced; well, that's what I did...
Btw, I took a look at the actual Bosch coils, it seems I was given the same pn for the right and left one... I say this because the original coils have different pn on them for right and left side...
Could the drop in power be caused by one or both of them anyway?

 

[powerofgreen]

Re: Can the MAF fail only when hot?

Oh and to clarify about the previous set of plugs I replaced: they were normal: no oil no burn marks on them; nothing weird. But I went ahead and replaced them anyway...

 

[gsxr]

Re: Can the MAF fail only when hot?

Where are you located? Your profile doesn't say. Last I checked there was no issue with availability of caps/rotors for OE, Bosch, or Beru.

The difference between left / right Bosch coils is orientation of the terminals vs the mounting, they are functionally identical. If you were able to install them without issue, they should be working fine, assuming they were genuine Bosch (photos here).

Hang on to the old F8DC4 OE plugs if they had low miles, they would be fine to re-use, and are NLA now (replaced by the Beru version, which are also fine).

 

[powerofgreen]

Re: Can the MAF fail only when hot?

I'm in Muscat(Oman). 4 years almost...
Many parts shops have MB parts; but for new models specifically.
Old models, you have to search more deeply!
The dealers too: mostly new models.
Let's say 80% of what I need is available. Now, for the brands, no choice; you take what's available; especially if you are in hurry...for some specific parts I go to the dealer and I have between 35 to 45% of discount most of the time and it's nice!
Most of the time I find Bosch parts in the aftermarket. Sadly, the caps and rotors: only Bremi!
That leaves no choice to me...
The coils are genuine Bosch, no doubt...
I don't know their life expectancy btw...

 

[gsxr]

Coils should last a couple of decades, same as the originals.

If you can't get quality parts locally, buy from a different country and have them shipped in. The OE/dealer parts are available but your dealer probably doesn't stock them, so they would have to order them. The dealer caps are very pricey though.

https://partssearch.mercedes-benz-classic.com/parts/A1191580102?tt=notDefined

https://partssearch.mercedes-benz-classic.com/parts/A1191580231?tt=notDefined

You should be able to obtain the Bosch (OEM) caps, and Beru/Doduco (OEM) rotors, from Europe/UK sources at reasonable prices.

 

[powerofgreen]

Yes, for sure they will be expensive OE!
I'm out right now and while at a traffic light and at "N", the idle was fine and steady with AC on; and suddenly I noticed a very quick mis and strong drop in the idle; as if the engine would shut down by itself, and straight after that it returned to its normal rpm(500)! It was Very harsh! And it did 3 times while I was waiting for the lights to turn green...
It took a secon each time...
It didn't do that with the previous caps and rotors..
I guess since they are old, each one has its pattern when failing...

 

[powerofgreen]

Dave, I will anyway buy a set of Bremi caps and rotors; I mean for the time being, just to see if changes occur at idle. And I will manage to order a correct set of Bosch/beru caps and rotors. These will take at least 2 months to reach my place...
Again I was driving an hour earlier and after stopping at a grocery and restarting 20 min later, the drop in idle/power reappeared! Not as much as before but noticeable enough especially when I put in reverse...
I had a lot of issues with this engine in the last 3 years, and I sorted a lot of them; including idle vibrations and shaking at idle; but this kind of persistent rough idle I didn't see before!!

 

[powerofgreen]

Re: Can the MAF fail only when hot?

On TFTSNBN (The Forum That Shall Not Be Named), there was a long thread where someone was chasing an ignition misfire issue and replacing almost every possibly part... and had swapped in used caps/rotors, which did not change the problem. Long story short, he eventually caved in and bought new caps/rotors, and the problem was solved. If it were my car, I'd try that next. Bosch, Beru, or OE caps; Beru or OE rotors. I'm not crazy about Bremi as they were never OEM for any M119 ignition components.

If you still have issues with new caps/rotors, I'd check resistance on all 10 of the plug wires. What do the plugs look like, btw? Do all 8 look similar, or are 4 different?

Last item is that rebuilt MAF you installed, but you can't test that without a digital scanner to view airflow readings, as mentioned back in post #2.

Sorry Dave; I forgot to answer your question regarding the plug wires... In fact they are the same; full set replaced about 2 years ago with a brand new Bremi set as well.
I changed the wires because the original Bosch set I had were on its way out and there were severe hesitations upon acceleration... So my indy suggested to replace the old wires. Of course the only option I had was this Bremi brand again..

 

[powerofgreen]

Guys... a very very important question here, and I hope to have a quick and conclusive answer...
I sometimes have an intermittent issue with the windshield wiper+headlight flasher(they work from time to time and mostly don't); also since last week the electric windows started to do the same: once every 2 to 3 days they don't respond to their switches!
I went to a car electrician who works on R129 and after some check up he said that it must be the ignition switch that's on its way out...
So I'm right now wondering if ever this ignition switch could in fact be the source of the engine loss of power I'm experiencing intermittently since almost 3 months???
It's the switch which delivers the voltage to the computers(EZL as well) right??
So I'm wondering if it could be the main culprit; even though caps and rotors play a role in the bad idle..??
Please guys, answer me......

 

[gsxr]

I can't give you a definite answer to the question, in if the ignition switch is suspect, it's relatively inexpensive and not terribly difficult to replace on a 124 (not sure about a 129). Wouldn't hurt to replace and see what happens.

Just don't get your hopes up that it will magically cure all your problems.

 

[powerofgreen]

Guys, I'm really unlucky...
I replaced both caps and rotors today and the idle seemed to improve consistently. In fact it was steady the first time I started the engine...
But, the second time I started it I felt some strong shaking the moment I turned it on...
I drove the car for about an hour(praying that It was just an illusion) at different loads and when coming back home, I slowed down a bit at a roundabout and I directly accelerated after that... and guess what happened??? Backfiring and strong hesitations from the engine!!! I must say that these are the same symptoms as a bad coil, but how in the world did it happen Only today; and just after replacing the caps and rotors????? If the main issue was coming from my coils; why did they wait until now(after all the searching/stress/tension) to show up??
I can't think of something else other than the coils, since everything has been checked/replaced!
Gosh! These coils are genuine Bosch; replaced 2 years ago(32000 miles)!
As well as the fuel pumps(again replaced 2 weeks ago)...

 

[powerofgreen]

If someone is interested in my story, I replaced the coils yesterday(I didn't buy new ones because I'm deeply upset about these 2 Bosch coils purshased 2 years ago!) So I just put back the old original coils I had on the car from the beginning.
I noticed a normal start up, more power at acceleration and slightly better shifting. Still didn't take the car on a long distance but I feel it was really a bad coils situation.
Btw, one of the Bosch coils I removed(the one attached to the fender) looked worse than the other one. The copper inner part of the nipple where the distributor cap wire connects to the coil looked like covered with a hardened gel(looked like wax).
I don't know what it is exactly; but that was the feeling I had when I first noticed it... Definitely not normal.
Also it was slightly less hot than the one closer to the engine(don't know if it's due to the fact that it's far from the engine heat).
The only thing that's worse with these old original coils is that the idle isn't really steady now(very small fluctuations at the rpm).
Is it due to they are old(24 years)??
Or is it related to the MAF itself?
Strange that before yesterday it was slightly better...
Will try to take the car on a long trip this evening and see what happens next...
Will keep you updated...
Thanks&regards.

 

[195910]

Its rather upsetting that its not getting resolved. The MAF and coils on the M119 LH are not common fault parts, I would still look at wiring if everything else seems good.

I will do a video on the harnesses soon.

 

[powerofgreen]

Yes it's upsetting...
I must say that even when I bought the car it had that habit of very subtle misfire at idle.. like a small shake from 3 to 4 seconds. Not that annoying; but weird.
I admit that the engine is running beautifully and seems to gain more power each time I update/replace any critical part like the fuel pumps or the MAF, but looks like this bad idle doesn't want to get resolved!
Finger crossed for the coils...
I will drive the car for as long as I can and at different loads and pray that the current issue gets resolved...
If yes, later on I will buy a set of new coils and see if it definetly cures the idle shake.
It's really strange that with these faulty Bosch coils I get a good idle with cold engine but bad idle/bad behaviour when hot. Whereas with the good old ones I get a bad idle but good running engine!
Regarding the wiring, they were checked and re-checked many many times and they are ok: non desintegration whatsoever.
Thanks guys...
I really appreciate the help...

 

[gsxr]

I must say that even when I bought the car it had that habit of very subtle misfire at idle.. like a small shake from 3 to 4 seconds. Not that annoying; but weird.

Are your OE spark plugs gapped to 1.0-1.1mm? This has been discussed elsewhere on the forum, the larger gap can help with the hot idle "hiccup" you describe.

It's really strange that with these faulty Bosch coils I get a good idle with cold engine but bad idle/bad behaviour when hot. Whereas with the good old ones I get a bad idle but good running engine!

Can you post a photo of the new/recent coils? Are you positive they are genuine Bosch, and not counterfeit Borsch? 195910 is right, MAF's and coils are not common failures, even at well beyond 200kmi / 300kkm.

 

[Klink]

Forgive me, I have not read this entire thread, but whenever a discussion of idle behavior comes up, two things immediately spring to mind: the spark plug gap as Gixxer just mentioned, and motor mounts. Collapsed, leaked out, and internally broken motor mounts remain very under-diagnosed conditions on these vehicles despite somehow that “everybody knows about them” If you don’t know their history, see if you can find the date code on them. Search the motor mounts topics on this forum and see what you can find out.

 

[powerofgreen]

I don't know about the gap on the plugs. But we didn't touch them; they were fitted in the holes straight after purchasing them. I've always bought OE non-resistor spark plugs. 2 times in the past 3 years: F8DC4.
The last time they were also OE but Beru.
I'm 100% sure the coils are genuine Bosch. One can tell from the quality/look/packaging/price. I will post pictures of them in about 2 hours.
I don't believe how they failed that fast!
I made around 350000 miles with them installed on my car, no more... could it be the excessive heat that killed one or both of them??
Afaik ignition coils last way longer than that... If it wasn't because of that EZL I replaced, I wouldn't have replace the original coils.
Are the coils known to influence the idle when they become old? I mean do they create idle fluctuations?
I don't want to buy new coils if the original ones I have are still good. Believe me I paid too much for this engine; almost double the cost of a used good one!

 

[gsxr]

Oh, I forgot to mention, the gel/wax you saw was almost certainly dielectric grease. However... I'm not sure it should be used for the coil high-voltage connection. That alone could be some of the problem. Klink could probably elaborate.

 

[powerofgreen]

here are the pics...
Enjoy...

https://ibb.co/ktgUbK

https://ibb.co/nuS2wK

https://ibb.co/fDg1qe

https://ibb.co/kSyxVe

https://ibb.co/kwL0iz

https://ibb.co/m3wsVe

https://ibb.co/fhzPbK

https://ibb.co/d9xSwK

 

[powerofgreen]

I'm sorry also dear Klink. Because only now I noticed your comment...
Regarding the plugs gap, I sincerly don't have any idea. As I mentionned earlier I replaced the previous set of plugs about a month ago and they were OE Beru made non-resistor plugs. My indy istalled them right away without any modifications whatsoever.

Regarding the engine mounts, well, you raised an interesting point... To tell you, I've replaced them as well, 2 years ago or so, and I swear the moment I started the car just after my indy finished the job, I felt a similar kind of vibrations coming from the engine! More like bouncing... And I immediately asked him why is it like that?? He told it's normal...
But the car didn't behave like this before that. Right after purchasing my SL, I have already changed the engine+tranny mounts because they were completely collapsed! And the parts shop saleman gave me "Trucktek". He told it's a well known German brand and I don't have to worry about the quality.. Guess what?? about 2 weeks later I started hearing loud bangs from what seemed to me the rear left wheel area... Every time I take off, if I accelerate a little bit harder I feel the shock and hear the bang!!!
Nobody could figure out what was the cause of that, until one day(1 year and a half later!) I saw a bunch of oil under the engine, and I took the car to my indy who directly put it on a jack and stated that the engine mounts were shot!
I went to the same parts shop and asked him for the best mounts he had, and he gave me the current mounts I have now on my car: Boge-Lemforder.
Of course, the shock and loud bang at take off completely vanished, but instead I have this vibration/shaking/bouncing at idle...
I forgot about it until you mentionned it in your reply!
Could it be the source of the trouble at idle I'm having right now?? Before installing these Boge mounts I didn't have this kind of weird shaking... that's true!
If yes, could the salesman have given me a worn out mounts?? Or is it the design of the Boge-Lemforder mounts(OEM supplier btw)?!!

thnxxxxx

 

[powerofgreen]

Update!

I took the car on the highway and drove it slightly agressively.
It has good power btw...
Back to the city, and after a small stop... Bad surprise AGAIN!
Jerking; loss of power; hesitations!!!
the same as yesterday but slightly less.
I can't describe at what point I'm upset... really!
All these efforts, for nothing...
What to expect?? Again the coils???
It's typically a situation of bad coils, but now that I'm thinking this jerking and these hesitations occured right after I installed these new caps and rotors...
Could it be the new caps and rotors??
Guys help... I'm out of my mind!!!

 

[gsxr]

I think at this point it will be very difficult to diagnose without a digital scanner, and/or oscilloscope, to see what's going on with the secondary ignition system. It's also possible that one or more of the new items installed are defective, which makes troubleshooting even harder, as you normally assume new parts are "good"...

 

[powerofgreen]

I think at this point it will be very difficult to diagnose without a digital scanner, and/or oscilloscope, to see what's going on with the secondary ignition system. It's also possible that one or more of the new items installed are defective, which makes troubleshooting even harder, as you normally assume new parts are "good"...

The only thing I can do right now; by myself, is to remove the HT leads and inspect them carefully for any sign of deterioration... It crossed my mind last night.
I've had a similar scenario 2 years ago just before buying the new set of plug wires. The car acted up almost the same way.
I removed the HT leads and found out the inside almost black of dirt! They were so old and rusty!
I directly sprayed some good CRC contact cleaner and the problem vanished straight away after that!
I went ahead and ordered a new set of wires; and as I said earlier in this thread, I couldn't find something better than the Bremi set I have right now on my engine...
The previous wires were all original red Bosch.
I hope it's a similar situation...
Right now I'm out of the city so no known good merc indy to go to!
Man, I keep on thinking and thinking about it.. what else is left??
From A to Z everything was replaced:
Battery
Alternator
EZL
coils
Wires
Caps
Rotors
Plugs
Fuel pumps
Fuel filter
Fpr
Injectors

I saw an improvement when I replaced the pumps: less noise; more power.
Also when I replaced the coils: more power.
Caps&rotors: better idle.
But this hesitation and jerking started right after replacing the caps and rotors...
I didn't do anything wrong while performing the job. I paid special attention when plugging in the wires; so no confusion or issue at the timing...
I hope I could find someone with an oscilloscope, but until now I didn't see any...
Any info would be greatly appreciated...

 

[powerofgreen]

Guys, I checked the HT leads and they are fine.
I re-checked the caps and rotors and the only thing I noticed is that one of the caps has the orange plastic plate not really sticking to the black surrounding. Actually you can push on the orange plate(the centre plate where the 5 pins are seated) and it will move out from the black surrounding disc that attaches the whole cap to the cam solenoid... I don't know if it's normal but it's the first time I see a cap like this...
After re-fitting everything back into place and restarting the engine I was again shocked! The idle is again too rough and the engine struggling to stay alive!
I drove a bit, but this time it was like it was firing 3 or 4 cylinders only... I accelerate and the car barely moves... too much hesitations; no power; backfiring; cutting out...
I don't know what to do...

 

[gsxr]

The caps are a 2-piece design, with a black plastic outer cap that sits over the main orange section with the brass contacts. This is normal for Bremi and Bosch caps. I believe the Bremi setup are "loose" so the black section will come off the orange section easily, while the Bosch are more tightly attached to each other.

I can't help with the misfiring though. If your car were in my shop, first thing I'd do is connect the SDS and view ignition voltages. Misfires generally appear as spikes in the voltage displayed in the live data; and this would indicate which cylinder(s) are causing the problem. USUALLY, it ends up being all 4 cylinders from one cap or the other. This lets you focus on just one cap / coil. Given your expenditure for parts, it may be worth the ~$500 USD investment in a SDS C3 system (search the forum for details).

 

[powerofgreen]

Thank you very much for all the help dear Dave!
I really appreciate...
Coming to your point, I've already been to 3 electricians to scan for codes, but 2 of them didn't have the year/model of my SL on their software. The 3rd one couldn't perform any scan because his scan tool was under maintenance...
I will do 2 more things tonight; for the peace of mind:
1/ refit the old caps I had before this new set I installed. To narrow the search. If ever it's one of the new caps that's the culprit, I will know.
2/ refit at least 1 of the old coils (not the worn out unit; the better looking one). Along with tbe old caps.
One thing just came to my mind: has the rotor got to be installed with the thick washer that comes in the same package or not?? I say this because when I inspected the caps it looked like something were touching the 4 pins and grinding the pins copper. They even look worn to the point they turned grey!
Could it be that the washers are pushing the rotors forward till the point that they were touching the pins and therefore loosing the spark????

 

[gsxr]

That is bizarre. There should be no washer between the rotor, and the rotor arm/bracket. The rotor should also not touch anything on the cap. You may want to remove the rotor bracket (single bolt in the center) and make sure that is fully seated, AND also make sure it's keyed properly. There is a locating pin which should fit into the slot on the back of the bracket. It's very clear when that is in the proper position. This also lets you check the back of the insulator caps (again) while apart. Use a drop of blue threadlock on the single bolt that holds the bracket in place.

Again - if any parts are rubbing, something is wrong... but I'm not sure what.

 

[Klink]

This sounds like there could possibly be a mixup with new and old version rotor brackets and rotors. Somebody could have put the washers there in an attempt to “make it work“ I am not in a position to produce any photos at the moment. Dave/GSXR, do you have photos handy?

 

[powerofgreen]

I just removed the caps and they look fine. Don't know why but these rotors are a pita... Everytime I try to remove them there must be a screw that doesn't want to move! On both sides one; only one screw is holding there so tightly I couldn't remove it! Anyway, the rotors look like well seated and tightened.
One thing I did, is to disconnect the coil next to the engine; just to see if there is any more drop in power.. and surprisingly nothing changed...
The engine started after crancking a few more times but then it idled the same way... no improvement.
I am thinking may be this old coil is also worn out..
Btw I bought a multimeter this evening and I tested the secondary resistance of the Bosch coil that looked better than the other one. It gave me 11000 ohm.
Perhaps I could try to swapp it with the one I disconnected for testing the idle.
May be......

 

[gsxr]

This sounds like there could possibly be a mixup with new and old version rotor brackets and rotors. Somebody could have put the washers there in an attempt to “make it work“ I am not in a position to produce any photos at the moment. Dave/GSXR, do you have photos handy?

I think you may be on to something, Klink!

Photos attached...

 

[powerofgreen]

My rotor brackets are same as the second picture you posted.
My brackets pn# 1191580640
Late style, right?
What about when I disconnected the passenger side wire; between the coil and the dissy cap?
I felt no change almost: same poor idle. Just crancking 3/4 more times before start up...
Could it mean that this coil was the culprit? Or even if both coils are worn out; does it point to the coils rather than something else??
One more thing: the idle isn't hunting; like you see when there is an important vacuum leak or when a breather hose is disconnected. It's pretty steady, but it's veeeery very poor! Feels like coughing more than idling. Really no power!

 

[powerofgreen]

I think you may be on to something, Klink!

Photos attached...

Attached picture of my rotor bracket.

 

[a777fan]

Attached picture of my rotor bracket.

Oof. Get yourself a good allen socket set. Using a torx socket in those allen head bolts is asking for a strip out.


Sent from my iPhone using Tapatalk

 

[Steve119]

My firm advise is to only use Beru rotors+caps+wires. I had Bremi and 1 rotor cracked, and half a year ago my left bank would die after driving 30 minutes.
All new from Beru now and problem is solved...

These ignition systems can do really weird things, and imo you can only go further in a reliable way with the best brand(s), imo Beru (or OEM MB).