1992 400E Very bad hot idle & no start.

[Heix]

At this point im kind of lost, i have replaced:

Rear crank position sensor with NOS Bosch Unit
New Bosch Lambda sensor
Fuel pressure is at 3.5 bar nicely

The problem:
You go for a drive and for a couple mins everything is ok, but when car gets hot its like switching to 4 cylinders, no power, terrible idle and when you try to accelerate...well nothing happens only slowly creeps to speed.
When you stomp gas pedal several times then it "wakes" up for a second. (when vehicle is in motion)

anyways... thing is that car is not even starting when hot, so I dont really start replacing parts randomly as it has to be something specific that prevents car from firing up... something electrical I assume...something expanding with heat and losing contact?

Car will start hot if you restart it immediately after shutting off, but leave it for around 5 mins it wont fire up until temp reaches 40C

Focus should be around engine and gearbox itself as when these are hot I get no start, everything else in the engine bay is cold - I tested it with hood open so only engine itself is actually hot when the issue develops.

Since no start issue cant really be linked to bad rotor cap or ignition leads I have not replaced them. Spark plugs are all looking good and consistent on all 8 cylinders.

It cranks nicely and when I crank longer it backfires so I assume it gets fuel.

Car is EU Spec if that matters!

 

[gsxr]

Sounds like the usual secondary ignition issues with condensation/liquid in the distributor cap(s). How old are the caps/rotors, and what brand are they?

Do you have access to Star Diagnostics with HHT-Win to view live data?

 

[Heix]

Sounds like the usual secondary ignition issues with condensation/liquid in the distributor cap(s). How old are the caps/rotors, and what brand are they?

Do you have access to Star Diagnostics with HHT-Win to view live data?

Definetely old and OEM caps, but if 1 of them is bad is it enough to stop car from starting? No diagnostics unfortunately.

Tomorrow I’ll take a look at rotors and caps.

 

[gerryvz]

Definetely old and OEM caps, but if 1 of them is bad is it enough to stop car from starting? No diagnostics unfortunately.

Tomorrow I’ll take a look at rotors and caps.

Plenty of threads here detailing the issues with caps, rotors and insulators. If you do install new caps, make sure you properly vent them before installing them. There's a thread in the "stickies" section of the M119 subforum on how to do this.

 

[gsxr]

Definetely old and OEM caps, but if 1 of them is bad is it enough to stop car from starting?

The classic issue allows perfect cold starting, then after 10-15 minutes of driving, the engine may start to misfire, idle very rough, and if shut off the engine will not re-start until it cools down (15-30 minutes or so). After this it may run normally, until the next cold start, when the cycle repeats.

More info here.

No diagnostics unfortunately.

Bummer. Live data will prove if the running issues are ignition related, by viewing the voltage on each cylinder from the EZL / DI in HHT-Win.

 

[Heix]

Thanks for the DIY thread! I just ordered new:
Bosch insulator
Cam O ring seal
Bremi distributor cap, (40€) it was the only one available, everything else like beru ja bosch are sold out everywhere…but its good enough to find out if the cap was faulty.


Parts will arrive next week and I will keep you updated.

 

[Heix]

Evening fellas, so I got my new parts and just about an hour ago finished replacing them.

As you can see on the photos passenger side distributor was full of condensation aswell contact pins weren’t best looking.

Now after replacing everything on right bank I let car idle to operating temp and then revved the engine and did a small quick drive, everything was nice, pulls well and no bad idle.

Left it sitting for around 5mins to test hot start, car started, but bad idle is back again.

So I fixed my hot start issue thats good news !
Now my theory is that I also have a faulty distributor on drivers side though I checked it and there was 0 condensation…contact pins however didnt look good though so Im gonna replace driver side aswell and see from there.

By following the DIY I also grinded extra “vent slats” on the new distributor cap to reduce condensation issue

Will update you hopefully this week

BTW all parts I replaced was OEM MB from god knows what decade.

 

[nocfn]

Without having the ability to live data things, a few issues to think about. Remove each spark plug and be sure there isn't any oil on the plugs. Gap them all to about 1.0 and reinstall. If possible, start the car in the dark shop (quickly to avoid carbon monoxide) so you can see if any of the wires are arcing from the coils and to each bank/spark plug. Be absolutely certain that that cap is evenly and squarely placed on the insulator. It can be difficult to do so with all the wires attached to the caps. We have all been thru this calamity, short trips do not help, turning off car and starting it up again, rinse and repeat. Post your findings.

 

[Heix]

Looks like Ive solved the problem.
I’ve been driving around and everything seems ok now.

I replaced distributor on the left side aswell and now there is no misfire or starting issues.

So in conclusion what happened was that I lost 2 distributors at the same time giving me a false thinking that I had a bad CPS because car refused to start when hot, if the car would have had 1 faulty distributor it would have started and I would have known immediately that there was an issue with ignition


Replacing both of the distributors ultimately solved the issue for me.

Thanks for stopping by

 

[gsxr]

If the problem returns in a few months, cut additional vent slots into the new caps as described in the thread linked back in post #5... along with fixing oil leakage from the cam solenoid.

 

[Heix]

Update:

Now just completed driving in rainstorm aswell and still everything is perfect, car pulls very well and good idle!

So if someone in the future has no hot start then there is a possibility that both distributors have gone bad…
check them first cause both of mine failed at the same time which apparently can happen they are easy to work on too

Conclusion:
Since both of my distributors failed at the same time (one of which didnt have condensation issue, just bad contacts) I rushed into thinking that it had to be classic hot temp related crank sensor issue….but it wasnt.
I also learned that M119 SHOULD be able to start with one properly working distributor, its enough for the engine to run as mine did after I replaced only one in the right bank and left bank still had the bad one.


Cheers,

Heix