Engine power loss/hesitation at high revs

[jay-h-e500]

Hi all ,

Have a 94 E500 with 166.000 km's . When under full acceleration at highway speeds, when the car is at 4500-5000 rpm or more it's like the car loses power holds gear and won't change gear at all and then if you hold the throttle still the car will start basically jolting back and forth violently.

Could it be the case of fuel filter being slightly blocked causing fuel starvation?
Or catalytic converters being blocked ?

Rotors, caps and leads are new .
Car has genuine f8dcu4 (if I can remember correctly)

Transmission has been rebuilt but it was doing it before the rebuild .

No ASR light illuminated

Any advice appreciated

James

 

[Kyiv]

Pull your LH module and take a look at its capacitors if any have leaked. It's a 10 min job

 

[jay-h-e500]

Pull your LH module and take a look at its capacitors if any have leaked. It's a 10 min job

Is the LH module basically the engine ECU. Located in the same housing where you plug the diagnostics in the engine bay?

Thanks for the reply

 

[Kyiv]

Is the LH module basically the engine ECU. Located in the same housing where you plug the diagnostics in the engine bay?

Thanks for the reply

Yes, it's located with all the other modules in a tray towards passenger side, where a battery would be. LH module is a fuel injection computer.

Does your fuel relay under the rear seat click when you start the car? If it does, it's definitely an issue with LH module. In my case it did not start clicking until outside temperature got below 0C. I pulled my module and it had 2 leaking capacitors, but tell-tale signs that the module was bad were before clicking started. About half a year prior to it clicking I had a similar occurrence to what your describe. It only happened once thought - at highway speed under full throttle - so I shrugged it off. It may not be your issue, but it's an easy inspection.

Do you have a blink code reader?

 

[jay-h-e500]

Yes, it's located with all the other modules in a tray towards passenger side, where a battery would be. LH module is a fuel injection computer.

Okay cool I will check it out in the morning and let you know .

Cheers

 

[jay-h-e500]

Yes, it's located with all the other modules in a tray towards passenger side, where a battery would be. LH module is a fuel injection computer.

Does your fuel relay under the rear seat click when you start the car? If it does, it's definitely an issue with LH module. In my case it did not start clicking until outside temperature got below 0C. I pulled my module and it had 2 leaking capacitors, but tell-tale signs that the module was bad were before clicking started. About half a year prior to it clicking I had a similar occurrence to what your describe. It only happened once thought - at highway speed under full throttle - so I shrugged it off. It may not be your issue, but it's an easy inspection.

Do you have a blink code reader?

No I don't have a blink code reader . Are they still available to buy ? Is the star diagnosis c3 another diagnostic option ?

 

[Kyiv]

No I don't have a blink code reader . Are they still available to buy ?

You need this or similar.

A proper MB diagnostic tool is much better of course. This link might be useful to you if you're not familiar with it already

 

[gsxr]

Star C3 is preferred (or, C4/C5 if it supports HHT-Win, required for the older OBD-1 cars). The blink code reader will be some help if you don't have SDS.

If full power is available until the violent jerking begins, that isn't plugged catalysts. Sounds like it's electronic somehow. Has the neutral safety switch been replaced yet? What happens if you leave the gear selector in 3 instead of D?

EDIT: Per Jon's post below, you could potentially have plugged cats... definitely worth testing so you can rule this out.

 

[emerydc8]

If full power is available until the violent jerking begins, that isn't plugged catalysts.

When my cats were clogged I think the power was quite normal up until the RPM hung up (circa 4000 RPM). His symptoms seem to be the same as mine when I went through this. If I held it in gear and tried to get it to a higher RPM it would backfire and jerk violently. It would be an easy check for plugged cats by tapping a vacuum gauge into where the three vacuum pods connect to one and sliding the gauge under the hood for a test drive. If you see zero vacuum at any point there's a good chance the cats are clogged.

 

[nic520]

Dear James,

try it in 2nd gear. Go slowly to 5.000 rpm. If it still is hesitating, it is not fuel, since you will not run with full load.
How and when did the problem start?
I had a similar problem, it was caused by the EZL.
N

 

[gerryvz]

I believe that it also may be plugged cats. The inability to rev beyond a certain point (~5,000 RPM) and the behavior of the car when trying to push past that point tells me that there is an exhaust flow issue.

Jon's advice to check vacuum at the point under hood next to the fuse box at a vacuum port is an excellent one.

 

[gerryvz]

I had a similar problem, it was caused by the EZL.
N

Can you explain more about the EZL caused problem you had? This is the first time I've heard of an EZL problem not either being the engine won't start at all, or (as I personally experienced in 2009) the engine only running on four cylinders.

 

[nic520]

Hi Gerry,

can you explain why the non-vacuum there relates to the higher pressure in the exhaust from clogged cats?
Nic

 

[nic520]

Hi Gerry,
I changed LH and EZL on a converted E420 to S500 items. The car worked fine before, did not go over 5000 rpm after. Changed EZL back to 420 again: worked fine. Changed for another 500 EZL: worked fine. Therefore it must have been caused by the EZL. Dave mentioned though, that some parts may not work together, so it might be a special problem related to my combination.

 

[gerryvz]

Engine vacuum is generated by the pistons moving in the engine, and gated (restricted) by the air intake valve (ETA) into the engine's intake system. It is effectively a measurement of the level of airflow restriction through an engine -- which is EXACTLY what @emerydc8 was getting at.

A car that is idling or operating at a low speed (say 1,500 RPM) is going to generate a high level of vacuum, as measured at the intake manifold (i.e. the vacuum line tree that is mentioned next to the fuse panel works well as a place to get a vacuum reading).

A car that is under load / accelerating will generate much less vacuum at the intake manifold, but will still generate some measurable/indicated vacuum. This will vary depending on engine RPM, and the throttle valve (gas pedal) position. But there will ALWAYS be some vacuum present and measurable.

If zero to negligable vacuum is being measured when the car is being operated at speed, then that is a good indication that there is a restriction in the system (see my first paragraph above).

You will know there is no restriction on the intake end of the engine, because the throttle valve (ETA) is working correctly, and the air filter is letting air pass through it. So therefore, you know the intake side is working fine. So the restriction would have to be on the exhaust side.

 

[gerryvz]

Hi Gerry,
I changed LH and EZL on a converted E420 to S500 items. The car worked fine before, did not go over 5000 rpm after. Changed EZL back to 420 again: worked fine. Changed for another 500 EZL: worked fine. Therefore it must have been caused by the EZL. Dave mentioned though, that some parts may not work together, so it might be a special problem related to my combination.

You cannot make statement such as "Therefore it must have been caused by the EZL"

Intermixing/intermingling parts for a 500 on a 420 engine and vice versa is NOT NOT NOT a definitive solution that you can make solid deductions from. You MUST MUST MUST use an LH computer and EZL for a 5-liter engine TOGETHER with the 5-liter engine. You MUST use an LH computer and EZL from a 4.2-liter engine with a 4.2 liter engine. You CANNOT mix and match, as you are using components not designed for the application together -- there may or may not be incompatibilities.

But if you use known-good components that are designed for the engine displacement you are using, then at least you can be assured that these components can be eliminated or considered as bad.

 

[gerryvz]

Can you explain more about the EZL caused problem you had? This is the first time I've heard of an EZL problem not either being the engine won't start at all, or (as I personally experienced in 2009) the engine only running on four cylinders.

EZLs have generally proven to only have TWO modes of failure, over the years. Experts like @Klink have confirmed this.

1) Full failure of the EZL. All eight cylinders dead. The engine refuses to start.

2) Partial failure of the EZL. One bank (four cylinders) dead. The engine starts and runs, but runs very roughly, accelerates much more slowly, and raw fuel can be smelled coming out of the exhaust.

 

[nic520]

Hi Gerry,

sorry, I did not intend to give wrong info. The LH and EZL were from a 500S and engine was 5000ccm.
It did not rev above 5000rpm.
Changing the EZL to another from a 5000ccm (other part no) did cure that, also using one from a E420.
Conclusion from my side was that the rev not above 5000 rpm was related to the EZL. I understand that this does not correspond to the defined EZL failures.

 

[jay-h-e500]

Hi all,

I removed the LH module and looked at the capacitors that where visible when the lid was removed under the plastic , everything looked all okay. After that I checked all the vacumn lines ,2 white plastic lines at the back of the inlet manifold , other 2 white plastic lines on the front of the inlet manifold that go to the passenger side front corner behind the headlamp and then the last 2 black plastic lines I could see that come from under the inlet manifold that go to the EZL and the other close by. I started the engine and unplugged the 1 on the EZL and could obviously hear the vacumn from the inlet and the engine note changed slightly but when I unplugged the other black vacumn line I could not hear or feel any vacumn coming from it. Could this be a culprit as the vacumn line is blocked ? Will attach picture of the pipe. Is it worth getting compressed air and blowing down the line ?

I am also thinking it could be clogged cats I have a superspersprint cat back exhaust which hasn't done much milage since been fitted to the car and when I look at where it attaches to the catalytic converters the left exhaust tube is a bronzey colour and the right exhaust tube is still normal stainless colour like the exhaust gasses aren't getting through and when stood behind the car o do get a smell of a bad catalytic converter .


Thanks for the replies

James

 

[gsxr]

Be careful with the vacuum lines. One is likely a source from the engine, but the other goes to the vacuum device. One should likely have vacuum present with the engine running, the other will not.

Also sounds like your cats are suspect. Easy test is to remove the crossover pipe from left manifold to main catalyst pipe and go for a (noisy) test drive...

 

[emerydc8]

Be careful about pushing the engine to the point that it is shaking violently or backfiring. I damaged a head gasket on my E420 trying to troubleshoot clogged cats doing just that. Luckily, Bar's head gasket sealant has worked to keep from losing coolant into the engine over the past five years, When I ran a check for exhaust gases in my coolant last month it came back negative, but I haven't pushed the engine that hard because I know the head gasket is compromised.

 

[jay-h-e500]

Okay ,

I thinking I'm gonna go with the conclusion the cats are blocked so I'm just gonna replace them, what's the best for replacements just to bolt on . I've seen a magnaflow system but it is in the states and I'm in Spain. And would also want a system to give a bit more noise as I have a supersprint cat back and it's not much different from stock.

 

[gsxr]

The Magnaflow doesn't have the best reputation, but is relatively inexpensive.

Since you are in Europe, I'd check out the Fox exhaust pieces. I *think* they will work with your aftermarket cat-back exhaust, IF your Supersprint is designed to bolt up to factory cats. Another option is the Leistung custom exhaust (search this forum) but that setup is $$$$.

Note that the M119 exhaust in general is fairly quiet, if you want to louden it up, it's not easy with any catalysts in place.

 

[Seangbadee]

You cannot make statement such as "Therefore it must have been caused by the EZL"

Intermixing/intermingling parts for a 500 on a 420 engine and vice versa is NOT NOT NOT a definitive solution that you can make solid deductions from. You MUST MUST MUST use an LH computer and EZL for a 5-liter engine TOGETHER with the 5-liter engine. You MUST use an LH computer and EZL from a 4.2-liter engine with a 4.2 liter engine. You CANNOT mix and match, as you are using components not designed for the application together -- there may or may not be incompatibilities.

But if you use known-good components that are designed for the engine displacement you are using, then at least you can be assured that these components can be eliminated or considered as bad.

Great point

 

[nic520]

Great point

I was refrring to my EZL and for this, it was true. If anybody wants to rely on principles, no problem. But I would not exclude possibilities based on principles. Principles may indicate a probability.
In the this case here, it might be the clogged cats. I would still try the test in 2nd or 1st gear to max rpm without much load. That is quickly done and will not cause much temp load.

 

[Catalin]

Okay ,

I thinking I'm gonna go with the conclusion the cats are blocked so I'm just gonna replace them, what's the best for replacements just to bolt on . I've seen a magnaflow system but it is in the states and I'm in Spain. And would also want a system to give a bit more noise as I have a supersprint cat back and it's not much different from stock.

Hello.... I have the same problem like you when i get full acceleration bettween 3000-4000 rpm the car has no power and it falls and after 4000 its not working fine... But only on full boost... If i go slowly i dont have a problem...did you manage to resolve it? and if yes.... What it was?

 

[emerydc8]

I had clogged cats on one of my cars about 12 years ago and was able to compare the vacuum behavior of both the good car and bad car. Maybe this will help you troubleshoot yours.

Post in thread 'Hanging up/Stumbling at 4000 RPM'
Hanging up/Stumbling at 4000 RPM | M119 Engine