Intermittent misfire after WOT

[jay-h-e500]

Hi everyone,

Have a issue with 94 E500, when starting up cold it's perfect and when the engine is at operating temperature and use full throttle like when overtaking another car , when I slow back down to normal speed and reaccelerate the engine will misfire until I either rev the engine in neutral then it will go back to normal or restart the engine but can misfire again even after sitting idle then taking off again .


Spark plugs are new (Genuine)
HT leads are new (Bosch silicon type )
Distributor Caps 2 years old less than 2000 miles (Bosch)
Rotor arms 2 years old less than 2000 miles (maybe Very)
Camshaft sensor is 1 year old (Genuine)
Crankshaft sensor 1 year old (genuine)

Fault started happening before the new spark plugs and HT leads , I have also removed and inspected the distributor caps and cleaned , there was slight condensation .

Any help would be appreciated as it's doing my head in now , and I just want it correct so I can enjoy the car .


Thanks

James

 

[gsxr]

James, it sounds like ignition system based on your description.

If you have not removed the rotor bracket to allow removal/inspection of the back side of the distributor insulators, that would be next. If you find liquid on them, replace the insulators. Bad news is, you may also have to replace the caps/rotors again, if the problem is not completely cured. Usually when all 3 items are replaced with new OE/OEM, it should remain fixed. Search the forum, there are multiple threads on this topic, with similar symptoms.

Also, check codes on all computer modules. If there are no persistent codes, it's even more likely to be ignition system.

 

[jay-h-e500]

Hi gsxr ,

Thanks for your reply , I've had a little look at the insulators , there was slight moisture on the back side of them , so maybe be now I will replace them all again, would it be worth trying another brand such as beru? Also I have a friend with another e500 and is the same year , you think it maybe worth swapping the EZL to see if it could be that .


Thanks
James

 

[gerryvz]

I believe that there only two brands of insulators: MB (factory) and Bosch (aftermarket). The insulators are not, as far as I know, available from Beru, Bremi, Karlyn, and so forth.

 

[gsxr]

Also I have a friend with another e500 and is the same year , you think it maybe worth swapping the EZL to see if it could be that .

If the car runs on all 8 cylinders some of the time, the EZL is almost certainly not the problem. Don't bother swapping it.

It's also possible that one of the caps or rotors are defective, despite only being 2 years old. Someone else recently had a defective rotor out of the box which was very difficult to diagnose, because new parts can't be defective, right?

 

[szvook]

James, you might have a leaking fuel injector(s). Have you considered doing a leak-down or a compression test?

 

[Unavita]

James, it sounds like ignition system based on your description.

If you have not removed the rotor bracket to allow removal/inspection of the back side of the distributor insulators, that would be next. If you find liquid on them, replace the insulators. Bad news is, you may also have to replace the caps/rotors again, if the problem is not completely cured. Usually when all 3 items are replaced with new OE/OEM, it should remain fixed. Search the forum, there are multiple threads on this topic, with similar symptoms.

Also, check codes on all computer modules. If there are no persistent codes, it's even more likely to be ignition system.

View attachment 112520

GSXR, how long should insulators last?

 

[gsxr]

GSXR, how long should insulators last?

Decades, if not contaminated... seems a lot of cars are running around just fine with the originals from the early 90's. Should be a 1-time replacement if the back side has liquid or there is other concern about damage or unusual appearance.

If they look perfect and are bone dry on the back side, they are probably ok, but it's cheap insurance if chasing ignition problems. I still recommend replacing them if original, when new caps/rotors are being installed. Best to do all 3 items simultaneously (and also the cam oil seals).

 

[JC220]

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[gerryvz]

I just replaced the original equipment insulators on my car (143K miles) last year. They were in decent condition and didn't cause any problems. Your mileage may vary, depending on usage patterns, climate, overall ignition system condition, and so forth.

 

[tuttebenne]

If the car runs on all 8 cylinders some of the time, the EZL is almost certainly not the problem. Don't bother swapping it.

It's also possible that one of the caps or rotors are defective, despite only being 2 years old. Someone else recently had a defective rotor out of the box which was very difficult to diagnose, because new parts can't be defective, right?

I resemble that remark! LOL

M119 Intermittent misfire - Defective brand new distributor cap | M119 Engine

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