Engine Performance Issues

[Woody123]

Hi, I am a new member, owner of a '98 C200 petrol, manual box with 109000 miles

Since I purchased the car back in march, I've experienced some issues with the performance of my engine..

The car was very sluggish and jerky, which I assumed to be due to the very few miles the car had covered with the previous elderly owner, these problems started to clear up a little with regular use.

I've since replaced the spark plugs, coil packs, and leads, which has improved the performance slightly, giving the car a bit more power but still doesn't feel right

However there is still a problem that has constantly been present..
I can't seem to rev past about 4K, when I floor the pedal, the car just seems to jerk and misfire, not revving any higher than 4k.

In the first minute or so of driving from a cold start, the engine barely pulls at all with a lot of hesitation and misfiring..

Anyone have any ideas?

So far I've cleaned the maf with a bit of contact cleaner
Sealed a tiny split on the vacuum line to the injector rail
Used a few bottles of redex in the tank (does that stuff even work?)
Checked air filter

I can't seem to find the problem..




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[LostKiwi]

Hi and welcome.
Do have an engine management light showing (and equally does it light before starting then go out)?

 

[bembo449]

try unplugging the MAF

 

[Woody123]

Hey thanks for the replies

- the yellow triangle lights up and goes away as it should

-I'll try unplugging it later and go for a little drive to see any difference


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[Woody123]

Disconnected MAF before going to work, barely any difference in the running/performance

Disconnected while engine running and only a very slight variation in revs but aside from that everything is the same.

So I guess my MAF isn't really doing anything at all?


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[Uncle Benz]

Sounds like bad maf to me. If it's really dead cleaning it will do nothing. Might be worth a gamble

 

[LostKiwi]

Generally if the MAF is bad it will run better with it disconnected. Given he saw little difference it suggests to me the MAF is OK.
I think it really needs some STAR time to look at live data and properly analyse whats going on.

A little more info - The car has a map of ignition and injection settings stored int eh ECU - this is called the base map.
Under normal conditions the car starts out with the base map and modifies it according to feedback from Lambda Sensor and MAF to get optimum values to use. If you disconnect the MAF you force the car to run on the inbuilt MAF. Therefore if the MAF is good there should be little difference in how the car runs. as the calculated values for fuel will be similar to the onboard map. If the MAF is bad the differences from the onboard map will be large and cause poor running.

OP, When you say it won't rev past 4k I hope you aren't doing this in Neutral because it won't rev past 4k in neutral.

 

[Uncle Benz]

What you refer to is alpha N. The ecu reverts to throttle angle and rpm alone to calculate engine load. It isn't refined, and can be used to pinpoint a faulty maf if you know what you are looking for. To a layman it will still run rough. It's a good test if you know what to expect.

 

[LostKiwi]

When I had my T5 Volvo it started to run like a bag of spanners. Disconnected MAF and it was near perfect (though down on power). Replaced MAF all sorted and back to normal.
The MAF was feeding duff info to the ECU.

 

[Woody123]

Thanks for the replies guys

Yes when I press the pedal to the floor/the revs get to about 4K the engine just seems to sputter and lose all its strength.
If I quickly come off the gas suddenly to change gear quickly the car lurches quite badly as if the brakes are being dabbed... not too sure if these issues are related.

Would an ordinary OBD2 read codes or would I need a full check on STAR?


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[LostKiwi]

Thanks for the replies guys

Yes when I press the pedal to the floor/the revs get to about 4K the engine just seems to sputter and lose all its strength.
If I quickly come off the gas suddenly to change gear quickly the car lurches quite badly as if the brakes are being dabbed... not too sure if these issues are related.

Would an ordinary OBD2 read codes or would I need a full check on STAR?

Your car isn't OBD2 compliant and has no OBD2 port. The diagnostic port on yours is a circular 38 pin connector under the bonnet.
Because of that you are seriously limited in code readers able to talk to the car.
CarSoft (not -iCarsoft) or STAR (or more specifically STAR with HHTWin) are pretty much your only options.

 

[Woody123]

Your car isn't OBD2 compliant and has no OBD2 port. The diagnostic port on yours is a circular 38 pin connector under the bonnet.
Because of that you are seriously limited in code readers able to talk to the car.
CarSoft (not -iCarsoft) or STAR (or more specifically STAR with HHTWin) are pretty much your only options.

Are ordinary garages likely to have that type of diagnostic to hand? Or would I have to go to a merc specialist?


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[LostKiwi]

Are ordinary garages likely to have that type of diagnostic to hand? Or would I have to go to a merc specialist?


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No idea and it will depend on the . individual garage.

 

[Woody123]

Finally got around to buying a new Bosch brand MAF sensor.

Even fitted it outside the motor factors to try it out on the way home and I can rev all the way to the redline now.

It’s still a bit jerky and slow accelerating in the mid range, but I guess that’s down to the ecu learning the new (correct) signal from the maf. Correct me if I’m wrong.

Thanks for the help though everyone much appreciated




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[LostKiwi]

Ideally you should have the adaptations reset in the ECU.

 

[Woody123]

Can I go about this by disconnecting the battery for a while or is there a better way?



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[LostKiwi]

Can I go about this by disconnecting the battery for a while or is there a better way?



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I think it needs appropriate diagnostic software.

 

[Woody123]

Am I right in saying that Because of the faulty MAF the ecu has adapted for its skewed readings, the adaptations need to be reset to start from a clean slate so to speak?

Would this explain why I’m now revving good, idling good but the mid range performance and smoothness seemed to disappear when I swapped the old MAF?

Sorry for asking so many questions, I am learning!


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