1998 C230 4200-4500rpm hesitation
 

Some time last fall my car developed a slight hesitation at about 4200-4500rpm under full throttle acceleration. There was no CE light, and no other symptoms.

The dealer diagnosed it as mis-fire and replaced the plugs, announcing it cured. It was not. They refused further diagnosis, claiming it fixed. I kinda forgot about it, as it's quite slight, and I rarely call on the car hard enough to feel it. Well, I'm kinda tired of it now, and it's begun to nag away at me. I am going to try to solve it myself since my warranty is now up.

The car drives and runs perfectly otherwise, and has not had a CE light. Fuel economy is spot on, no oil usage, nothing out of the ordinary.

Here's my thinking...

1. Fuel filter, or fuel pump? Maybe a fuel pressure regulator?

2. Misfire? I have my doubts about this one, as there is no CE light, but you never now. Plugs are only a few months old, but...

Once it clears the "rpm zone" it pulls pretty cleanly to redline and shifts perfectly.

Also, it seems like if I slightly let up on the throttle, it clears the "rpm zone" better than if the pedal is depressed to the floor. I'm not sure if the M111 has two fuel pumps, but this condition makes think if so, one might not be keeping up.

Help!

Wondering aloud...

Would a degrading AMM cause this symptom? No rough idle. No CEL. Hhhhmmm.

Quite possibly. You need to look at the adaptation numbers. If your partial load adaptation is above 1.15 I'd worry about it.

Steve,

Thanks for the reply! I am taking the car to the shop tomorrow to FINALLY get the SRS light out. (Had to order the bag module...) and I'll hook the SDS up to it and check those values.

While I have it "on life support.." is there anything else I should be checking for? I have to have the SDS on it anyway to check the side bag operation.

I would recommend checking your actual values for both engine and trans adaptations. If you're not familiar with reading/interpretting them, we'll be able to help you with that here. Check engine smoothness as well, as you can quantitatively see how each cylinder is runnung-very useful. I'd print out these values to use as a reference.

No more until next Monday...
 

My indie just couldn't get me in this morning as planned, so we're going to spend the day with the car next Monday. It's running well and can wait. We'll read the adaptation values then. The fuel filter is due anyway, so I'll swap that out.

He's seen the same problem on M111 and M104's (and others) and it's been the AMM 90+% of the time. We suspect the adaptation values haven't reached the point to throw a CE light, but the AAM is going south. This is the original AMM on the car. If the values warrant, we'll swap the AMM and recheck.

Anyway, thanks for the help so far, and I'll update the thread when more info comes in.

Well, things are going downhill. Thank goodness the car goes in on Monday! Now, any time the throttle is over 3/4, the car stumbles quite badly. I am surprised that there is no CE light at this point, though the idle is strong and smooth.

I'll be REALLY happy when this is fixed, though I think by the time I am done this week, I'll probably be a couple grand light. The bloody side bag and module come close to $600 parts alone, and I'm probably going to be shelling out another $500 for an AMM. (Canuck, remember?)

Maybe I'll just find a W123 240D with no airbags and no AMM. :rolleyes:

Update...
 

Well, haven't dived into the SDS yet, as we've been taking care of a few maintainence items first. Changed out the coolant and swapped the fuel filter. Went to change the plugs and found...

The plugs ends are in BAD shape. Replaced all four and the plugs. Without any more diagnostic work, I'm sure those rotten ends have been causing some problems. Also, the valve cover gasket is leaking like crazy into the plug-well. Unfortunately, there is not a gasket to be had in town, so we're at a standstill for the day. Tomorrow a new gasket arrives, and then we'll begin SDS work and finishing the diagnosis on the stumble. My mechanic wants to tackle some other jobs, so my C230 sits until "the morrow..."

I'm doing my 60K a bit early tonight and am worried that I'll pull the plugs to find the spark plug seals leaking. Hopefully, all is well. Hope your car turns out alright.

If it were the oil shorting out the secondary side of (I assume) the #4 plug, it should misfire and set a code, but I have seen this before on M111's, just like 104's. I'd be concerned that becaise you're having a noticeable decrease in performance that the engine control module isn't recognizing misfires, maybe because the ring gear (crank angle sensor) adaptation was never "learned" the last time it was lost (by a dead battery or whatever may have occurred). This is a critical operation.
Other than that possiblity it does kinda stink of a MAF sensor.
The number of fuel pumps isn't dictated so much by the engine as by the chassis. The 202's have one in-tank pump.
Gilly
PS That gasket is a REAL pain to install correctly, not as bad as a 104, but close.

Gilly,

Is there a way to ensure that the crank angle adaptation is being learned? If not, will I have to replace parts?

As a side note, this evening I took the car around the block before putting 'er away in the shop, and she FLEW through 3500rpm, feeling much better. Of course, the hesitation was worst when pulling a higher load (read: higher gears) and I didn't have the space to try that. But, we can only solve one problem at a time, eh?

2500km's out of warranty and she is spending my money like there is no end to it...

2500km's out of warranty and she is spending my money like there is no end to it...[/QUOTE]

John,
The fact that you're refering to the car as a SHE, should explain the money-spending part.
:D

The adaptation can be learned at any time. It needs to learn RPM range (segment) 1 and load range 2 to have misfire recognition. I am unsure on the 111 motor exactly what you need to do to learn it. On some of the V engines for example you need to select 4th gear and drive it 1 minute at about 45mph, I'd have to try to confirm that, but that's an example of how this stuff gets adapted (learned in). We were told once this segment is learned, that the rest of the rpm/load ranges will be learned in automatically. But I have seen cars where other segments were learned in, but this one wasn't.
The ring gear adaptation can be checked using SDS (to see which segments have been learned). Instructions for achieving adaptation to ensure misfire recognition should all be spelled out on SDS also. I'd also see where the fuel trim is running, should be fairly close to 1.00.

Gilly

Solved. Finally.
 

Okay, dived into it in detail today. Didn't expect to solve the problem with new plugs, ends or valve cover gasket (which is a bear, thanks for the warning). And it didn't. Then came out the SDS. Fuel trim is out, over 1.00. Why no CE light? Hhhmm. 1.15 won't trigger? Has to go to 1.32? I didn't think so, but what the heck do I know?

Anyway, installed a new AMM and took it for a drive. Puuurfect. Fuel trim right on 1.00. Reinstalled old AMM and drove it. Bog-bog-bog.

Diagnosis complete, Doctor: Air Mass Meter. Well, nothing like throwing another $511 in the mix, right?

So, hopefully my little gal is taken care of for a while. New side bag and module, new plugs, new coolant, new fuel filter, new plug wire ends and new valve cover gasket. No SRS light and no hesitation. $1400 in parts alone. Don't call asking for money, I'm feeling a little light right now. But, it's the first money I've spent on the car other than tires and brakes and filters in nearly seven years. Shouldn't complain too much I guess.

Thanks for the help everyone. Helped to keep me on track during diagnosis. While I'm still paying shop labour (no matter how much input you provide or help, mechanics are in business, folks, so if your car is in their shop, pay up) it meant I could start from a point where diagnosis went quicker.

Yes, it has to peg to set a code (self-adaptation at partial load at LIMIT)

Gilly

Ah. Thanks. My mechanic was sure of that, but I of course, stubbornly, was thinking the opposite. Good to know, as I was a little freaked that there was a degradation in performance without throwing the CE light on.

We sure went through the car with a fine toothed comb, and pretty much everything is now renewed. All the suspension looks good, no leaks (other than the valve cover gasket) and no other concerns. I recently changed the oil/filter and cabin dust filter and engine air filter. Brakes are about 40% rear and 60% front, so they'll be fine for some time.

Only things left are to replace the pitted windscreen (next spring) and the cracked headlamp lense. Probably do the lense after the snow goes and the rocks are cleared as well.

Yes, there is some flexibility there, that's the whole reason behind this self-adaptaion, it can adapt to different conditions, and it's expected it will creep one way or another, especially later in the engine life (engine wear). Ideal is 1.00, that's right in the center. But if the mixture starts running too rich or too lean, it has to eventually stop adjusting the mixture and call it quits as far as self-adapting anymore; if it keeps leaning out the mixture, well as anyone can say it won't run well without enough fuel, and of course if it does at least keep running, in a too-lean condition the motor will eventually "melt down". Just the opposite, too rich is no good either, especially for the environment and the cats, and eventually you'll flood the engine. As you can probably guess, the MAF sensor being incorrect can lead to this self-adaption being all wrong. The MAF sensor helps determine the self-adaptation, the front O2 sensors determine the actual Lambda cycling of the mixture (rich-lean-rich-lean), the rear O2 sensors aren't really for anything except determining that the cats are doing their job.

Gilly

Wow, that last post is awesome, and yes, I do know it was from 3 years ago...but nothing like using the search button to find relevant info eh? :pleased:

How do I determine what the current fuel trim is on my vehicle? What is the expected life of an 02 sensor? Especially one that perhaps was cooked by a clogged cat at 110K miles.
Cat was replaced with Magnaflow Cat for $300.
Anyone else using these? Are they OK?

I'm pretty good about staying up on things.
Fuel filter was replaced 30K miles ago,
plugs are recent, all coil packs were replaced around 80K, generally runs good, but a little sputtering, and even an occasional backfire perhaps. Seems to be dumping too much fuel.
MAF (same as a AMM?) was replaced at least twice by the dealer under warranty, and
I cleaned it just a few months ago.

Could just the 02 sensor be causing this?

I just called a parts store I've dealt with a lot in the past. They have a Bosch universal 02 sensor for around $80, you have to solder the connector.
He swears it's the same as the original, just without the connector.
I know from experience that 02 sensors do tend to be the same, and bosch is the main supplier and designer, and each car mfg tends to jack the prices up.

Anyone try a universal before?