rallyguy

Admittedly this is more of a rant at this point, but I definitely welcome the opinions and possible solutions to the problem listed below. Additionally, I have not had the best luck with more than one dealer in the past so it was with great reluctance that I dropped off my 01 CLK430 this morning. But, after replacing what I considered to be the culprit parts on my own, I realized that the use their proprietary computer scanner, and most likely ability to reset some stuff might be in order. Yes, the car is out of warranty, but honestly, I would be just as upset if wasn’t due to the wasted time involved.

Problem: When accelerating with the throttle at about 75% the engine will cut out at 3500 rpm. I mean completely fall on it’s face for a second then catch and start accelerating again. Usually the second acceleration is not with the same intensity as the first 3500 rpm though. HOWEVER, the car accelerates like mad with the throttle wide open. Similarly, the car runs perfectly at half throttle even above 4k rpm. The car has done this since I bought it a few months ago. I have spent the last few months fixing many problems but this one has eluded me.

Parts replaced by me: Mass air flow meter, spark plugs, both pre cat oxygen sensors, fuel filter, air filters, and changed the oil plus some Eibach sprins and Bilstein shocks, but they are pretty unrelated.

The dealer: So they call me many hours later to tell me the car is done and the tech cant duplicate the problem. (NOTE: that there has not been one time when I tried to duplicate this and it wasn’t there.) So, quite reluctantly and with my best smile I go to get my car. He explains that they ran full diags on the car and that the fuel trim was at its limit. I was a little skeptical as it didn’t seem to be affecting half throttle (WOT is excluded from this part because WOT is not a closed loop feedback system), but since I had recently replaced a MAF and o2 senosors I thought maybe that threw it for a loop. So they proceed to tell me I should also do motor mounts and a few other things which I knew and just hadn’t gotten to. I did tell them I do almost all of my own work so to their credit they didn’t try to sell me on them or anything. Moving on, I pull out of the dealer lot and get on the gas……..yup, it stumbles!!!!!! This wasn’t 100 feet. I could almost see the guy who took my $244 watching me as the car regained power and continued. Convinced it was my imagination, I rounded the block and headed back trying to repeat the symptoms and sure enough, every single time. Pulling back in with not more than one mile more than when I pulled out I, no longer smiling, march back in. “I assure you the tech drove it and didn’t notice anything, but let me get him for you” I hear. “I assure you I drove it and didn’t notice anything” I hear as he arrives. We go for a test drive and pull out of the lot, get on the gas and he falls forward as the car stumbles hard. “Hmmmm, he ponders, I didn’t notice that” I hear. So I proceeded to do it again 3 more times while circling the block. He suggests it might be the transmission, and specifically slipping from 2-3. I ask why the tach drops, and why the trans doesn’t slip at WOT? Or, at half throttle at the same RPM? We get back the stealership and go to the advisor. The tech suggests to him the trans is probably slipping because it is a high mileage car (for the record, clk430 = 90,000 compared to my Dodge Colt = 301,000).

To their credit: They did offer to do another 1 hour of diagnosis at no charge to see if they can find the problem. Did I mention that I cant wait!!!

Anyone else have some good suggestions?????

ThrillKill

If you b i t c h enough, they will give you a loaner. Worked for me. I wouldn't pass on a free diagnosis and by now they've realized they screwed up and will probably not try a fast one.

CurYousGee

let me know what you find out....my accord does that...i always suspected the tranny....

benzmodz

It is a long shot but as you know the oxygen demand, fuel load and sensors all work on the mapping of the ECU. What if the ECU has a bad memory map caused by a partial ram fault and the lookup table in the ECU is affected at a precise value. So the lack of information at a certain point results in 0.0 fuel being read back from the data table instead of X0.0 where X is the nominal value.

Because of the interlock the only way to test the ECU is with a matching ignition key also.

I would flash the engine control unit if it is the version and type that can be flashed and then see if the FAT table in the boot sector maps out the supposed bad sector and relieves the fault.

If the problem is vacuum it may be also a function of pressure over time.

I would be looking at the cam and crank sensors too.

55 ON IT

Have them do a tranny service. Then reset the codes.

benzmodz

Isn't it odd how many fault conditions do not show up on diagnostic.

rallyguy

I tried to get a rental (with malice intentions) and they werent going for that.

I personally dont think the idea of a gap or missing data in the fuel map is that far off. Remember that at WOT it is running open loop mode, so I actually think there is a gap somewhere in the map that at and above 3/4 throttle it is hitting that point and when it gets to WOT it is no longer looking at (for) whatever is missing. I also thought this could also be coming from a resistor or other electrical component in the DME that has aged and changed value. This happens on the Mitsu ECU's a lot. They have a few caps that leak out and the acid actually eats the traces on the PCB and you get funny readings back. This DME could be having a similar issue?

I figure at this point they will look at it again on Monday so I cant get much done between now and then anyway. If they dont find something definitive I was going to pull the DME my self and send it out for an upgraded flash and see what changes when that comes back. If I am going to be spending money at the dealer having it flashed I might as well get some value out of it. The car is past warranty anyway.

You mention that the key and DME are a matched pair, I assume similar to the E46 BMWs and I guess all newer BMW's huh? (They actually have an EWS III unit that also matches and they use RFID in the key to make sure everything is copesetic. Can the benz DME be re-programmed, or is it a one shot thing? I assume only the dealer can do this? Are there other aspects of the system or is it just the key and DME? So I basically want to know if I can buy a key and DME from a junkyard to try in my car?

Thanks for all the replies.
Chris