1992 500E - misses badly after warm-up/DM codes
 

PLEASE HELP

I have a 1992 500E that was running perfectly and then one day it started to miss at idle after the engine warmed-up. When cold it does not miss. It only happened once or twice in a day then became progressively worse over the next few weeks. As the engine gets warmer, it misses more consistently and will miss all the way to 2000 rpm, over 2000 it goes away, but the car is not driveable with this condition.

I have replaced the caps, rotors, plug wires, plugs, air filters, fuel filter etc.

I intitally pulled the following codes from the Diagnostic Module LED.

Code 3 - Lamda control out of range - Bank 1- Air, fuel metering or ignition problem.

Code 6 - Idle speed faulty.

I reset the codes and I installed a new O2 sensor. The problems did not go away and now I get Codes 3 and 6, and
Code 18 - Adjustable camshaft timeing solenoid circuit open or circuit short - Bank 1.

Also, when checking the codes, (via the DM module), when I get Code 6 the Electronic Throttle Actuator will start buzzing and seeking, it sounds as though it is trying to re-learn and you can hear it buzz, click, change tone the go back to the original buzzing. It goes through one cycle, and then continues to buzz with the ignition on and does not stop from this steady state buzz.

I have not checked the wiring harness yet, the car has 130K miles, although the ground wires coming out of the harness look fine. I did smell recently a smell like hot wiring though.

As far as the Lamda, O2 sensor goes, the chart I have for Code 3 says to check the LH-SFI module, and I do not have an adaptor to use my homemade code reader with the 38 pin connector.

Any logical diagnostic steps and suggestions would be greatly appreciated. Obviously I will check the wiring harness.

I was thinking O2 sensor from the beginning as the idle miss starts as the engine warms up and gets worse as it is at full operation temp. Although the new sensor did not eliminate the problem and the it seems to center around the camshaft timing solenoid circuit and Bank 1. Is Bank 1 the left cylinder bank?

Thank any and all of you for suggestions and help.

500Espeed

The code 6 is pointing towards a bad ETA (which could be just bad wiring for that harness). The bad news is ETAs are of course very expensive. The good news is it may just be a bad potentiometer on the ETA and the potentiometer for your ETA is replaceable for about $50. The bad news is the replacement potentiometers seem to be getting scarce - possibly a conspiracy to sell more ETAs. Are you getting any ASR lights?

Eta/asr
 

Hi deanyl,

Thanks for your input. As far as the ASR is concerned. Yes, before these problems, (misfire when warmed-up at idle), started, the ASR when into a limp-home mode twice within 2 months time when I was under full throttle acceleration, going from 2nd to 3rd manually at redline onto the freeway. Both times I pulled over turned the car off, restarted and the car ran fine.

As far as the misfire when the car is warmed-up I would swear it is ignition related, it is not a stumble like there is improper fuel delivery, it is a mis-fire, and when the car is fully warmed, it does not go away on acceleration until you hit about 2000 rpm, actually the longer you drive it when it is missing badly under. 2000 rpm, it acts as though it is loaded up.

I didn't know the pot could be replaced on the ETA, where could you find one.
I found a place on the East Coast that rebuilds them with a 2-3 day turn around, and gives a lifetime guarantee all for only $400, seems like a great deal and they have been in business for quite some time.

Thanks,

Bill

More info on potentiometers:

http://www.europartsdirect.com , then model / fuel injection / fuel injection

http://www.sg-motorsports.com/AFS%20Pot%20write-up.htm

Also try a search - there are several good threads.

Potentiometer
 

Oh, you are talking about the airflow meter potentiometer. I thought you were speaking of the pot inside the ETA, which is not replaceable. Do you have any info. only the adjustable camshaft timing solenoid circuit being open, of course I realize any or all of these problems could be related to something small that is seemingly unrelated. I hope to get to the bottom of this soon, as I miss driving the car.

I will post pictures later for all you 500E fans.

Thanks,

Bill

Same thing.

<<and I do not have an adaptor to use my homemade code reader with the 38 pin connector.
>>

Just put alligator clips on your tool leads and stick a wire into the 38 pins.
You want pin 1 for neg/blk, pin 3 for pos/red, and the odd color goes to the pin designated for the module you want to get codes from.

Those pins are here for your chassis 124.036
http://www.geocities.com/MotorCity/Downs/1039/mercedes/cs1000_mb.pdf

I would start with pin 4 [ page 29...]

your car misses when hot...
 

Just saw this post and you may have fixed it but my 1991 300 ec coupe did same thing. After many repairs over the years it turn out to be a sensor that talks to the fuel injection system & the elec fan system. Its a 4 prong sensor called water temperature sensor . It sends bad info to fuel injection system which causes too much fuel to engine which makes it act like it is getting flooded. As you speed up this fuel gets handled...Hope that helps.

My coup has several water temp sensors, so look fot the one with 4 prongs.

Before you do anything else (IMO), if the 2 wiring harnesses are original - change them both out. They may look fine from any exposed areas but under all the wrap I'm willing to bet money that the insulation is cracked or gone in places and the bare wires are in contact with each other causing the gremlins. BTDT on my car years ago. The orginal harnesses were made out of a bio-degradable castor bean concoction and MB has admitted that they 'degraded' way too fast causing all sorts of electrical problems. Original owners of such sub-standard quality were 'goodwilled' new harnesses (usually) up until very recently.

It is possible that the ETA is fried on these very hot running M119s but first and foremost, rule out them wiring harnesses. Just my 2 cents living with this car for almost 10 years now. :cool:

The pots are no longer available. You need to check these guys:

http://www.500ecstasy.com/forums/index.php