Hello,

I just found this forum and think it's great.

As you may have gleaned from the subject, my '87 300E (140K) is having problems stalling. I have been having just about all the stalling problems possible for the last couple years. My new fiance is ready to kill me for the amount of money I spent on this car as her '98 Camry, while boring and painful for longish trips, is very reliable.

Currently the stalling problem manifests itself under the following conditions.

Start cold - all is fine. Drive until warm (30 minutes or more). Turn off car for 30 min. to 1 hour. Engine temp on warm start is just below 80. Car will stall when stopping quickly or slowing for a turn. Braking slowly will sometimes avoid the problem. The danger of stalling will continue for 30-45 min. Sometimes longer. When braking quickly the tach just drops all the way to 500 then dies, no sign of catching around 1000 or 800. Car will start up immediately. When acting up, the idle will seem to fluctuate between 700-900.

Over the past couple years just about everything has been replaced, idle speed valve, over voltage relay, fuel pump relay, various micro switches, distrubutor, injectors, hall sensor. The last thing replaced was the ECU itself upon dealer diagnosis. I bought a used one last september and the problem appeared to go away until about 2 months ago.

Disconnecting the ECU alleviates all problems but makes for hard cold starts. But I am not convinced this is the problem (I don't know if it ever really was) as disconnecting the ECU also bypasses all the other electrical stuff and makes the car run on mechanical fuel injection. My recent online investigations, including these forums make me suspect the fuel pump relay (again) or the fuel pump check valves. I can hear the fuel pump on cold start, and I believe the fuel pump relay controls this, but is it possible that forward braking momentum is causing it to shift and let the car stall? Remember it does hesistate briefly at about 500 rpm before it stalls. Same question for the check valves, would forward braking momentum cause these to close when they shouldn't be?

Any other ideas would be appreciated as I do like driving this car. I also plan to check the allen bolt on the TDC sensor, whcih I believe is near the oil filter?

Thanks alot,
Garth Gillespie

Hi,
About the stalling problem, I bought an '86 300e a couple of years ago. I haven't had any problems with it stalling, but I found a website called: http://www.mercedesproblems.com/
If you go to this site, you can select your make and read up on the other people's problems and what they did to fix them. Personally, I prefer this forum to that one. This forum is for people who want to fix their cars and not just ***** about them.
Anyway, back to the issue, apparently, quite a few people have had problems with the 300e stalling. Only one guy that I remember was able to fix this problem by replacing the wiring harness. Perhaps the wires get brittle. Who knows. Anyway, check that site and continue to check this one. You'll get your answer.
Oh, tell your Fiance that Camery's may be okay, but they don't reflect your superior taste!
Good Luck

__________________
Kyle De Priest
2007 e320 Bluetec
2013 GLK 250 Bluetec

YOU ARE IN LUCK! I just went through this on a car...I spent two days on the same problem and, after talking with two of the other techs on this board, fixed it! (Thanks to DOC, and BROTHERTON!)

You will need to monitor the fuel plate sensor. It WILL stall the car! It is located just under the fuel distributor to the front side of the engine. It has 3 wire connected. If the signal goes open for a split second, the controller will turn off the idle speed system..This causes the stall. Also it will change the amperage to the EHA. This causes problems.

The thing you can do is remove the sensor (MARK FIRST!) Then clean only the sensor portion with a clean pencil eraser. Reinstall and see if it helps.

If not, you will have to replace.

__________________
Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

Hi Donnie,

Is the Fuel Plate Sensor the same as the Fuel mixture Sensor on a 190E (2.3)? If so, how can you monitor it - do you need special tools for this or is this something best left to a dealer?

I have a similar problem on my 190E. I cleaned the contacts on the Fuel Mixture Sensor and it seems to be better but I'm not sure it has entirely solved the problem. It stalled once on the first day after cleaning the contacts but has not stalled since. I'm just wondering, do you need to drive for about 100km afterwards for the ECU to reset?

VJ

__________________
190E 2.3, 1988

Thanks Benzmac, I was hoping you would reply.

I immediately tried to get to the sensor, but it is not exactly easy to remove. I don't have a small enough philips head ratchet. I will take this to a mechanic I trust and have them do this.

Any ideas on why the symptoms only exhibit after the car has been turned off for 30-60 min?

Because I can hear the fuel pump when I turn the key I believe it is not the fuel pump relay giving out but what is your opinion on the fuel pump check valves?

Thanks,
Garth

Fuel pump check valves don't play a part in running. They keep the pressure in the system after stopping which prevents hard hot starts.

The airflow potentiometer is rather easy to test. There is a power wire and a ground and the signal wire. The signal wire will have about 1-4v depending on the airflow. The critical value at idle is around .8v. The important thing is consistant readings. Values that change by more than .1v with constant airflow are probably bad. If you remove the device from the airflow meter the semiconductor that the wiper rides on can be seen to be worn through on the ones that can't be cleaned. As Donnie pointed out the traces can be cleaned with an eraser if the path isn't worn through. The area worn through will always be in the idle section.

One other alternative on your early 300e is a service bulletin changing the idle speed. Basically you get to a connector under to fusebox. You get the wire that comes from term 50 on the starter to the KE- controller. Separate the wire at the connector and ground the side that goes to the KE controller. Separate and insulate the wire that goes to the starter. This will increase the idle speed while in gear by more than 50rpm. It can make the difference.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks Steve.

I will have the potentiometer checked out. I have just doubled checked all the work orders and this piece has not been replaced. It still has the (original?) yellow paint marking the position.

I looked for this part in the parts shop but couldn't find it. Any idea how much it runs should it turn out to be bad?

Also, any theories on the "only after warm start" scenario? Does it behave differently once engine temperature is hot vs. passing through this point from a cold-start?

The mechanic I will be going to is more of a specialist with BMWs. He's been doing nice work on my Audi and also works on Mercedes, but they are not his bread and butter. The dealer has been taking my money thus far for this stalling problem and the problem remains.

Thanks again,
Garth

Unfortunately the airflow potentiometer is only available preset on the airflow meter. It isn't as expensive as that would seem but the labor to replace it is also a bit as the whole thing is replaced which requires all the adjustments to the fuel distributor. Its a bunch cheaper than the fuel distributor.

As to temperature. I imagine it has to do with the amount of airflow at idle. Once warm the amount of airflow at idle is lowest and also the largest portion of total one spot movement. This is the place that wears out first and is also the time when the idle is lowest. Because of this I would highly recommend the simple rpm fix. Not only will it give you more idle to oppose the problem but it will also add more air so the airflow meter will be it the position that seems to work better.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Ah. Well I will have the mechanic try the cleaning first and see what happens. If there is no change I will opt for the idle increase. I have a couple questions about that.

So all the rewiring happens at the connector beneath the fusebox? Does either wire remain connected to the connector after the procedure? The one to the KE is grounded. For the starter wire ... by insulated do you mean the wire to the starter is just wrapped in electrical tape and nothing remains connected to the connector?

Right now, I wish I lived in Florida, but I am on the other side of the continent in San Francisco.

Thanks!

__________________
Garth Gillespie
87 300E
92 Audi 100CS Quattro

You should have the wiring diagram. Identify the connector by the function. The wire is going from the starter terminal 50 to the KE controller. It passes through this connector beneath the fuse panel (there are two similar large connectors there). I don't remember which side is male and which is female but both sides of the connection can be taken out (this is a ten or twelve wire junction) of their sides of the connector. On side is taken to ground (the side that goes to the KE controller), the other side has to be isolated. The way to tell which side is which is to separate them and engage the starter. The side that goes to the starter will have battery voltage on it while cranking (the other should not.

Yes, the wire from the starter side can be left out of the connector insulated and attached to nothing. It can also be left in its connector if the other side is removed. Leaving it in its hole with nothing across from it does a nice clean job. Just take the KE side out of its connector and ground it. JUST KEEP IT FROM THE STARTER SIDE.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Got it. Thanks very much! I'll post the results.

__________________
Garth Gillespie
87 300E
92 Audi 100CS Quattro

One last question.

I can't bring the car in until tomorrow so I have one more day to think about this.

If the stalling problem turns out to be the potentiometer, could this fluctuation of voltage actually damage the ECU/KE Controller? I ask because the ECU replacement did make the problem go away for awhile and when it acted up again my first thought was that there is another problem that is damaging the ECU. So if I simply clean the potentiometer or replace the entire air-flow meter will I still experience problems because the ECU is damaged and I will need to acquire another used ECU?

Probably thinking too much...

Thanks.

__________________
Garth Gillespie
87 300E
92 Audi 100CS Quattro

The ECU is very durable in these cars. I doubt it that you could hurt it. Thr airflow pot can't, of itself, hurt the controller. Running twelve volts down the ground wire would do it in, but any partial of the sensor voltage will only be misinterpreted.

BTW the airflow sensor part# 103 074 01 14 was more than I thought at $462 MB list.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

That's about the price I saw too. I'm figuring about 3-4 hours labor for an air-flow meter replacement? It's good to hear the ECU is pretty durable. I wonder if I ever needed to replace the first one. Second-guessing the dealer is becoming a hobby.

So is this misinterpretation by the ECU of the voltage from the potentiometer that is possibly letting the car die coming to a stop?
It either gets the right reading and idle continues or it gets a wrong reading and the error condition allows the stall?

Thanks again.

__________________
Garth Gillespie
87 300E
92 Audi 100CS Quattro

Well one air-flow meter later and the car seems to be behaving again. The inside of the potentiometer was badly corroded with rust. The mechanic accused the high pressure engine washers but I have never done this to the car. It did however look like water had gotten in there.

Thanks to Steve and Donnie for their help. Now I plan to put back the old ECU and see if anything changes. I doubt it will.

Any ideas on how to approach the dealer who spent alot of my money and didn't fix this? I'm thinking I will first write to the dealership and see what they do, if I am unsatisfied with their response I plan to write to the local MB rep and possibly the BBB.

Thanks again!
Garth

__________________
Garth Gillespie
87 300E
92 Audi 100CS Quattro