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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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Discussion Starter · #1 ·
Hi all. This has been an issue I have been chasing for the better part of a year now and its really been a bummer.. Just a warning, this will be a very long post, so grab a beverage and enjoy.

Background: The car in question is my 1986 W124 300TE Euro spec M103. This car was imported over from Germany and its history is largely unknown, but the car seems to have been serviced regularly at the dealership in Germany. This car was originally auto, but since then I have (painfully) swapped it over to the 5 speed dogleg manual (found in the 190E 2.3-16). Mind you, these issues existed before the trans swap.. regardless, the transmission has really no impact on motor function on these cars.

Problem: The random stall issue. When the car is cold it fires right up without hesitation, reaches operating temperature and everything seems to be fine. After 15-25 mins of running at operating temperature, it seems like the idle drops suddenly and runs a tad rough for a few seconds and recovers. If you give it throttle (only when completely warm) the first 5% of throttle if jabbed will cause a slight hesitation (while sitting in neutral). The bigger issue is that the car has stalled when test driving it randomly when I let off the gas and push the clutch in when coming to a stop. The stall is so silent, you wouldn't notice until you see the dash light up and it starts right up as if nothing happened. Otherwise, during driving it accepts WOT and other ranges of throttle just fine. In addition, if the car sits when hot for about 15 mins, it is an absolute pain to start. Sometimes it will take a long crank with an occasional pedal pump to get it started. This makes me suspect fuel pressure loss, but where....

What I have done/replaced/repaired/tested: (All parts are either MBZ OEM or Bosch)

Fuel:
1. New fuel filter.
2. New injectors.
3. New injector seals.
4. New fuel accumulator.
5. Swapped fuel distributor from parts donor (running and driving). The original on the car was constantly dripping fuel in, I tried replacing the seals and the issue persisted. It was likely the shaft was too worn or damaged.
  • The duty cycle was adjusted accordingly. I forget the values off the top of my head, but I remember finding a forum post that went in great detail about it.
  • The potentiometer was adjusted to the specified voltage and was tested for dead spots (no dead spots present). I don't remember the values off the top of my head again.. But I can check if needed.
  • The EHA seals were replaced and the EHA is untouched.
  • The O-ring under the fuel distributor was replaced.
6. New O2 sensor.

*For the fuel, I rigged a testing apparatus and flow tested the new injectors (uses the OEM lines and pump on the car). None of them leaked and all of them had a flow that was within 1% difference between the adjacent one. Aka they all flowed nearly the same.

I have not tried testing the FPR. I forget the process, if anyone remembers.. I had the link somewhere. I do have a spare from the working parts donor however.

Ignition:
1. New spark plugs (Denso T20EP-U).
2. New spark plug leads.
3. New distributor rotor.
4. New distributor cap.
5. Swapped ignition coil before between another working one in case that was the suspect, no difference..
6. Reapplied thermal paste under the EZL. Swapped with another working one as well, no difference..
7. New crankshaft position sensor. Old one tested fine.. but what the ****, why not.

Air:
1. New air flow monitor (pot) rubber boot (sits under). The old one was all cracked and full of holes. Not sure how the car ran at all with it..
2. Replaced the ICV with a known working one from a donor. I have 3 more.. all of them including the one on the car actuate correctly when voltage is applied and all look clean. I haven't tried driving since then, but again.. still don't think this is the issue since the hot restart issue persists and stubble described above.
3. Replaced vacuum lines, checked for vac leaks.. none present.
4. New air filter.


Electrical:
1. I have a bunch of used OVP relays and have swapped between them and have not noticed a difference. What are the chances they are all dead? I accidentally ordered the wrong OVP (6-pin OEM MBZ, I need the 9-pin) so if anyone needs one, id be happy to sell it.
2. Fuel pump relay.. I have another one and could try swapping it, but I really don't think this is it..
3. Coolant temp switch. Tested resistance and function, all within spec.
4. Throttle micro-switch. There is continuity between the pin closest to the firewall and the one the furthest away. When the switch opens, the continuity stops. Seems ok?
5. ECU.... I know these rarely go bad and I doubt mine has.. But is there a way to test it? Would suck *** if it was the culprit.

*Haven't tried replacing the battery, the one on the car is quite old at this point. However, when the car is on there is a consistent 14.2 Volts at the terminals, so the alternator works.

Other (unrelated):
1. New valve cover gasket.
2. New valve stem seals.
3. All new fluids, PS/brakes, oil, coolant etc..
4. New exhaust gaskets.

I've likely missed something, but if its brought up it will likely jog my memory.. I swear ive been through the whole car at this point minus replacing the engine block ha.

Whoever can help me figure this out, leave your paypal and I'll buy you a beer/coffee/tea, because lord knows I've been through many myself trying to chase these demons.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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Have you taken any fuel volume and system pressure readings (system, control (warm + cold), rest) yet?

If not, start there. Bosch mechanical injection does not work properly if the pressures throughout the entire fuel system are out of spec.
 

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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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43 Posts
Discussion Starter · #3 ·
Have you taken any fuel volume and system pressure readings (system, control (warm + cold), rest) yet?

If not, start there. Bosch mechanical injection does not work properly if the pressures throughout the entire fuel system are out of spec.
Hey Sbaert! Hope you have been doing well.

I did take pressure checks sometime ago.. but I will run through the system again today since a few variables have changed. I need to dig up my notes about the testing procedures again, but I'll go ahead and test it and post the results .
 

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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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Discussion Starter · #5 ·
In classical fashion, my fuel testing gauge kit has decided to break specifically on the one fitting that I need to check the chamber pressures.. I'll have to order in another CIS testing kit and will report back once it arrives.
 

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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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43 Posts
Discussion Starter · #6 ·
I’d check the main harness for any bare wires
I'll look over the harness at some point, but I'd imagine a short in the wiring would cause intermittent issues that aren't correlated to heat right? I forgot to mention, I've inspected all the grounds, cleaned them and made sure all was well there. I believe this year wasn't plagued by the degrading insulation used by Mercedes.
 

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W124, 230E 5 speeds Manual, 1987
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That Silent Stall happened to me last year and mostly when pressing the clutch or when AC is on. My problem was simply a Bad Throttle position Switch which you never mentioned in your replaced parts list. it is easy to test. just like the microswitch. it has an IDLE Contact and a WOT Contact.
Automotive lighting Headlamp Auto part Font Automotive wheel system
 

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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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Discussion Starter · #8 ·
That Silent Stall happened to me last year and mostly when pressing the clutch or when AC is on. My problem was simply a Bad Throttle position Switch which you never mentioned in your replaced parts list. it is easy to test. just like the microswitch. it has an IDLE Contact and a WOT Contact.
View attachment 2709755
Good call. One thing I missed when looking over the electricals. I’ll try and test it today and let you know what I find. Do you think temperature would affect it? Would be interesting to see if it failed as everything got hotter.
 

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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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Discussion Starter · #9 ·
That Silent Stall happened to me last year and mostly when pressing the clutch or when AC is on. My problem was simply a Bad Throttle position Switch which you never mentioned in your replaced parts list. it is easy to test. just like the microswitch. it has an IDLE Contact and a WOT Contact.
View attachment 2709755
Just tested the function of the TPS. Contacts 1-2 have continuity when the TB is closed. Contacts 2-3 have continuity when the throttle body is at WOT. Looks like its not the TPS unless it randomly fails when the engine gets hot.
 

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W124, 230E 5 speeds Manual, 1987
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Just tested the function of the TPS. Contacts 1-2 have continuity when the TB is closed. Contacts 2-3 have continuity when the throttle body is at WOT. Looks like its not the TPS unless it randomly fails when the engine gets hot.
Mine started to fail when I drove the car for a long day in hot weather, and it was very random at first. When the car was rolling downhills I could feel the deceleration function not working correctly and sometimes the car feels like it won't decelerate when I lift my foot off the throttle and suddenly it will decelerate randomly for some seconds and so.... but in the end, it was a total failure.
Since you have replaced most of the injection parts I guess you should check the wiring between all sensor plugs and ECU Pins, especially for the TPS, Microswitch, and ICV.
But before doing this I want to suggest a little trick I use in order to identify if the problem is mechanical or electrical. When the engine is off, unplug the ECU, start the car and drive it without ECU. if your system is mechanically working well with a properly adjusted mixture, correct fuel pressure, and no vacuum leaks, it should run perfectly even without the ECU intervention. do this and see what happens and update us.
 

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1986 Mercedes (124T) 300TE euro, 1989 Mercedes 300TE (US), 2006 Mercedes C230 sport (6spd)
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Discussion Starter · #11 ·
Mine started to fail when I drove the car for a long day in hot weather, and it was very random at first. When the car was rolling downhills I could feel the deceleration function not working correctly and sometimes the car feels like it won't decelerate when I lift my foot off the throttle and suddenly it will decelerate randomly for some seconds and so.... but in the end, it was a total failure.
Since you have replaced most of the injection parts I guess you should check the wiring between all sensor plugs and ECU Pins, especially for the TPS, Microswitch, and ICV.
But before doing this I want to suggest a little trick I use in order to identify if the problem is mechanical or electrical. When the engine is off, unplug the ECU, start the car and drive it without ECU. if your system is mechanically working well with a properly adjusted mixture, correct fuel pressure, and no vacuum leaks, it should run perfectly even without the ECU intervention. do this and see what happens and update us.
I finally got some time after work to give it a test. I unplugged the ECU and tried to start it and nothing. If it caught, it would run for maybe half a second and die. So possibly a fuel issue? As soon as I reconnected the ECU it started up right away.

Correct me if I’m wrong, but the ECU and other accessories are there to optimize the mixture, but it should work in the instance of complete failure of the systems.
 

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I finally got some time after work to give it a test. I unplugged the ECU and tried to start it and nothing. If it caught, it would run for maybe half a second and die. So possibly a fuel issue? As soon as I reconnected the ECU it started up right away.

Correct me if I’m wrong, but the ECU and other accessories are there to optimize the mixture, but it should work in the instance of complete failure of the systems.
It could have some troubles starting without the ECU if the engine is very cold and in cold ambient temp.
Try to warm the engine a little and then try to start it without the ECU. You can unplug the ECU when the engine is running, I know some would say it is not recommended but I have done it millions of times without any problems.

1- Are you sure about your mixture adjustment? What deposit color can you see on your spark plugs if you remove one?

2- When you swapped the Fuel distributor did you keep your Original EHA? Basically, each EHA is factory adjusted based on the differential pressure between the upper and lower chamber of the Distributor, so for each distributor, there is a particular EHA Adjustment, this will cause hesitation and poor acceleration if misadjusted but probably won't cause any Stall.

Note: If there is a considerable fuel pressure loss this could be simply identified by the buzzing of the fuel pump, it will have a different noise from when it is under good pressure.
 

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...If it caught, it would run for maybe half a second and die....
I have seen this exact symptom several times with a worn voltage regulator being the culprit.

I'd replace that with a new Bosch unit first and foremost considering the age of the cars.

Everything else is going to cost more.
 

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Discussion Starter · #14 · (Edited)
Okay gentlemen. My fuel testing gauge has finally come in so I finally have some measurements to share:

Cold Engine OFF
  1. Top Chamber + Fuel relay jumped = 5.6 bar
  2. Top Chamber + Fuel relay jumper removed = 2.85 bar
  3. Bottom Chamber + Fuel relay jumped = 5.2 bar (~5.15 bar)
  4. Bottom Chamber + Fuel relay jumper removed = 3.4 bar
Cold Engine ON
  1. Top Chamber = 5.6 bar
  2. Bottom Chamber = 5.2 bar (~5.15 bar)

Furthermore, I decided to try disconnecting the ECU and seeing what would happen once the engine was warm, but I had a sneaking suspicion that with these values the EHA was probably pegged trying to correct. If I disconnected the EHA the engine would get much more unstable. The same condition would happen when the ECU was disconnected. On WOT and heavier throttle the engine was fine, but at idle its getting way too much fuel.

I replaced the ICV in case the old one was starting to cause issues (but I doubt it). I've also left the gauge on and will read it after an hour to see where the pressure is, in case its leaking back to the tank. Does anyone know how long the pressure should remain in the system?
 

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Discussion Starter · #15 ·
It could have some troubles starting without the ECU if the engine is very cold and in cold ambient temp.
Try to warm the engine a little and then try to start it without the ECU. You can unplug the ECU when the engine is running, I know some would say it is not recommended but I have done it millions of times without any problems.

1- Are you sure about your mixture adjustment? What deposit color can you see on your spark plugs if you remove one?

2- When you swapped the Fuel distributor did you keep your Original EHA? Basically, each EHA is factory adjusted based on the differential pressure between the upper and lower chamber of the Distributor, so for each distributor, there is a particular EHA Adjustment, this will cause hesitation and poor acceleration if misadjusted but probably won't cause any Stall.

Note: If there is a considerable fuel pressure loss this could be simply identified by the buzzing of the fuel pump, it will have a different noise from when it is under good pressure.
Just posted a response in regards to the mixture, but I like to respond to individual questions as well. I've replaced the plugs a few times now usually using cheaper plugs during any adjustments etc since they foul up anyway. I haven't pulled them this time, but I have a feeling with the duty cycle its at, they're likely black due to a rich condition. As for the EHA, I'm not entirely sure if this is the original EHA that has been mated to this distributor. I think I'll correct the duty cycle first before touching the EHA. Do you think a delta of 0.4 between the chambers would necessitate the need for an EHA adjustment?
 

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Discussion Starter · #16 ·
I have seen this exact symptom several times with a worn voltage regulator being the culprit.

I'd replace that with a new Bosch unit first and foremost considering the age of the cars.

Everything else is going to cost more.
I remember checking the voltage regulator months ago. The brushes seem a good length and the battery is at a constant 14.2V with no signs of the idiot light going off. I could replace it, but it seems to be working steady. Ill keep an eye on the voltage and document it over time to see if I see any trends.
 

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Discussion Starter · #17 · (Edited)
I took it for a spin and it was getting dark and I noticed once I turned the lights on the dash got dimmer. Drove it back home (died on me again once, but fired back up) and checked the voltage. When it was sitting it would hover at 12.3V uh oh. Lights on + hold down a window to create a strong draw and the voltage dropped to 10.2V.

I went ahead and grabbed a new battery since this one was due to be replaced, but it seems like the alternator has given ghost. I have another one in storage and will swap it out and then see what happens. It could just be low voltage situations causing all these issues, but I still feel like something is still off. Ill try and swap the alternator tomorrow and go from there.
 

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Alright. I've adjusted the fuel distributor so that the duty cycle is right at 50%. I took it for a spin and it was getting dark and I noticed once I turned the lights on the dash got dimmer. Drove it back home (died on me again once, but fired back up) and checked the voltage. When it was sitting it would hover at 12.3V uh oh. Lights on + hold down a window to create a strong draw and the voltage dropped to 10.2V.

I went ahead and grabbed a new battery since this one was due to be replaced, but it seems like the alternator has given ghost. I have another one in storage and will swap it out and then see what happens. It could just be low voltage situations causing all these issues, but I still feel like something is still off. Ill try and swap the alternator tomorrow and go from there.
Swap your voltage regualtor first as most of the times those fails and not the alternator. Try to replace it before the alternator as it is 5min job and test it again. Before testing check your OVP relay Fuse. This may be shot if there was a voltage spike due to bad regulator.
 

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I remember checking the voltage regulator months ago. The brushes seem a good length and the battery is at a constant 14.2V with no signs of the idiot light going off. I could replace it, but it seems to be working steady. Ill keep an eye on the voltage and document it over time to see if I see any trends.
Just posted a response in regards to the mixture, but I like to respond to individual questions as well. I've replaced the plugs a few times now usually using cheaper plugs during any adjustments etc since they foul up anyway. I haven't pulled them this time, but I have a feeling with the duty cycle its at, they're likely black due to a rich condition. As for the EHA, I'm not entirely sure if this is the original EHA that has been mated to this distributor. I think I'll correct the duty cycle first before touching the EHA. Do you think a delta of 0.4 between the chambers would necessitate the need for an EHA adjustment?
A delta of .4 is typical and doesnt require any adjustment
 

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Discussion Starter · #20 ·
Swap your voltage regualtor first as most of the times those fails and not the alternator. Try to replace it before the alternator as it is 5min job and test it again. Before testing check your OVP relay Fuse. This may be shot if there was a voltage spike due to bad regulator.
Will do. Fingers crossed I have a new fuel pump relay and OVP on the way (last few have been cancelled, no stock) and will swap them out so I can at least rule that out. Another thing that I'd like to try is to swap out the ignition coil itself and see if the issues persist. When I was running into these issues with my Datsun, it ended up being a coil that would begin to break apart once it got hot. Starting to wonder if it could be the same issue here. Either way, I need to sort the voltage problems first. Ill keep everyone posted.
 
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