Suspected air/fuel ratio issue with a 94 E320
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94 W124 E320, Ford Excursion Limited V10, 02 BMW E39 525i
Suspected air/fuel ratio issue with a 94 E320
Hello there! Sorry for the long and poor description, and I hope I'm not posting in the wrong forum. That's my first post.
I've a 1995 Mercedes W124 E320 with ASR/ABS. It idles fine but refuses to rev over about 2k rpm. If I press the throttle beyond that limit it starts to hesitate till it dies at wide open throttle. After many tests it seems like it's an air/fuel ratio issue that MAY be caused by Throttle Position Sensor (TPS). I've access to TPS wiring diagram. I'm not an expert, but it seems like this TPS is a 2 potentiometers connected in parallel. Here's a diagram exactly copied from the original diagram, and here are the readings using a multimeter set on 2K ohms. Do these readings indicate that there's a single potentiometer that's not functioning? And if so, if they're connected in parallel, does that affect the TPS functionality? Or do they back each other up? As I understand, the variable resistance tells the ECU the exact position of the throttle so it injects an appropriate amount of fuel. Sorry again for the long and poor description. Any input would be greatly appreciated!
Thank you very much!
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2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
Sounds like classic ecco-junk disease. All 94/95 W124s came with "biodegradeable" wiring harnesses which disintegrates over time. Both the main engine wiring harness and the Throttle Body Adapter (TBA) are affected. You need to check the date codes on these items - they must be 1998 or later. Search the various forums for where to check for the date codes. Until the ecco-junk wiring is replaced (both the engine harness and the TBA), you will never be able to diagnose the issue or get the car running correctly. Mercedes took a lot a heat for this issue, but never owned up to it. It's one of those little hidden time bombs in the W124 family.
Last edited by Floobydust; Apr 13, 2020 at 09:32 PM. Reason: typos
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94 W124 E320, Ford Excursion Limited V10, 02 BMW E39 525i
I did already ☹️ In fact, I went through everything I can think of. It's been a whole year and I'm frustrated.
Thread Starter
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94 W124 E320, Ford Excursion Limited V10, 02 BMW E39 525i
Sounds like classic ecco-junk disease. All 94/95 W124s came with "biodegradeable" wiring harnesses which disintegrates over time. Both the main engine wiring harness and the Throttle Body Adapter (TBA) are affected. You need to check the date codes on these items - they must be 1998 or later. Search the various forums for where to check for the date codes. Until the ecco-junk wiring is replaced (both the engine harness and the TBA), you will never be able to diagnose the issue or get the car running correctly. Mercedes took a lot a heat for this issue, but never owned up to it. It's one of those little hidden time bombs in the W124 family.
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94 W124 E320, Ford Excursion Limited V10, 02 BMW E39 525i
Here's a video that describes the issue. That fluctuation at idle increases in frequency if I rev it, till it dies at wide open throttle.
Video link Google drive
Video link Google drive
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2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
While the usual problem is the ecco-junk wiring, the potentiometers in the TBA do fail sometimes. I think either way, you are going to have to find a new (used) TBA with the later date code. I learned the hard way that you can't fix/rebuild the main engine harness. For each piece of cracked insulation that you fix, there are half a dozen more right behind it. It's a loosing battle.
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Thread Starter
Newbie
Joined: Apr 2020
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94 W124 E320, Ford Excursion Limited V10, 02 BMW E39 525i
While the usual problem is the ecco-junk wiring, the potentiometers in the TBA do fail sometimes. I think either way, you are going to have to find a new (used) TBA with the later date code. I learned the hard way that you can't fix/rebuild the main engine harness. For each piece of cracked insulation that you fix, there are half a dozen more right behind it. It's a loosing battle.
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MBWorld Fanatic!
Joined: Nov 2002
Posts: 1,028
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From: Massachusetts
2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
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A Speeduino setup would have that engine running perfectly for a few hundred bucks but one has to be savvy and able to put it all together. Add to it that you could actually tune your own engine and it would be well worth the effort. The older systems have become very disappointing and were never great when they worked. I agree with you, scrap it.
