Limp mode+ASR

[SirEmil]

Well this is a long story. My uncle bought his W124 500E 1992 back in year 1999 The car have gone into limp mode 4-5 time every year since he bought it.

During 2019-2020 it started to happen more often, so in 2020 we changed the engine harness. After this the car went into limp mode almost every time we drove it. 2021 we changed the trottle body and thought it was a success to the problem, the car ran perfect for a short period of time. Then it started to go into limp mode again!

An addition to the story is the ASR light that have came on over all the years my uncle owned the car, unfortunately there is no common thread between the ASR light and when the car go into limp mode.

The list of things that have been changed:
Spark plug + wires
Engine Harness
Throttle body
Rotor+distributor caps
Ignition coils

I recently sent the e-gas modul and the throttle body to a company in Germany since I might thought the e-gas modul was broken. They did a combined test in a simulator with no errors.

When the car is cold and have been standing for a few hours it always run perfect, after a drive of 10-15 minuter it starts to run bad and go into limp mode. The ASR is sometime on and sometime off as a mentioned before.

I pulled the fault codes last summer.

What should I do with the car? It´s so frustrating.

It´s quite hard do describe the history of the problem. Maybe the problem is more like the engine misfire.

Best Regards
Emil
Sweden

 

[gsxr]

Hello Emil,

Most of the time, limp mode is due to the ETA (throttle actuator), failed or mis-adjusted NSS (starter lockout switch), or in some cases a mis-adjusted throttle cable. There can be other causes but those are the top 3, IMO.

You have 2 issues with your codes displayed on HHT-Win. First, those are likely old codes that could have been stored years ago. You must clear all codes and drive the car, then see which codes return quickly. Any codes which do return immediately, need investigation. Second, your SDS is not communicating with the most important module, E-GAS (EFP). Check the SDS Mux and also check the 38-pin diagnostic port for corrosion or bad connection at pin #7. The codes on the E-GAS module will help identify the cause of limp mode. E-GAS module failures are quite rare, and it sounds like you already have ruled that out. To check the NSS you need HHT-Win live data from E-GAS (EFP).

When you "changed the throttle body", did you install a brand new one? Or a professionally rebuilt one? If not, send your old/original to Don Roden at RFC Electronics in USA for a rebuild & failure analysis report.

Oh, and welcome to the forum!

 

[SirEmil]

Hello Emil,

Most of the time, limp mode is due to the ETA (throttle actuator), failed or mis-adjusted NSS (starter lockout switch), or in some cases a mis-adjusted throttle cable. There can be other causes but those are the top 3, IMO.

You have 2 issues with your codes displayed on HHT-Win. First, those are likely old codes that could have been stored years ago. You must clear all codes and drive the car, then see which codes return quickly. Any codes which do return immediately, need investigation. Second, your SDS is not communicating with the most important module, E-GAS (EFP). Check the SDS Mux and also check the 38-pin diagnostic port for corrosion or bad connection at pin #7. The codes on the E-GAS module will help identify the cause of limp mode. E-GAS module failures are quite rare, and it sounds like you already have ruled that out. To check the NSS you need HHT-Win live data from E-GAS (EFP).

When you changed the throttle body, did you install a brand new one? Or a professionally rebuilt one? If not, send your old/original to Don Roden at RFC Electronics in USA for a rebuild & failure analysis report.

Oh, and welcome to the forum!

Thanks for your reply! I should have joined this forum for a very long time ago. All threads I been reading here over the years is amazing. The knowledge!

Been thinking and maybe it´s not accurate to describe how the engine is running with limp mode. Misfire/not running on all cylinders is probably more accurate.

The throttle body is a rebuilt by this company in Germany. When I sent the e-gas module for combined testing they also tested the throttle body with no errors. The company who did the combine test is "ecu.de" also in Germany.

What is the SDS Mux?

Unfortunately it´s winter here in Sweden so I have to wait until May before I can drive the car.

 

[gsxr]

Limp mode is when ABS+ASR lights turn on, and the first half of throttle pedal travel has no effect... restarting the engine will reset limp mode, until it occurs again.

If you have a misfire 10-20 minutes after a cold start, that sounds a lot like moisture in the distributor caps, most likely the passenger side. There are many threads on the forum discussing this. Adding ventilation slots to the caps may help, or even cure, the problem. However you also need to remove the rotor & rotor bracket and inspect the back side of the insulator / dust shield. If there's liquid on the back side, that may cause misfire issues also. Cleaning doesn't always work, new ones wouldn't hurt. I'd add the vent slots on the caps. Off-brand parts may cause issues as well. Oil leaks from the exhaust camshaft seal, or intake advance solenoid, may cause misfire problems too.

Star Diagnostic System (SDS) multiplexer (Mux) is the box between the car and laptop computer. No communication between the Mux and diagnostic port probably indicates a bad connection. Check the diagnostic port X11/4 closely, if there is any sign of corrosion or otherwise isn't perfect, consider replacing it (details here). If you clear all fault codes and *immediately* get CAN communication errors again, without even starting the engine, there could be an issue with a short between pins 2+3 of the diagnostic port as described in that link.

You can also use a hand-held blink code reader on pin #7, if you get analog blink fault codes but the SDS still won't communicate, it could be an SDS or Mux problem (this can be difficult to diagnose).

Bummer you can't drive the car for a few months! That will slow down troubleshooting...

 

[TerryA]

@SirEmil, Welcome Aboard!

I’m glad you found the 500E board. It’s to bad that you weren’t here sooner. Your troubles may have already been solved. There are a lot of knowledgeable people here including gsxr who is one of the best.

So far (knock on wood) my 93 with 143K miles on the clock has been trouble free. I’ve had the ASR light come on a few times but go away after recycling the ignition key.

A lot of trouble seems to start with disturbing the eco wiring somewhere. I see you changed the upper harness which is the worst offender.

When I bought my car in 2004 with 89K miles I was told to change the harness so I bought one in 2005 and still have not installed it at 143K miles. My fear is once I start moving the wires around my troubles will begin and will lead to other wire breakdowns. Anyway, I plan on waiting until something happens to change my mind. I’m sure my climate here in SoCal has helped in my case.

Many members have experienced your limp home mode and have solved it with the boards help. Stick with us and life with your 500E should improve.

Anyway, Emil Welcome Aboard

 

[SirEmil]

Thank you all for the warm welcome

It´s definitely not limp mode then!

I haft to be honest, the answer you have given me in a few hour is incredible. My local dealer don´t have the knowledge sadly to this
type of car anymore. I'm truly grateful

I will get to you guys as soon the winter is over.