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Discussion Starter · #1 ·
Hi guys,

I have a 1992 E34 M5 3.8. A previous owner installed an aftermarket Link Storm G4+ ECU for odd reasons. Along with this he installed Bosch 465cc injectors and a broadband lambda.

When I bought the car it used too much fuel and it felt kinda jerky. I had the car remapped and it became a different car. Much better with a normal fuel consumption. However, this didn't last and the car was kinda moody. I decided to abandon the aftermarket ECU for many different reasons and go back to stock. One of the reasons was that you need expertise to tune the car, and that I never felt comfortable with it. Also I had two people driving behind me telling me that my car smelled an awful lot of (unburned) fuel.

I'd rather don't want to make this post about whether or not to go standard ECU or standalone. The Link Storm G4+ ECU utilized only the TPS, a sensor measuring the barometric pressure and a temperature sensor. There were no sensors on the intake at all.

The ECU that was in the car while a previous owner installed the Link ECU was long gone so I had to source one used.

The last trip I drove with the aftermarket ECU the car behaved kind of normal.

So, the MAF sensor was brought brand new 3 years ago. However it was not utilized by the aftermarket ECU, but was/is mounted in the car. It has less than 10.000km. We installed the used stock ECU along with a brand new original lambda sensor that was mounted in the X of the supersprint exhaust. We also installed brand new original fuel injectors. we changed the oil and installed a new air filter. The oil smelled quite a bit of fuel. Another good reason to get rid of the aftermarket ECU. We also replaced the intake hoses on the plenum and new vacuum lines. The TPS was also replaced last summer.

This is a car that gets driven about 3-4000km each summer.

So, the problem. The car started right away with the new parts described above. However it doesn't feel too good to drive. On stable, low and medium throttle it feels quite a bit jerky, like the car holds back. It also feels kind of like towing a trailer, a bit pulsating. On full throttle it feels fine.

This behavior came as a direct result of the work we did going back to stock. However, the car has always been a bit up and down, but it actually became worse going back to stock ECU, and that wasn't what I'd hoped for.

I know a guy who has a completely rebuild engine, same car as mine. Everything in that engine is brand new. He also has the same problem now! He rebuilt his MAF and has new crank and cam sensors. He also has the same problem as me.

Is there anyone out there that can shed some lights on this issue please?

This is my car:






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I have the same problem with my 1994 M5 Touring. At cruising or even light acceleration it feels like it’s surging and the ride isn’t linear or smooth. Under full acceleration the car is fine. I had BMW rest everything in the car and they can’t find what’s going on. I’m about to try a local M Specialist.
 

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Discussion Starter · #3 ·
Interesting, we are 3 then. Let's update each other if we find the solution. I don't have the capacity to put it to a shop at the moment. The other guy I talked about is a mechanic so hopefully he'll figure something out. Please keep me updated 😊
 

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Running/driving problems are usually a result of something wrong with 3 things - air/spark/or fuel.
 

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Discussion Starter · #5 ·
Running/driving problems are usually a result of something wrong with 3 things - air/spark/or fuel.
Yes, but it needs to be isolated more. Clearly it isn't easy since garages and mechanics struggle to find the culprit. Maybe someone on this forum had the same behavior and found the cause.
 

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Yes, but it needs to be isolated more. Clearly it isn't easy since garages and mechanics struggle to find the culprit. Maybe someone on this forum had the same behavior and found the cause.
Understood. Good luck.
 

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Hi Sven.

How is your TB´s? Do you know when was the last time that those parts are synched? I also have little lumpy ride, when cruising at part throttle and I am pretty sure that my car needs TB sync. There are many topics in this forum about that those TB´s should maintain regularly.
 

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Discussion Starter · #13 ·
Hi Sven.

How is your TB´s? Do you know when was the last time that those parts are synched? I also have little lumpy ride, when cruising at part throttle and I am pretty sure that my car needs TB sync. There are many topics in this forum about that those TB´s should maintain regularly.
Hi!

I don't know. I would assume they were synchronized when the engine was rebuild approx 19.000km ago. I've received this tip from someone else as well. It's a good thing to get checked out. However, wouldn't the experience most likely be quite similar with the aftermarket ECU as well if the sync was considerably off?

Another question I have. I changed the TPS last summer. Would this need to be calibrated to the stock ECU, and what is the procedure for this?
 

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Discussion Starter · #14 ·
I have some news. The guy I told about in my initial post that has a rebuild engine with all new parts told me to unplug the idle control valve and try to drive the car then. Aside from a very on/off throttle response at low speeds most of the symptoms went away. Even though he had all new parts he's tried with a new idle control valve without any luck. He doesn't have an answer for this.

What does this mean?

Of course this needs to be plugged in. But can anyone make sense of why the car doesn't jerk when this plug is disconnected?
 

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I would disconnect the mechanical portion of the top speed limiter. It looks like the cruise control actuator but is by the firewall and low down. I had a jerking sensation in two of my 3.8 M5's and that's what it was both times. Only 3.8's.
 

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Discussion Starter · #16 ·
I would disconnect the mechanical portion of the top speed limiter. It looks like the cruise control actuator but is by the firewall and low down. I had a jerking sensation in two of my 3.8 M5's and that's what it was both times. Only 3.8's.
Hi there!

I don't think I have cruise control on this car. At least there is no handle for it on the steering column.Cruise control is not on the list of options either:

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I believe that Hartge M5 means the speed limiter. That caused problems in my car also. I removed the whole thing, but it basically only needs removing the cable or the connector.

Here is link to other topic about the limiter. Post #19 shows the picture of it.
 

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I believe that Hartge M5 means the speed limiter. That caused problems in my car also. I removed the whole thing, but it basically only needs removing the cable or the connector.

Here is link to other topic about the limiter. Post #19 shows the picture of it.
Yes, the speed limiter. On two of my 3.8's they malfunctioned and started pulled back as I was accelerating. It felt jerky, but it didn't do it all the time. Finally disconnected the top speed limited cable and it stopped. Just a thought this might be the problem in your case.
 

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Discussion Starter · #19 · (Edited)
Yes, the speed limiter. On two of my 3.8's they malfunctioned and started pulled back as I was accelerating. It felt jerky, but it didn't do it all the time. Finally disconnected the top speed limited cable and it stopped. Just a thought this might be the problem in your case.
Hi again,

I appreciate all the feedback I can get. However I think there's something else wrong with my car.

Since I unplugged the connector to the idle control valve it doesn't want to idle properly. I'm told it will fix itself since the connector is back and connected where it should be. I've disconnected the negative terminal, driven the car 10 miles and started / stopped multiple times. It stills idles too low and unclean.

I did a test yesterday where I removed the black lid saying 'M-power' and I noticed the coil pack on cylinder 5 was a bit lose. I tightened it and the car seemed a bit better while cold. However as it warmed up it became a lot worse. It's usually the other way around.

I then decided to check the coils / spark plugs by unplugging the connectors to the coils one by one while the engine was running. For each cylinder the result was the same. As soon as I unplugged the connector for the coil it ran badly, but normalized while reconnected. The idea was to see if I unplugged a coil and the engine didn't change its characteristics - then I'd know something was wrong with that coil / spark plug.

I decided to remove at least one coil and to check a spark plug. Unfortunately I don't have the right tools and the plugs are very deep on these engines so I didn't manage to get the plug to come out with the socket. However I managed to losen one spark plug and when I looked at the emtpy socket it was full of oil. Crap. We changed the valve cover gasket 6000km ago and I felt we did a pretty thorough job :-(

I did notice that all the 10mm nuts for the valve cover was more lose than I'd consider normal so maybe tighten them up will help. It seems like everything unscrews itself on these engines due to vibrations :-(

I need to get a longer and magnetic socket to remove the spark plugs, check them, and clean the oil before reinstalling the spark plugs. I'm not sure what will happen then but I don't have high hopes.
 
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