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BMW E32 – E38 750iL V12 No Acceleration and Stalling

March 31, 2010

This answer is applicable for many BMWs in addition to the one listed below.

Q
1991 750iL
I have a 750 iL which I’m trying to work on myself. I have put just about everything new on this car. It runs but will not accelerate above 1500 RPM. After a while it will shut off. I also tried my code reader but it shows E in the Fc window. Could you please help me get my car running right?

A
The 750iL engine is operated as two separate 6-cylinder engines, on a common crankshaft. There are two complete engine management systems, engine control units (ECU) and all. If one side is malfunctioning, the engine may still run in a “limp” mode, but may eventually shut down …. as you have noted. We really do need to check on the fault codes. The “E” that you are getting, with the code tool is indicating that the tool cannot properly connect with the vehicle’s ECU (in your case, it could be either one). We need to verify if the malfunction is in the code reader tool or the vehicle.

In order to test if the “E” is due to a faulty tool or a fault with the vehicle, you can try the code reader tool on another BMW (most models from 1988 through 2000) to see if it will properly access the ECU (no “E” code). If it does, the problem is within your vehicle. The common problem is excessive resistance in the wiring harness and connectors,between the DLC (Data Link Connector) and the ECU. This shows up on the older BMW models due to oxidation and corrosion on the harness connectors. If this is suspected, you can apply DeoxIT compound (electrical component cleaner and contact enhancer) to the DLC pins, the crimped pin-to-wire connections (under the plug) and to the pins in the ECU harness connector plug (after removing the harness plug from the ECU). Remember that your 750iL has two ECUs. This may clear up the potential poor connection and allow the tool to work.

Click below for DeoxIT contact cleaner:

* If you have no other BMWs available for you to test the tool on, you can send the tool to us and we can test it here.

Once we can access the potential fault codes, we can start our diagnostic track.

While we are waiting to check for any fault codes, let’s perform a Power Balance test (if you have not done so already). This test may help us to determine if just one side of the engine is running or if one side is running stronger than the other.

With the engine running, pull the spark plug wire connector from each spark plug (one at a time) and observe how the engine reacts. With a properly running engine, you would find that as each cylinder is “killed” (when the spark plug wire is disconnected) the engine will obviously miss and run poorly, and each cylinder will give a similar level of performance reduction. If we have one or more cylinders that are running poorly ,or not at all, when the plug wires are disconnected on these cylinders, the reduction of engine performance will be less apparent …. or none at all. In the case of your 750iL, we would be interested in determining if one whole side of the engine is running poorly, or not at all.

Tom Wrote back:

Q
Thank You for the information about Deoxit.  It worked, and I got codes 1,2,3,4,5,6,7,8.9 in the (In) window. My code booklet only shows answers for 1,3,8, If there is a manual on the codes please let know so I can purchase it .

A
I think you may have used the code reader tool incorrectly. You mentioned that you saw the 1 through 9 numbers after you had the “In” indicator showing. If this is the case, you just reset the service & inspection reminder. The “In” indicates that you were in the Inspection reset mode and the 1 through 9 displays are what the tool shows as it performs the reset.

Check the fault codes as follows:

1) Plug the tool in.

2) Turn the key to the Ignition position.

3) The tool should read “Fc”. This indicates that it is in the fault code reading mode. If it does not read “Fc”, push the Select button until the tool reads “Fc”.

4) Push the “Go” button.

5) The tool will now display the chart number to use (in the code book). If the vehicle is older than 1996, the tool will display “FF”. In this case, use the FF Fault Table Locator chart in the code book, to determine which chart to use.

6) Press “Go” again. The tool will now begin to display any stored fault codes. If there is more than one fault code. a new code will be displayed each time the “Go” button is pressed.

Note that since your BMW is a V12 model, you actually have two complete engine management systems (one for each side (bank) of the engine. Therefore you have two Engine Control Units (ECU). The tool will read the 1st ECU when in the “Fc” mode. After you read the 1st ECU, Press the Select button until you see “Fii”. You will now be reading the second ECU. Continue by pressing the Go button, as before.

2 Comments
  1. Darryl permalink

    I have a 1995 E38 750 I can start the car, but when I push on the gas pedal, nothing happens.

    • Have you checked for any engine management fault codes?

Comments are closed.