95 740i engine won't rev up

[technoggins]

Hi,

I have a 95 740i 66K that won't rev up beyond a certain RPM. It is totally temerature dependant....the colder the engine, the lower the max rpm I can get before the SES lights up, and the engine cuts out.

To give you a complete example:

If I were to go outside right now (30 degree ambient temperature) and try to start the car, it will start, rev between 200-600 rmp, with a definate 'cut out' at 600 rpm, and a reignition at 200, unless it stalls. This will continue 'pulsing' like this for about 3 minutes, untill the engine temp is 1/3 the way up.

Once the engine temp is 1/3 up (guage on dash), the engine idle will smooth completely out and idle fine without any pulsing. If I try to press the gas pedal, it will 'cut out' and begin pulsing again untill I let up on the gas (barely pressed to begin with).

After the engine has been idling smooth for about 5 more minutes, and the dash temp guage is at full operating temp (half way), I then can try to press the gas pedal and get the engine to rev up to about 2K before it starts pulsing again.....cutting out at 2k and reignition around 1k.......

After idling for about 20 minutes, I can actually drive the car, but I can NEVER get the RPMs over 3K before it 'cuts out'.

I took it to an independant mechanic who used a Snap-On scanner. It reported a crankshaft sensor fault, and a 'vehicle speed cirsuit sensor' fault.

I replaced the crankshaft sensor, but no change. I have cleaned the MAF, no change. I have removed and cleaned the Idle Control Valve, no change. I have replaced the sparkplugs, no change.

I have tried disconnecting various sensors to see how it impacted the problem: disconnect the MAF, and the engine speed goes down, but no change to the cut out problem. Disconnecting the crankshaft position sensor gives no indication of change either plugged in or not. I have disconnected the knock sensors without any change.

I am suspicious of the cam sensor because it doesn't seem to have any effect when I connect or disconnect it.

I have sprayed carb cleaner around the intake manifold while the engine is running to try to detect any leaks via engine reving up, but it does not, so I assume thereare no leaks. I have also sprayed carb cleaner around all the air intake tubing and connectors to make sure there weren't any leaks there. Am I correct in assuming that if there was an air leak and I sprayed carb cleaner into it, the engine rpm would respond? I don't want to use starting fluid for my air leak test for obvious reasons.

I do not have access to a scanner again. I think I will just be relegated to the 'stomp' proceedure to get DME codes. Every time I try the stomp proceedure, I only get one code, not several codes pulsed out one after another. Is anybody else familiar with using this proceedure for getting error codes?

Clearing these codes....I think I can just unplug the battery for a few minutes to clear the codes....right? OR, use the dash button tricks to get into test mode and clear the codes there? Anybody have experience with this?

I have the Bentley repair manual for this car, but it doesn't give any instructions for testing the sensors...just instructions for replacing them. Does anybody have instructions for testing the MAF, Knock, temp, crank and cam sensors?

Thanks!
Jamie

[lincolnmaster80]

Sorry for the late responce, but if you haven't figured your problem out, I'll try and offer a solution.

If I'm not mistaken, the E38's have two crank shaft sensors. Not sure where the other one is located, but the code won't specify which one has failed, if I remember that right. Your suspicions about the crank sensor may be correct in this case.

At first instinct, it sounded like a MAF problem or false air problem. But since you checked that, it's probably the aforementioned crank sensor. Hope this helps.