735i cranks but won't start

[Shadower]

I have a E32 735i, I drove to a store today, it started up fine. Then when I tried to leave it wouldn't start, it cranked, but wouldn't run. I finally got it running by pressing the gas paddle while cranking it. I made a few more stops, and it happened again on the next stop, but started up again fine without giving it any gas on the last try. Anyone know what could be wrong?

[redhed]

Hmmm..... I'm no mechanic, but have you checked your air and fuel filters?

[Micah McGinnis]

Ok, you have a 1987 BMW right? I bought an L6 with the same simptoms except mine has given up and the starting. I have read resently that older BMWs can have problems with their ECU (Electronic Comtroll Unit). The problem with mine is that it isn't sending enough voltage to the coil to make a spark big enough to jump the spark plug gap. The person I have bought my car from said that it ran fine, then wouldn't start, than he got it to start but wasn't sure what he did to do that. Then I just stopped starting all together. This is the ECU on its way out. The way to check to see if it is your ECU causing the problem is to check your ignition system. Get a volt meter, or multimeter and put it on your coil primaries- the + and - wires. have someone crank the engine for you will you read the voltage. Mine read about 9 volts. Not good being that it is supose to take the voltage from your battery (12 volts). If you have a good reading that I have just wated your time. If not the ECU should be located behind the glove box. Remove it and the cover that shelds it from the glove box and it just unplugs. Now if I am right I beleave your ECU can come from a bmw 1985-1988 535, 635, and 735. If so the numbers on the tag will be:0261200059. I am currently bidding on one on ebay. You can get them rebuilt by a company called Vertex Automotive- http://www.vertexauto.com/dme/ and I beleive it runs about $350. First I would try your locate auto salvage yards.
Please e-mail me to let me know if this was useful.

[Kiwi_Steve]

MY guess is that it will be electrical, and possibly the coil although I have only just bought my E32 (which is nothing like the model Micah is describing - but the fault could be something similar) - Our ECU is in a box under the hood on the (let me think for a minute - we drive on the right hand side here in New Zealand ) ...ummm... passenger side for you guys - there are 4 screws on the lid - the other box on the other side is full of fuses.

I had a similar problem with the engine dying randomly recently and pulled the plugs from ALL the computers (ABS as well because the brake warning light was coming on when it died) and re-seated them - this has, to date, cured that problem.

I really know very little about the E32 having only just got it - but there is an electrical troubleshooting guide that has been put on the web for me to download by a friendly BMW guy called Rob here: http://homepage.ntlworld.com/rob.nicol/BMW/

Anyway, keep us posted and let us know how you get on with it.

regards

Steve

[Dunowen]

I have a 1990 735il which had same problem you described, and fix had to do with the pressurized gas line. As it was explained to me, when you shut off engine, gas line to engine ramains pressurized by means of a check valve which is part of a continuous gas line loop back to the gas tank. This constant pressure in gas line allows engine to start when you next use car. If the check valve in the gas line fails, then there is no pressure in fuel line at start up, and you get the problem you describe. Once my check valve was replaced, no more problems at start up. This check valve only affected performance of engine at start up, and car always ran fine once it was underway, even with the malfunctioning check valve.