1996 850 glt random no start

weird beard · Post by **weird beard** » 19 Jul 2014, 21:43

Always starts when cold. If I stop to get gas for example, it sometimes won't restart. Cranks but wont start. Wait a while and it will start. Fires right up, no sputtering, no excessive cranking. No fault codes. As it does this randomly, I was for the most part, unable to troubleshoot it until today when it wouldn't start again, period! Not getting any spark. Tried a known good coil, same. It started to rain so I had to abandon troubleshooting. Previously installed brand new main relay. Fuel pump comes on, fuel pressure at rail. Don't know if injectors are firing. Didn't try to pull codes when it wouldn't start so I don't know if the ecm is coming online.

Just tried to start it now after waiting 4 hours, fired right up as if nothing was ever wrong.

First question, since I have fuel pressure, does this rule out an issue with the main relay or at the fan shroud or its wiring? Will the fuel pump still come on if the relay is not working or the wiring is bad?

Second question, will a cam or crank sensor intermittently fail in this manner?

Third question, can a failing ignition switch cause this? Everything else comes on, even the heater, it cranks but wont start.

I heading to the wrecking yard tomorrow, willing to try a cam sensor, crank sensor and ignition switch or anything else suggested.

Post by **erikv11** » 20 Jul 2014, 07:51

(1) sounds like the fuel pump relay (number 103) is fine. The relay at the shroud has to do with the injectors firing, although this one does not commonly go bad.

(2) Yes! This sounds like a cam sensor failing/failed.

(3) Doubtful. Usually the dash lights go crazy and there are assorted other, odd symptoms.

(4) Good plan; why not grab the ignition switch you may need it soon anyway.

weird beard · Post by **weird beard** » 20 Jul 2014, 23:32

Picked up 2 used crank and cam sensors today. Installed one of the cam ones. If it doesnt act up again, I will buy a new one. If it does, I will try the other cam sensor first and make my way to the crank sensor. One concerning discovery was that the cam sensor I had appears to be newer than the used ones. It is not however, stamped "bosch" like the used ones. Do the aftermarket ones have I higher failure rate? It is identical except for the casting of the cover not having any markings

Post by **tolaussen** » 21 Jul 2014, 02:48

Please post your further findings if any. I have also strange starting issues when engine is medium warm... Starts up fine when cold/hot.

weird beard · Post by **weird beard** » 23 Jul 2014, 01:17

So far so good. Hasnt been a problem yet. Will update again