No Start '87 BMW 325e

[pastamosta]

This weekend I was working on my car and replaced the center bearing and guibo on the drive shaft and fixed some exhaust leaks. Anyways I finish up, drive home, it runs great for about 30 minutes, and then all the lights on the center console flash and the car dies. I pull over, let it cool off, start it up, and it runs for about another mile and dies again the same way.

*(Most likely the cause of the problem) While I was working on my car I hooked up the battery charger opposite for about a minute before I corrected it... the battery terminals are ghetto.

I pull it home later that night and start diagnosing. It's cranks over, its getting spark, but no fuel. The fuel pump is getting no signal/voltage, but it works (I hooked it up directly to the battery and it pumped out fuel). All the fuses and relays are looked good (I'm going to replace the fuel pump relay just in case, but I waiting for it to be shipped to me). The only other thing I would think that's wrong is something happened to the wire from the relay to the fuel pump, but I checked it over and I couldn't find anything blatantly wrong.

I thought hooking up the battery opposite would blow out a fuse or something, but I can't find anything wrong... anyone have any input?

[jlevie]

Spark but no fuel pressure at the rail is a bad fuel pump relay, wiring fault, clogged filter, or failing fuel pump.

A battery charger probably doesn't have enough power to damage anything in the car if hooked up backwards. And it may well have gone into short circuit protection when connected backwards. i presume you didn't try to start then car in the interval that the charger was mis-connected, in which case the only things exposed to a reverse current situation would be those that are connected to un-switched power (interior lights/radio/OBC, alternator, cluster, and DME). Damage to the DME is possible, but unlikely. So look for other causes of the fuel issue.

[Knockenwelle]

Check for proper voltages at the relay connectors (supply AND signal) for the main and fuel pump relays. Try jumpering confirmed battery power to the fuel pump power output at the pump relay to see if the wiring to the pump is intact. Fusible link is my first thought, though that will usually kill spark, too. Main relay is a possibility, as there are some electronics in there, like diodes, which do NOT like reverse polarity. While the main relay signal circuit IS switched power, the power circuit is not. Relay pinouts can be found in the electrical pages of the BMW repair manual.

[pastamosta]

Finally found the problem, one of the wires going to the fuel pump relay was corroded and broke off right where it goes to the relay box.

Thanks for the help.