1988 e30 cranks, no start. Yes with fuel pump connected directly to the battery.

[jojoluca]

My 1988 e30 (convertible, manual) died on me while driving on a secondary road; before the car stopped, I could start it again, ran for 5 more minutes, and died for good. I towed it back home and tried to diagnose it. I checked the fuel pump's fuse and relay. I also checked the main relay, and all three are OK. I found out that the pump doesn't run when I open the switch and crank the engine. It occurred to me to try and energize the pump with a battery, and it ran. Then I connected it directly to the cigar lighter, and the pump runs, the car starts, and I can drive it (i don't mean to, but as a reference, I took it out and had no issues with enough flow to accelerate it). I read about the Crankshaft Position Sensor as a possible culprit, but I guess if it would be the reason I shouldn't have gas, but neither should have spark, which I definitely have, am I wrong?. As an additional and possible clue, before this complete dying situation, I had a couple of incidents while accelerating and revving over 3.5k RPM to pass another car, and the engine had a frightening hiccup but recovered immediately on each instance (like 10 of them). What line of diagnostics should I follow to find out who is keeping my fuel pump unenergized? Any ideas? Thanks!

[aryahmmr]

that's an interesting issue. Have you tried jumping the fuel pump relay and just checking the voltage to the fuel pump, as well as the current draw of the fuel pump?

[jojoluca]

Thank you!
I started checking the voltage at the fuel pump relay and took it from there. It is solved now!


I followed a checklist (see link below) to discard problems back to front: 1- The fuel pump was working (I tested with a direct connection)
2- The fuse (#11) was ok.
3- The fuel pump relay was dead: connector #30 should be hot with 12V.
4- I looked for an electric diagram for the fuel pump (see below). If you follow the line from the battery to the fuel pump relay, it shows that it feeds directly from the battery. And if you look at the main relay, which is sitting on the left side of the fuel pump relay, it has the same scheme, feeding directly from the battery.
5- I checked connector #30 at the main relay, and it was hot.
6- I jumped both connectors #30, and the car started!
Now I had to find where the cable from the battery to the fuel pump relay was damaged.
7- The cable goes down from the relay base and around behind the alternator, parallel to the left side engine block, up by the diagnostics port, and to the battery, in a continuous thick black pack. Nothing in the route looked wrong.
8- At the battery post (+), I had 4 cables; one looked suspiciously crooked. I checked continuity, and that was the guy. It went back to the fuel pump relay.
9- I changed the end connector and had the car back to running condition.
10- After fixing the electric issue, I cleaned the Idle Control Valve, eliminating the hiccup I reported when accelerating.


My car: 1988 BMW E30, 325i, Convertible, Manual transmission, Battery at the front.


I'm putting together the resources I found while looking for the solution:
This is the diagnostic list I followed (on pages 4-6):
https://www.yumpu.com/en/document/read/36491443/bilsteins-b16-ridecontrol-bavarian-autosport
Note: it is an old newsletter from Bavauto called Fast times -Fall 2007
These are the electrical diagrams for each e30 model (link taken from vertbmw)
http://www.armchair.mb.ca/~dave/BMW/e30/
This is the video I used as a guide for cleaning the Idle Contro Valve:
https://www.youtube.com/watch?v=ZbF0V7nlxao&t=173s