Help!!! No power at fuel pump!

[Ga325is]

Hey guys thanks in advance.

1987 325is.

Had power at pump last weekend but no fuel pump operation. So I replaced the pump today but now I have no power at the pump. I have swapped the relay with a known good one and also checked fuse 11. What else is there? I have no pressure at the fuel rail and no pressure at the filter.

Really need to get this running ASAP!!!

[vpilarrt]

Fuel pump doesn't normally get power unless the engine is turning over. However you can jump the relay to make it run otherwise.

[Ga325is]

ok so i jumpped the relay and the fuel pump comes on. Now to figure out why the relay is not engaging... Guess i will have to try another relay. What other reason would cause the relay not to engage?

[vpilarrt]

Next step is to check for power at the relay pins and continuity of wires:

Pin 86 - 12V at Start and Run (key On)
Pin 30 - 12V at all times
Pin 85 - signal from ECU Pin 3
Pin 87 - connects to fuel pumps, you have already verified this since the fuel pumps run when the relay is jumped

[Ga325is]

Ok heres what I have so far

Pin 86 - powered with key in run (verified with test light)
Pin 30 - powered all the time (verified with test light)
Pin 85 - how should I verify this? Will there be voltage present at all times?
Pin 87 - jumped from both pin 86 and 30. Fuel pump comes on.

So how do I test pin 85?

Thanks for all your help.

[Bryanlopez325]

I had this issue a while ago check your fuses relays cps and dme and also your connection to the fuel pump after replacing all of that junk turned out it was a bad connection

[TobyB]

For pin 85, connect your light to +12v and 85. Make sure it's a small test light, not a headlight.

Then crank. It should light up when you're cranking.
t

[boggz412]

Check your cps (crank position sensor).



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[Jackle30]

I had this problem because the harness to the in tank fuel pump was cracked, so continuity was intermittent.

[Poorboyz]

Intermittent problems are the worst. I'm currently having one although not electrical.

GL

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[jalopi]

Yeah, fuck intermittent electrical problems. What you really need for those is a lab scope (imagine a graphing multimeter)

Unfortunately, lab scopes (especially the good ones) are expensive as fuck

[AndrewBird]

The only thing you would need a oscilloscope for would be to check for a working CPS. Everything else can be diagnosed with a test light and once you do so, you should be able to verify within a certain amount of doubt that the CPS is good or bad.

OP, do you have spark? A bad CPS will also kill spark.