Troubleshooting help with 95 525i stall, now no-start

[shu328]

Hey all,

Long time! Would be great to get some confirmation from the experts before buying & replacing parts...

1995 525iT M50TU w/ 5sp swap
07/94 build date
197000 miles

Not a DD -- more of a utility car. Does not get driven often, but car was starting & running perfectly fine. I was about 1/2 mile from home in 2nd or 3rd gear the engine just dies out completely. Cranked it repeatedly and it turns over just fine but would not fire... Had 1 time out of 20 or so where it fired up and idled briefly but as soon as I tried to give it gas it just died out again.

Stomp test after all of this gives only 1221 (Oxygen sensor 1) however I have not seen a CEL in the car pretty much ever. I'm thinking this code was thrown somewhere in between the stall and my multiple attempts to start the car. Perhaps just a lean condition showed up hence the 1221 code.


Facts:
- New rebuilt injectors
- Newish OEM MAF
- New Main / DME relay as of early 2015
- Newish OEM coils
- Relatively fresh OEM Bosch plugs
- Replaced fuel pump last year with used one after another mystery no-start. Fired up right away after this and has run perfectly fine since.


Steps taken so far & Questions:

1. Replaced fuel filter. No difference in results

2. While cranking, measuring 10.5V @ fuel pump harness across Pins 5(+) and 4(-). Is 10.5V normal or should I really be expecting/needing much closer to 12V even while cranking? I wasn't ready to say 100% that's a bad thing. After all, the fuel pump should be operating while cranking and therefore I should expect some voltage drop right?

3. I did not pull the gas line to the fuel rail to check fuel pressure yet. I instead decided to check for spark first. Pulled a plug and with the coil housing grounded with a separate wire to the dedicated ground strap for the coils I do not have spark while cranking.

4. Tested CPS and got 625 ohms where the spec is 540 +/- 10%. I decided it was likely faulty and cut the wires, ordered replacement. The new unit tests at 508ohms so let's hope that's good enough!

Regarding the 10.5V @ fuel pump on cranking...

I guess I could jump the fuel pump relay and confirm I'm sending 12.0V to the fuel pump, then measure what it's receiving to double check. Either way I didn't spend much time on looking into the fuel side further because I had no spark...

Question: If I find there to be 12.0V at the fuel pump relay but then still 10.5V at the pump harness, what could be the cause of this? Bad ground? Anyone happen to know where the actual grounding point for the fuel pump harness is? Would this be shown somewhere in the ETM? I have a fairly decent amount of rust in the back end so I suppose it's possible just that harness is not getting sufficient connection to ground. However I tested a few points elsewhere on the car and have a solid 12.0V


Would be great to get some input on what everyone thinks my next troubleshooting steps should be!

Thanks in advance!

[moroza]

You don't have spark? Bingo. Was there a smell (or visible cloud) of fuel shooting out the spark plug hole when you tested spark?

New DME relay? Is there a CEL when you turn the key to ON without starting? If there isn't, the DME is not getting power. On the other hand, the DME also grounds the fuel pump relay. Where are you measuring the voltage - near the engine or back at the pump itself? What's the voltage in ON without cranking?

10.5V while cranking doesn't sound wrong. The fuel pump is grounded, according to my wiring diagrams, under the rear seat. This ground is not prone to corrosion and is shared with a lot of other things.

[shu328]

You don't have spark? Bingo. Was there a smell (or visible cloud) of fuel shooting out the spark plug hole when you tested spark?

New DME relay? Is there a CEL when you turn the key to ON without starting? If there isn't, the DME is not getting power. On the other hand, the DME also grounds the fuel pump relay. Where are you measuring the voltage - near the engine or back at the pump itself? What's the voltage in ON without cranking?

10.5V while cranking doesn't sound wrong. The fuel pump is grounded, according to my wiring diagrams, under the rear seat. This ground is not prone to corrosion and is shared with a lot of other things.

Really good info, thanks man.

DME / Main Relay was replaced in early 2015, but yes I also DO have a CEL with key in Position 2

And actually when I was cranking testing for spark, the fuel pump harness was still disconnected at the pump. Yes, we could smell gas but not insanely strong however.

I'm about to go swap in the new CPS and try to start her up, so we'll test the theory here shortly!

[shu328]

Update:

Installed the new CPS. Took only a few min to install it of course but a while to get the cable routed properly ... had to remove the engine hoist bracket right by the VANOS in order to get the CPS cable routed behind everything so it would have enough length to get down and into the connector U bracket...

Didn’t need to worry about spacing the CPS off at all from the crank, basically just installed it and tightened down the 5mm hex bolt and done!

And, as expected, she fired right up on the first try!

[moroza]

So 625 ohms compared to an expected 540 is enough out of spec to not work? I would not have expected that, but if that's all it was, great.

[shu328]

So 625 ohms compared to an expected 540 is enough out of spec to not work? I would not have expected that, but if that's all it was, great.

Yep! I was a little surprised the 625 was ‘enough’ out of spec as well... but i suppose these older control circuits are a bit fussy!