87is low power to coil/no start

[davtbaum]

Hey guys,

New to working on e30s (bought my 87is last week! :)), trying to diagnose a no start on my vehicle. It has been a transient issue since I've bought it, refusing to turn over occasionally during cold start. So far this has been my testing process:

1) Checked fuel line going into fuel rail post crank - wet with fuel.
2) Pulled a plug and grounded to valve cover, no spark (new plugs).
3) Ohm-tested the coil, little over spec, replaced the coil, still no spark
4) Checked voltage to coil in ON and RUN, heres where it gets weird, 0V with leads attached to the coil.
5) Read up a whole bunch about the ignition wiring/switch, checked the inline fuse in the trunk along the hot line and it was OK.
6) Went back to the coil and found that with leads detached from the coil, I'm getting 9.46V. Am I missing something here? I don't see why I shouldn't be seeing at least the 9.46V with the coil leads attached.

Any thoughts/suggestions? I've done some searching and have read scary things about the reference sensor on the flywheel going bad, causing the DME to not see TDC and therefore refuse spark AND fuel injection.
(http://www.e30tech.com/forum/showthread.php?t=93083) Does this only apply to the e cars?

Thanks for the help!
David

[davtbaum]

An update! Turns out I did have power to the coil, I was measuring + and - on the coil, instead of + and ground.

Next step was to connect a light to the coil + - to watch for flashing when cranking. No light, so I'm assuming the dme is not signaling ground to the coil to initiate spark. I then ohm tested the CPS, which checked out with 544 ohms. Finally, I swapped out the main relay with a known working one and still no luck :(.

Any suggestions?

[jlevie]

Unless you were using an LED test light you may not see evidence of the DME grounding the coil to produce spark. Check to see if there is power at fuse 11 (fuel circuit) when cranking. No power there and no spark would mean:

No timing data is reaching the DME (bad CPS, bad harness)
No power or a bad ground to the DME (no START signal, bad main relay, bad fusible link)
Bad DME

[davtbaum]

Hey Jlevie,

First and foremost, thanks for all the help! I've been referencing your post here http://spece30.com/forum/41-electric...otally-stumped and have found that pin 27 of the DME is outputting an unusual 2-4v. I'm thinking this means that the DME is never receiving he start signal from the ignition switch?

Just to clarify the 2-4V is not during crank but the key turned to ON

[davtbaum]

Another update! She fixed herself (for now).

After isolating the start signal as the issue, I took a look at the wiring diagram to find that the OBC relay intersects the ignition switch to the DME. Following this post http://forums.bimmerforums.com/forum...-start-88-325i, I unplugged and tested the c1 and c2 connectors on the OBC and they checked out, so I moved BACK to the DME and found 27 to be at 12V as it should :/.

So she started right up of course, although I am certainly not convinced this issue is resolved. Ideally I think I should bypass the OBC relay entirely, but not sure if anyone has done that or would suggest it. Thoughts?

[SmokeE30]

You shouldn't have any issues if you want to delete obc relays as their only on 13button obc cars for the coded start function so it won't start untill you enter the correct code on the obc.