M42 Crank/No Start What Am I Forgetting?

[johngalt]

New to me 1991 318is, brought in from out of state needing a CA smog check. Replaced leaking rubber fuel filler hose, put in new spark plugs and an oil change then took it out for a spirited drive to give it a good warm up on the way to the smog check. Heard a pop up front at 70+ mph, lights came on, engine died, coasted to the side and got towed home. Have had a crank/no start ever since.

-- Replaced noisy fuel pump and fuel pump relay. Pump runs when jumped at the relay.
-- Replaced fuel filter.
-- Replaced engine control relay because I had a new spare.
-- Cranks just fine.
-- Have spark when cranking, but plugs dry.
-- No codes (just 1444) after stomp test.
-- 12v at the firewall power connection and Check Engine light works, so ruled out the fusible link.
-- New Bosch CPS installed (not the BMW part) with a bracket that's 70 degrees off the location of the original, and not as deep (the one I removed had a smaller protrusion that extended another 1-2mm, although this is supposedly the compatible part number according to 3 different websites)
-- Old CPS resistance of ~1200 ohms; new CPS resistance at 540 (correct according to Bentley)
-- Wire connections all appear to be tight

What am I forgetting? I thought I was getting down to the CPS as culprit, and it does seem like the old one was faulty, but still not starting.

[bmwman91]

What sort of POP was it? Did it sound like a misfire or backfire?

Get a good close look at the crank damper and make sure that the outer ring has not separated from the inner hub. The rubber that bonds them can fail, especially given how old these cars are and the fact that many are still using the original damper.

[johngalt]

Definitely misfire, not backfire. I'll take a look at the crank damper. Thanks!

[roguetoaster]

Yep, second check the damper, a quick check for potential failure is to set the crank to TDC 1 and look in at cam lobe position (pointing in and up at each other is correct IIRC). If there's a disagreement it's probably a bad damper since the chain system tends to be reliable excepting the idler wheel.

[crookedarm]

I have a faulty CPS and ordered the same Bosch one you did. It's "held" an idle for 15 seconds at most with varying air gaps, part of me thinks it's not the correct sensor. I bought a used one off AWDBOB, hopefully that fixes the issue.

I found that the E36 M42's have a similar looking CPS [clocked correctly] and priced reasonably, but have no idea if they are interchangeable. Maybe you want to be the guinea pig?

https://www.r3vlimited.com/board/for...ensor-question

EDIT - My original issue was on day's above 80 degrees on say mile 15 of an 18 mile commute, the car would die, like flipping a switch. I'd be interstate speeds, 75-80, slip it in neutral, coast for 10 seconds and the car will start right back up with no issues. Not sure if the ambient temp had anything to do with it or not, just an observation. During my research the CPS was found to be an option and also the DME relay. So I replaced the relay and found that the connection point between the harness and sensor had some slop in it, certain a "new" CPS will fix the issue at this point.

[johngalt]

Well, the crank damper appears to be fine. I didn't remove it from the car but did a visual inspection and also wasn't able to deflect it by hand. The toothed portion seems to spin fine under cranking, leading me to believe that the rubber is intact and holding everything together. Let me know if I am thinking about that incorrectly. I'll give another try with a different CPS to see if I get a different result, and if not I'll go back to the top of the list and run through it all again.

[roguetoaster]

Did you check timing agreement, crank to camshafts?

OTOH, can confirm the poor experience (poor operation, but not a no start) with the seemingly randomly clocked Bosch CPS.