Help What is this is Part and why....

[rblevins]

Is it "humming"? My Step moms vert wont start ran for about 2 weeks after a new (used, new to us) m20 (stock) was placed backed in the car would start most of the time and then randomly not and leave us stranded? We could go back that morning and it would crank right up. Now the problem was intermittent and would leave us stranded but about a month ago started to go to the store and now wont start turns over all day long but nothing. Mechanic told us was a Motronic DME (just replaced it with one from on the boards here.) so not the issue.

Pulled the number 1 plug out to see if it was getting spark but nothing. I read on a ?'s type page somewhere to check the relays (fuel pump and main). The main was changed a month ago when the problem began. and the fuel pump one looks fairly new. I just tried a rotor button thinking the original was worn out but not the problem either. Now im no mechanic but WTF else could the problem be.

Oh and I heard the CPS could be the prob but the damn thing wasnt even plugged in when I went tracking it down and im sure it never was to begin with?

[BrownBeanE30]

maybe it might be the little censer on the fly wheel i think that sends the signal for the car to get spark that might have broken off cause my buddy had the same problem on his e30

[Cabriolet]

year of car might help.

if im not mistaken there was never a sensor on any vert fly wheel.
all the timing comes from the CPS and tachometer from the spark plug wires.

no spark means CPS is bad, coil is bad or main relay.

[rblevins]

Year of the car is a 88 vert

[Stevie30]

Sounds like the shielded cable running to the crankshaft position sensor is shorting on the cooling fan pulley or the timing cover.

[rblevins]

Sounds like the shielded cable running to the crankshaft position sensor is shorting on the cooling fan pulley or the timing cover.

Nope Not this I re-routed the wire over the top away from the fan and pulleys I had the exact problem 2 days ago on my coupe when I did the water pump and it got caught up in the pulley.

[nomansland92]

no spark means CPS is bad, coil is bad or main relay.

+1 not to much can go wrong, these cars are pretty simple thats pretty much your options of things that could be wrong

[rblevins]

only thing i havent checked is the cps but it makes no sense the damn thing was unplugged the whole time and never caused a problem ill check it tomorrow, what ya mean by coil? and the main relay is brand new

[delatlanta1281]

The coil is the cylinder on the passenger side wheel well. It has a wire leading to the spark plug loom.

[rblevins]

Wow So I now feel dumb lol after almost 900 buck later and 2 mechanics.

The problem was the main Relay!

Autozone had given me what looked to be the exact relay that I needed but the circuit pattern inside the relay was not right thus causing the car to start!!!!!

I figured it out by just randomly thinking "hmmm wonder if I try my fuses outta my coupe" And she cranked right up!

Come to find out that no parts store apparently has the right main relay Dealer item only well at least around here! So to the BMW junk yard I go tomorrow!