Hard starting (intermittent)

[noid]

My e30 (87 325is) is being weird when starting. It will crank and crank and then out of no where will start and run perfectly. Then I will turn the car off and then try to turn it back on and it will crank and crank, and will not start. This happens regardless if cold/warm. No Check engine light.

To me it doesn't seem to be fuel related or intake leak related because one second its running great then the next second it wont start again.

What would you guys suspect?

[bmwstudent]

are you losing fuel pressure when you shut it off, you'll have to plumb a gauge to check. Check for spark while cranking to see if your getting that right away too.

[noid]

are you losing fuel pressure when you shut it off, you'll have to plumb a gauge to check. Check for spark while cranking to see if your getting that right away too.

I haven't plumped in a pressure gauge, but I highly doubt it is pressure related because it will start 1 second and then not start the next second, I don't even give it time to be able to loss pressure.

It does NOT sputter or sound like it wants to start when it is not starting, it just flat out cranks and cranks without any signs of life. Then a second later it will fire right up like nothing is wrong.

Tonight out of 15 starts it would start 50% of the time within a couple seconds of cranking, and the other 50% it would just crank and crank.


Leads me to believe it is related to a sensor that is feeding inconsistent information to the DME. I tested the CPS and it reads 520 ohms which seems about right.

Did a stomp test and it indicated 1233, which is a fault with the TPS WOT position. Would this feed information to the DME to tell it not to start?

Coolant temp switch?
Relays? Which relays to check?
Any other suggestions?

[bmwstudent]

Not sure, but you can check it with an ohmmeter. I don't have my Bentley in hand but the info is in there to check it.

[long tall eta]

possibly cps

[jlevie]

A failing CPS is a good possibility.

[603Racing]

Failing CPS, or a corroded connection. What's that connector called, C191? The round one under the intake that likes to corrode. Several vital systems run through that connector.

[noid]

Connections are clean since its a cali car.

Without an oscilloscope there is no other way to check the CPS other then ohms right?

Logically thinking though, if the CPS is so intermittent why is it only messing up when attempting to start the car, yet performs well while the car is running?

[jlevie]

A weak CPS, which can only be diagnosed with an oscilloscope, may not be producing sufficient signal at cranking speed but may produce an acceptable signal at higher engine speeds. Since the CPS is probably 26 years old and may have lost some of it magnetism, replace it with a new OE part on general principles.

[603Racing]

Jim's probably right.

As for corrosion.... other things besides weather can cause corrosion of c191. It's directly under the throttle body, so if it's ever leaked fluid it can land right on that connector. Not saying that's your problem, but it's free and very easy to check.