Cranks, but no start.

[avery0829]

I just got my 88 325is drove like a dream. Until this morning I go to start it like usual boggy and the idle jumps around then dies. I try to start it again and nothin just keeps cranking.

When I got the car I was told the plug wires needed to be changed and that the temp sensor might be bad also (his reasoning was that when it was cold after a couple days the idle would bouce around alittle and kinda boggy when cold then go away after 30 seconds)

Would unpluging the sensor make it start? Any other ideas?

Thanks a lot for any help.

[jlevie]

No fire when cranking will be a fuel or spark issue. If you have spark, but no pressure at the fuel rail, the cause will be a bad fuel pump relay or failed pump. If no spark and no fuel pressure at the rail, the cause will be a bad main relay, bad CPS, or failed DME.

Hard starting or a rough idle on a cold engine is most likely to be the result of an intake leak. Other possibilities exist, but until possible intake leaks are eliminated there's no sense in looking further. An 88 is 20'ish years old at this point and replacement of every hose that connects to the intake as well as new dipstick o-rings, oil filler cap, ignition wires, distributor rotor & cap is the place to start. Oh yeah, while doing that replace the O2 sensor unless it has been replaced recently.

[s52e30m3]

I've had similar issues. Turned out to be injectors.

[DCColegrove]

Sounds like a no fuel... Started... Ran like shit...Wont restart...

Pump?

[avery0829]

Well heres how it went. I took the the intake boot of sprayed alittle starting fluid. It turned over, but I had to hold the gas for like 5 minutes. Once I let off the idle jumped around from like 1000 to 1700 quickly.

Next I unplugged the big MAF? sensor on the airbox and ran like normal...Then plugged it back in once it was warmed up and drove amazing like it always had...

Ideas on why?

[hahmeta]

i had similar issues after changing my spark plugs with brand new ones and putting in 19lb injectors.

in my case, i'm kind of hoping it's the ECU relearning everything. It's getting better but slowly...

[avery0829]

It has pretty new plugs so, I wouldn't think that is the problem.

[Keven]

How do I test the fuel pump relay?

[Philo]

To test FP relay: pull box, check for power at relay(red wire)/pin30. If that fails check the fusable link in the right rear of the trunk. Check pin86 + pin85 with a voltmeter/multimeter while turning over the car. You should get a change in reading. Finally jump pin30 to pin87 with a fused wire. If the pump runs then it's either a faulty relay or bad reference sensor.

I think I got it all there. I didn't have my bentley on hand.

[vr2jetta]

Hard starting or a rough idle on a cold engine is most likely to be the result of an intake leak.

My 90 325i was a MAJOR PITA to start cold. Turned out to be the smallest tiniest intake leak! It was between the charcoal canister and the little valve before the throttle body. It amazed me to how minuscule the leak was and how it effected the start up. Now it starts right up and idles better.

[Keven]

To test FP relay: pull box, check for power at relay(red wire)/pin30. If that fails check the fusable link in the right rear of the trunk. Check pin86 + pin85 with a voltmeter/multimeter while turning over the car. You should get a change in reading. Finally jump pin30 to pin87 with a fused wire. If the pump runs then it's either a faulty relay or bad reference sensor.

I think I got it all there. I didn't have my bentley on hand.

What is this box? Im looking in my fuse box in the engine bay and I dont see any of what your talking about. Nor the fuseable link in the trunk. Maybe its different in my 84?

[Philo]

No, I just assumed you knew what you wanted to test. The fuel pump relay that is. I will post details in the morning (it's late and i'm tired)