Hot start stall

JHZR2 · Oct 9, 2008

Hello,

My 91 318i has 114k miles. It runs great except in one instance.

If it starts cold, it starts perfectly - no issues. If I get the car up to full temperature, shut it off, then re-start it, it will catch and then die within a few seconds. If I do this again and again, this will happen over and over. However, if I start it hot, idle it at 3000RPM or so for a few seconds, then it will idle smooth and will not be a problem again at all, until I re-start it again in the same fashion.

I have a new fuel pump (the old one was a bit noisy), and I have the check valve on the fuel line. I have new injectors (not necessary, but I thought I could quiet a tick which I couldnt), a new ICV and O2 sensor within the last few years.

The car runs great and yields good fuel economy. No problems with power, operation up to redline, etc. AC blows cold, though the idle is stronger and more consistent with the AC on. The car is great besides a parasitic load on the battery which seems as if it may be a bit troublesome - and Im working on. It is irrelevant, as Ive had this issue for longer than Ive had to bother with this battery load.

Any thoughts???

Thanks,

JMH

wirelessF · Oct 9, 2008

I'm thinking vapor lock. Any fuel lines running near any heat sources? Exhaust manifold, cats, etc?

JHZR2 · Oct 9, 2008

Id think so too, except that this is a new issue. The fuel lines run on the bottom of the car, the opposite side as the exhaust.

What about something like a fuel pressure regulator? I replaced the fuel pump as the connector was corroded and the pump was getting noisy. It wasnt necessarily required, but all the same, I did it to be sure of no issues down the line. I have to wonder if a new pump could induce a failure that wasnt seen before?

Then again, id imagine an FPR would be more of an issue at high RPM, and the car pulls strong to redline...

Thanks,

JMH

demarpaint · Oct 9, 2008

Could be vapor lock although you probably would have had that problem long before. Or it could be a temperature sensor that controls the fuel mixture when starting hot/cold. I had a similar problem with my E-150 and it turned out being the EGR valve..

Frank D

pickled · Oct 9, 2008

FPR could be a culprit here...do you have a fuel pressure gauge that you could hook up and see what's going on?

JHZR2 · Oct 9, 2008

No EGR, and no codes via CEL or checking through the OBDI process. No FP gauge, but I suppose I ought to have my mechanic look at it.

mechtech2 · Oct 10, 2008

On an old one, it would be the cold start valve.
On yours, start with a GOOD cleaning of the throttle body bore and plate, and the idle air motor.

JHZR2 · Oct 10, 2008

Can you give a bit more info on the idle air motor? Is that the motor that moves the idle air control valve???

The valve is recent, but it certainly may be dirty, Ill give that a shot, but any additional hints on the motor would be great!

Thanks,

JMH

ThirdeYe · Oct 10, 2008

Sounds like the main fuel relay to me, but I could be wrong. My Acura did the exact same thing yours did. It would start perfect cold, but when hot it would start, then just die instantly. The fuel pump would prime, but there was a bad solder that wouldn't connect properly to keep that fuel pump running.

JHZR2 · Oct 10, 2008

Thanks... apparently the O2 sensor relay and the fuel pump relay are the same, so tomorrow Ill swap them after a hot shutdown and see if it helps...

Best,

JMH

mechtech2 · Oct 11, 2008

Get the mechanical stuff out of the way first.
The idle air motor is the idle air control valve, or a half dozen other names.

JHZR2 · Oct 11, 2008

Well, I tried swapping the fuel pump relay with another exact, same 4-prong relay. It didnt seem to help.

After the engine cools, ill do the ICV cleanout.

THanks,

JMH

BuickGN · Oct 11, 2008

I'll have to ask my friend what he did to fix this problem on his BMW of the same vintage. It had the same symptoms as yours. The timing of the stall was right about when I put it in gear and started to let out the clutch. It would die no matter how much gas I gave it once the stall started. More than once passengers thought I couldn't drive a manual. If I high idled it for a while it didn't do this.

JHZR2 · Oct 12, 2008

odd, but Ill say that it sure seems less likely to happen now that I have a fresh group 49 battery in there. Perhaps spinning up the engine a tad bit quicker (though I cant note it to be true) helps it to start more robustly. Ill be doing the ICV soon, and also check for a ruptured FPR, as that seems to be a common issue, causing extra fuel to go in at startup and stall-outs on E30 cars...

JMH

Hot start stall

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