Hot start stall

[JHZR2]

My 91 BMW 318i is my commute to/from work car. Runs great, decent mileage, fun, etc. I'm using for chores and errands today (hot, humid), and after getting up to temp, I'm now getting a stall at every restart. It is better if I start with a slight press on the throttle, or rev it up right after start. However, if I don't get a decent load on it, it will still sometimes stall after I let it idle... After loading it, idle is rock solid stable.

Any thoughts? I have a new fuel pump (I bought the car years ago as a flood title car, and felt that the pump was getting buzzy). And know that there is a functional check valve in the fuel line...

Thanks!

 

[mechtech2]

"After loading"? What does that mean?
Anyway, clean your throttle body bore and plate real nice, and maybe the idle air control valve.
Also, any vacuum line or intake leaks should be made perfect.

 

[JHZR2]

Loading - puting the car under a real load, vs. just revving to to 2000, 3000 or whatever RPM.

As we know, revving an engine to 2000RPM out of gear is quite different than taking it to 2000RPM for traction purposes, and accelerating the vehicle. The fuel flow quantities are quite different, which is why I made the point.

I do routinely clean the TB, and did the MAF not too long ago. ICV is kept clean too, though Ill have a look at it again. No vacuum leaks, I check for that routinely too.

The oddest part to me is the temperature dependence. A slightly or fully cold engine does not show this whatsoever.

 

[George7941]

You can uase a spark indicator and a noid light to see if you are losing spark or injector pulse. Also, monitor fuel pressure with a gauge, when starting to ensure that it is normal.

 

[JHZR2]

Would the spark issue possibly be so intermittent that it is only at hot starts and only for the duration from startup to the first time the engine sees load? I can imagine it is fuel related...

 

[mechtech2]

If it stalled only hot or cold, an ignition part may be at fault.
But it fixes itself under the same temp conditions.
MAybe an internal leaky fuel system or injector - maybe a pressure regulator.

 

[George7941]

Originally Posted By: JHZR2
Would the spark issue possibly be so intermittent that it is only at hot starts and only for the duration from startup to the first time the engine sees load? I can imagine it is fuel related...


I just reread your original post and I agree that it is probably not the spark. I was thinking of a 'dead stall' but that is not what you have.

 

[Trav]

Originally Posted By: JHZR2
Loading - puting the car under a real load, vs. just revving to to 2000, 3000 or whatever RPM.

As we know, revving an engine to 2000RPM out of gear is quite different than taking it to 2000RPM for traction purposes, and accelerating the vehicle. The fuel flow quantities are quite different, which is why I made the point.

I do routinely clean the TB, and did the MAF not too long ago. ICV is kept clean too, though Ill have a look at it again. No vacuum leaks, I check for that routinely too.

The oddest part to me is the temperature dependence. A slightly or fully cold engine does not show this whatsoever.


Check the boot hose to the throttle body carefully.This appears to be only occurring in closed loop(hot engine),check the TPS.The BMW's in the early 90's had some TPS problems,they didnt always display the same symtoms or CEL as on newer cars.

 

[JHZR2]

Well, another oddball instance showed up today. The car hasnt been used for nearly two weeks, as I found two screws in a tire, and didnt bother to make the time to get them fixed - I just let the car sit. Anyway, we needed to pull it from the driveway today, and I had my wife start it - it caught then stalled.

Did it a few more times with the same effect.

Then, I had her start it with a little throttle, and then get it moving ASAP. i.e. she started it and it was at 1500 RPM, she then let out the clutch and got the car moving.

After that, no stall. Steady as a rock.

Any ideas? This time it was cold... never saw that before.

 

[JHZR2]

Originally Posted By: Trav


Check the boot hose to the throttle body carefully.This appears to be only occurring in closed loop(hot engine),check the TPS.The BMW's in the early 90's had some TPS problems,they didnt always display the same symtoms or CEL as on newer cars.


I appreciate your reply, and didnt reply back when you made it... I checked the boot hose and all the "breather" hoses that go to/from it, but there were no issues. I keep after them pretty well...

How would I check the TPS issues? throttle works fine in regular use. The car is OBD I and no CEL. Is it just a matter of trying a part and seeing what happens???

Thanks!

 

[mechtech2]

How about an odd ball system that uses oil pressure to allow ignition or fuel.
Some cars have this as a 'safety'.
So if you have this pressure sensing switch, check it out.

 

[JHZR2]

OK, thanks. Ill look into that. The oil dummy light goes out instantaneously, but it does not mean that another switch is working right.

Thanks!