Warm start issue again

[JHZR2]

Every year when summer hits...

91 318i 131k

Cold start, beautiful. Hot start, stall indefinitely unless idle elevated AND drive to load it for a bit. After it steadies, idles beautifully.

Good o2, injectors, icv, fuel pump, no vac leaks.

Doesn't happen to hot engine in cold weather, only hot engine in hot weather.

Ideas???

 

[Colt45ws]

Does it have a MAF?

 

[Hermann]

Vapor lock?

 

[chubbs1]

Have you tried different gas stations?

 

[hate2work]

Originally Posted By: JHZR2


Doesn't happen to hot engine in cold weather, only hot engine in hot weather.

Ideas???


Move to the Yukon

I know it helped such things quite a bit when they started putting the fuel pump in the gas tank, which eliminated vapor lock. The engine isn't overheating is it?

 

[JHZR2]

This happens every year, on gas from NYC to Richmond (as that is where my car drives - its not just one station). My car has the fuel pump in the tank, and it was getting a bit buzzy a few years back, so I replaced it with an OE unit.

It does have an MAF which I cleaned a year or two ago - didnt help. No CELs.

 

[Trav]

Check the IAT sensor.
Also on a lot of cars even newer ones with OBD II a slow MAF will not trip a CEL but cause all sorts of strange issues, cleaning usually doesn't help.

 

[JHZR2]

IAT sensor? Sorry... Not aware of that acronym.

 

[OVERKILL]

Originally Posted By: JHZR2
IAT sensor? Sorry... Not aware of that acronym.


Intake Aircharge Temperature

 

[Trav]

Sorry about that. It is as OVERKILL posted it.

It could look like one of these, I don't know where it would be located exactly. It may have even be incorporated into the MAF or other sensor on U.S. models. Some say "it is on the drivers side, adjacent to the foglight and in the air dam."
It sounds tricky to pin down the exact location on this model, maybe just to many variables i don't know, Euro models are usually in the boot to the Throttle Body.
Check with BMW or the service manual.

http://www.autopartswarehouse.com/partse...CFURd5QodzVDmeA

 

[tdpark]

How about the fuel pump relay, i had 2 cars that had the same problem and both ended up being a fuel pump relay, one was a honda and one was a volvo. Only time the car would not stop was when it was hot. Check to see if the fuel pump relay has any scorch marks or smells like it electrical burning.

 

[JLoy]

+1 on the relays. I have a honda that developed a summertime no start. Found the main relay to be the culprit. When it does not start you should check for your fuel delivery and spark. If those are good, then I would look at the sensors. I would be willing to bet you will find that it has spark and no fuel. I would want wiring diagrams and a fsm to troubleshoot this one. Good luck,

 

[JHZR2]

Ive swapped the relays on there as a matter of troubleshooting - no help.

Did it REALLY bad today. Had to floor/nearly redline the car under acceleration to get to the point where it would idle and not stall. Of course after that, it idled beautifully forever after.

 

[chrome]

So it appears to be:

1) Ambient air temperature dependent (summer time vs winter)
2) Only when starting and initial idling (after which will idle ok)
3) Only when starting on a warm start (cold starts are perfect)

The symptoms does point to a sensor that is exposed to ambient air temps, which is the IAT. That sensor plays an important role in air-fuel mixture suitable for a cold or warm start.

Just a extra thought, I seem to recall the in-line 6 BMW engines having an extra "injector" at the intake manifold, seems to be responsible for enriching the mixture for cold starts. I was wondering if the 4 cyl has that too? Suppose that injector leaks slightly, and after shutdown will leak enough fuel into the intake manifold resulting in a too-rich mixture for warm starts? So that may be why flooring the accelerator seems to help the start?

 

[Trav]

Quote:
Did it REALLY bad today. Had to floor/nearly redline the car under acceleration to get to the point where it would idle and not stall. Of course after that, it idled beautifully forever after.


Does it smoke at all when this happens?

 

[JHZR2]

no. car never smokes that I can tell.

 

[JHZR2]

Originally Posted By: chrome
So it appears to be:

1) Ambient air temperature dependent (summer time vs winter)
2) Only when starting and initial idling (after which will idle ok)
3) Only when starting on a warm start (cold starts are perfect)

The symptoms does point to a sensor that is exposed to ambient air temps, which is the IAT. That sensor plays an important role in air-fuel mixture suitable for a cold or warm start.

Just a extra thought, I seem to recall the in-line 6 BMW engines having an extra "injector" at the intake manifold, seems to be responsible for enriching the mixture for cold starts. I was wondering if the 4 cyl has that too? Suppose that injector leaks slightly, and after shutdown will leak enough fuel into the intake manifold resulting in a too-rich mixture for warm starts? So that may be why flooring the accelerator seems to help the start?


Seems accurate but I do not believe the M42 has a cold start injector. Will be looking into the IAT sensor though.

 

[Vikas]

This is pretty old car. Did they have all those sensors in those days?

 

[OVERKILL]

Originally Posted By: Vikas
This is pretty old car. Did they have all those sensors in those days?


In short: yes.

To use a domestic example, in 1989 the 5.0L Mustang had:

1. 8 individual injector drivers in an ECM with an Intel CPU used for sequential fuel injection.
2. Throttle Position Sensor
3. Barometric Pressure Sensor
4. Air Charge Temperature Sensor
5. Engine Coolant Temperature Sensor
6. Oil level sensor
7. Oil pressure sensor
8. EGR position sensor
9. Thick film ignition, triggered by hall effect sensor
10. Mass Airflow meter
11. Dual oxygen sensors (bank specific)

And I'm sure I'm missing a few.

So, to assume that degree of sophistication AT MINIMUM for a German car of similar vintage is a must. It probably has a lot MORE stuff than the above

 

[mechtech2]

Air tamp sensors do have an effect.
But the coolant temp sensor is far mosr important for this.
This is NOT your temp gauge sensor!
I'd spray clean your MAF with dedicated MAF cleaner, and check your coolant temp sensor values, or just get a new one and pop it in.