Trouble Starting After Driving Opinions

[RyWar]

Hey all,
Looking for opinions of what this issue might be. Here's what's going on.

Car: 1989 325i
Engine: M20 - intake, chip, exhaust

The car has no problem starting after it has been sitting for a period of time. ie starting it in the morning is no issue, fires right up without hesitation.
However if you drive the car, get heat into it, turn it off and try to start 20 mins or so later the car will not start. It cranks but will not fire. The crank is strong and doesn't seem like a battery issue.
If you drive the car get heat into it, turn it off and start it immediately it starts right up. You can repeat this several times without issue. Engine is hot, car off, car on, car off, car on without issue
It is when the car sits for a short period of time after driving that the issue occurs.

I'm suspecting my fuel injectors may be leaking into the head after parking and flooding the engine. Which would explain why it starts immediately after (fuel has not had a chance to pool) and why it starts after long periods of sitting (injectors have stopped leaking and pooled fuel has evaporated).

Thoughts? Has anyone experienced a similar situation?

Thank you all!

[e30davie]

Have you got any history on the fuel pump? is it an oem pump? or uprated? how about the fuel pressure reg?

i wonder if you have some kind of vapour lock situation going on.

The fuel injector theory sounds good if they all leak, but surely it would be unlikely that they all leak. and then the non leaky ones would fire normally? maybe? i dunno. i mean if they are oem injectors that you havent had cleaned etc, might be worth doing anyway just so you know.

[TobyB]

I agree with flooding- one easy thing to try to test this:

floor it when it won't start. That should clear the engine of unburnt fuel,
and it should catch more quickly- AND run unevenly at first, once it catches.

Like davie, I'd be looking for root causes, if that test isn't conclusive- make sure you have spark, that the injectors are firing, fuel pressure's good, etc.

Something like an intermittent crank sensor can do things like this, too. When the engine shuts down hot, all sorts of things heat up.
And starting takes a much more robust system than running does...

hth

t

[RyWar]

e30davie The previous owner had told me he replaced the fuel pump. Not sure it is OEM and not sure about the fuel pressure regulator.

TobyB I've tried flooring it when it won't start, doesn't seem to help at all. I have a fuel pressure gauge right before the injectors and fuel pressure is good around 40psi or so.

[e30davie]

Is it 40psi when its playing up?

[ADEN]

E30 doesn't do fuel priming when ignition on. Fuel pump is activated when ecu gets the rotating signal from CPS, Check fuel pressure when cranking (when problem accure) as e30davie told you and confirm.

[ADEN]

E30 doesn't do fuel priming when ignition on. Fuel pump is activated when ecu gets the rotating signal from CPS, Check fuel pressure when cranking (when problem accure) as e30davie told you and confirm.

[Dspill]

I had a similar experience where my 3251C wouldn't start after sitting hot, as if the heat soak in the engine room was causing something to fail. If I opened the hood while the car was off (to cool) it seemed to help. I changed one of the coolant temp sensors (the ECU one) and the problem almost vanished...but not completely. It's now somewhat rare, but if I get gas on a hot day I may experience this same symptom - after 5 minutes of sitting. If you learn something new please share it.
To restart successfully, I have to play the throttle long enough to get the car into Drive and then everything settles down fine.

[TobyB]

Hmm. probably not flooding, then. I would next check spark when it's not starting.
Just carry a spare plug and ground wire- when it won't start,
pull a plug lead, ground the plug, and set it where you can see it while cranking.

Also, see if the fuel pump runs when it won't start.
As ADEN says, without a crank signal, you won't. If you are, that helps narrow it down.

hth
t

[bmwman91]

Does the car run 100% properly when it is fully warmed-up?

[finnmole]

I had the same issue, though the car would eventually start after about seven seconds or so of cranking...then ran rough for a bit. I replaced the fuel injectors thinking they must be leaking...didn't help. I believe it was the FPR in the end.