Hard Hot Start... Sometimes

[heifetz17]

This issue is commonly caused by a weak fuel pump or a bad check valve. When a fuel pump starts failing, it's often when it gets hot. This would explain why it's hard starting after running. The faulty check valve allows fuel pressure to drop off after shutting the car off, and the pump is slow to re-pressurize the system so it'll start again. Once cold, the pump starts functioning normally again until it gets hot, so on cold starts it pressurizes the system quicker for faster starts.


It's likely getting colder in Portland than it was in July when you started this post. The colder weather may keep this from happening as much. Keep an eye on it, especially when Spring comes around and see if it starts acting up again when the weather gets hotter.

[PDXPeter]

Thanks! I was wondering if the check valve could be faulty. Seemed to be the most likely culprit.

[Zambuzan]

Wow this explains a lot for me lol. Every time I go get gas, I turn the engine off when its already hot, fuel up, and then when I go to start the car again it takes a few cranks... Not sure if its such a big problem that I need to fork out $260 for new fuel pump assembly

[jeffnhiscars]

My new Bosch external was only $106. If the in tank pump goes you can hear the external sucking it's brains out.

[Zambuzan]

My new Bosch external was only $106. If the in tank pump goes you can hear the external sucking it's brains out.

Everyone says that these are audible and they "hum" but I must be deaf because I can't hear mine AT ALL, even when I pull the rear bench up. Not sure if it's stock or what...

[IS300E30]

Anyone got a resolution with this specific starting issue.

Starts perfect when cold. After driving then sitting for 35 minutes, then trying to restart my car too struggles on the first attempt, second attempt it starts perfectly.

[digger]

fuel injector issue.

[noid]

Anyone who thinks this is fuel pressure related, should know that its a very specific window of time where this happens; if you wait a few hours it starts immediately and so fuel pressure in this context makes no sense.

Many people never experience the issue just by the nature of how they drive their E30 (frequency between starts).

For those who have experienced the issue, could you post the year of your E30?

I'm starting to wonder if its fuel cooler, or dual pump specific (87').

[IS300E30]

Anyone who thinks this is fuel pressure related, should know that its a very specific window of time where this happens; if you wait a few hours it starts immediately and so fuel pressure in this context makes no sense.

Many people never experience the issue just by the nature of how they drive their E30 (frequency between starts).

For those who have experienced the issue, could you post the year of your E30?

I'm starting to wonder if its fuel cooler, or dual pump specific (87').

Mine is a July 1987 325i convertible

[digger]

i had the issue on an 89, swapped in random 19 lb from some ford junk as a test and issue resolved. i then purchased a new modern more sensible flowing set as didn't need 19 lb and didn't want to re-tune and never had the issue. The injectors were not leaking as had them tested and it wasn't a pressure bleed off issue. Perhaps the old solenoid doesn't like the heat with age as without fuel flowing to cool it the temp may heat soak a bit when the engine is shut off

[laidback93]

Anyone who thinks this is fuel pressure related, should know that its a very specific window of time where this happens; if you wait a few hours it starts immediately and so fuel pressure in this context makes no sense.

Many people never experience the issue just by the nature of how they drive their E30 (frequency between starts).

For those who have experienced the issue, could you post the year of your E30?

I'm starting to wonder if its fuel cooler, or dual pump specific (87').

1990 325is. I have this same hot start issue very rarely, but it happened last week which surprised me because it's been a long time. I went into CVS for about 10-15 minutes so I guess I hit that "sweet spot".

I have new injectors, FPR and a couple year old fuel pump. I replaced the OEM fuel pump about 4 years ago and the check valve failed on it within a couple months. Bad batch of aftermarket fuel pumps is what I heard from several sources.

Anyways, I've chalked it up to normal behavior as you have done too.

[moatilliatta]

I've had this happen with new injectors also.

[e30davie]

Does the oem ecu prime the fuel pump before it starts? or does it only run when the engine is cranking? I cant imagine bmw designed it such that it takes ages to start when its hot, that wouldn't keep customers happy.

my m20 has always started immediately on mega squirt but i've got the fuel pump running before the engine starts (for 2s I think once ecu is turned on), i also have a priming pulse (that helps clear the injectors of air i think and gives it a dose of fuel), as well as starting enrichment. no excuses and it fires into life immediately every time.

[digger]

Does the oem ecu prime the fuel pump before it starts? or does it only run when the engine is cranking? I cant imagine bmw designed it such that it takes ages to start when its hot, that wouldn't keep customers happy.

no it doesn't prime, only when engine is rotating.

[e30davie]

ah, well thats not going to help.