89 635Csi Hot Start Issue

[sbr2]

All,

I've consistently experienced an issue with my bimmer that a hot start will take two full crank cycles to get going. By that I mean I hold the key in the ignition position and it cranks but no spark. With the second crank cycle it will fire up and get going. Maybe 1 out of 10 times in a hot start it will come with a lumpy idle where if I put my foot on the gas the car will come close to dying on me before getting past it and operating normally but as soon as I come close to being at a stop it will become lumpy again.

Ideas? And merry (early) christmas!

[RSheiman]

Well, I have an extra ECU just for such a situation so that it allows me to exclude that as a cause. It may be yours. Try to borrow one or find one cheap somewhere that you know works well. Swap it out and see. The solder joints crack and can act up when warm.

[sbr2]

Well, I have an extra ECU just for such a situation so that it allows me to exclude that as a cause. It may be yours. Try to borrow one or find one cheap somewhere that you know works well. Swap it out and see. The solder joints crack and can act up when warm.

Interesting, I'll try to get my hands on an ECU.

[DesktopDave]

The ECU is the most likely culprit but there are a few others too. I'd test the easy stuff first, like the engine temp sensor. If that's failing, the ECU will run the mixture too rich and the car will be reluctant to start when it's warm.

The crank angle sensor can also be on the way out. If the ECU doesn't get a solid CAS signal it won't prime the fuel pump. You might also want to have a fuel pressure test performed. A weak pressure regulator or a stuck injector can cause trouble like that too. I've also seen coils, dist caps and plug wires that will fail when they heat up.

[6000Shark]

This is most likely an electrical issue because if you were losing fuel pressure then you would have even more trouble on cold starts. Definitely check your connections before just throwing parts at it.

[sbr2]

Roger that, I haven't had time to further pursue the issue yet. Been fixing some issues on my merc, but I'll do a fuel pressure check first.

[sbr2]

Picked up a Reman ECU and swapped in this weekend - no change in the time it takes for a hot start.

[conditioner]

Fuel injector? If injector is leaking while engine is hot, it'll flood the system and cause hard to start when hot. Any issues during cold start?

[sbr2]

https://drive.google.com/file/d/1Sxl...usp=drive_link

I'm not sure why the sound cut out, but that is a video of my cold start. Very quick from turn of the key to ignition.

Worth noting that I replaced the fuel injectors and spark plugs and it still takes a bit of cranking in hot start conditions like it did before I replaced things.

[sbr2]

https://drive.google.com/file/d/1rNP...usp=drive_link

Still giving me this hot start issue - thoughts?

[sbr2]

It was the fuel filter. It was factory original.

[RSheiman]

If that's the case, you may want to pull the in tank fuel pump and clean the screen at its base and also look inside the tank to make sure there is no debris so as to not suffer the same fate in a few months. Glad you gave us follow-up and got it sorted.