Author Topic: warm/hot start issue (Read 2645 times)

jakeb · « **on:** July 03, 2012, 12:44:29 PM »

I am having an odd warm/hot start issue so I come to all of your for some suggestions.

This is an m42 swapped into a 2002 and it has a turbo on it. Running stock motronic as a draw through AFM. 42lb injectors

Car runs fine when running....AFR under cruise is right at 14.7 (adjusted by the o2) and under WOT/boost I am right around 12.5:1 give or take. Idle is smooth, pulls great, in or out of boost. No odd hesitation really anywhere.

But if I shut the car off warm/hot it will not restart right away unless I disconnect the fuel pump relay....crank, it starts, and then plug the relay back in either as it is running or if it stalls plug the relay back in and it will start right back up. This problem is blowing my mind....

Crank sensor at ~600ohm
cam sensor at 1437ohm
Tested the AFM and getting a variable reading between pins 1 and 2 when opening the door.

I am running a coil over plug setup.
It does not always prime the pump for some reason. Shouldn't it ALWAYS prime the pump when going to key pos 2? Or if there a timer of some sort in the DME?

I am running a emulator plugged into the DME. Maybe I should burn a chip with my current tune and try that. But the oddest thing is it starts if you do not allow the fuel pump to run.

Fuel pressure is at 43psi and stays there if it sits, so I don't think the injectors are leaking.

What else can I test, try?

thanks all

bmwman91 · « **Reply #1 on:** July 03, 2012, 05:46:22 PM »

All I can guess is that the pump is on its way out. The internals may be worn and unable to start moving when the system is pre-pressurized. Running the car briefly drops the pressure in the system, allowing the pump to start moving. That's just my guess anyway. If you are running larger injectors, a TRE performance high-capacity pump might be a good investment anyway.

If it was dying, the addition of a turbo might have been a death blow. The fuel pressure regulator always tries to keep the fuel pressure 43 PSI above manifold pressure. Since manifold pressure is hitting your max-boost pressure, the pump is working harder when you are boosting, and if it was old and worn, that might have been the end of it.

jakeb · « **Reply #2 on:** July 03, 2012, 07:35:13 PM »

The fuel pump is actually brand new but there was a trouble when I first set this up with a restriction in the return and it was running something like 80psi of pressure. So maybe it messed the pump up....

What about the next time that I think it will do it run the pump for a few seconds?

bmwman91 · « **Reply #3 on:** July 04, 2012, 03:58:27 AM »

You could try that, sure.

jakeb · « **Reply #4 on:** July 18, 2012, 04:27:04 PM »

hot start problem fixed!! The problem ended up being with the tune and the bigger injectors. Finally found where in the tune the cranking tables lives and I was able to pull things back. Starts perfect now. Sure is fun with a bit of boost.