Author Topic: hot start problem (Read 2428 times)

jakeb · « **on:** November 10, 2011, 06:12:38 AM »

I am having a hot start problem on a car I am building. It is a e30 m42 but it does have a added turbo...tuning the stock motronic.

Tuning is going ok but if I shut the car down hot it will not restart right away. If I wait 20 minutes or so it will start, but starting right away it will just crank and crank. The way I have found to start it after a hot start is to put the pedal to the floor and enable flood clear mode and then it will start fine. Or if I disconnect the fuel pump it will start and then once it starts I reconnect the pump. It works better if I do the flood clear mode method rather than the pump method.

The injectors are twice as big as stock ones but I have adjusted the tune with an osrich2 and tunerRT pro...

any ideas?

wazzu70 · « **Reply #1 on:** November 10, 2011, 03:14:16 PM »

The car is running too rich. After you shut the car off there is still excess fuel in the cylinder, when trying to start it is adding more fuel instead of emptying out the chamber.

This is why turning the fuel pump off or using flood clear works.

jakeb · « **Reply #2 on:** November 10, 2011, 05:32:53 PM »

That is what I think as well...my AFR at idle is between 14-15. I could lean the idle out a little bit more. While cursing around under light throttle I am right at stoich. Under heavier throttle and out of boost I am still a little rich, maybe near 12.5. Under boost I am right around 11-12.5. So I can lean still lean it all out some.

Or could I possibly have a leaky injector? That is another thing I am going to check this weekend, or maybe even later tonight. I would think with a leaky injector it would start ok right away after shutting it down but have more trouble after sitting a little bit. So there is time for them to leak. It is...shut it down, and try to restart right away and nothing.

jakeb · « **Reply #3 on:** November 10, 2011, 08:22:12 PM »

Well another quick update.... I checked for resistance on the AFM and i 10kohm from pins 2-5 when I moved the vane. I happen to have 3 extras from all the m42 swaps I have done. 2 of the 3 had around 10kohm from pins 2-5 when moving the vane. One was around 200-700ohm when moving the vane, that is also about the same reading I get on my personal car. So I swapped that out.

Going to try that tomorrow. I also ran the car for a little bit and then clamped down the return fuel line to see if I loose any pressure to spot a possible leaky injector.

There is a spot in the bin where I can adjust enrichment a little bit so I might be able to alter how much it injects during a hot start. Could change it so it doesn't add anymore fuel...or very little at least.