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At 02:51 PM 5/5/2004 -0400, you wrote:
Hi all, I spent a couple of hours the other day gathering clues to my rough running problems. First the facts, then my theories. I'm looking for any input.
Assorted clues: Several additional clues may shed some light on the situation. Mostly centering around the Fuel Pump. I have noticed that if the engine is running rough from being too rich (wont run leaner because of the surging) and I turn the engine off (by shutting off the fuel pump) the will run perfectly smoothly for several seconds before it stops.
I had previously that turning off my alternator caused my engine to stop. I turns out that turning off the alternator just makes the mixture leaner.
Check the voltage on the ECU and the injectors. (A scope would be helpful here.) The funny business with the alternator makes me think that the load on the electrical system is somehow changing the available voltage to the injectors and/or the ECU.
As the engine idles down, the alternator voltage drops. This could be causing the ECU and/or injector voltage to drop below some threshold level.
Running up and down the fuel pressure will change the current draw on the pump. If the pump current draw is changing the voltage to the injectors or the ECU, it could cause the problem you are having.
Inadequate ground paths as well as undersized feeds can cause this sort of problem. Is there a nice stout ground strap between the engine and the airframe?
I have also seen cheesy circuit breakers that drop an inordinate amount of voltage.
1) Check some key voltages at high speed and at idle. Make notes.
2) Connect a stout charger to the system and see if it changes the behavior.
3) Make a few 10 gauge clip leads and connect critical points directly to the battery (and ground). Note changes in behavior.
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