Contour Enthusiasts Group Archives Forums Modifications 3.0L Duratec ?Help tracking down the stuttering problem....Long...

I look forward to something, but wouldn't you think that you would have issues at High RPM, like pinging if your fuel pressure was off?

I check mine a lot, but my stuttering issue is definitely got a mind of its own. I decided to go back and try the 19# injectors with the GReddy, and the problem persists either way. The only problem with the 19# injectors is that my modified stock MAF doesn't work at all. The only headway I have made so far was with the 24# injectors and the modified stock MAF. With the stock unmodified MAF and 24# injectors the problem was the same, just fuel trimmed like a biitch. With the cut out center post I got the best driveability. The stuttering was mostly gone. I had to increase the signal with the Greddy like 15% above 3K rpm though.

Here is an interesting thought: The only time the car didn't stutter is when the engine was cold and the car was first started. This meant that the air was at its most dense. If the engine was cold it wouldn't warm the air much as it goes through the air intake. IF??? the AF ratio were actually too rich, then at cold startup it would have the most dense air and therefore the fuel would have enough oxygen to combust correctly. NOw lets say that 5 minutes later the engine is warm and it is warming up the incoming air. The air gets less dense and would theoretically require less fuel to keep a good AF ratio. If the fuel being dumped in hasn't been reduced, then perhaps the mixture is too rich?
When I cut the centerpost out of my MAF, I got a lower voltage reading throughout the RPM range. THis would signify less airflow and would require less fuel. Evidently it is reading a lot less airflow because I have to richen it up so much with the GReddy above 3000 rpm.
Maybe you could also look into this possibility when you are playing with your APEXi. I know you wrote that you tried leaning it out, but you must make sure that the car is getting an unmodified signal at idle and light cruise loads. You must also reset the pcm everytime you do any major adjustments like leaning out the AF.

Anyway, I will be going back to the 24# injectors in the morning with the modified MAF and my new airflow map in the GReddy. We'll see what that does.

warmonger