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Old 10-15-2001, 09:15 AM   #1
HRE | giulio
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Join Date: Nov 1999
Location: NY USA
Default Is the ECU closing the injectors?

When the ECU sees fuel pressure skyrocket, will it compensate by shortening the injector's open time?
And if so, what gadget is there to trick it into seeing 'normal' pressures?

Thanks,
g
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Old 10-15-2001, 10:08 AM   #2
efoo
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the ECU has no fuel pressure sensor to read -- it "senses" something is up when the regular injector pulse widths start making the car run super rich (O2 sensor reading), so it starts closing down the pulse widths to make the car run stoich again.

however, this is only done during closed-loop operation. during WOT, the ECU reverts back to static injector pulse widths in some tables someplace. perhaps what you want to do is fool the ECU into thinking you're at WOT most of the time except at normal cruise. You don't want to be at WOT all of the time though; your idle and low end will probably suffer greatly.
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Old 10-15-2001, 02:35 PM   #3
HRE | giulio
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Thanks for the reply efoo.

So why would it go lean with high fuel pressure... or how can i 'fix' that?

When i start a run from idle, and WOT the whole time A/F is perfect.

But if i'm cruising in 4th/5th and WOT, it's lean.

I just dont get it.

Setup: 255 pump, 6:1 FPR, stock injectors, SAFC, 4~6psi on EJ25.

Thanks,
giulio
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Old 10-15-2001, 02:56 PM   #4
efoo
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Quote:
Originally posted by giulio
When i start a run from idle, and WOT the whole time A/F is perfect.

But if i'm cruising in 4th/5th and WOT, it's lean.
It isn't ECU-related, IMHO. That's simply due to the fact that your engine is under higher load to begin with when you go WOT in 4th/5th instead of from a stop in 1st. I do my TEC-II tuning runs in 4th gear for this reason -- what's safe for 4th gear is a little rich for 1st gear, but safer.

Try easing into the gas and then going WOT slowly in 4th/5th -- I bet you won't run lean. If that happens, it means your RRFPR isn't reacting quickly enough and you're getting a transient lean condition on throttle tip-in. On the TEC-II, I can set a parameter that dumps in 10% more fuel for a brief period when I really nail the gas hard, so that's how I get rid of that problem.

If you go lean even when getting on the gas slowly, you just need more fuel across the board under boost, that's it.

-Edwin
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