Stock ECU..where's my fuel cut???
05-22-03, 01:58 PM
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Stock ECU..where's my fuel cut???
My former Pettit ECU has given up the ghost, so for now I went back to a stock ECU I had lying around. I have a very mild streetport, downpipe and catback, and I get significant spiking on the transition, so I have to stay off the throttle until I get something else or fix my boost spiking. Anyway, my AFR Gauge (not a wideband) seems to indicate that WOT I'm plenty rich. And here's the strange thing...I got into it a bit too much last night and spiked to about 14 psi. I immediately let off, but...no fuel cut? Shouldn't I have hit fuel cut by then? No detonation either, so that's good, but...why is my stock ECU not acting stock? Any ideas?
jds
jds
05-22-03, 02:34 PM
#2
Originally posted by neevosh
This is what the fuel cut #'s are.
RPM ABS. CUT OFF(PSI) SEA LEVEL CUT OFF(PSI)
1000 26.5 11.8
1500 26.5 11.8
2000 26.5 11.8
2500 26.5 11.8
3000 26.9 12.2
3500 27.1 12.4
4000 27.5 12.8
4500 28.0 13.3
5000 26.9 12.2
5500 26.0 11.3
6000 25.8 11.1
6500 25.4 10.7
7000 25.4 10.7
Mazda took into account that there may be boost spikes at transition and raised the cut-off pressure. Also, boost has to be sustained above the cut-off pressure for a certain period of time before the fuel cut takes place.
This is what the fuel cut #'s are.
RPM ABS. CUT OFF(PSI) SEA LEVEL CUT OFF(PSI)
1000 26.5 11.8
1500 26.5 11.8
2000 26.5 11.8
2500 26.5 11.8
3000 26.9 12.2
3500 27.1 12.4
4000 27.5 12.8
4500 28.0 13.3
5000 26.9 12.2
5500 26.0 11.3
6000 25.8 11.1
6500 25.4 10.7
7000 25.4 10.7
Mazda took into account that there may be boost spikes at transition and raised the cut-off pressure. Also, boost has to be sustained above the cut-off pressure for a certain period of time before the fuel cut takes place.
05-23-03, 02:56 PM
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I did not realize the ECU was intentionally ignoring spikes...yep, sounds like the explanation all right.
I had a Pettit ECU, but something happened to it. It started off by simply giving error codes for the knock sensor and refusing to run the AC, and then it started throwing me into something reminiscent of limp home mode at random times. I should probably just get a PFC and stop whining.
jds
I had a Pettit ECU, but something happened to it. It started off by simply giving error codes for the knock sensor and refusing to run the AC, and then it started throwing me into something reminiscent of limp home mode at random times. I should probably just get a PFC and stop whining.
jds
Originally posted by Mahjik
Well, I believe that last statement is what is causing you the problem (which is why people don't recommend open exhaust with the stock ECU). If it's just a spike, the ECU probably won't respond to it (or respond quick enough).
Well, I believe that last statement is what is causing you the problem (which is why people don't recommend open exhaust with the stock ECU). If it's just a spike, the ECU probably won't respond to it (or respond quick enough).
05-23-03, 11:01 PM
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I believe the stock ecu only cuts the fuel if the boost is over 10 psi for a straight 3 seconds. The stock ecu is actually pretty forgiving, runs fairly rich through all rpms. Problem is with open exhaust you see boost creep, and the ecu doesn't compensate for it. From what I understand up to 12 or 13 psi spikes are dangerous but not automatic detonation, but the spikes 14+ are the ones you gotta worry about...
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