LetThePoniesRunFree

Here is an on-going problem I have. Short term trims are not agreeing bank to bank below 3Kclosed loop. No exhaust leaks, (per sniffer), no intake leaks, ( per smoke test),and the injectors have been flow benched tested within 2%. Open loop WOT runs are fine, technically as I haven't dropped a cylinder yet. For the life of me I can not figure out why the short terms in closed loop are off by about 8%. I'm 99.9% sure I'm not getting any unmetered air into the intake. I'm scratching my head trying to figure this out. The really weird thing is there is no drivability issues at all. I realize 8% isn't THAT big of a deal normally, but man, it it's a big of enough difference to drop a cylinder. Any of you guys or your tuners ever come across this?

ASUSMC

Sounds kinda like a tune issue. If at WOT everything runs fine, i.e. no boost loss, car doesn't fall on its face, then I don't see it being any kind of mechanical impedence on the system. What fuel pump are you running, what is fuel pressure like at those rpm's with the issue? Any aftermarket fuel rail issues where you simply may not be getting enough fuel pressure to the injectors when not at WOT?

cliffyk

Differences in the switching times and waveformsof the O2 sensors could account for this, you'd have to scope their outputs to see it.If they have a few (10k+) miles on 'emit's not unusual for them to age differently.[/align][/align]Are you talking about an instantaneous difference of 8%, or a range offset of 8%?[/align]

LetThePoniesRunFree

It's basically a continuous offset of 8%-10% before the ecm switches to open loop. The O2's are new, (less than 10k miles), Bosch units I replaced to try and fix the problem. When the ecm switches to closed loop, the trim data goes deadaccuratebetween bank to bank.

cliffyk

Are they Bosch units specifically spec'd for the newer (1998+) 3.3 Ohm heater circuits? The older 6 Ohm heaters will not react quickly enough to the controlled heater cycling of the newer design, and because they are so far downstream of the exhaust port they can run cold and give wacky readings--of course this doesn't explain why one bank is consistently below the other???[/align][/align]Is the lower bank pushing into negative numbers? This could indicate a heater malfunction--I'm thinking it's a sensor operating temp issue, or maybe the sensors are that much mis-matched. I've seen a number of negative posts about the Bosch sensors, however in my other "Miata" life (one sensor only) I've neverhad a problem using the Bosch 13275 "sort of generic" 6 Ohm heater 4-wire sensor...[/align]

oxfordgt

Do you still have your EGR?

LetThePoniesRunFree

Yah, I've never had a problem with them and the data didn't change at all compared to the factory ones that I thought could be faulty.

I switched the 02's across banks and the data stayed the same for each side. I guess I can rule out the 02's causing it.
I also switched injectors side to side without any change in data.

I was told even a "pin hole" size exhaust leak could cause this. I hoping that's all it is and I can live with that. But it would be nice to know so I don't hold my breath every time I go WOT.

Yes, all emissions are still intact. Gotta love CA[:'(]

cliffyk

This is from the factory manual[/align] The short term trim % is the amount the PCM has varied the mix from what it thinks "should be" the desired a/f ratio to what is required for the O2 sensor to report the ratio it (the PCM) wants. The phrase "fuel delivery variability" in the above paragraph makes me wonder if what you are observing is a factor for the fuelbeing delivered first tothe bank 1 rail, and then via the crossover tube to the bank 2 rail?

The PCM has to use different short term trims to get the ratios it wants because of the different rail pressures???

This is 110% speculation on my part as I am relatively new to the Mustang world, and the only other ECU I've ever gotten this far into is on my '92 Miata...


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LetThePoniesRunFree

The fact that the trims are off during idle~3k until the ecm switch's loops and thatmy pump duty cycle peaks at only 78% WOT/red line, I don't think it's a fuel delivery/pressure/volume issue. If it was the ecm would adjust the pulse width on the leaner bank to compensate, up to a point.

I appreciate the idea though. Any help is better than none at all, especially at this point. [&:]

99mustanggt

Although you've already ruled out the 02's,I just wanted to add that during open loop your 02 sensors are'nt even being looked at by the pcm,thats why when you get into closed loop your stft's even out because the pcm is looking at your 02's and realizing the problem.