james_85Z28

For some reason my car is falling out of PE mode at WOT, causing it to run extremely lean (no power) and do all the things, like turn on the EGR and CCP, that you would expect accordingly.

Attached is a pic of the scan made at the track Sunday. The mounds are gears 1,2,3 and 4. In fourth gear is where you see my O2 drop to ~50 and the EGR be commanded on and so forth. The O2s for gears 1-3 were between .860 and .890. The RPM spikes are ~6000 RPM with a pulse width of 8.50 mv and a duty cycle of 90%. If I hesitated between shifts more then the ECM remained in PE mode. I swapped ECMs in the pits, burned another chip, disconected the EGR and CCP wiring and the problem still occured. Could the high duty cycle cause problems with the ECM and force it out of PE mode? As you can see from the graph gears 1-3 remained in PE mode at 100% throttle without a problem (dropped out of PE mode during shifts because I lifted) and it dropped out of PE at the spike in 3rd gear but vever returned to PE mode when 100% throttle was applied in 4th gear. As soon as 100% throttle was applied in gears 1-3, PE mode was enabled.


I ran it at the track the weekend prior and this problem happened in the other gears but I was unable to scan it during the runs. I did record it doing it in 3rd gear as well on Sunday though. I am unable to duplicate this on the street (too fast too soon...) but I keep thinking it's related to the injectors and their duty cycle. Since it remains in PE mode in gears 1-3 and in 4th gear if I shift lazily or shift at 5400 RPM, I keep leaning towards the injectors causing the ECM to do something funky rather than the PROM. I reviewed the PROM and as didn't see anything that would tell it to go out of PE above 75% throttle, etc.

I just got this engine running a couple weeks ago after installing AFR 190s, Super-Ram, Accel 219 cam in a 350 shortblock. The fuel pressure is stock (no AFPR installed), 6* base timing, AXXD based PROM, T56 trans.

Any ideas?

RBob

iTrader: (1)

I have seen this happen where the ECM thinks that the TPS is in error. If the ECM thinks the TPS is in error it will substitue a value that is too low to enable PE.

This condition doesn't always set a DTC either. There is another status word (MW1) that needs to be decoded. It has two bits that define wheter the ECM thinks tha the TPS is in a low or high error condition.

Some things to check: the TPS setting while at closed throttle. Make sure it isn't on the high side (or lower it some anyway).

Check the TPS with a DVM (or scanner) for dead spots or a jumpy spot. IE make sure the TPS is good.

Can also double check the cal parameters for TPS error trip points. That may not be set properly.

Double check the MAP stuff also. The MAP KPa value looks to be too low for WOT at 4200 RPM. It may in error causing the PE mode to drop out.

RBob.

james_85Z28

I'll take a look at the TPS, thanks. I do believe it is on the high side of the acceptable range.

The MAP value at WOT is usually at 96-98 KPa but once it drops out of PE the MAP falls to the level shown, 60-80 KPA, most likely due to the conditions experienced by the problem.

Thanks,
james

Ed Maher

I'd venture that MAP reading tells the whole story. WOT but low MAP is probably confusing the ECM and making it drop out of PE.

If the MAP is normally 96-98 at WOT, it would not drop to 85 because the car wasn't running right out of PE. If anything the MAP should go up since the VE would go down with the engine missing.

MAPs are cheap. If i saw that on a scan from my car that'd be my first move.