rough idle running rich

[blaze15301]

I got my car back up and running i switched over to a 0411 ecm after i fried the other one. here are the specs on the car

97 corvette
long tube headers
no cats
no rear 02
0411 pcm

The car starts and runs, but I am having the same issue as before it is very rich. the 02 sensors are saying it is lean my wide band is showing rich. at idle it will go to 8.5 on the afr gauge then start to stall out till i give it gas. All the plugs are black and sooty so it definitely is running rich. When i disable the ltft in the scanner it seems to run a little better. I checked for vacuum leaks with a smoke tester didn't find anything. i put the car into speed density and it idles a lot better, but i don't have my afr hooked up to hp tuners yet so i didn't want to leave it like that, I am at a loss here on where to go from here.

[dhoagland]

Post the Tune and the log

[blaze15301]

22-06-19 18-04-50.hpl
99 corvette stock vats delete mil delete.hpt

ignore the aem wb stuff I am still working on the math so it all reads correct.

[blindsquirrel]

This is not something that can be fixed in the tune file - I don't know if that's what you're looking for or not.

How sure are we that the front O2s aren't plugged into the rear O2 harness connectors and vice versa? How sure are we that someone before you hasn't changed the wire locations in the O2 connectors (harness side)?

screenshot.19-06-2022 22.44.58.png

[dhoagland]

Hmmm
I question the o2 sensor wiring, or the sensors themselves, from this log.

You say same problem as before.
So you were running rich at idle and in the process of repairing that you had an ECM failure?

[blindsquirrel]

Running rich, apparently from the plugs, but O2s pegged out lean. Adding fuel like crazy but O2s never come up above 100mV.

Funny thing is, if you look at the O2s in the log that's exactly what downstream O2s will look like when everything is working.

[blaze15301]

the o2 sensors have maybe 100 miles on them. I repinned the harness for the 0411 pcm. when i went to go write to fail the maf my ecm bricked.I had this issue before the ecm swap as well. im just trying to figure out what it could be because I am at a complete loss. tomorrow i will have to trace the wiring for the 02 sensors and see if they are wired wrong. as far as the wiring looks from when i changed them they look to be stock and in stock location. The rears have different harness plug ins. those are still there as well just nothing plugged into them.

[dhoagland]

the o2 sensors have maybe 100 miles on them. I repinned the harness for the 0411 pcm. when i went to go write to fail the maf my ecm bricked.I had this issue before the ecm swap as well. im just trying to figure out what it could be because I am at a complete loss. tomorrow i will have to trace the wiring for the 02 sensors and see if they are wired wrong. as far as the wiring looks from when i changed them they look to be stock and in stock location. The rears have different harness plug ins. those are still there as well just nothing plugged into them.

Okay, help us understand.
You had this vehicle running well, then started having (you fill in) issues.
OR
I just got this car and I'm having the issues noted in OP

Where I'm going with this is there appears to be issues getting o2 info back to the ECM...
So it seems you are looking at each end of the circuit (at o2 sensors and ECM pinout) but ignoring everything in-between.
This is based off looking at one log with no real vehicle history.

I'm not sure what tooling you have
You could verify that the o2's are getting uninterpreted input voltage and ground and then monitor the signal at the sensor.
Then verify you have the same signal, at the proper pin location, at the ECM.

[blaze15301]

Sorry for the miscommunication.

The car has always ran rough. Even before the ecm swap.

I got the vehicle from someone who just threw the exhaust on it with no history has to what they did before hand or to it. It was a over sight on my part.

You guys gave me some more stuff to go over I'll take a look tomorrow and post what I find. I can post the log file I had before the ecm swap as well if that would help any.
Thank you for the help.

[blindsquirrel]

The O2s did this same thing in the log from the previous thread with the previous PCM.

The O2s appear to be working just fine! If they were stuck at 450, or stuck high or stuck low even when cold I'd agree that it's a wiring or sensor or PCM issue. But they start out cold at a perfectly normal 450mV, both start waking up at the same time, and they both go low and stay there even though trims are going to +70% at times. Plugs and the way it runs (and the WB, if that's to be trusted) indicate it's rich. NOTHING makes the O2s ever go rich - previous log showed they did go to ~500mV during a WOT spurt (IIRC) but never above that, and mostly they stayed down in the 50-100mV range with no switching, just flat lines.

No exhaust leaks upstream of the sensors, right? Would be really weird to have leaks on both sides that affected both sensors the exact same way and by the exact same amount though.

MAF g/s looks high, really high, I would've expected forcing SD mode to have eliminated that and made a big improvement. Generally, MAF g/s at warm idle (for engines over 2L - does not apply below that) should equal engine displacement - around 5.3 g/s for a 5.3L, around 6.0 for a 6.0L, etc.


I don't know what more I can offer without having it in front of me and able to check things myself but I'm really curious to know what the cause turns out to be.

[blindsquirrel]

Try this. Post a log.
99 corvette stock vats delete mil delete MAF FAIL.hpt

I did check multiple other repository files with same year/same OS and the only changes from stock here are VATS/column lock stuff and DTCs.

Just out of curiosity, what's up with the EVAP DTCs? Only some disabled? EVAP parts still there and trying to kill the light from some specific EVAP fault?

Cats still present, just rear O2s turned off? Sensors completely removed/unplugged or just turned off?

[blaze15301]

When you use a 99 up corvette os on a 97 or 98 you have to disable the pressure codes for the tank everything else stays the same. The cats are gone as well as the rear 02 sensors. I'm going to force SD again and do a a log then go from there.

[dhoagland]

You guys gave me some more stuff to go over I'll take a look tomorrow and post what I find. I can post the log file I had before the ecm swap as well if that would help any.
Thank you for the help.[/QUOTE]

It would not hurt. There might be something in common that might spark a different idea

[blaze15301]

here are 2 logs files one from before the ecm swap and the new one is with the maf disabled.

22-06-03 15-23-04 june ice cream.hpl before the ecm swap



log 2 214 is one the one i just did. i used the tune with the maf disabled that blindsquirrel sent. the car is still running extremely rich. about 10 minutes into the drive i turned LTFT Learn and Command Closed loop off. My afr immediately went from 9.3 to 12.6 and stay around that till i came back to let it idle.

I also checked the wiring all the way back to the ecm and everything is where it should be. none of my fuses are blown, the wiring checks out.

[blaze15301]

Thanks for all the help guys i figured out what the problem was. one of the ground wires for the rear 02 sensor was melted a little bit so i repaired it then changed my 02 sensors out and the car runs alot better. I am not seeing any surging or running to rich now.

Here is the log files i just did.test4.hpl test 3.hpl

[blindsquirrel]

I think the sensors were all sooted up. Unless it was creating a ground loop type thing I don't think a signal ground shorted to ground would cause that. In the log before these, in SD, they did finally start almost-nearly switching (even before the point where you forced it open loop). If you could've kept it from adding so much fuel all the time they probably would have cleaned up.

This is MAF re-enabled, AIR pump disabled & cat codes turned off.
99 corvette stock vats delete mil delete - cat stuff AIRpump.hpt

[blaze15301]

I think the sensors were all sooted up. Unless it was creating a ground loop type thing I don't think a signal ground shorted to ground would cause that. In the log before these, in SD, they did finally start almost-nearly switching (even before the point where you forced it open loop). If you could've kept it from adding so much fuel all the time they probably would have cleaned up.

This is MAF re-enabled, AIR pump disabled & cat codes turned off.
99 corvette stock vats delete mil delete - cat stuff AIRpump.hpt

Thank you. The 02 sensors were fouled pretty bad. Now on to figuring out the right math for my wideband and the fuel gauge.

[blindsquirrel]

I noticed the MAF at idle looks a bit more plausible too.