To tune or not to tune, that is the question

[LeftVentricle]

Several things become evident based on this chart. First, my suspicions are confirmed, in that the transmission is not transmitting all the power, and that I am running on Cavalier code, not Celebrity. There's also the little matter of the pig rich mixture. The guy even said that at 4500 and above I basically pegged their sensor at 10:1, which means it went even richer than that.

They offered to tune it for $425. Should I take them up on it?

[SappySE107]

$425! hell no. You could at least try one of my chips setup for your 3.1 first. Much cheaper and has a 30 day money back guarantee. Otherwise get the programmer setup and tune it yourself for much less. Fixing that rich condition shouldn't be hard.

[manicmechanix]

What I don't get is if you have the ECM and prom that went with the Cavalier engine why would the fuel curve be that messed up and run that rich? It would seem at 10:1 AFR you'd be blowing black smoke and overheating the Cat. I'm no tuner and I don't mean to cast aspersion on this dyno run but I've heard operators can and do skew the results. I could be wrong but I just don't see how a factory engine with matching prom and ECM could run that overly rich unless the injectors were changed or something. and that doesn't explain why it's running lean below 3500 rpm at WOT, open loop.

[Superdave]

Stock $A1 code runs pretty rich at WOT, Ben's chip should fix that.

Just to confirm, you are running stock injectors right?

[LeftVentricle]

ECM is original to the Celebrity, prom came from the Cavalier. Could that be causing the problem?

Injectors were ordered for the Cavalier, but the part numbers were the same for both '92 Cav 3.1 and '89 Celebrity 2.8, and have the same flow rate of 15 pounds.

I don't know how the results could have been skewed. I watched the entire process, and saw nothing amiss. AFR was measured from exhaust gas out the tailpipe, basically like an emissions sniffer test. Only thing I didn't like is that they ran the first pull in second, then balked when I asked to run it in third, saying they didn't think my brand new, T-rated tires could withstand the potential speed.

Tangentially, the car pretended to do 125 on that pull.

What does Ben's chip change?

[SappySE107]

fuel, spark, idle speed, fan turn on, etc. I have tweaked the 3.1 on a dyno and on the street so I have a good tune for them.

[manicmechanix]

ECM is original to the Celebrity, prom came from the Cavalier. Could that be causing the problem?

Injectors were ordered for the Cavalier, but the part numbers were the same for both '92 Cav 3.1 and '89 Celebrity 2.8, and have the same flow rate of 15 pounds.

I think this should work fine. The Celeberity and Cav. should had the same ECM, but I'm not sure if the mem-cal is totally the same. I think so.

I don't know how the results could have been skewed. I watched the entire process, and saw nothing amiss. AFR was measured from exhaust gas out the tailpipe, basically like an emissions sniffer test. Only thing I didn't like is that they ran the first pull in second, then balked when I asked to run it in third, saying they didn't think my brand new, T-rated tires could withstand the potential speed.

Tangentially, the car pretended to do 125 on that pull.

How can you possibly accurately measure the AFR after the Cat? This car does have a Cat right?

[LeftVentricle]

How can you possibly accurately measure the AFR after the Cat? This car does have a Cat right?

Yes. If not for AFR, why would they do that?

[1meanz]

dont most of them do that? either that or use a o2 or something right?

[manicmechanix]

Yes. If not for AFR, why would they do that?

Well as far as I know all testing after the Cat is going to really tell you is how well your Cat is working. Why they would do that? My guess is because they're too lazy to loop a wideband O2 sensor where the original O2 sensor is located. I don't see how any reading after the Cat can be valid, but maybe some knowledgable tuner people can comment on that.

[TiredGXP]

An O2 sensor placed after the cat typically reads .5 leaner than precat readings, but this varies.

Lots of controversy over whether a WB in the tailpipe is of much use, here's a couple of threads that discuss this

http://www.hptuners.com/forum/showthread.php?t=21602&highlight=tailpipe

http://www.hptuners.com/forum/showthread.php?t=12789&highlight=tailpipe

[manicmechanix]

An O2 sensor placed after the cat typically reads .5 leaner than precat readings, but this varies.

Lots of controversy over whether a WB in the tailpipe is of much use, here's a couple of threads that discuss this

http://www.hptuners.com/forum/showthread.php?t=21602&highlight=tailpipe

http://www.hptuners.com/forum/showthread.php?t=12789&highlight=tailpipe

Thanks for the info. I need to do some tuner reading. On top of the variable the Cat adds, with or without a Cat, I seriously doubt a heated wide-band O2S would get hot enough to give a valid output at the tailpipe. There might be sophisticated equipment that i don't know about that can, but still I doubt that's the case. If you could just stick an HO2S anywhere, automakers wouldn't be putting two of them ahead of the converter right up next to the exhaust manifolds since the one downstream from Cat would suffice.

[SappySE107]

They use them both to check cat efficiency.