Car is a 1997 Z28, with a 383 Stroker, LE3 Heads, Cam, Ported Intake, 42 Lb. Injectors, Pace Longtubes.

It is converted to OBD1 from ION, and tuned more so locally.

We are having problems with it running in Open loop. More specifically, its hates to idle when cold. The O2 Reading are poor, and vary from 4-70 on both banks. It seems the heaters, and/or sensors are dead.

However, once the car is warmed up, it runs fine, and the O2's read perfectly.

I have done an LS1 lately, that had similar issues, and with the long tubes headers, we installed different O2's, the rear ones from a corvette, to help them out. I believe the part number was 13911. It was having activity problems, and people were saying since they are further away from the motor, you can run into those issues.

Back to the LT1, can these have the same issues?

What would cause the car to run poorly like this in Open Loop, but fine in closed? Its mostly, bad idle issues. I have tried tuning and tuning, with no luck, it will idle at 500 constant when cold, but once it warms up, doesn't even have a hiccup, and idles perfect.

Thanks in advanced, if anyone needs more info, please post and I will respond ASAP.

 

This means your open loop parameters need some tuning. Closed loop works OK because the PCM is using the O2 sensors to correct the fuel mixture.

 

What do i need to change??

last night the o2's were 150-200 till the car warmed up. My old Le2 setup the o2's were higher than that durring open loop warm up


Thanks

 

You can adjust open loop AFR by changing the Open Loop AFR Vs Coolant Temp Vs. MAP table. If you want to make it richer, make the values in this table lower.

However, there may be a broader issue at play here. I'd also make sure your MAF calibration tables and VE tables are well-tuned.

 

Well after looking at the mail order tune

All VE tables are stock

and

The MAF conversion tables are off, for my slp 85mm



FIX=

I am changing the maf tables tonight, and i have a VE program. You have to drive around for 30min , all types of driving, BUT NO power enrichment mode( have to turn that off for VE logging), then the program figures what the VE tables need to be to keep you LT fuel trims at what ever you choose, 128 or what ever..

I guess i will try and mess with that next week,

Thanks for the help

 

Is this VEmaster program you are talking about?

 

If the sensors were not warm enough, or were "dead", the readings would be closer to 450mV. When they aren't generating any voltage on their own, the PCM sees its own bias voltage. The fact that the O2 sensors are showing a lean condition would indicate that are probably working, and the exhaust is truly lean. Have you checked the coolant temp sensor to insure its triggering the correct level of cold start enrichment? Almost seems like it may not be seeing any cold start enrichment at all.

I'm assuming you are no longer running an AIR pump, because those O2 values would actually be correct with the pump functioning.

 

First step would be to get your MAF tables correct. What are your long term fuel trims at idle and partial throttle in closed loop? That will give you an idea of how much you need to correct your MAF. Once the MAF is calibrated, then start messing with the rest.

Dan