I’m having trouble with a CTS-V running vastly different fuel trims in the first 5 to 10 minutes after startup compared to when the car is more heat soaked from longer running time.
It is a 2011 CTS-V with a comp cam, ID850 injectors, long tube headers, upper and lower SC pulleys.
I did the complete tune using the same method as I used on several previous CTS-Vs, mapping the MAF separately and them mapping the VE equations using the BlueCat tool. I’m using an NTK wideband and generally follow the tuning procedure outline by Greg Banish (eficalibrator) from the classes I have taken.
I thought I had the car dialed in very well, but a few days later the customer came back with a lean code. Sure enough, when I checked, the fuel trims were 18% lean at idle and low rpm.
So I re-mapped the SD section and rechecked the MAF, made a few adjustments until the fuel trims were perfect and sent the car on its way.
A week later the car is back. The fuel trims are now 22% lean at idle with coolant almost up to full temperature. But after the car runs a little longer the fuel trims are pretty close to dead on, and just above idle the car is too rich and sometimes stumbles, as if I need to undo the enrichment I did when the car came back last week.
I thought we might have a vacuum leak that “sealed up” as the motor got hotter, so we smoke tested the intake and exhaust systems with the car cold and found no leaks.
I thought the factory o2 sensors might just be slow to warm up with the long tubes, so I reinstalled the wideband and checked. The wideband matches the factory O2 switching points pretty well, so I’ve ruled that out for now.
Right now I’m stuck. If anyone could take a look at the tunes and datalogs and offer suggestions I would appreciate it.
Dan
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The wideband was going through the warm-up cycle during the first 18 seconds of the datalog, so pay no attention to the “AFR error inverse” or “Wideband O2” during the first 18 seconds.
Yeah, I know that the fuel trims are off at higher rpms when I free revved it neutral. Yeah, I know that The MAF g/s doesn’t perfectly match the VE g/sec. But both of these things actually matched better in an earlier version of the tune before I started trying to fix the temperature inconsistency. I’ll straighten that out once I get the car to be consistent.
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