Vaccum leak?
03-04-2007, 06:36 PM
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Vaccum leak? --------------------------------------------------------------------------------
I'm tuning a '02 T/A with a built longblock (not stroked) w/ heads, decent size cam, full exhaust, fuel system upgrade, and an ATI Procharger setup. The car is still MAF based for the time being. The customer put a GM 85mm MAF on it, and left the screen in place.
In SD, idle and part throttle tunes out perfectly. The moment I re-enable the MAF the fuel trims peg out to +25%. Via RTT, I've added in approx. 256% more to the stock values to the MAF transfer (for this particular MAF) just to get the fuel trims to come down. That's insane! Just to give you an example, at 1500 hz the value is 3.64 g/sec, whereas the stock transfer value for that MAF is around 1.42 g/sec. We either have a fairly large vacuum leak, which I tend to believe is the issue, or either this car is just going to have to be tuned in SD period.
As a side note, the Idle Desired Airflow is reading quite low (around 4.xx to 5.xx g/sec), which is much lower than I would expect, even when the STIT isn't really indicating any adapting to keep the car idling (which idles absolutely great in SD mode).
Any and all suggestions and questions are appreciated.
Thanks,
Mike
I'm tuning a '02 T/A with a built longblock (not stroked) w/ heads, decent size cam, full exhaust, fuel system upgrade, and an ATI Procharger setup. The car is still MAF based for the time being. The customer put a GM 85mm MAF on it, and left the screen in place.
In SD, idle and part throttle tunes out perfectly. The moment I re-enable the MAF the fuel trims peg out to +25%. Via RTT, I've added in approx. 256% more to the stock values to the MAF transfer (for this particular MAF) just to get the fuel trims to come down. That's insane! Just to give you an example, at 1500 hz the value is 3.64 g/sec, whereas the stock transfer value for that MAF is around 1.42 g/sec. We either have a fairly large vacuum leak, which I tend to believe is the issue, or either this car is just going to have to be tuned in SD period.
As a side note, the Idle Desired Airflow is reading quite low (around 4.xx to 5.xx g/sec), which is much lower than I would expect, even when the STIT isn't really indicating any adapting to keep the car idling (which idles absolutely great in SD mode).
Any and all suggestions and questions are appreciated.
Thanks,
Mike
03-05-2007, 10:03 AM
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Because of the limitations in the PCM, you might not be able to do the VE/MAF tune as listed in the sticky. You might have to skew the injector table first. What I mean is, put the MAF back to stock and reduce the injector table until your AFR comes back in line. If you can do that and keep the injector table linear, then you can go back and tune the VE based off of the false injector numbers. Then, re-enable the MAF and make any final tweaks. That way, you can run the MAF and if it fails, you'll have the VE table to fall back on. Doing this is backwards and your VE table will most likely be pretty rich until you back the numbers out, but (in theory) it should work.
03-05-2007, 11:22 AM
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Originally Posted by SSpdDmon
Because of the limitations in the PCM, you might not be able to do the VE/MAF tune as listed in the sticky. You might have to skew the injector table first. What I mean is, put the MAF back to stock and reduce the injector table until your AFR comes back in line. If you can do that and keep the injector table linear, then you can go back and tune the VE based off of the false injector numbers. Then, re-enable the MAF and make any final tweaks. That way, you can run the MAF and if it fails, you'll have the VE table to fall back on. Doing this is backwards and your VE table will most likely be pretty rich until you back the numbers out, but (in theory) it should work.
Anything else to try?