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I have a 97 tbird with a 97 NPI short block from Ford and 99 PI heads & intake. Over all the car runs very strong. Two issues may be related: 1) The idle is a bit rough. New IAC helped but should be better. Idle speed seems low ( approx 600 in drive ) 2) While cruising at 30 mph in top gear (OD) and applying light throttle I get some fairly severe spark knock. Opening the throttle will downshift and all is ok.
I suspect that there is too much timing in the 97 NPI EEC at both idle and part throttle for the 99 PI heads. Does any one know?
Any trhoughts on a fix? Maybe a 99 4.6 auto mustang EEC? Not sure if EGR or returnless fuel impact/changes.
 

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tune? have u checked into getting a blue oval chip? no personal experience, but there's A LOT of talk about it. That, IMHO would be much less hassle than trying to get a completely different computer to work. try out blueovalchips.com or do a search on custom tuning, you should get plenty of hits. :)

And Welcome to the Forums!
 

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the commanded idle speed in drive is 550 RPM in a 97 4.6 EEC, so thats fine, but how it gets there is a different issue......in a stock tune, the EEC assumes that the TB blade is open enough at "closed throttle" so that 0.44 #/min of airflow is allowed (which is roughly what is needed to idle at the target RPM in neutral).......when more airflow is needed in idle/drive, the IAC does the rest.........so in other words, with your car at normal operating temps, it should barely idle in neutral with the IAC unplugged (at least decently enough so that the car doesnt stall).......you can use the throttle stop screw while the IAC is unplugged to let in enough air so you can work back down to the point where it just barely maintains idle without stalling....once you fine tune this point, plugging in the IAC once again will result in a much more stable idle


also you have to make sure that the voltage from the TPS is as close to 0.99V as possible, but not over 1.0V DC....you do this by hooking up a digital multimeter to the lower 2 wires from the TPS and loosening the screws that hold it.......then rotating the TPS slightly while the ignition is on to get the output voltage as close to 0.99V DC as you can

unfortunately, the very low 3-4 upshift and immediate torque converter lock causes engine load to rise a lot when applying throttle.....since you now have 10.5:1 compression ratio instead of 9.0:1 when you had NPI heads, the timing curves need to be adjusted for proper operation......if you had a complete PI engine, then the timing would be alright, since complete PI engines have about 9.3:1 compression

you would not be able to use a 99 mustang auto EEC because of what you said: returnless fuel system....not only that, you would need a '99 mustang MAF meter......you are simply better off getting an Xcal2 programmer setup for a PI head swap.....i recommend Justin @ www.vmptuning.com
 

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Premium gas may help w/ the ping, if your not already using it... the compression ratio is most likely causing the ping.
 

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I have a 97 tbird with a 97 NPI short block from Ford and 99 PI heads & intake. Over all the car runs very strong. Two issues may be related: 1) The idle is a bit rough. New IAC helped but should be better. Idle speed seems low ( approx 600 in drive ) 2) While cruising at 30 mph in top gear (OD) and applying light throttle I get some fairly severe spark knock. Opening the throttle will downshift and all is ok.
I suspect that there is too much timing in the 97 NPI EEC at both idle and part throttle for the 99 PI heads. Does any one know?
Any trhoughts on a fix? Maybe a 99 4.6 auto mustang EEC? Not sure if EGR or returnless fuel impact/changes.

I would imagine with a 600RPM idle someone has retuned that car. I would pull out the ECM and make sure there isn't a chip installed. Also check to see that the EGR is working, or you might have a small vacuum leak. A PI headswap still shouldn't ping even with the higher compression.

SCT tunes will disable the fault for a bad DPFE on almost all their tunes, ask me how I know.................What happens is that if a DPFE is even plugged in the ECM will run the EGR added timing to the full amount thinking the EGR is working, whether or not the DPFE is reading anything at all. If your EGR valve is closed, line is clogged, or was deleted and there is a DPFE still attached, that would explain what you are getting if indeed there is already a retune in the car.

If you are not getting a check engine light and have no tune for sure, then simply unplug the DPFE and see if the problem goes away.
 

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i agree with the previous post check your egr, vac lines, and dpfe sensor.
 
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