vpc/gcc na-t Q
 

i finally tuned my na-t to 11.5-11-8 a/f using my fjo and vpc/gcc. the temp outside was a cold evening @ 65 degrees. but w/ the same settings @ 85 degrees daytime outside, the a/f changed to mid 10. a/f. is this normal? should i be constantly changing the gain when outside temps change?

tia
MIke

weather changes the density of the air coming in. Therefore making your car richer or leaner, but I thought the vpc/gcc combo had provisions for this. I think you only set the gain once, and set all of the rpm knobs. But I have never dealt with a vpc.

Where did you mount your temp sensor?



gadgetSC-t

vpc has an air temperature sensor that goes into the intake manifold that compensates. I think it might have something to do with the vpc chip. I have bought a BAD vpc chip from mvp motorsports, It idled funny where I thought it was something wrong with the injectors. It turned out to be a bad chip. Try checking on that.

thanks for the reply guys.

gadgetSC-t: my temp sensor is located @ split Y near the egr solinoid area. i'll try moving the temp sensor closer to the throttle body. is there a way to check if the temp sensor is bad? another thought is that the egr gases are heating up the sensor, but wouldn't that cause a lean condition?

Single7: my car idles fine. i hope that its not a bad chip or this will be my 3rd bad one. :)

thanks
MIke

if it is by the egr, could heatsoak be a concern?

i was wondering the same. but i remember reading in supraforums that a heat soaked temp sensor was causing lean conditions. my problem is a rich condition during a hot day and normal a/f's (11.5) during a cold day. but i'll try moving the sensor to see what happens.

i forgot to mention. the conditions i'm mentioning are happening @ wot. the car actually runs fine. i tuned the fuel myself using a fjo wbo2sensor. i just noticed the a/f differences between a hot day and cold evening.

thanks
MIke

hey mike, i think your temp sensor is fine. dave henry suggested that the best place to put it was in front of the throttle butterfly on the TB. i don't think it'll matter a whole lot but if you have the TB coolant bypass it'll be mounted in a cooler place at least.

I read on suprafroums, one guy took some type of plastic "thingy" and drilled/tapped it. Basically he used the thingy as a insulator between the engine and the vpc temp sensor.

the air temp sensor does heat soak - ideal locations are
in the throttle body before the butterfly as mentioned or
easier way in intercooler pipe directly before the throttle body
i saw the plastic mounting bung also - but its still inside
the intake where its not the true 'air temp' reading

supra dr,

why would the temp vary before the butterfly vs the pre tthrottle body ic piping?

sorry i wasnt clear enough - intercooler pipe & prebutterfly on throttle body
would be the same temp. (opitmum locations in my opinion) the plastic
bung was used on the intake manifold asm. where the vacuum fuel filter
was removed on gte engine for vpc temp sensor install (thats where hks
tells you to put it) the problem is the intake manifold heat soaks over time.
AEM guys were having problems w/ this - calculated a/f ratios would change
because their sensor became heat soaked /saturated, & wack out their readings.
when nothing really changed the sensor was giving false info to the computer.
the problem is still here w/ vpc set up but you dont know it unless your
running a wide band o2 (the vpc is piggy back & the ecu hides the problem)
back to basics - all o.e.m. cars w/ air temp sensors have the sensor mounted
in the air box/air intake pipe.(true ambiant air temp) on a turbo car the true
ambiant air temp is on the cold side (after intercooler) before the throttle body plate.
anything after that engine heat skews the actual temp that the sensor is tring to read.
easy enough?