Idle surge issue
- Thread starter baggett3_27
- Start date
nyuk98gt
15 Year Member
baggett3_27:
Disclaimer: not a supercharger guy (but a good reader of tech threads).
Problem could be IAC flow not being quite right, backwash into the MAF (depends on the location of the blow-off valve return into the intake tract), disturbed air at the inlet filter (is it protected from 'fan wash'?), a small vacuum leak in the intake tract, or a MAF function that is not quite right.
You don't mention whether this is a suck-through or blow-through MAF but that is important info for the smart people who know about superchargers. Are you doing the tuning or can you just make minor adjustments to a 'canned' tune? Can you post pictures of the intake tract (if it is not a stock Vortech set-up)? Details matter when it comes to exorcising the idle demons.
HTH,
Chris
Disclaimer: not a supercharger guy (but a good reader of tech threads).
Problem could be IAC flow not being quite right, backwash into the MAF (depends on the location of the blow-off valve return into the intake tract), disturbed air at the inlet filter (is it protected from 'fan wash'?), a small vacuum leak in the intake tract, or a MAF function that is not quite right.
You don't mention whether this is a suck-through or blow-through MAF but that is important info for the smart people who know about superchargers. Are you doing the tuning or can you just make minor adjustments to a 'canned' tune? Can you post pictures of the intake tract (if it is not a stock Vortech set-up)? Details matter when it comes to exorcising the idle demons.
HTH,
Chris
nyuk98gt
15 Year Member
baggett3_27:
Thanks for the additional info. Since you've checked for vac leaks (none) and the unplugged MAF gives pretty good idling and the exhaust smells rich then it has to be the tune. Call up your tuner and ask what items he wants datalogged so you can provide him enough info for a tune adjustment. Of course, if you're doing the tuning then let's discuss datalogging details.
Chris
Thanks for the additional info. Since you've checked for vac leaks (none) and the unplugged MAF gives pretty good idling and the exhaust smells rich then it has to be the tune. Call up your tuner and ask what items he wants datalogged so you can provide him enough info for a tune adjustment. Of course, if you're doing the tuning then let's discuss datalogging details.
Chris
I ordered a base tune from VMP to get me to the dyno, but I haven't received it yet. I do have the SCT tuner with livelink, so I can datalog. I'm also waiting on the SCT PRP I ordered to fine tune the car. I'm in the UK so there are no SCT tuners, but I have dyno shop that says they can do it if I with the SCT software. What are the things I should datalog for tuning?
nyuk98gt
15 Year Member
baggett3_27:
Sorry, I missed your location. Justin at VMP is a talented fellow when it comes to tuning so you made a good choice. The dyno tune will, presumably, keep your engine safe for heavy- to full-throttle. The around town driving is often challenging but, with the PRP, you can do it with some time and effort.
OK, the IAC controls the idle speed and spark is used to trim idle speed. There are a bunch of modifiers for IAC (idle air), cold idle conditions, and warm idle conditions. You will see all of these in the PRP (Advantage) parameter list. First thing is to tune the MAF function. "Everything" depends on an accurate MAF function. Also, don't forget to sign up at sctflash.com for the ProRacer forum (it is available only to PRP owners and SCT dealers). Lots of info there and helpful people, too. Once you get the MAF sorted out and it is perfect (<--not exaggerating) you can start working on the idle. That will be datalogging the following: isc_air, isc_air_correction, RPM, spark, STFT1, STFT2, idle_speed_commanded, load, MAF, ECT, spark source, ECT, IAT. With these parameters, you will see what the IAC is being told to do. If the isc_air_correction is too high (+/-) then you have to adjust your isc_air_N and isc_air_D tables or the isc_air table. Justin can give you some good direction (better than me since I have not tuned a supercharged engine - see disclaimer, above). You can also send your datalog to VMP and let them review it and give you some things to look at. Data is vital when tuning our cars (any late-model car). You have a laptop to collect the data, yes? The XCal can only hold a small amount of data so a laptop is pretty much required.
OK, that should get you thinkin'.
Chris
Sorry, I missed your location. Justin at VMP is a talented fellow when it comes to tuning so you made a good choice. The dyno tune will, presumably, keep your engine safe for heavy- to full-throttle. The around town driving is often challenging but, with the PRP, you can do it with some time and effort.
OK, the IAC controls the idle speed and spark is used to trim idle speed. There are a bunch of modifiers for IAC (idle air), cold idle conditions, and warm idle conditions. You will see all of these in the PRP (Advantage) parameter list. First thing is to tune the MAF function. "Everything" depends on an accurate MAF function. Also, don't forget to sign up at sctflash.com for the ProRacer forum (it is available only to PRP owners and SCT dealers). Lots of info there and helpful people, too. Once you get the MAF sorted out and it is perfect (<--not exaggerating) you can start working on the idle. That will be datalogging the following: isc_air, isc_air_correction, RPM, spark, STFT1, STFT2, idle_speed_commanded, load, MAF, ECT, spark source, ECT, IAT. With these parameters, you will see what the IAC is being told to do. If the isc_air_correction is too high (+/-) then you have to adjust your isc_air_N and isc_air_D tables or the isc_air table. Justin can give you some good direction (better than me since I have not tuned a supercharged engine - see disclaimer, above). You can also send your datalog to VMP and let them review it and give you some things to look at. Data is vital when tuning our cars (any late-model car). You have a laptop to collect the data, yes? The XCal can only hold a small amount of data so a laptop is pretty much required.
OK, that should get you thinkin'.
Chris
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