Forgot to mention I've been using Scan 94/95 for data logging and recently started using TunerPro RT.
Forgot to mention I've been using Scan 94/95 for data logging and recently started using TunerPro RT.
94 Z28 Auto/ Powerdyne BD11A Supercharger/ MSD 6A Ignition,Blaster 2 coil and MSD Opti/all forged rotating assembly/ .525"-duration 305 cam/ 24lb injectors/ Hooker long tube headers/ tuned/ NOS fuel pump
Battery voltage going low is probably just from lack of RPM's to the alternator, should fix itself when you fix the idle problem. The timing is also directly related to RPM, ie it's not that it's pulling timing due to knock or too high of idle, just that when the engine is turning that slowly there is more time for the mixture to burn at any given advance. For example the time between 20 degrees BTDC and TDC at 900 rpm is roughly the same as the time between 10 degrees BTDC and TDC at 450 rpm.
I'm not particularly familiar with that setup but my guess is that you need to adjust the physical throttle stop (or start by cleaning the throttle body if it's dirty), that will allow a bit more airflow getting the IAC valve back into a range where it can be effective.
My guess is that the bigger cam is pulling less vacuum which means at the same IAC opening the car is getting less air and producing less torque due to lower VE because of increased overlap. If that's the case and opening the throttle a bit restores a proper idle rpm then the next thing you can expect to do is decrease the VE in the lower rpms ranges and increase it in the higher rpm ranges to better match the cam. Of course you'll want to do this based on your data logs.
Attached is my most current data log. It was just sitting in my driveway with no drive time. As you look through my log you will notice a few times where I rev the engine and then when the rpms drop is when I put car into gear.
94 Z28 Auto/ Powerdyne BD11A Supercharger/ MSD 6A Ignition,Blaster 2 coil and MSD Opti/all forged rotating assembly/ .525"-duration 305 cam/ 24lb injectors/ Hooker long tube headers/ tuned/ NOS fuel pump
Thanks for the reply. So if I adjust the throttle stop screw should I do the tps sensor adjustment by drilling out the 3 sensor screw holes and moving it accordingly?
94 Z28 Auto/ Powerdyne BD11A Supercharger/ MSD 6A Ignition,Blaster 2 coil and MSD Opti/all forged rotating assembly/ .525"-duration 305 cam/ 24lb injectors/ Hooker long tube headers/ tuned/ NOS fuel pump
I don't think you'll need to. I think the amount of adjustment needed is so small that closed throttle tps voltage will still be within the normal range. There are certainly people more knowledgeable/experienced than me who could provide more specifics about where you want your IAC counts to be, and i'm sure you can find some forum posts discussing that, but I know you don't want it maxed out during idle. I would start by adjusting the throttle stop until it can idle at the target rpm with IAC counts below 140 and see if you can find better information on where it should be. Basically you want it to have enough adjustment both ways to be able to handle temperature and barometric pressure changes, along with extra load from accessories such as A/C, power steering, etc. When I get some more time i'll take a look at the xdf in tunerpro because there are probably some setting where the code predicts how many IAC counts need added when shifting from P/N into gear, and that might also need some adjustment to get a smooth transition, but that's more fine tuning and can come after...
Just some thoughts...
Firstly i'd try cracking the throttle blades to see if idle improves and iac tries to close some. You then know you have some control.
I'd strip check clean iac passages and throttle body.
See where the throttle blades are.
The blades are generally better being as closed as possible on an LT1 as this supposedly stops split BLM's (I've not directly witnessed that but altering the timing does)
I drilled out the iac passage in the front of the throttle body which allows more air in through the iac and iac counts go lower.
I would suggest iac counts around 40ish (1/4 - 1/3 of the range to allow some control) It will open up quite a bit whilst starting off cold. and will increase as driving speed increases.
Switching heating fans on also increase the iac around 10 points which then will come down again.
If you motor needs a lot of air i've read that people drill hols in the throttle blades like they do on carbs rather than cracking the blades.
On carbs if the blades are cracked you move over the transfer slots affecting the mixture.
I don't there is anything like that on the LT1 throttle body though.
HTH some
Mitch
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
Ok so I cracked the throttle blades and adjusted tps sensor to .66v. IAC's went down into the 60's, so that helped. I did a data log using EEHack but when I try to attach to this post it says invalid file. How do I attach this file so I can have somebody look at my log?
94 Z28 Auto/ Powerdyne BD11A Supercharger/ MSD 6A Ignition,Blaster 2 coil and MSD Opti/all forged rotating assembly/ .525"-duration 305 cam/ 24lb injectors/ Hooker long tube headers/ tuned/ NOS fuel pump
Did you zip the file?
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