I have a large ol ****pile of tuning problems with my 96 LT1. Local tuner has had it a few times but these problems can't get resolved so I acquired JET DST tuning and ecmpro logging software.

The cold start idle problem centers around an inability to idle correctly unless I give it some throttle. After about 10-15 seconds of feathering the throttle, it will idle on it's own.

I grabbed a log yesterday and today I tried to adjust the TPS. Initial monitor says the tps % 0 and tps volts .922. I adjusted the setscrew until it read 2% and turned off the car. I unplugged the tps and turned key on for 10 seconds. I then turned off the key, plugged in the tps. when I turned on the key on again the tps was still 2% and the tps volts 1.2. Wasn't it supposed to adjust to 0% when it was unplugged?

I have a csv of the log from yesterday. Click on the link in post # 3. I need some advice on how to get the tps volts to around .75, knock the iac counts down to 60-80 and get this thing to light off like it should. I got the cam from AI, it's the 230/236 @.050 they sell.

Thanks!

 

signature didn't show so here's what the car has:

96 Formula - rebuilt LT1 w/AI 200cc h/c/i package, LS1 lid, BBK 58mm, Pacesetter LT/GMMG, T56-steel 3-4 shift fork and billet keys, McLeod Street Twin clutch, Denny's Nitrous Ready DS, Moser 12 bolt, 3.73s w/33 spline & Eaton posi, 1350 pinion, dual in-tank Walbro 255lph pumps, Hochkis springs, 35mm (frt) & 25 mm (rear) Suspension Techniques solid sway bars, Kenny Brown SFC, BAER 2 piston w/13"x1.25" rotors, Spohn torque arm, custom LCA w/Spohn relocator, custom PHR w/BMR relocator

 

maybe this link will work:

https://docs.google.com/leaf?id=0Bw7...3MjQz&hl=en_US

 

Have you slotted the BBK TPS mounting holes. What you have to do is get the TPS sensor voltage between 0.45 and 0.75 volts and at the same time get your IAC counts into 30-50 range. EG Adjust the TB stop till IAC = about 40 then adjust the TPS physical mounting sensor position until the voltage is in range. Then shut down and reset the IAC, power it up and the TPS should read 0%, voltage s/b in range and the IAC should be in the range to control idle. . It may take a couple or gyrations to get it all correct. After that insure TPS closed timing tables have been increased in the 400-1200 range into high 20's to low 30's to smooth out the idle and and up the vacuum a bit, w/your setup your MAP Kpa is probably in the mid-high 50's" at 700-800 idle speed. After all that insure IDLE RPM is stable to what the desired RPM is set at. I would verify fuel trims in idle, then proceed to drivability tuning and then WOT tuning.

I am not familiar with OBD2 tuning tables but they have to have a coolant temp to RPM start table, make sure your IAT and coolant temp sensors are reading correctly and that table is calling for higher RPM when cold, also there should be coolant temp to AFR table that ups AFR when cold. If the tables look OK then it's hopefully is just probably your IAC is already opened all the way (160) is max and it can't open any more to keep the cold RPM up to speed.

 

Thanks Bob. I'm going to work on the tps slotting and iac tonight or tomorrow. Also, I'm going to make sure I'm getting idle air into the intake idle air passages and not dumped in to the plenum. I might have time to get some table info posted up if I have time. If I didn't have to work I would have a lot more time to work on the car!

 

https://docs.google.com/leaf?id=0Bw7...5NmRh&hl=en_US

BETTER!! But still have some work to do. I got the intact tract back on and made a few cold adjustments. I checked the tps volts before i hit the key and it looking great at .5. It fired right up but idled at 1500. I made a few more adjustments to the setscrew on the tb and grabbed a log. It fired up nicely and idled what i think is a bit low (~850) at first but at least i didn't have to throttle it to keep it going. then it started idling up and stabilized around 1050. I noticed the iac counts slowly lowered to 0. I dunno for sure but would that indicate a vacuum leak since the iac pintle is closed and the idle is still at 1050? Or would that indicate the setscrew is set too high, letting air in around the tb blades?

It seemed like the more i lowered the setscrew, the more it struggled on the initial start. I want to go lower on the setscrew but the low initial rpm aint cool. What's next?

 

I pretty much wrapped this up this past weekend after working on it for seeeeveral days. The main reason I couldn't get the idle right turned out to be the iac valve. I replaced it and stuff started falling in place and acting like it should. I've got a smooth idle, well as smooth as a 230/236 cam can be and iac counts in the 30s with idle around 1000. tps is 0% at .490 volts.

Another contributor was finding out my fuel pressure was 47.5, not 43.5. After I changed the injector constant from 42 lbs to 43.9 lbs and changing the cylinder volume to reflect a 355 and not a 350. It acts a lot better now but I still have more work to do. It has a small flat spot off idle and and I'm working out some decel bugs.