LT1 cold start idle tuning

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Aug 9, 2011 | 06:14 PM

Brettmc

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From: St Louis MO

LT1 cold start idle tuning

I have a large ol shitpile 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 below. 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.

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

Thanks

Aug 10, 2011 | 07:52 AM

bjankuski

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From: Glenbeulah Wi

I looked at your scan and some items need clarification. Why is there no MAS readings? The injector pulse is very high after start-up but the WB readings are still at 15:1, but the commanded AFR is in the 7's? The intake manifold pressure after start-up is also very high. It appears to me that the car is going very rich at start-up and then it recovers after you step on the gas. I would reduce (less fuel) open loop AFR and the start-up AFR and time delay. I also would like to know why there is no MAS readings.

Aug 10, 2011 | 10:32 AM

Brettmc

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From: St Louis MO

That is another question. The MAF is connected but the tuner that has been working on this car for 2 years at some point checked the speed density box so this car is running on the ve tables. How long ago he did this, I have no clue. I would think the maf values would show in the pcm even though its running in speed density mode. Maybe I have a bad maf??

How can it be rich at startup when the wb reads in the 15s?

i'm going to slot the tps mounting holes tonight or tomorrow night. If I can get the volts down to .6ish I think it will act a little better. To do this I'm going to remove the bbk tb. i want to be sure idle air is being routed to the idle air passages in the intake before anything else.

Aug 10, 2011 | 12:38 PM

bjankuski

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From: Glenbeulah Wi

I am not sure if I trust the WB numbers, all of the data suggests the WB readings are not accurate. If they are accurate you may actually need more fuel for the first 15 seconds of running. If you look at your injector pulse widths and map pressure they are both really high for the 700 RPM the car is running. Also the commanded AFR is in th 7's for the same area. After the car idles OK the AFR is commanded in the 12's and the injector pulse width is in the 3's and 4's.

Last edited by bjankuski; Aug 10, 2011 at 12:43 PM.

Aug 11, 2011 | 09:43 PM

Brettmc

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From: St Louis MO

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?

Aug 11, 2011 | 09:46 PM

Brettmc

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From: St Louis MO

Yeah, I noticed the difference in the wb reading and what the pcm ratio was. I guess i'll put it on the stands this weekend remove and test the wb. I've noticed that with the key on engine off it won't go dead lean but neither is it in free air.

Sep 2, 2011 | 12:57 PM

lionelhutz

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From: South Western Ontario

It sounds like you just opened the throttle enough to replace the pedaling on a cold start. The problem is likely in the computer tuning, not the throttle body, so you will have to close the throttle again to get the proper IAC count at hot idle and then fix the tuning. This is assuming there isn't a mechanical issue...

Peter

Sep 2, 2011 | 02:15 PM

Brettmc

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From: St Louis MO

Every programming change I made didnt produce results....until I replaced the iac. Now I've got a decent cold start and no more valve clatter on hot starts. By no means finished tho...still have a lot of tuning to do.