Possible bad program/tune????

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Jul 13, 2007 | 11:05 PM

kokamo

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From: Liberty HIll, TEXAS

Possible bad program/tune????

Hey guys, I'll try and make this short......

I have a 69 Camaro......I took the LT-1 engine and auto trans out of a 94 Z-28 to put in the 69.

I had the PCM mail order tuned for the 383 LT-1 I built out of the stock 94 motor.

I got it all running and it clatters VERY BAD under light to moderate throttle. This is major preignition well under 3K RPM.

Is it possible he just did a tune for the 350 using 350 parameters instead of 383 parameters by accident? If so, would it make sense that it's pinging so bad?

Thanks for any input guys,

Joe

Jul 14, 2007 | 02:42 AM

smoknta

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From: Evansville, IN

Contact your tuner, they should be able to verify that the tune is correct or not.

Jul 14, 2007 | 06:00 AM

fergymoto

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From: Rock Hill, SC

Make sure you have the drive shaft on your distributor indexed right. If it is off a tooth is can be advanced and do this. I had a '94 opti for my truck and it came with the shaft in it already, I installed it and the truck would ping just revving it in neutral. Here come to find out someone had forced the shaft on in the wrong place and it was advanced.

Jul 14, 2007 | 10:07 PM

kokamo

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Staging Lane

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From: Liberty HIll, TEXAS

Quote:

Originally Posted by smoknta

Contact your tuner, they should be able to verify that the tune is correct or not.

I finally got in contact with him. He told me that the timing is slightly faster than stock....or at least close to it. Lt-1 motors naturally have aggressive timing and such a little bump up should not have that big of a difference.

Quote:

Originally Posted by fergymoto

I thought about this for a while......when I built the engine myself, I made damn sure it went together correctly. The index marks are dead on where they are supposed to ge. There was no forcing, nor was it hard to put together. This entire build went together smooth as glass.

As far as compression goes, I never really did CC anything or get exact measurements. It has a Scat 383 crank, KB flat top 2 VR pistons .020 over, all rings meet stock clearancing specs, stock heads with polished chambers and mild to moderate port work. So I am assuming compression isin't an issue.

What I really need to do is take all the fuel out of the tank, and put in some fresh 93 octane. The fuel thats currently in it is about 2 months old.

I'll try that and reply back with results.

Thanks guys,

Joe

Jul 15, 2007 | 01:05 AM

MEAN LT1

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From: jacksonville,FL

Ive had fuel in my tank for 4 months and longer and never have experienced this before. If you want I can look at your tune and see if anything is out of the ordinary?.

Jul 15, 2007 | 08:28 AM

Karl Ellwein

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From: Southern Maryland

If you hear it rattling then it's rattling. No matter what you see for spark advance in the tune I would back off on the PCM timing (4 to 6 deg at least) until the rattle goes away.
If the cam/crank/timingset/opti is advanced (unknowingly) then that could be causing the spark rattle.

reason I say this is because I had a 383 motor that rattled like yours and I had to back the PCM timing off way down to 30deg (in the high load areas) and just scratched my head. Until I found that the cam was 6 deg advanced....meaning the distributor was 6 deg. advanced too.

Karl

Jul 15, 2007 | 09:05 AM

kokamo

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Staging Lane

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From: Liberty HIll, TEXAS

Quote:

Originally Posted by MEAN LT1

Ive had fuel in my tank for 4 months and longer and never have experienced this before. If you want I can look at your tune and see if anything is out of the ordinary?.

Mean, thanks or the offer man, I really don't have any way to look at the files myself. I really need to learn how to do the program thing. Again, thanks for the offer.

Quote:

Originally Posted by Karl Ellwein

Karl, thanks for the reply. I am 200% sure the timing is dead on. I even took pictures to prove this when/if I had problems later on. The timing chain is a basic stock replacement for a regular ole 350 LT-1. Nothing special like any kind of retard/advance features you see on a few other timing chain sets. This one is strait up dot to dot just like factory.

I'll get that fuel changed out today and see what will happen.

Thanks again guys,

Joe