Some LT1 woes

[MazdaX]

Hey Guys ..not new to the F-body scene but new to the 4thgen LT1's and am encounting problems already lol..

I purchased a 1993 Formula Firebird withe auto trans/LT1 engine/all power options and the only mod done was a K&N intake filter. Anyways the car has 88,xxx miles and when I purchased it ..ha...it had been sitting since 2006 with same fluids internally and gas in the tank. I got it around 2 weeks ago ( paid 900.00 =P ) and after a new battery , oil change , radiator drain&fill and a couple shots of starter fluid into the intake it fired right up but idles like crap. I went to check the RPM's and it was steady at about 800 or so but the motor was shaking. I was then thinking worst possible scenario - badhead gasket , hole in a piston , etc..Anywho I let it run for about 15 minutes to reach OT and then killed the motor and pulled the oil cap to check for white build up - none. There wasn't any moisture int he old oil either...

I went on to fire it back up , shot out a puff of smoke for about 1 second then ran normally at 800 rpm or there abouts without issue but motor still shakes. I tapped the gas pedal and took it up to about 2,500 rpm and it shook some more , let it fall back and tapped again to about 3,500 rpm and it was smooth after 3,000. So it runs and doesn't die - went to dmv got a temp 96hr permit - drove it 30 miles to my work place

On the drive it didnt act as if it were going to die..the brakes barely worked , the struts seem sloppy and it was extremely 'jerky' at stop lights as if it was lurching forward in sharp jabs while brakes applied..ohhh and the oil pressure light is going berserk all over the place. I pulled over at the next shoulder spot and popped the oil cap while running and it was spitting oil all over inside the valve cover so at least the oil pump seemed to be good - back to driving to my destination.

I got the car to is temporary parking spot and it was temp right in the middle , everything was working , never died or acted as if it was going to but the idle still very rough and the transmission very jerky while driving unless at cruising speed only at stop lights or stopping the car keeps trying to lunge forward. Anywho...I run it dry on the old gas which was about 1/10th of a tank and fill it up with some good 91 octane gas and toss in a can of B-12 and ran it for a while 15-20 minutes but no smoothing out of the idle.


The person I purchased the car from is a friend and a very responsible driver and not one to always mash the gas and gun it all over town and he said it was running primo- when parked so what can this be ? The is no CEL , SES , Oil needle all over , jerky , everything else works fine...Any ideas ? It does have a cracked intake boot but with taping and hot glue it didn't fix it either and sorry about the long post just thought I would try to give as much info as possible.

[Genopsyde]

i'm 100% sure your problem is ignition related. start looking at the condition of the spark plugs. you may also have optispark issues.

[MazdaX]

Is there anyway I can trace the problem without having it diagnosed while running and hooked up to a dealership scanner ?

[Genopsyde]

see if any of the spark plugs are wet with gas, if they are then they aren't firing.

[Morley]

Check for evidence of water on/in the optispark. If it got wet it is toast.

[MazdaX]

Is there any way to do a HEI mod to it ? I know on my old 1993 mazda mx-3 I had the same type of thing with the whole 'optispark' and when they over heat they would fry but you could do an external GM HEI mod to if and fix it.

[Morley]

Originally Posted by MazdaX

Is there any way to do a HEI mod to it ? I know on my old 1993 mazda mx-3 I had the same type of thing with the whole 'optispark' and when they over heat they would fry but you could do an external GM HEI mod to if and fix it.

Yes and no. You'd need to get a modified LT1 intake, modified to accept an HEI distributor. Then you'd need a wiring harness for an old TPI car and the ECM..basically go backwards in time. The newer PCM won't interface with an HEI distributor.

[MazdaX]

Originally Posted by Morley

Yes and no. You'd need to get a modified LT1 intake, modified to accept an HEI distributor. Then you'd need a wiring harness for an old TPI car and the ECM..basically go backwards in time. The newer PCM won't interface with an HEI distributor.

not the whole official HEI set up...heres a link you guys can browse over and see if the same methods apply just different wires.

http://www.clubprotege.com/wil/howto/hei/index.htm


Would it work the same way ? Seems like the optisprk is a serious downfall to the motor with 1 - being in the front and exposed like that to elements and 2 easily killed by water .