hello, i have a 1994 firebird formula lt1 wich has a anoying problem. when i bought it it was missing a litle and the service engine light was on, i had it checed for codes and it came up with the optispark and knock sensor. i changed the optispark, knock sensor, waterpump, sparkplugs and wires, now its not missing anymore like it did before and no service engine light but now it wont rev any higher than 2500-3000 at that pont it starts knocking and just stops reving even thogh it feels like it wants to go higher, but the further i push the gas the higher the knocks get without the rpm going any higher. while the car is cold it works fine, sound like its running a litle rough but still works fine, then when it has warmed up the problem starts, most of the times i can drive it for hours as long as i dont turn it of, if i turn it on again wile still hot it wont rev higher than 2500-3000 and sometimes it just starts doing it even thogh i havent turned it of and on again. the service engine light does come on when it has warmed up but will go out if it cools down. i checed for codes again after having driven it for an hour and it came up with the optispark, icm and knock sensor. I'm guesing the icm or maf sensor(saw a simular problem where the maf sensor was the problem) i tried unnpluging the maf and i didnt see, hear or feel any difference with how the car was acting both hot and cold, exept the service engine light and both fans came on while it was unpluged
hope someone has some ideas about this problem

also my friend was saying its the alternator, wile cold the voltmeter in the dash reads just above 13v at idle but when it warms up it drops down to 13 or just below 13 at idle :S

sorry for the bad english, im 16yrs old from iceland

 

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I have a starting problem when it gets hot also never did it before until I did my heads and cam swap and had the PCM tuned so maybe timing Is off idk but very tired of it

 

Do a search for the ICM cooling mod. sounds like a potential fix for your problem...

 

Changed icm still having the same problem. drove it today for an hour worked fine for 30min but when standing still at idle for 5 min it started getting very hot like the second fan wasnt kicking in and when i drove of it started backfireing at 3000rpm and quikly wouldnt rev higher than 1100rpm, after a wile of driving in 6th ger at 900rpm the service engine light came on and it started working normaly again and both fans came on. also tried unplugging maf sensor but didn't change anything

I'm thinking maby coolant sensor :S

 

check to see if spark plug wires didn't get mixed up somewhere when you did the change its a little harder on these cars. Also check your egr it might have carbon build up see if the pintle valve moves freely. It could also be your cats backing up or possible dirty injectors I've seen this before. You can also check your fuel pressure as well. Ernest

 

Thanks i'll check these things. But shouldn't those things couse it to have problems all the time, it works fine while it is cold and when the service engine light turns on
don't the lt1's have a limp mode it goes into when the ses light goes on?

Edit: Took it for a spin today, everything happend like usualy eventualy wouldt rev higher than 3500 and was getting hot after idleing at standstill so i stopped unplugged MAF to get the SES light and both fans on. Seconday fan came on but stil wouldn't rev. Eventualy it wouldn't go higher than 1100rpm so i tried letting of the gas and downshift from 4th to 2nd gear and forced it to rev that way and it did and after that worked fine again, until i turned it of, then it wouldn't start again barely turned over. I Tried unplugging the spark wire from the ignition coil but still it was hard for it to turn over :S