Car breaking up on top end
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Joined: Aug 2002
Posts: 317
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From: Charlotte NC
Car breaking up on top end Recently I blew both head gaskets on my car. I ordered new head gaskets and they were replaced, while doing that ew went ahead and replaced the opti spark since it was looked rusted and like it was about to crap out. After everything was back together we put to car on the dyno to make sure everything was in tact and running properly.
The car now will only pull till 5200-5300 and starts going crazy. It will not even make it to 6K. On the dyno you can see the graph looks like someone on a heart monitor lol. My first thought was it had to be the opti, but the shop insisted that it was brand new and had to be something else, so we have went through everything since then. The car has a T trim making about 11 psi.
Anyone have any idea what it might be or do you think it was my first guess of the opti being bad out of the box??? Any help is much appreciated
The car now will only pull till 5200-5300 and starts going crazy. It will not even make it to 6K. On the dyno you can see the graph looks like someone on a heart monitor lol. My first thought was it had to be the opti, but the shop insisted that it was brand new and had to be something else, so we have went through everything since then. The car has a T trim making about 11 psi.
Anyone have any idea what it might be or do you think it was my first guess of the opti being bad out of the box??? Any help is much appreciated
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From: its as intense as the time i forgot how to sit down
if i remember corectly someone else had that exact problem,and they put in a stronger aftermarket opti and it fixed everything,ill see if i can find the article and post it for you
what valve springs are you running? i used to have the same proble, right at 5300 power would drop 90rwhp before the car hit 5400rpm, i replaced opti with a dynaspark and same thing, turns out it was valve float caused by crappy spring shims
Thread Starter
TECH Apprentice
Joined: Aug 2002
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From: Charlotte NC
The car has already made 650 before with the same valves and all. We checked those and they are fine, no valve float.
We have tried a new coil, pcm, 2 sets of wires, 3 sets of plugs and hours of tuning.
The opti that we had on the car that was just taken off was the one that made 650 and it was a gm opti, so I shouldn't need to go to a different opti, I think I just got a dud out of the box.
We have tried a new coil, pcm, 2 sets of wires, 3 sets of plugs and hours of tuning.
The opti that we had on the car that was just taken off was the one that made 650 and it was a gm opti, so I shouldn't need to go to a different opti, I think I just got a dud out of the box.
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Joined: Nov 2004
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From: league city,tx
I'd check the opti(you can get a bad one out of the box). Also don't forget that since you had blown head gaskets it would probably be a good idea to replace your oxygen sensors(coolant can foul these real easy) and I would double check for any leaks in your sc piping & intake manifold!
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Thread Starter
TECH Apprentice
Joined: Aug 2002
Posts: 317
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From: Charlotte NC
OK so a new opti was tired and nothing. Its not quite as bad but the car is still down a good 50 hp and the bad thing is that this is with the aftercooler using ice as well and the numbers before were w/o. I honestly don't know what to do with this thing.
is it a sudden loss? or 50 hp loss all the way across the power band?....your sure nothing changed in the valvetrain? still think it sounds like valve float...
you have a data log of it? be interesting to see if your getting any kind of knock, maybe somethign is causing false knock and your pcm is pulling timing?
you have a data log of it? be interesting to see if your getting any kind of knock, maybe somethign is causing false knock and your pcm is pulling timing?
Thread Starter
TECH Apprentice
Joined: Aug 2002
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From: Charlotte NC
Bascially the stock PCM wasn't up to the task for the power the car was making and the fuel that it needed. Just had to go back and keep tuning until it got as good as we could. A fast system, or big stuff would allow alot more out of the car esp if a larger head unit where used on the blower.
Thread Starter
TECH Apprentice
Joined: Aug 2002
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From: Charlotte NC
we pulled a little timing out of the car and had to try a few different settings with the gaps on the plugs. Also did end up having one bad plug wire that was replaced and that did help some now. The car now has a slight miss at part throttle around 3500 rpms on rare instances. Guess it has to be rpm/throttle combo to find it.
