high end miss...
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Joined: Oct 2003
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high end miss... ok i've been fighting this ever since i installed my ported heads and 306 cam about 3 years ago
my car will miss between 5800-6500
it really only does it under a higher load, like in 3rd or 4th gear.
i know its not the rev limiter.
i've changed the following parts
3 different optis
who knows how many sets of plugs and wires
2 different coils and ignition moduals.
2 sets of vavle springs
new fuel pump
many fuel filters
ran without accell box
ran with steve's accell box
put a new ground on the motor
re adjust rocker arms
02 sensors
i know their something i've missed.
http://home.earthlink.net/~blkchevyz/dynosmall.jpg
my car will miss between 5800-6500
it really only does it under a higher load, like in 3rd or 4th gear.
i know its not the rev limiter.
i've changed the following parts
3 different optis
who knows how many sets of plugs and wires
2 different coils and ignition moduals.
2 sets of vavle springs
new fuel pump
many fuel filters
ran without accell box
ran with steve's accell box
put a new ground on the motor
re adjust rocker arms
02 sensors
i know their something i've missed.
http://home.earthlink.net/~blkchevyz/dynosmall.jpg
11 Second Club
Joined: Oct 2002
Posts: 895
Likes: 0
From: Austin, TX
sounds like maybe a bad connection to the comuter.
I would be looking for a problem in your tune, or a loose wire in the harness...
Those sudden cuts look like a drop in voltage or a spark sinal not sent on one cylinder.
Have you scanned the car?
Did it give the Multiple Random Misfires code, or did it identify a particular cylinder for the miss?
I would be looking for a problem in your tune, or a loose wire in the harness...
Those sudden cuts look like a drop in voltage or a spark sinal not sent on one cylinder.
Have you scanned the car?
Did it give the Multiple Random Misfires code, or did it identify a particular cylinder for the miss?
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http://home.earthlink.net/~blkchevyz/chris1.uni
thats the data master file from that dyno run...
its a 94 so i dont get any miss fire codes.
not really sure what to look for in the tune? i've tried added and removeing both timing and fuel
thats the data master file from that dyno run...
its a 94 so i dont get any miss fire codes.
not really sure what to look for in the tune? i've tried added and removeing both timing and fuel
TECH Resident
Joined: Jun 2002
Posts: 943
Likes: 2
From: Houston
i dont think it has to do with tuning...sounds likea hot spot in the head or somethign similar causing detonation. try running a higher octane fuel or buy some race gas mix and see if the problem goes away. if it does, then its simply detonation, if not, then its a misfire and you can go from there. But two of the more common reasons for misfire after a head swap are heat spots and plug wires. rarely will a computer start glitching because you swapped heads, there is no reason for the computer to malfunction for any reason because of a heads cam swap. the only things thing that the computer will deal with for the most part will be the a/f ratio or false knock(LT4 KM will generally solve this) created by the higher lift cams and larger rocker arms. Sounds like detonation, try the race fuel and see if it goes away, if not then you truly have a misfire and can go from there.
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Joined: May 2004
Posts: 405
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From: Knoxville, TN
My friend and I have built his LT1 three different times. We came across this very same miss. It took us a very long time to find the problem causing the high end miss. What we did was hooked an OBDI from our friends Dealership and ran it down the road. We ran it hard past 5800 rpm and it did miss. We went back and they printed out a scan sheet of what all the sensors and injectors were doing. This print out had readings a couple times a second. Turned out that the whole time this 94 LT1 had been missing up past 5800 rpm was because of the TPS sensor(throttle body position sensor) had been glitching or shorting out after it was at 100%. Print out showed that the sensor read 100%, then 0%, then 100%....all within a second. See this made the ECM think that we let off the gas, and it never through a code. I hope this helps you LT1 fokes. By the way he runs a 7.05 in the 1/8th mile @100 mph. 
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Verdad Gallardo TECH Regular
Joined: May 2004
Posts: 405
Likes: 1
From: Knoxville, TN
Originally Posted by Gangly
Awesome! I never even would have thought to consider that, thanx for the input "200Z28SS".
My friend and I have built his LT1 three different times. We came across this very same miss. It took us a very long time to find the problem causing the high end miss. What we did was hooked an OBDI from our friends Dealership and ran it down the road. We ran it hard past 5800 rpm and it did miss. We went back and they printed out a scan sheet of what all the sensors and injectors were doing. This print out had readings a couple times a second. Turned out that the whole time this 94 LT1 had been missing up past 5800 rpm was because of the TPS sensor(throttle body position sensor) had been glitching or shorting out after it was at 100%. Print out showed that the sensor read 100%, then 0%, then 100%....all within a second. See this made the ECM think that we let off the gas, and it never through a code. I hope this helps you LT1 fokes. By the way he runs a 7.05 in the 1/8th mile @100 mph.
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damn this is an old post.
i blew it up last year but after looking i think my issues was i had to much lift for the gm 1.6 rock arms... think they are only good for 570 or so and i had 600. they had some wear marks, looks liked the polly locks where hitting.
i blew it up last year but after looking i think my issues was i had to much lift for the gm 1.6 rock arms... think they are only good for 570 or so and i had 600. they had some wear marks, looks liked the polly locks where hitting.
