LT1 car cuts out above 6k rpms?
03-10-2009, 10:15 PM
#1
LT1 car cuts out above 6k rpms? Helping a friend solve this problem. Started a couple months ago, then his msd opti went out and he got a new one for free from them, now the car runs again but still cuts out up top.
97lt1
stock heads
lt4 hotcam
slp mid length/shorty headers
3" y pipe
electric water pump
ported tb
msd opti/wires
think that's about it
we put a new fuel filter on today and I could still blow through the old one so it doesn't seem like that was the problem...we also check 1 plug on each side and they were kinda white but not bad
any other ideas?
97lt1
stock heads
lt4 hotcam
slp mid length/shorty headers
3" y pipe
electric water pump
ported tb
msd opti/wires
think that's about it
we put a new fuel filter on today and I could still blow through the old one so it doesn't seem like that was the problem...we also check 1 plug on each side and they were kinda white but not bad
any other ideas?
03-11-2009, 12:00 AM
#4
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My buddy had a similar problem on his old car and it ended up being the timing chain sprocket was missing a couple teeth...
Just an idea to check even though its kinda a pain to check that...
Just an idea to check even though its kinda a pain to check that...
03-11-2009, 06:48 AM
#6
Helping a friend solve this problem. Started a couple months ago, then his msd opti went out and he got a new one for free from them, now the car runs again but still cuts out up top.
97lt1
stock heads
lt4 hotcam
slp mid length/shorty headers
3" y pipe
electric water pump
ported tb
msd opti/wires
think that's about it
we put a new fuel filter on today and I could still blow through the old one so it doesn't seem like that was the problem...we also check 1 plug on each side and they were kinda white but not bad
any other ideas?
97lt1
stock heads
lt4 hotcam
slp mid length/shorty headers
3" y pipe
electric water pump
ported tb
msd opti/wires
think that's about it
we put a new fuel filter on today and I could still blow through the old one so it doesn't seem like that was the problem...we also check 1 plug on each side and they were kinda white but not bad
any other ideas?
OK, dumb question, but you do have a tune on the car and the stock rev limiter raised - right?
03-11-2009, 11:34 AM
#8
Maybe valve float. Mine fellon its face at 6K RPM last year cause the springs could not control the valves with my cam. Replaced the beehives with Patriot extremes and it reved to 6.5K with no float.
Here is a good before and after showing the float. Look at the end of the power curve:
Here is a good before and after showing the float. Look at the end of the power curve:
03-11-2009, 12:13 PM
#9
coil is msd as well replaced the same time as the first msd opti last summer
he said he has the lt4 knock module, my scanner says he's picking up about 1 degree kr, nothing major
car has a tune as its a swap car into a 92 camaro, the car did not used to do this, it started in Aug when he raced a nitrous cobra on the interstate and accidentally revved to 7k
engine now has 100k miles on it, 40k on the cam and springs...maybe the springs have gotten weak?
he said he has the lt4 knock module, my scanner says he's picking up about 1 degree kr, nothing major
car has a tune as its a swap car into a 92 camaro, the car did not used to do this, it started in Aug when he raced a nitrous cobra on the interstate and accidentally revved to 7k
engine now has 100k miles on it, 40k on the cam and springs...maybe the springs have gotten weak?
03-12-2009, 12:51 PM
#13
03-12-2009, 03:12 PM
#14
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Hey guys i'm the friend thunderstruck is speaking for. I'm running a '97 coil so that picture doesn't work but i know where to find it on shoebox.
I guess its necessary for the "cut-out" to be described better, it's like a random miss-fire that causes the car to shudder quick once, it sometimes occurs under 6k rpm, but not often and only under heavy loads. where i noticed it the most was running at the track when i took the car to 6.5k rpms and it "missed" 3 times at the top of 3rd.
the coil is an msd coil that's less than a year old (haven't tested yet tho), not sure how old the icm is but i've tested it already and it checks out. I tested each plug wire individually last summer as well and got very low resistance numbers so i'm pretty sure they're still good. upon inspection i can't find any burnt wires. we were in a little bit of a time crunch so i only checked 2 spark plugs (number one and number four) both of which had a little bit of white looking powder on the prong (weren't fouled).
I'm worried because this is what it has done the past 2 times right b4 the msd opti-spark goes out. that's right i'm on my third msd optispark in less than a year
I guess its necessary for the "cut-out" to be described better, it's like a random miss-fire that causes the car to shudder quick once, it sometimes occurs under 6k rpm, but not often and only under heavy loads. where i noticed it the most was running at the track when i took the car to 6.5k rpms and it "missed" 3 times at the top of 3rd.
the coil is an msd coil that's less than a year old (haven't tested yet tho), not sure how old the icm is but i've tested it already and it checks out. I tested each plug wire individually last summer as well and got very low resistance numbers so i'm pretty sure they're still good. upon inspection i can't find any burnt wires. we were in a little bit of a time crunch so i only checked 2 spark plugs (number one and number four) both of which had a little bit of white looking powder on the prong (weren't fouled).
I'm worried because this is what it has done the past 2 times right b4 the msd opti-spark goes out. that's right i'm on my third msd optispark in less than a year
03-12-2009, 04:02 PM
#15
Hey guys i'm the friend thunderstruck is speaking for. I'm running a '97 coil so that picture doesn't work but i know where to find it on shoebox.
I guess its necessary for the "cut-out" to be described better, it's like a random miss-fire that causes the car to shudder quick once, it sometimes occurs under 6k rpm, but not often and only under heavy loads. where i noticed it the most was running at the track when i took the car to 6.5k rpms and it "missed" 3 times at the top of 3rd.
the coil is an msd coil that's less than a year old (haven't tested yet tho), not sure how old the icm is but i've tested it already and it checks out. I tested each plug wire individually last summer as well and got very low resistance numbers so i'm pretty sure they're still good. upon inspection i can't find any burnt wires. we were in a little bit of a time crunch so i only checked 2 spark plugs (number one and number four) both of which had a little bit of white looking powder on the prong (weren't fouled).
I'm worried because this is what it has done the past 2 times right b4 the msd opti-spark goes out. that's right i'm on my third msd optispark in less than a year
I guess its necessary for the "cut-out" to be described better, it's like a random miss-fire that causes the car to shudder quick once, it sometimes occurs under 6k rpm, but not often and only under heavy loads. where i noticed it the most was running at the track when i took the car to 6.5k rpms and it "missed" 3 times at the top of 3rd.
the coil is an msd coil that's less than a year old (haven't tested yet tho), not sure how old the icm is but i've tested it already and it checks out. I tested each plug wire individually last summer as well and got very low resistance numbers so i'm pretty sure they're still good. upon inspection i can't find any burnt wires. we were in a little bit of a time crunch so i only checked 2 spark plugs (number one and number four) both of which had a little bit of white looking powder on the prong (weren't fouled).
I'm worried because this is what it has done the past 2 times right b4 the msd opti-spark goes out. that's right i'm on my third msd optispark in less than a year
03-13-2009, 02:23 AM
#16
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Again, like said above have u checked fuel pressure i ran into the same problem with my stock pump. It was low on fuel pressure at hight rpm but i didnt figure out why the car was missing up in the higher rpms until i was on the dyno and had fuel pressure guage on the car? Check the easy things first before u blame the opti again. Goood luck
03-13-2009, 05:36 PM
#17
We'll give it a shot, he has a gauge on the rail and a walbro 255 pump we just need to find a good way to test it at that rpm where we can see a gauge
I'm personally not a fan of just free revving an engine that high but he might not be as bothered
I'm personally not a fan of just free revving an engine that high but he might not be as bothered
03-13-2009, 05:40 PM
#18
That's how I found out that my fuel pressure was dropping to 20psi @5000rpm, but only under load.
