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View Full Version : High RPM miss fire

JerzLT1
10-02-2008, 12:59 AM
any idea what it could be guys? its a head/cam LT1. could the stock fuel pump just not have enough to feed it?
NJSPEEDER
10-02-2008, 10:48 AM
Pull a plug and check it. If it doesn't have the light brown haze on it you are leaning out.
JerzLT1
10-03-2008, 10:45 PM
would that cause it to break up in high rpms though? almost like the power cuts out and then comes back in
sweetbmxrider
10-04-2008, 12:02 AM
is it tuned?
JerzLT1
10-04-2008, 01:44 AM
yes
Pampered-Z
10-04-2008, 10:36 AM
So does it have a mis, or is it cutting out? Also howh high in to the RPMs are you when this mis/cutout occurs?

If it's actually cutting out then I'd guess first that you might be bounching off thr rev limiter. A miss could be a weak coil or Opti, even the gap on the plugs.

A stock FP will handle near 400 HP without a problem, if it's in good shape.
JerzLT1
10-04-2008, 08:36 PM
feels like its cutting out to me, Ron said it feels like a miss. its over 4k but def not the rev limiter. the car should be putting near 400 to the wheels
IROCdan330
10-05-2008, 03:42 PM
The way to know if its your fuel would be first to put a gauge on it, tape it to the windshield, and drive it...watch for a drop in fuel pressure when your "miss" occurs. second, a datalog at high RPM couldnt hurt...you would be able to see injector pulse width and see if they are static at your "miss" and beyond. If you have means of doing so, let me know and I'll dig up the formula for injector duty cycle for you.
LTb1ow
10-05-2008, 03:50 PM
Sounds like a coil to me.
KGP
10-10-2008, 08:48 AM
If you have means of doing so, let me know and I'll dig up the formula for injector duty cycle for you.

Here you go.. with an online calc to figure it out. ;)

http://www.injector-rehab.com/kbse/idc.htm
98tadriver
10-23-2008, 09:32 PM
id say its in between a miss and it cutting out. its not violently bucking, but its definately noticeable in the upper rpm range 4500+
LTb1ow
10-23-2008, 10:24 PM
Borrow a coil and throw it on there. And your not getting any opti death alerts are you?
JerzLT1
10-24-2008, 01:21 AM
no it runs fine other then that, the car is almost back together so well see how it is with the new fuel pump in it... now if only i could get a real day off lol
LTb1ow
10-24-2008, 04:42 PM
And of course, its always a perfect excuse to get a new MSD or likewise coil.
camaroracer1992
11-03-2008, 03:28 PM
id say go entire MSD ignition on the car. are you running nitrous? what are the gap on the plugs?
LTb1ow
11-03-2008, 03:38 PM
MSD opti is iffy in its price tag being worth it. But spark plug wires, coil and 6AL are all good stuff.
crainholio
11-04-2008, 12:58 PM
I'd remove and inspect each plug wire, chances are you'll find one that got too close to the header primary and got toasted.
TurboDiverArt
11-05-2008, 08:35 PM
So does it have a mis, or is it cutting out? Also howh high in to the RPMs are you when this mis/cutout occurs?

If it's actually cutting out then I'd guess first that you might be bounching off thr rev limiter. A miss could be a weak coil or Opti, even the gap on the plugs.

A stock FP will handle near 400 HP without a problem, if it's in good shape.

I'd vote opti but without experiencing it no way to be sure. opti's an expensive guess.
JerzLT1
11-19-2008, 09:20 PM
well the car is back on the road with the new fuel pump in and it seems to be fixed as far as cutting out. there just seems to be a slight break up up top now and i think its tuning because it smells so mad like fuel that its burning my eyes. time for a 58mm TB, AFPR and a dyno tune