High RPM Miss I've had for years that I can't figure out
04-30-2012, 05:39 PM
#1
High RPM Miss I've had for years that I can't figure out In 3rd and 4th above 5000 I usually get a hickup or 2. I can't tell in 1st or 2nd since I just spin through those gears 
. No idea whats causing it, no SES lights, not valvetrain related, a/f is good.
Couple of dynosheets showing it.
. No idea whats causing it, no SES lights, not valvetrain related, a/f is good. Couple of dynosheets showing it.
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04-30-2012, 09:30 PM
#8
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Not to hi jack your thread but I'm also having a high rpm miss. Car is stock not sure on plugs or there gap. I do have a set of accel plugs to I was going to put in when I installed my headers
Last edited by 96RamAirTA; 04-30-2012 at 09:37 PM.
04-30-2012, 10:24 PM
#9
Do you have a datalog that we can see more information and in smaller increments then a dyno graph? A sensor can be showing blips of incorrect information that causes the stumble, and being able to trace the information the computer is getting step by step as its happening will help narrow it down.
I would first try checking all your plugs to see if any are noticably different from the rest due to specific cylinders misfiring, then put them all back in @.035.
Its obviously not fuel related, since your A/F is spot on for the whole run. What is your compression ratio? It starts happening right around where your torque should be peaking, which is the engines highest load. That leads me to believe it may be blowing out the spark, and a tighter gap may help you. I know that with my tr55s dropping from .045 to .030 at my tuners request cleaned up my dyno graph quite a bit, and I was only 11:1 CR.
I would first try checking all your plugs to see if any are noticably different from the rest due to specific cylinders misfiring, then put them all back in @.035.
Its obviously not fuel related, since your A/F is spot on for the whole run. What is your compression ratio? It starts happening right around where your torque should be peaking, which is the engines highest load. That leads me to believe it may be blowing out the spark, and a tighter gap may help you. I know that with my tr55s dropping from .045 to .030 at my tuners request cleaned up my dyno graph quite a bit, and I was only 11:1 CR.
Last edited by Puck; 04-30-2012 at 10:28 PM. Reason: more info
04-30-2012, 10:41 PM
#10
Do you have a datalog that we can see more information and in smaller increments then a dyno graph? A sensor can be showing blips of incorrect information that causes the stumble, and being able to trace the information the computer is getting step by step as its happening will help narrow it down.
I would first try checking all your plugs to see if any are noticably different from the rest due to specific cylinders misfiring, then put them all back in @.035.
Its obviously not fuel related, since your A/F is spot on for the whole run. What is your compression ratio? It starts happening right around where your torque should be peaking, which is the engines highest load. That leads me to believe it may be blowing out the spark, and a tighter gap may help you. I know that with my tr55s dropping from .045 to .030 at my tuners request cleaned up my dyno graph quite a bit, and I was only 11:1 CR.
I would first try checking all your plugs to see if any are noticably different from the rest due to specific cylinders misfiring, then put them all back in @.035.
Its obviously not fuel related, since your A/F is spot on for the whole run. What is your compression ratio? It starts happening right around where your torque should be peaking, which is the engines highest load. That leads me to believe it may be blowing out the spark, and a tighter gap may help you. I know that with my tr55s dropping from .045 to .030 at my tuners request cleaned up my dyno graph quite a bit, and I was only 11:1 CR.
Is there any free OBDII data logging software? My tuner looked over the logs and couldn't find anything wrong with them on the dyno.
04-30-2012, 11:15 PM
#11
I tried an igniton box and it did nothing for the miss so I doubt it's the spark blowing out. As far as the plugs they looked fine when I changed them 10k miles ago, but if I can't figure it out I'll probably try tr6's gapped @ .035 and some top end cleaner the next oil change for the hell of it.
Is there any free OBDII data logging software? My tuner looked over the logs and couldn't find anything wrong with them on the dyno.
Is there any free OBDII data logging software? My tuner looked over the logs and couldn't find anything wrong with them on the dyno.
Proscan is supposed to be good as well, but IIRC its close to 200 bucks for the kit. Don't know any others off the top of my head, I'm an OBDI guy
.If you weren't already on a nice finished build I would suggest spending that money instead on an OBDI swap so you can datalog and tune it yourself for any future mods, but that wouldn't make sense for you.
05-01-2012, 03:36 PM
#12
Ghetto data log inc. It had a hickup in this vid right around the time the MAF went from 300ish to 286.
http://www.youtube.com/watch?v=-qiQ2aGNJZc
http://www.youtube.com/watch?v=-qiQ2aGNJZc
05-01-2012, 08:10 PM
#15
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i had a similiar issue happen with my c5 after installing an ASP underdrive balancer/pulley . missed above 5000rpm. turns out the pulley was bad. put a new slp ud pulley on and it cured the problem. worth a shot to check it. it was a pain in the butt to do on the vette, as i had to pull the steering rack to get to it. fbodies are easy compared to c5s lol
05-01-2012, 09:23 PM
#16
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Check your wires...
a plug wire wont arc to a different ground other than the plug strap if the resistance to cross the gap is less than the least resistance to a different ground on the chassis/motor.
As the load/pressure increases the resistance increases... you might have a wire that is just barely exposed and it takes a large amount of resistance increase to cause it to choose another grounding source. adding an ignition box would not fix this issue and might possibly cause it to get worse. Thats why i asked...
Have you had your ICM Tested repeatedly to ensure the high rpm mode is working correctly??
Your voltage drop is just the increased demand... nothing i would worry about.
a plug wire wont arc to a different ground other than the plug strap if the resistance to cross the gap is less than the least resistance to a different ground on the chassis/motor.
As the load/pressure increases the resistance increases... you might have a wire that is just barely exposed and it takes a large amount of resistance increase to cause it to choose another grounding source. adding an ignition box would not fix this issue and might possibly cause it to get worse. Thats why i asked...
Have you had your ICM Tested repeatedly to ensure the high rpm mode is working correctly??
Your voltage drop is just the increased demand... nothing i would worry about.
05-01-2012, 10:27 PM
#17
Check your wires...
a plug wire wont arc to a different ground other than the plug strap if the resistance to cross the gap is less than the least resistance to a different ground on the chassis/motor.
As the load/pressure increases the resistance increases... you might have a wire that is just barely exposed and it takes a large amount of resistance increase to cause it to choose another grounding source. adding an ignition box would not fix this issue and might possibly cause it to get worse. Thats why i asked...
Have you had your ICM Tested repeatedly to ensure the high rpm mode is working correctly??
Your voltage drop is just the increased demand... nothing i would worry about.
a plug wire wont arc to a different ground other than the plug strap if the resistance to cross the gap is less than the least resistance to a different ground on the chassis/motor.
As the load/pressure increases the resistance increases... you might have a wire that is just barely exposed and it takes a large amount of resistance increase to cause it to choose another grounding source. adding an ignition box would not fix this issue and might possibly cause it to get worse. Thats why i asked...
Have you had your ICM Tested repeatedly to ensure the high rpm mode is working correctly??
Your voltage drop is just the increased demand... nothing i would worry about.
05-01-2012, 10:30 PM
#18
I have a friend that swears by extra grounds for any phantom problem like this. It is cheap and easy to try.
Might consider trying a autolite 103 just to further rule out detonation.
Far as the ICM I thought like you did they worked or were dead sometimes temperature sensitive and only died hot, BUT then I tried helping a guy diagnose a car that was just soft under hard throttle, drove perfect normally but pedal to the floor just felt soft, eventually he kind of threw his hands up in the air and started putting old parts back on the car. Well when he did heads/cam he had replaced the ICM and coil just because they were off. Swapping in the original ICM fixed it. The aftermarket replacement was just "soft" and it is the only case like that I know of.
Might consider trying a autolite 103 just to further rule out detonation.
Far as the ICM I thought like you did they worked or were dead sometimes temperature sensitive and only died hot, BUT then I tried helping a guy diagnose a car that was just soft under hard throttle, drove perfect normally but pedal to the floor just felt soft, eventually he kind of threw his hands up in the air and started putting old parts back on the car. Well when he did heads/cam he had replaced the ICM and coil just because they were off. Swapping in the original ICM fixed it. The aftermarket replacement was just "soft" and it is the only case like that I know of.
