high rpm stutter (6k and above) are the plugs the culprit?
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high rpm stutter (6k and above) are the plugs the culprit?
dyno'd my car saturday evening after swapping to my 10-bolt with 4.10's for a comparison between a 9" and a 10-bolt.
when I went to start the car, and pull it on the dyno, it wouldn't start, just cranked; I knew then I was on borrowed time with an opti. let off, twisted the key again, and it started, I proceeded to pull it on the rollers.
upon doing so, I revealed that I have a stuttering problem right at 6k rpm and continues upward.. on top of that, my dyno numbers are 10hp and 20ft lbs LESS than before. obviously, something's up.
I contemplated valve float being the problem, but my power peaks at 5700rpm, holds within 3 or 4hp of its peak till 6000rpm, and then DROPPED, I mean, 75hp within 100rpm DROP.
I really dont see how it could pull so clean, straight to 6k and then drop like a lead balloon. if it slowly lost power, then dropped 50hp over a 500rpm range, I could see it, but go from 345hp to 270hp when only going from 5900rpm to 6000rpm?
I replaced the opti today, and it doesn't have this problem in first or second gear, but still does it in the high gears (3rd and 4th) the car has plenty of gas in it as well.
I haven't changed the plugs in about a year (only 3k miles worth of driving though) and they are the stock replacement NGK TR55 plugs gapped at .050"
I am also running an MSD coil on the car.
should I possibly try a colder, NGK TR6 plug? or possibly buy another set of TR55's and try gapping them at .045" or .040" instead?
when I went to start the car, and pull it on the dyno, it wouldn't start, just cranked; I knew then I was on borrowed time with an opti. let off, twisted the key again, and it started, I proceeded to pull it on the rollers.
upon doing so, I revealed that I have a stuttering problem right at 6k rpm and continues upward.. on top of that, my dyno numbers are 10hp and 20ft lbs LESS than before. obviously, something's up.
I contemplated valve float being the problem, but my power peaks at 5700rpm, holds within 3 or 4hp of its peak till 6000rpm, and then DROPPED, I mean, 75hp within 100rpm DROP.
I really dont see how it could pull so clean, straight to 6k and then drop like a lead balloon. if it slowly lost power, then dropped 50hp over a 500rpm range, I could see it, but go from 345hp to 270hp when only going from 5900rpm to 6000rpm?
I replaced the opti today, and it doesn't have this problem in first or second gear, but still does it in the high gears (3rd and 4th) the car has plenty of gas in it as well.
I haven't changed the plugs in about a year (only 3k miles worth of driving though) and they are the stock replacement NGK TR55 plugs gapped at .050"
I am also running an MSD coil on the car.
should I possibly try a colder, NGK TR6 plug? or possibly buy another set of TR55's and try gapping them at .045" or .040" instead?
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I had a high rpm miss and found it was a bad coil but there was no real way to test for it except to swap in another coil. My miss was starting at about 5200 rpm though.
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Originally Posted by LT1Falcon
how come you are not considering the opti. you even stated "I knew then I was on borrowed time with an opti." it does have some opti symptoms
I replaced the opti today, and it doesn't have this problem in first or second gear, but still does it in the high gears (3rd and 4th) the car has plenty of gas in it as well.
I'm gonna hook a fuel pressure guage to it and see what's up. as far as I know, the car still has a stock pump in it (not the OE pump, someone already cut an access hole). lol, we've joked saying I'm next in line to receive a walbro 255, seeing as I've went longer than anyone else on the stock replacement pump w/o problems
I'm going to ohm-out all the plug wires and see if there is any excessive resistance in any of them (they are msd's) as well as change the plugs (something I need to do anyway) if nothing else changes, I'll check out the coil to see if it's giving me fits.
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Originally Posted by nighthawk15
If the fuel pressure is good, I'm gonna put my money on a weak coil.
if it is, a coil is MUCH cheaper than a pump.
#10
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Well I just noticed the part where it only happens in the upper gears...very odd. Still could possibly be a coil though I suppose but I don't know why it wouldnt happen in every gear. Much stranger things have happened I suppose.
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man this is the exact same problem my cas is having. have you figured it out yet. i also have the MSD coil. i have a thread (cap and rotor) just a few threads down. i dont think it's a fuel pressure issue i am running a walbro 255
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Originally Posted by nighthawk15
Well I just noticed the part where it only happens in the upper gears...very odd. Still could possibly be a coil though I suppose but I don't know why it wouldnt happen in every gear. Much stranger things have happened I suppose.
#13
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Originally Posted by racerns
Sometimes a high rpm miss can be hard to detect in 1st and 2nd since you blow through the miss so fast before you have to shift.
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you have to realize, that ONE COIL is trying to fire EIGHT cylinders at 6000+ RPMS. a distributor type ignition was not really built for that. If I was you, I would look into that LS1 coil-over conversion for the LT1s.
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Originally Posted by ThoR294
you have to realize, that ONE COIL is trying to fire EIGHT cylinders at 6000+ RPMS. a distributor type ignition was not really built for that. If I was you, I would look into that LS1 coil-over conversion for the LT1s.
I've ran this car for almost 2 years, twisting it beyond 6k and have yet to have a problem like this. not to mention, countless drag cars still use a conventional distributor and single coil setup. it may not be ideal, but I doubt this is totally to blame
I've thought about the LTCC, or the LS1 coil conversion as an option. but both still rely on the rather problematic opti-spark.
I'm about 2 steps away from drilling a hole in the back of the intake and putting a TBI truck distributor in the back of the intake, converting over to a TPI computer and harness, and driving the wheels off the car!
how many people do you hear have problems with their tuned-port or even TBI truck's with re-occuring ignition problems? losing SEFI and going to batch-fire is well worth not being stranded on the side of the road, 400 miles from home when I decide to drive the car to the beach.
#18
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Originally Posted by ThoR294
you have to realize, that ONE COIL is trying to fire EIGHT cylinders at 6000+ RPMS. a distributor type ignition was not really built for that. If I was you, I would look into that LS1 coil-over conversion for the LT1s.
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Check the harness connection that goes down to the opti along the passenger side of the intake manifold. Sometimes it can be corroded and cracked, or just old and dirty and that is causing the high rpm miss.
It wouldn't hurt to pull the plugs and take a look at them. A new set of NGKs won't run you more than $20 anyways.
How is the condition of the plug wires? Are you positive they aren't burnt/cracked/worn or touching any heat sources (or arching)? Try putting a little bit of dielectric grease in each of the plug wire boots when you swap the plugs out. It helps to keep moisture out and improve conductivity.
It wouldn't hurt to pull the plugs and take a look at them. A new set of NGKs won't run you more than $20 anyways.
How is the condition of the plug wires? Are you positive they aren't burnt/cracked/worn or touching any heat sources (or arching)? Try putting a little bit of dielectric grease in each of the plug wire boots when you swap the plugs out. It helps to keep moisture out and improve conductivity.