plug gap & missfires
plug gap & missfires Kind of a long story but here goes. A year or two ago I put full exhaust, a LS6 intake, and a higher stall converter on my car. After everything was put on it was misfiring bad at higher rpms and under load. My tuner said to gap the plugs to .35 and see if that would fix it....well it seemed to, so all was well. I had a bunch of exhaust leaks and stuff from all the slip fit crap that I had welded up and everything seemed to be fine. Well, when it started getting cold again this season I started having lock up issues that turned out to be do to the computer seeing to many misfires. I had the computer straightened out so I can at least drive the damn thing until I get it fixed. Also, it was misfiring a couple of times at WOT and when it shifted at WOT. I decided to go back and double check all the stuff I did related to misfires. So I just got done pulling the intake back off and replacing the gaskets. It kind of looked like they were leaking but it was hard to tell. Also, there seemed to be a lot of oil in the intake and ports considerimg I have a good set of catch cans on the PCV system. I'm about to put new TR55 plugs back in it tomorrow and test all the wires to make sure there are not any shorts or breaks in them. So, now my questions are this, is it possible that some engines just respond differently to different plug gaps? If not, is having to gap the plugs to .35 a good indicator of there being a problem? Also, could the oil in the intake be causing the misfires? It didn't seem like there was enough to cause a misfire but obviously I don't know these things. Thanks for reading my life story, lol, and any help you can provide.
Forgot to mention that the car has 92K miles, before I changed the gap on the plugs the first time I swapped coils out w/ another car & that didn't help & I tested all the plug wires & they all seemed good.
Yes, having to reduce the gap to 0.035" to eliminate misfires is indicative a problem, particularly on new plugs.
Your sig indicates MSD wires, which have been the subject of many reports of intermittent problems. You might want to try some different wires even if the MSDs pass a standard ohm test.
Your sig indicates MSD wires, which have been the subject of many reports of intermittent problems. You might want to try some different wires even if the MSDs pass a standard ohm test.
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Doubt it's the plug wires. Sounds like a questionable tune & maybe oil/carbon. Use a top end cleaner like sea-foam & a bottle of Techron injector cleaner in a 1/2 tank of 93 Octane. Are the heads ported? If heads are ported & thread sealer was not used on the rocker arm bolts, oil can run down the threads into the intake valve runner. Check your catch can routing as well. Should not be getting much oil in the intake w/ a properly routed catch can.
Most likely tune related. Post says .035" was requested soon after mods/tune were made. Find a different tuner to have a look @ it. No way .035" is required for the minimal amount of mods made to the engine.
Most likely tune related. Post says .035" was requested soon after mods/tune were made. Find a different tuner to have a look @ it. No way .035" is required for the minimal amount of mods made to the engine.
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Doubt it's the plug wires. Sounds like a questionable tune & maybe oil/carbon. Use a top end cleaner like sea-foam & a bottle of Techron injector cleaner in a 1/2 tank of 93 Octane. Are the heads ported? If heads are ported & thread sealer was not used on the rocker arm bolts, oil can run down the threads into the intake valve runner. Check your catch can routing as well. Should not be getting much oil in the intake w/ a properly routed catch can.
Most likely tune related. Post says .035" was requested soon after mods/tune were made. Find a different tuner to have a look @ it. No way .035" is required for the minimal amount of mods made to the engine.
Most likely tune related. Post says .035" was requested soon after mods/tune were made. Find a different tuner to have a look @ it. No way .035" is required for the minimal amount of mods made to the engine.
I'm changing out the plug wires today for some stock ones.
You want as much gap as your ignition system can reliably
fire. Now there's the rub.
Peak cylinder pressure sets the voltage required.
System voltage, spark dwell, insulation integrity all down
the line (coil, wire, pinholes, moisture, etc.) set the
voltage available. Silicone grease in the boot, good
coil-pack electrical connections, etc. are all freebies
if you discount elbow grease.
The narrower the plug gap, the weaker the burn, the
more crust you make and keep in the hole and the
easier it is for that crust to bridge the gap, losing you
energy (which is arc voltage = distance, and coil current)
Stock gap should be zero problem for stock system in
proper condition. If you have a problem, short gap is
not fixing it, it's covering it up.
fire. Now there's the rub.
Peak cylinder pressure sets the voltage required.
System voltage, spark dwell, insulation integrity all down
the line (coil, wire, pinholes, moisture, etc.) set the
voltage available. Silicone grease in the boot, good
coil-pack electrical connections, etc. are all freebies
if you discount elbow grease.
The narrower the plug gap, the weaker the burn, the
more crust you make and keep in the hole and the
easier it is for that crust to bridge the gap, losing you
energy (which is arc voltage = distance, and coil current)
Stock gap should be zero problem for stock system in
proper condition. If you have a problem, short gap is
not fixing it, it's covering it up.
Everything else is stock, other than what I mentioned. So your saying put sea-foam & Techron in my tank at the same time? My catch can routing is fine, a modeled it off of several different examples I found on here.
I'm changing out the plug wires today for some stock ones.
I'm changing out the plug wires today for some stock ones.
Doesn't have to be @ the same time. Change your oil afterward, though. However, as stated earlier, the information you provided leads to the tune as the issue. I think that you have too much timing @ higher RPMS, more than the knock sensors are pulling & it's causing a miss-fire. Could also be a number of other things in the tune. The tune needs to be looked @.
gap your spark plugs to .060 which is the stock gap, ill would even go .058 or .059, dont go as low as .035 on a stock internal engine your just hurting it, and not double but triple check your gap, trust me I'm even going to gap my plugs again because I think I gapped them wrong, make sure though the gap is that and check your tune, clean your maf, and put some injector cleaner on your gas tank and all good 
I made it worse......its shaking at idol and the check engine light is flashing very very dimly in time with the engine RPM's. I'm at a lose, I have no idea what to now, other than re-gaping the plugs back to where they were. I don't think I'd feel safe driving it the 45 minutes to my tuner.
I took a q-tip and very gently cleaned the MAF with some sea-foam. Gaped the plugs to .050, changed out the plug wires with a set of Duralast from auto zone, and changed the intake gaskets with some Felpro ones.
If I did have an intake leak that I fixed could my tune be that far off to cause this.
I took a q-tip and very gently cleaned the MAF with some sea-foam. Gaped the plugs to .050, changed out the plug wires with a set of Duralast from auto zone, and changed the intake gaskets with some Felpro ones.
If I did have an intake leak that I fixed could my tune be that far off to cause this.
Last edited by CayenneRedV6; Dec 21, 2010 at 04:42 PM.
Where did you get that gap? I am not saying its wrong since I don't have the OP's original owners manual, but most of the plug vendors NGK, AC Delco, and Bosch are showing 0.040" while Champion (alone) is showing 0.050" for their offering.
If NGK's site shows .040 and I had to gap to .035 is that really showing that big of a problem? Couldn't it just mean my coils are worn out and old? They have 92K miles on them.
And I re-cleaned the MAF with alcohol....no change.
And I re-cleaned the MAF with alcohol....no change.
Last edited by CayenneRedV6; Dec 21, 2010 at 06:12 PM.