Cylinder 6 misfire!!!! Help!!!!!
Cylinder 6 misfire!!!! Help!!!!! I have a tsp 408 that I just put a new set of cnc'd ls3 heads and Intake on, and now I am getting a misfire on cylinder 6.
I have done the following
1) change plugs
2) change wires
3) change coils
4) changed injectors
5) Spark plug tester and is showing fire
7) Compression test 180 on cylinder 8,6,4, and 2
8) rocker arms are tight and working very well
9) I looked for broke valve springs( all are new and in good shape)
The plug is dry but carbon fouled!! any help would be great!!!!!!!!!
I have done the following
1) change plugs
2) change wires
3) change coils
4) changed injectors
5) Spark plug tester and is showing fire
7) Compression test 180 on cylinder 8,6,4, and 2
8) rocker arms are tight and working very well
9) I looked for broke valve springs( all are new and in good shape)
The plug is dry but carbon fouled!! any help would be great!!!!!!!!!
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
How did you determine it was #6...? Is that the only plug that is carbon fouled...?
Have you tried moving that injector to a different cylinder...? Have you moved the coil to a different cylinder...?
Have you tried moving that injector to a different cylinder...? Have you moved the coil to a different cylinder...?
Does it only missfire at idle? or does it do it at say 2500rpms.
Also, did you check for correct push rod length? The heads could be shorter deck.
Also, i agree with Joecar, move the fuel injectors around if you see something odd also. If it follows, then just replace the bad injector.
Also, did you check for correct push rod length? The heads could be shorter deck.
Also, i agree with Joecar, move the fuel injectors around if you see something odd also. If it follows, then just replace the bad injector.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote
10 Reasons the LS7 Is GM's Most Extreme Naturally Aspirated V8 Engine Ever
Verdad Gallardo TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
What if one of the replacement injectors is bad...?
The plug is getting carbon fouled because that cylinder is burning overly rich... a leaky injector can cause this, and so can insufficient air (is intake and/or exhaust valve opening all the way...?).
The plug is getting carbon fouled because that cylinder is burning overly rich... a leaky injector can cause this, and so can insufficient air (is intake and/or exhaust valve opening all the way...?).
Have you used a "noid light" or a voltmeter to see that the
injector is being fired electrically? Look for differences from
adjacent cylinders. Measure volts from BAT to the low side
of the injector for better resolution.
Now I have heard, but can't confirm, that misfires sometimes
show up on the next cylinder in the firing pattern, from where
the action really is. But if #6 plug condition is different than
the bank-neighbors, that's probably saying that you've got
the right hole.
I don't think soot necessarily says rich. It could be a lean
misfire. Either way you get elevated HC. I think to get a
rich misfire you'd have to be mighty damp, and there are
not that many failure modes that will cause excess pulse
width or stuck-on. Still reading the voltage (as proxy for
PW) will tell you if the #6 is getting treated any differently.
Now given that this is a new top end, I would not rule out
a bad vacuum leak at the intake manifold, at that runner.
This could be checked with propane while watching the
misfire counts in real time. I have one of those weed
burner torches which without the "hat" will reach in real
nice, but about any unlit torch would probably do.
injector is being fired electrically? Look for differences from
adjacent cylinders. Measure volts from BAT to the low side
of the injector for better resolution.
Now I have heard, but can't confirm, that misfires sometimes
show up on the next cylinder in the firing pattern, from where
the action really is. But if #6 plug condition is different than
the bank-neighbors, that's probably saying that you've got
the right hole.
I don't think soot necessarily says rich. It could be a lean
misfire. Either way you get elevated HC. I think to get a
rich misfire you'd have to be mighty damp, and there are
not that many failure modes that will cause excess pulse
width or stuck-on. Still reading the voltage (as proxy for
PW) will tell you if the #6 is getting treated any differently.
Now given that this is a new top end, I would not rule out
a bad vacuum leak at the intake manifold, at that runner.
This could be checked with propane while watching the
misfire counts in real time. I have one of those weed
burner torches which without the "hat" will reach in real
nice, but about any unlit torch would probably do.
I pulled the intake and the intake valve for number 6 was white. The rest of the intake valves were wet and darker looking. I have ordered two new valves, one intake and one exhaust. The new parts will be here weds. I am going to lap in the new valves to make sure they are seating correctly.
TECH Resident
Joined: Nov 2011
Posts: 812
Likes: 0
From: NJ
this is what i was thinking. sounds like the exhaust valve may be hanging closed.