#4 won’t fire
Thread Starter
Teching In
Joined: Aug 2012
Posts: 19
Likes: 2
#4 won’t fire I have been trying to figure out for the life of me why #4 cylinder isn’t firing.
ls2 out of a 06 GTO Going into a 1966 chevelle
has been rebuild with stock bottom end all GM original replacement components.
ported heads, ported fast 102 and ported original 90 mm TB. tick performance SNS torque max cam. Holley terminator max x wiring and ecm. Still waiting for the MAP sensor to come in but all the other sensors have been replaced with GM replacements.
i have tested the injectors with noid light and are operating correctly.
coil is working and spark is getting to the plug and working correctly.
the valve train is operating as it should, at least visually i had the car cranking while i watch it .
i have swapped plugs, coils and injectors from working cylinders.
the plugs are foul and the motor is running rich, very rich. My iac is around 90% when should be no higher then 10% and my map is around 60-75% while running.
I know I need a tune but feel everything should be working before I send off for a tune. Could it be so rich on #4 that it completely drenches the plug not allowing it to spark? Or does anyone have any ideas of where I could go next to try and figure this out?
TIA,
Gus
ls2 out of a 06 GTO Going into a 1966 chevelle
has been rebuild with stock bottom end all GM original replacement components.
ported heads, ported fast 102 and ported original 90 mm TB. tick performance SNS torque max cam. Holley terminator max x wiring and ecm. Still waiting for the MAP sensor to come in but all the other sensors have been replaced with GM replacements.
i have tested the injectors with noid light and are operating correctly.
coil is working and spark is getting to the plug and working correctly.
the valve train is operating as it should, at least visually i had the car cranking while i watch it .
i have swapped plugs, coils and injectors from working cylinders.
the plugs are foul and the motor is running rich, very rich. My iac is around 90% when should be no higher then 10% and my map is around 60-75% while running.
I know I need a tune but feel everything should be working before I send off for a tune. Could it be so rich on #4 that it completely drenches the plug not allowing it to spark? Or does anyone have any ideas of where I could go next to try and figure this out?
TIA,
Gus
TECH Fanatic
Joined: Jan 2018
Posts: 1,059
Likes: 198
I've been chasing a similar gremlin, coincidentally also on cylinder 4, but occasionally cylinder 2.
I've tried all of the above, plus a compression test, which came out great (200-210psi across the board (454ci)) and an inline spark tester (also looks good).
Not sure what's going on but I'm starting to suspect a poor fit between the injectors and the connectors on the wiring harness. Hence my last post: https://ls1tech.com/forums/generatio...s-ls1-ls6.html
But honestly I'm stumped, grasping at straws, and looking for ideas.
I've tried all of the above, plus a compression test, which came out great (200-210psi across the board (454ci)) and an inline spark tester (also looks good).
Not sure what's going on but I'm starting to suspect a poor fit between the injectors and the connectors on the wiring harness. Hence my last post: https://ls1tech.com/forums/generatio...s-ls1-ls6.html
But honestly I'm stumped, grasping at straws, and looking for ideas.
TECH Fanatic
Joined: Jan 2009
Posts: 1,063
Likes: 475
From: Bostwick, GA.
A couple items...
" Still waiting for the MAP sensor to come in but all the other sensors have been replaced with GM replacements".
** What are you using in the interim?
** Map reads in KPA not %.
What's the Map reading key on, engine off?
"Could it be so rich on #4 that it completely drenches the plug not allowing it to spark?
** yes.
Without seeing the tune and a short startup data log all you're going to get is more guesses.... Like mine.
Post the tune and a log. They have to be in a zipped file.
" Still waiting for the MAP sensor to come in but all the other sensors have been replaced with GM replacements".
** What are you using in the interim?
** Map reads in KPA not %.
What's the Map reading key on, engine off?
"Could it be so rich on #4 that it completely drenches the plug not allowing it to spark?
** yes.
Without seeing the tune and a short startup data log all you're going to get is more guesses.... Like mine.
Post the tune and a log. They have to be in a zipped file.
Thread Starter
Teching In
Joined: Aug 2012
Posts: 19
Likes: 2
@oldbuzzard
Thanks for the help, I appreciate it.
A couple items...
"Still waiting for the MAP sensor to come in but all the other sensors have been replaced with GM replacements".
** What are you using in the interim?
- the original one from the GTO
** Map reads in KPA not %.
- Yes KPA, my bad
What's the Map reading key on, engine off?
- Around 90
"Could it be so rich on #4 that it completely drenches the plug not allowing it to spark?
** yes.
-Would it be just #4 wouldn't it bounce around?
Without seeing the tune and a short startup data log all you're going to get is more guesses.... Like mine.
Post the tune and a log. They have to be in a zipped file.
-I have a computer that doesn't have the slot for an SD card, so I have an adapter on order I hope to have it in today.
I'm also going to get a tester to test my compression today as well just to make sure.
Thanks for the help, I appreciate it.
A couple items...
"Still waiting for the MAP sensor to come in but all the other sensors have been replaced with GM replacements".
** What are you using in the interim?
- the original one from the GTO
** Map reads in KPA not %.
- Yes KPA, my bad
What's the Map reading key on, engine off?
- Around 90
"Could it be so rich on #4 that it completely drenches the plug not allowing it to spark?
** yes.
-Would it be just #4 wouldn't it bounce around?
Without seeing the tune and a short startup data log all you're going to get is more guesses.... Like mine.
Post the tune and a log. They have to be in a zipped file.
-I have a computer that doesn't have the slot for an SD card, so I have an adapter on order I hope to have it in today.
I'm also going to get a tester to test my compression today as well just to make sure.
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
Yes, a compression test on all cylinders will be a good idea.
Next, are you sure its #4 that isn't firing? If you have headers, the easy way to check is with an IR thermometer which typically cost around $25 now. Comparing all cylinders while idling can be very informative too.
You say the car is running super rich. Is that because you installed bigger injectors? Did you put the injector size into your Holley Terminator software? If not, why not do it now. The easiest way to fix a super rich condition is by increasing the injector size in the tune.
Which bank of your engine is the Holley O2 sensor installed in? (This might help me help you in the future.)
You never mentioned "spark plug wires". Did you swap those too?
Coincidently #4 is giving me trouble too with my Holley ECU. My IR thermometer shows its running 50+F hotter than the others and that bank seems to be running leaner than the other. (Please no comments on my problem here.)
Next, are you sure its #4 that isn't firing? If you have headers, the easy way to check is with an IR thermometer which typically cost around $25 now. Comparing all cylinders while idling can be very informative too.
You say the car is running super rich. Is that because you installed bigger injectors? Did you put the injector size into your Holley Terminator software? If not, why not do it now. The easiest way to fix a super rich condition is by increasing the injector size in the tune.
Which bank of your engine is the Holley O2 sensor installed in? (This might help me help you in the future.)
You never mentioned "spark plug wires". Did you swap those too?
Coincidently #4 is giving me trouble too with my Holley ECU. My IR thermometer shows its running 50+F hotter than the others and that bank seems to be running leaner than the other. (Please no comments on my problem here.)
TECH Fanatic
Joined: Jan 2018
Posts: 1,059
Likes: 198
Mine is rich too, and here's my theory about it:
- when there's a misfire, unburned fuel and oxygen goes out the exhaust port and mixes with the rest of the exhaust from that bank.
- that increases the amount of oxygen in the stream where the O2 sensor is
- the O2 sensor sees extra oxygen, and interprets that as a lean mixture in all cylinders
- the PCM adds more fuel to for the cylinders in that bank
- the 3 cylinders that ARE firing are now running rich
- so now your exhaust stream has excess unburned fuel from 3 cylinders plus the raw fuel from the misfiring cylinder
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TECH Enthusiast
Joined: Dec 2017
Posts: 676
Likes: 72
I had a jeep straight 6 with the same issue. wouldnt fire number 3 no matter what. after alot of parts swapping and messing with stuff we figured out that the exhaust header had never been drilled out where the tube for number 3 attached onto the collector. probably isnt your issue but who knows.
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Verdad Gallardo TECH Fanatic
Joined: Jan 2018
Posts: 1,059
Likes: 198
I've been chasing a similar gremlin, coincidentally also on cylinder 4, but occasionally cylinder 2.
I've tried all of the above, plus a compression test, which came out great (200-210psi across the board (454ci)) and an inline spark tester (also looks good).
Not sure what's going on but I'm starting to suspect a poor fit between the injectors and the connectors on the wiring harness. Hence my last post: https://ls1tech.com/forums/generatio...s-ls1-ls6.html
But honestly I'm stumped, grasping at straws, and looking for ideas.
I've tried all of the above, plus a compression test, which came out great (200-210psi across the board (454ci)) and an inline spark tester (also looks good).
Not sure what's going on but I'm starting to suspect a poor fit between the injectors and the connectors on the wiring harness. Hence my last post: https://ls1tech.com/forums/generatio...s-ls1-ls6.html
But honestly I'm stumped, grasping at straws, and looking for ideas.
I wish I could remember who made the previous harness so I could name and shame them, because I've been chasing this problem for a while and I've got some pent-up aggravation saved up for them, but oh well.
OP I hope you find your gremlin.
