Agrivating Misfire
Thread Starter
Teching In
Joined: Apr 2011
Posts: 6
Likes: 0
From: china grove nc
Agrivating Misfire Hey folks. I'm new to here, so please be patient with me. I guess first, I should give you a bit of background.This was my first transplant of a Gen 3 into anything and I chose of all things a 1980 Jeep J10 pickup. Anyway,ever since I got it in and running, I have had a problem with a misfire on cylinder 3. I have checked everything I can think of and am beating my head against the wall. When it is a cold start, the miss is very pronounced. after it warms up, you can barely feel it, but it is still there. Under harder excelleration, you can hear a popping noise out the drivers side exhaust. I have checked and changed plugs to E3s, new plug wires, new coil pack, checked and cleaned the injectors, ran a compression check (They all were surprisingly high to me 170 to 180 psi.), and replaced the intake manifold gaskets. They were actually leaking.
None of this has changed anything. The only mods that have been done to it at this point was a Hotrod tune from PCM in Mooresville. They deleted the EGR, rear O2s, Evap, MAF and set it up for speed density, VSS, and all other transmission inputs/outputs. I also fabricated a set of long tube fender exit headers. Other than that, no other mods yet.I do have a cam on the way for it, but I want to get this problem squared away first.
Thanks everyone ahead of time for the help.
Daniel the Noob.
None of this has changed anything. The only mods that have been done to it at this point was a Hotrod tune from PCM in Mooresville. They deleted the EGR, rear O2s, Evap, MAF and set it up for speed density, VSS, and all other transmission inputs/outputs. I also fabricated a set of long tube fender exit headers. Other than that, no other mods yet.I do have a cam on the way for it, but I want to get this problem squared away first.
Thanks everyone ahead of time for the help.
Daniel the Noob.
TECH Resident
Joined: Mar 2012
Posts: 821
Likes: 4
From: Elkridge MD
might be a long shot here, but I had a pesky misfire that was caused by one of the plug boots being to close to the header (not touching, mind you, just close). To remedy this I made up a new wire for that plug, and routed it around and under that primary tube.
Like I said, probably a long shot
Like I said, probably a long shot
Thread Starter
Teching In
Joined: Apr 2011
Posts: 6
Likes: 0
From: china grove nc
That's actually the way my plug wires are routed. I remote mounted my coils on the firewall and ran the wires under like the old Chevys with Ram's horn manifolds. Ran it at night in the dark to see if I was getting a crossfire
Joined: Apr 2007
Posts: 330
Likes: 1
From: Chicago, Illinois (far south)
Maybe start with the easy things first. Looks like you already did some of them.
Swap wires from bank to bank...then see if the problem moves.
Plugs...then see if it has moved.
Then try the injector harness...then check again.
Then injectors.
How are you verifying the no spark? I have one of those things that looks like a pen that rests on the plug wire and shows spark/no spark.
A noid light can tell you if it is harness related provided it does not jump over to the other bank when you swap the injector harness. It can be before the injector harness that plugs in near the rails.
I had a pin hole near the O2 bung that was causing a misfire. It took quite some time to figure that out. With the car running, I was under the car and noticed a very minor bit of air coming from near the O2 sensor. While that was out, I also found one where the collector merge was. I swapped to manifolds and all was well after that.
Thread Starter
Teching In
Joined: Apr 2011
Posts: 6
Likes: 0
From: china grove nc
The header leak kind of got my attention. I did hand make the headers and weld the bung into the collector. I dont hear any leaks and I was very particular about my welds, but there could still be a leak somewhere. If i did have a leak around the collector, wouldn't that set off the whole bank and not just one cylinder? This may sound dumb, but what are the chances of the PCM firing that cylinder either late or early? I used a noid light on the injector harness and my spark tester was one I purchased off the Snap On truck that comes by the shop I work at. The weird thing about this is that it has never set off the engine light. The only code i have that is reoccuring is the opposite bank oxygen sensor heater and it is just once in a while.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
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 Thread Starter
Teching In
Joined: Apr 2011
Posts: 6
Likes: 0
From: china grove nc
There is spark. I first used a Bluepoint spark tester that went inline of the plug and wire. at the spark plug end, I have a good fire. then I removed the plug and replaced it with an old plug from a tune up. (Just so I wouldnt be running the cylinder to open air. Cant stand to hear that noise.) I grounded the plug to the header and started the engine. Had great spark. I know I am getting fuel also because I can smell raw gas at the header when its cold. Reved up to about 2800 rpm or more, I hear that cylinder popping as if it is firing the fuel too late. Lower than that, its just a shake from the miss. This is driving me absolutely crazy trying to find this problem.
You have to start transplanting items from known good cylinders to the bad one. If you move everything over, including the wiring/plugs, injectors, clips, spark related components, you should try a next ECU(just to rule it "logic" out), make sure the plug is tight, and possibly re-ground or verify the grounds are good.
If everything is new/replaced and the problem persists you might have a broken piston or similar valve/mechanical related failure, do a leakdown test against known good cylinders. Eventually the idea is some reading or output will be different on that one cylinder and lead you to the answer.
If everything is new/replaced and the problem persists you might have a broken piston or similar valve/mechanical related failure, do a leakdown test against known good cylinders. Eventually the idea is some reading or output will be different on that one cylinder and lead you to the answer.
Thread Starter
Teching In
Joined: Apr 2011
Posts: 6
Likes: 0
From: china grove nc
Thanks to all y'all for all the help and suggestions. I went ahead and swapped plug wires to the other side and the miss didn't change. I switched the coil harnesses and no change. Same with the injector now. I ran a compression check. All cylinders ranged from around 165 to 180 psi.I didn't check the rockers with a dial indicator, but I did run it for a minute with the valve cover off. (What a mess) It looks to be moving about the same on number 3 as the rest. I have a new cam to go in it, but I was sort of waiting to get the miss fixed before swapping that. It's a Texas Speed 224r. I'm figuring it would make it really hard to find a miss with all that lope. I'm not gonna give up. I know this is gonna end up being something SO stupid that I'm gonna kick myself when I do find it.