2002 Pont Bonneville - 3800 Misfire

[steven kiser]

i'm not convinced the skip is going away at higher rpm's. we have spark, fuel, compression, and exhaust. the list of contributing issues is narrowed to, correct firing order, correct injector wiring, vac leak, sticking valve, bent push rod. that's about all i can think of right now. we don't want to overcomplicate this. when the injector was out did fuel leak from the rail? i've seen rust balls in injector rails. #'s 3 and 4 are opposite which can lead me to think that the intake has an internal crack. if the valve is sticking you may or may not get a noise. you see the rocker moving, is it the same as the others? looking through the oil fill will give you a very, very, limited view to base any decisions on. the way i would do it is to remove valve cover, and crank it over. see if there is a noticeable lift difference. with the engine running feel the rockers for any slop. i'm old school and that's the way it was done back then. you can grab the rocker and feel any looseness in it. if you think you feel something remove rockers and with a flat bar across the top of the valves see if there is any height difference. are we assuming that both plenums are good? in the past i've done the same and been wrong. i cracked one when the engine i removed rolled and apparently the same thing happened to the replacement. look at this as the car came into the shop with this issue not as a result of a replacement. on occasion i'll overlook the obvious because i'm so deep in it. a good example is i replaced a battery because it would go dead after sitting overnight. i tested it and it was bad (dead cell). off it went and a week later i got the call, it was doing it again. i jumped in and went through everything, unplugged everything that wasn't controlled by the key and unplugged the ignition switch. i was stumped. another tech asked if the battery was good. yes it was good, it was new. i tested it to humor him and it was bad. take the oil cap off and see how much vac there is. if it sounds like a hoover then the intake may be bad. if the engine changes the way it's running then you may have an intake issue. on a way out there note, is there a possibility that this engine wasn't the dead nuts match? i know the super charged is different and i think there were intake port changes in the early 2000's. maybe we can't see the forest through the trees.........i hate when someone say's that to me but........

[orangedoggarage]

plugs.jpg (221.99 KiB) Viewed 3349 times

Pulled the valve cover and the plugs this morning, we replaced the double platinums with copper plugs a couple days ago (no change) and here are the #3 and #5 plugs respectively (3 on the left 5 on the right) the pushrods seemed worn, so we pulled 2 from the old motor, checked lengths etc, and installed in new motor, with no change in behavior. when we had the intake off yesterday, we found no cracks etc.. but did find a couple cracked hoses which we replaced, and the miss in cyl # 4 has gone away now. I don't see any cracks in the springs and they feel tight. I'm still pulling my hair out, and i'm running out of hair at this point. any help appreciated. gona try smoking the intake manifold now to see if there's any diff. btw, there is no excessive whooshing noise coming from the oil fill when its running, I have heard that on the Dodge motors before, and this one seems normal, we sprayed all over to check for leaks, and we can't see or hear anything. tried an oil cleaner yesterday to loosen up any stuck parts and it had no effect. The color of the #3 plug troubles me now, we did have the exhaust disconnected at the crossover, but it made no difference, i guess there could be a mouose nest in the pipe, byut i's think it would be worse at higher RPM's not smoother. The Genisys stops counting misfires at about 1500 RPM's and seems to wotrk fine, the only code in the genisys is the p0300, but the other scan tool I think calls it a p0303.

[ricmorin]

Yeah, that number three plug looks wrong. There's something going on for sure.

[steven kiser]

what's on the thread of the plug. the right looks fine, the left no so much. you're not putting any anti seize on it are you?

[Tim Martin]

From my perspective, the number 3 plug appears to be suffering from lower running compression.

[orangedoggarage]

not anti-seize, prolly just some gunk

[liljoe]

From my perspective, the number 3 plug appears to be suffering from lower running compression.

Me too!!

[orangedoggarage]

Update-
Pulled the intake manifold and the head off. Intake gaskt was in very bad shape, head gasket looked ok, definitely a difference in the way the valves looked, but couldn't find a problem with them sealing. replaced gaskets and re-installed. same problem still exists. Valve springs look fine, no cracks or breaks, they're tight, i can't twist or turn them, and there doesn't seem to be anything binding the valves or pushrods. I can only figure I'm missing something, but I have no idea what. The intake passage on #3 looked much cleaner than the other cylinders (no sludge or soot buildup) this i attributed to the bad intake gasket maybe allowing something extra to pass through (coolant or possibly crankcase gasses).

[steven kiser]

well, going way out on a limb here, and i mean way out. the plug is over heated or at least that's what i see. i've seen weak exhaust vale springs cause this allowing exhaust into cylinder and one time i had a real head banger and decided to yank the engine (i had replaced this one with a used) when i took the exhaust manifold off a decent sized piece of old exhaust gasket was restriction the port. were the vales discolored when the head was off? i may have considered using a head off of the other engine.