Re: AW: [Chrysler300] 300G Missfire

The plugs may be some form of extended reach or aftermarket which is wrong plug . Fancy aftermarket plugs can hassle you . Go stock replacement NGK . It may only happen in certain cylinders depending on the indexing of ground electrode which is essentially random ( and that is ok) unless someone did index them — highly unlikely . ( sometimes done for racing) . If the ground electrode “ bend” is on bottom toward piston when tight on block / head much more likely to be hit if too close (that points to a temp solution too ) . If on top when assembled that is like 1/4” more room ..

Note that piston hitting plug has nothing to do with cam at all . Either the plug is too close to piston ( milled Head ? Thin gasket ?) , wrong plug , or excessive piston height in bore above deck of block ... or pistons in bore turned wrong way . ( unlikely) Normally , carefully checked at a rebuild with clay , dial indicator etc . Remote possibility really violent detonation ,as in mixed firing order ? But that would not come on , on a trip . Did you “ get on it” on way home ? Did This happen after working on plugs/ wires? More likely to physically hit more , at high rpm , might have been on edge of that . Fast run closed it .

I once drove a “rebuilt” engine 360 dodge truck I got cheap ( guess why ) oil blowing out of dipstick etc . Blew dipstick out of hole ! I Drove from Toronto to Boston , Truck barely running, shaking and smoking , bought it intending to put another engine . After buying new engine , pulled old one ( actually new!) we noticed two adjacent wires were swapped at cap ( from the guy’s very first day!) engine was actually perfect . I never thought of that ! “ Runs rough” was his story . He gave up . He had changed everything . But kept putting same wires and cap back . That could happen to any of us , rather unfortunately . Since then I try to number wires with those bands.

I would try for instance a copper plug washer - space it back , also —- mark on plug insulator the orientation of the ground electrode see where it ends up on those cylinders (now ) before putting a washer . Washer will change index too. Could play with thickness to get optimal. I would personally try hard not to have to pull apart . 20 k miles says good motor? As does good compression test . Residue probably a red herring . Exhaust Cannot generally get out of head / manifold , — although check heat riser operation and choke pots , exhaust heat pipes , elbows , manifold etc . Stuck heat riser raises hell at speed , I have seen floor of rams under the carb melt . It sticks shut while sitting in storage , it is sitting shut. Weight should move freely . If melted there = low vacuum , runs awful . Two cylinders side by side = Could-be exhaust leak into ram at point those two join under the carb in , plenum . Obviously cannot run with shorted plug, go after that first ?

Interesting thing , let us know what you find .. check plug wire ohms too generally under 40 k ohms . Good luck,

John

MSent from my iPhone not by choice

On 30 Mar 2020, at 4:27 pm, lars.kirschke@xxxxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

Additional note: if you´re running a ballast resistor with your petronix, check that too. It might be that your coil has worked well with the petronix because of the ballast resistor. If that is bad this will cause problems over time.
Also check petronix page for trouble shooting.

Von: Chrysler300@xxxxxxxxxxxxxxx <Chrysler300@xxxxxxxxxxxxxxx> Im Auftrag von lars.kirschke@xxxxxxxx [Chrysler300]
Gesendet: Montag, 30. März 2020 22:18
An: 'Richard Osborne' <reomotorsports1@xxxxxx>; '300 Club Group' <Chrysler300@xxxxxxxxxxxxxxx>
Betreff: AW: [Chrysler300] 300G Missfire

Hello Richard,

just a few cents from across the atlantic.

Before getting into a lot of wild guessing, it would probably best to check if the spark plugs are bent again. To be honest it would be pretty irritating that the piston would hit a spark plug, but wont hit a valve.
There is possibly something in your cylinder 3+5 which causes the bent plugs tips. It might also cause the (exhaust) valve to stick or not close properly which than would explain the fumes near the intake..
As it appeas to two cylinders my guessing would be parts of the intake manifold gasket. When changing the spark plugs and they are bent again use a bore scope to see if there is something in the cylinder, or if the piston top has damage.

If the spark plugs are not bent, check for your petronix. In general i´m happy with them, but they can go bad too.. Had problems with one after two years of flwless driving. Found out I was running a coil with wrong ohm resistance, killed the electronics. But it took a few thousand miles.

As said make an effort to check a few things and isolate the problem – than we might all get closer to the problem.

Good luck

Lars

PS: if you dont hear any knocks your rod bearings should be ok. If the compression is ok, the likelyhood of having a broken piston ring in your cylinder is very small. Also chances would even be reduced as it apears in two cylinders at same time.

Von: Chrysler300@xxxxxxxxxxxxxxx <Chrysler300@xxxxxxxxxxxxxxx> Im Auftrag von Richard Osborne reomotorsports1@xxxxxx [Chrysler300]
Gesendet: Montag, 30. März 2020 21:19
An: 300 Club Group <Chrysler300@xxxxxxxxxxxxxxx>
Betreff: [Chrysler300] 300G Missfire

Hello,

My G engine is mostly stock. I have a Pertronix ignition and a Mopar Performance Cam (Which I degreed to the ORIGINAL Ram engine specs, not the Mopar Perf specs) and lifters. Stock pushrods and rocker arms. The block was over-bored .040 therefore it had new pistons installed. This engine was built close to 20 years ago and I am guessing I have put around 20-30,000 miles on it since. Otherwise, engine is stock.

Last Fall, my son and I drove the car approx 120 miles to a car show. On the way home, it developed a miss, a cylinder or cylinders not firing. It seemed to get worse as we continued home and the freeway.

The car was parked and only taken out of the garage once or twice for very short drives since then. The miss seemed to be still there, but not as bad as it was on the freeway. A few weeks ago, we got it out to take my son to his Confirmation. On the way to church, the miss turn into a serious miss-fire. It was violent. It rattled EVERYTHING. clearly not a miss, but cylinders not firing when they should. I did not notice any backfiring thru exhaust or intakes..

When replacing the spark plugs. we found #3 and #5 electrodes squashed and therefore zero gap. There was no evidence of mechanical interference (broken valve,piston…). Also, I have always run the car hard enough that it is difficult for me to believe there is any carbon buildup which could’ve broken free and caused the spark plugs being compressed. We ran a compression check and found each of the cylinders very close and good (115-120). We also replaced the cap and rotor. Plug wires were not replaced as I don’t have an extra set and the wires on the car appear OK.

The car fired OK and seemed to run good, there was a very slight hint of a miss, but otherwise seemed OK. I let it idle and get up to temp. On the test drive, it started to miss-fire again, and again it was violent, massive vibrations throughout the car. We brought the car home and parked it. I noticed the front face of the intake manifold on the drives side (in front of the master cylinder) looks to have exhaust gas residue on it. I have yet to re-fire the car and feel for exhaust leaks, nor have we removed the spark plugs, but I am suspecting there will be issues with #3 and #5 agains as they are positioned close to the intake manifold where the exhaust gas residue appears. While the car is at idle, no exhaust leak can be heard..

I'm asking for suggestions in trying to diagnose what may be happening, prior to taking the intake and valve cover off? I’m more inclined to believe this is a mechanical problem vs an ignition issue. Could this be wiped lobe(s) on the cam? Could a lifter collapsed? Bent pushrod(s)? What else?

Thank you,

Richard Osborne
Columbus, OH