Re: [Chrysler300] 300G Missfire

I never got into this on ram , “ I did what I was told” by FSM , but I sure would like to correctly understand this . More to it I think , — than at least I ever realized.

This reply from me is prompted by a big WCFB dance last year on this . Stumble off idle . Experts in WCFB are not — was the takeaway.

What bothered me ( later you will see why) on the WCFB is idle timing spec is which one ? Vacuum and static ,or static ... Can’t both be right . If not static , then what is it really running at — when idling, vacuum connected ? Spec ?

Can’t be “ no spec”.

On WCFB / hemi there are are extensive instructions how to set static timing to a certain number with a 12 v light , engine stopped, and spec from that is apparently the same as running , ( although not explicit about how it works) so that says to me, no vacuum is acting , yet connecting vacuum connection May move it. Not always.

In checking — some WCFB carbs do have some residual vacuum in advance line . ? But Enough to move it ?

I now feel it is possibly often due to incorrect or bungled rebuild that gets the throttle plates not fit right leaving ( some ) vacuum in advance line . Very touchy thing to get right .

There is a 50’s carter WCFB service book , 350 pages , covers hundreds of WCFB . I printed and read it. When they do have ported vacuum , all seem about the same spec (mechanical QC spec ) when leaving factory .. upper part of vacuum Port is supposed to be exposed , visible at normal idle setting , and so it is venting most idle vacuum above throttle plate . — If throttle plate closes all the way or correctly positioned inside bore. As it opens off idle and still normal high vacuum it adds timing ( yes!) . If this is wrong , it not closed , it sits already advanced , = you start from stop , vacuum there drops(!!) you can get a stall or stumble at tip in . Just as you pull out into traffic . Got that? But this is WCFB — and all this makes sense to me . Then vacuum curve is tuned by Carter / Mopar for MPG at part / light throttle only , no real role at idle ?

Strictly from an engineering design point of view , why would you advance the vacuum timing at idle in the first place ( — to the full ability to advance it has , — obviously , Max vacuum is at idle) Seems way too much . What would it do just off idle then? Retard? And they are never used like that later on . All are Ported vacuum , today on Edelbrock ?

Other way Causes idle timing to depend on idle vacuum ? Engine stumbles = you would lose timing , makes it stall?

Anti stall is manifold vacuum — for what it does — yes. Do We want advance to move like that does? Maybe they needed that due to all this other stuff

Air bypass valve on rams complicates all this . Maybe something in ram carbs addresses this? Maybe not — too . I do not know.

No position , trying to understand intention of Chrysler . While no way now to find the hard intention , I think most if not all Mopar WCFB static is also the running idle timing . What I would do . What it is too, if you run no vacuum connected at all ( like race setup)

By the way all this is a source of much controversy on dual quad WCFB corvette site. Still goes on , lots of theories and opinions ,80% of them wrong. but that is a different distributor .

On rams following the FSM works. Wish we knew the why . Cynically ,might relate to some of the famous ram idle hunting/ instabilities. ..

best , and thank you , John

Sent from my iPhone not by choice

On 3 Apr 2020, at 8:55 am, <dverity@xxxxxxxxxxx> <dverity@xxxxxxxxxxx> wrote:

Ram cars have full vacuum at idle. The throttle blades are closed at idle, so have no effect on ported vacuum. The same port is on the left carb for the anti stall solenoid. Timing should be checked with the vacuum advance plugged. Total timing is checked with it plugged also.

Don

From: mailto:Chrysler300-noreply@xxxxxxxxxxxxxxx

Sent: Thursday, April 02, 2020 7:38 PM

To: JAMES FABER

Cc: Richard Osborne ; 300 Club Group

Subject: Re: [Chrysler300] 300G Missfire

Sounds odd vacuum at idle throttle closed I think is supposed to be zero , but not sure on Rams. See long thread a few months back on WCFB idle vacuum abs spark advance. I am convinced sopposed to be no advance at idle .. No one knows

Sent from my iPhone not by choice

On 2 Apr 2020, at 6:42 pm, JAMES FABER fabe7445@xxxxxxxxxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

Use one of the inexpensive hand held infrared pyrometers (Harbor Freight $20) to read each exhaust port on the manifold.. The cold - cooler one is your problem cylinder.

Jim

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On Thu, Apr 2, 2020 at 6:24 PM -0400, "Richard Osborne reomotorsports1@xxxxxx [Chrysler300]" <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

Thank you again for the continued comments. Here’s the latest. Please be kind, this old brute is supposed to be an escape, but I seem to have too many other things on my mind, this would’ve been much simpler a few years ago.

Removed all the plugs, none were squashed (previously, #3 & 5 were squashed). All gaps were good. Only #7 and 8 looked darker than the rest. I’m not reading too much into that at this time, they only ran for a short period..

Seems to idle rough, like with a miss, pulled cylinders #1,2,3,5,7,9 at the cap with definite changes in idle, they were all firing, I was convinced issue was on left side and I was tired of bending over the car, so I didn’t do the rest.

Should it be pulling vacuum at idle? It does.

Timing with vacuum disconnected: idle = 7 degrees, Total = 27 degrees

Timing with Vacuum connected: Idle = 27 degrees. Total = 47 degrees!!!!!! That seems way too much to me?!?!?!

There is a possibility the balancer slipped, I can’t remember if I had it redone or not. I do have a timing tape on it which makes reading much easier.

I tried the stick to the ear trick, but couldn’t hear anything different around the motor. Not sure this means much, but….

Couldn’t feel any exhaust leaks around where I though there was some.

What am I missing?

Thanks again,

Richard Osborne

On Apr 1, 2020, at 8:38 AM, Richard Osborne reomotorsports1@xxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

Thank you to everyone who has taken the time to respond. I apologize for the delay in my response, but here is some additional information in related to some of the inquiries:

I only use Champion plugs, RJ12YC for the 300G, this is the successor to the original plug, slightly hotter, but same reach.

First thing I asked my son when he told me the plug gap was closed was if he had dropped them when he put them in the car last year. He said no.

I don’t think any pistons hit the plug, The plugs showed no evidence of a hit. If things were that out of whack, all of the plugs would have been hit.

The compression is OK based upon the old starter, only removing 1 plug at a time to test, cooler weather and a mediocre battery.

I do not have another BB distributor.

The cam is a “Mopar Perf. Six Pack” cam, specs are similar to the original grind, not radical.

I have heard of high cylinder pressure squashing the plug, if this is the case, it will be the first time I have seen it. But again, the misfire is violent!

I had the machine shop assemble the bottom end, I assembled the rest. My biggest mistake on this was thinking that since they were famous for building alcohol Hemi’s for TA/AA and TA/FC and tractor pulling motors, that a street engine would be easy. I overlooked the fact that those other motors get pulled apart all the time and frequently. This was the one motor I built that I NEVER wanted to take apart again, looks like this will be the second time (having heads off)….

I am hoping to have my son take the plugs back out in the next few days and will advise. Good thing he likes old cars and is flexible. Doesn’t seem to bother him to have to take the front tires off, remove the ram panels just to remove the plugs…..

Thanks again for the feedback, I’ll advise when we dig into it again.

RIchard

On Mar 30, 2020, at 3:19 PM, Richard Osborne reomotorsports1@xxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

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