Richard, you're on the right path.....ruling things out is progress. And you've been getting some great advice from a number of members here.
I'm not familiar with cross-ram dual carb setups, I've been wrenching on single carb B/RB Mopar engines my
whole life but have two thoughts that might give food for thought. If its idling rough but has normal
vacuum and response is progressively worse depending on throttle input, you may be onto something with one carb being a problem and not feeding a whole bank correctly, essentially either starving or flooding part of the engine.
Also, I threw this out after your first post. Considering the damaged plugs as a symptom its easy to rule out valve train early, but I still think you need to follow up with inspecting it. A broken keeper or spring, a bent or broken push rod(s), or a bad lifter
could give you the rough running situation, particularly under load. I have personally had pushrods split and push right through rockers and have had my share of bent pushrods due to higher lift cams and too heavy a spring for the stock rockers. The engines
with bent push rods performed similarly to what you are describing.
Also, have you considered your torque converter as an issue? Food for thought anyway.
From: Chrysler300@xxxxxxxxxxxxxxx <Chrysler300@xxxxxxxxxxxxxxx> on behalf of Richard Osborne reomotorsports1@xxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx>
Sent: April 13, 2020 7:20 AM
To: Richard Osborne <reomotorsports1@xxxxxx>
Cc: 300 Club Group <Chrysler300@xxxxxxxxxxxxxxx>
Subject: Re: [Chrysler300] 300G Missfire
I appreciate the ongoing dialog and encouragement. Here is the latest as well as an appeal for specific thoughts.
The transmission mount appears OK. I’ve hung on to the theory of the transmission or Ball and Trunion moving around because I really am not getting any backfiring. My son removed the driveshaft and inspected the B
& T stating it appeared OK. He repacked the B & T (he said it was pretty dry) and re-installed the driveshaft.
I found an old ugly coil in my toolbox and swapped it out. I am assuming the old coil was good because I kept it. This did not change things.
I sprayed brake clean and some carb cleaner around carb bases, intake mounting surfaces to cylinder heads and the vacuum port for the brake booster. This did not change idle. Therefore, I am assuming no serious vacuum
leaks.
During the test drive. it behaved the same. Slight miss felt during light/nomral acceleration. Then violent vibration under harder acceleration.
Once again, I power braked the car in the garage, this time to the point of braking the rear tires loose. This lead to the violent “misfire”. The Limited Slip does, however, still work.
The chokes are working on each carb. I do not, however, have heat riser butterflies in the exhaust manifolds, but this has been the case since day 1 after the restoration. I do not notice any screws or parts missing
from the carbs.
An interesting thing: When I manually choke each carburetor with my hand, the right side seems to be more sensitive to the “choking” vs the left side. By choking the right side, it seems to kill the engine much easier.
Since this carb feeds the left side cylinder bank, could this indicated that the left side of the engine is “weaker” than he right side? Remember the #3 & 5 cylinders had the electrodes on the spark plugs squashed.
The car doesn’t idle as smooth as I think it should, and not because of the cam. With the car up on jack stands and idling, the horns visibly vibrate due to the non smooth idle..
Comments and Question: The carbs haven’t been touched in 15 years (approx). Although I don’t drive it everyday, I do drive it every few months at least, so the fuel gets burned off. I try to fill it up prior to Winter
and I do put Stabil in the fuel. I coated the fuel tank with Eastwood fuel tank stuff to minimize rust inside of tank. Probably has the original fuel filter from when I restored the car. I’ve never had fuel issue as I have another old Dodge that has gone for
periods of a year+ without firing and it is very dependable for starting even after long periods of dormancy. Now, I had the epiphany that on the ram cars, unlike regular engines, each cylinder bank is fed by a unique carb. So, if there is an issue with the
right side carb, only the left side cylinder bank will be affected. Question, is it possible that there is a serious fuel devilry issue with 1 carb, that it could cause the violent vibration that I had previously thought was a misfire? Basically, the engine
only running on 4 cylinders? As a point of note, the accelerator pump seems to be working the same for both carbs and I assume pumping OK. I don’t have carb kits for these, so I don’t want to dig into them until I do have rebuild kits (I was planning on doing
this sometime this year anyways). Is there a possibility that some junk/debris got into the carb and is preventing fuel delivery during higher needs?
Thanks again. This is in a perverse kind of way fun. My sons are helping and learning at the same time, even my non car interested son.
Best regards,
RIchard Osborne
Again, I want to thank people for the continued input. While I am fortunate enough o remain very busy with work, I am able to delegate tasks to my willing 17 yr old son.
He took each plug wire off to check the resistance. This was a new venture for him and myself. Here are the numbers, to me, it seems very difficult to read anything from this, because each wire is of a different length,
by default, they will have different readings, correct?
#1 16
#3 13.1
#5 13.7
#7 15
#2 7.7
#4 10.5
#6 10.6
#8 13
Also, we waited until late at night and dark to run the engine at idle and up to 3,000RPM to look for dancing sparks, we saw nothing.
Next, I asked my son to look at the transmission mount to see if it looked OK and see if perhaps the engine was sitting crooked. He said it looked OK, I will go view for myself as well as see if it may be
broken and therefor allowing the engine to shift.
Prior to putting the car on jack stands, I power braked (pushed accelerator and brake pedal at small time) it and although it was a relative short period of time, it didn’t mis or break up.
Still thinking of additional things to look at prior to tearing into the engine.
Thanks again,
Richard Osborne
Thank you again to those who have continued to respond.
I appreciate Don Verity confirming that the engine should be racing vacuum at idle, tis had me perplexed. Additionally, I became excited when he mentioned his experience with a worn Ball and Trunion. Although I replaced
mine less than 5 yrs ago (I think), it sounded very plausible based upon the violent shaking. I had my son take the driveshaft out to inspect. He managed to repack the B&T and reinstall before I could inspect.. He said it was dry, but didn’t see any scoring.
The fact I don’t get backfiring made me think this was the issue.
I had hardened valve seats installed in the heads.
Short of pulling the intake and valve cover, I think I will try to back the timing off a couple of degrees just to see what happens. Seems like I had it set a couple of degrees higher than I remembered. I was running
premium diligently and probably have slacked off of that in recent years.
I may look at trying to measure the resistance in the wires, electricity is not my friend. Might be a good learning experience for my son.
Thank you again and stay safe.
Richard Osborne
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
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
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
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Posted by: Ryan Hill <ryan_hillc300@xxxxxxxxxxx>
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