340 Not firing on all cylinders

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Den's Dart

Den's Dart

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Guys, I know this may seem like basic trouble shooting to you but help a newbie out here please (without tearing me down preferably! :D )

Started the Dart up on the weekend for the first time since the winter and noticed it just didn't sound right (Didn't sound the greatest when I put it away in the fall to be honest!). So I took my infra red temp guage and took some readings at the manifold. Atleast one cylinder is definitely not firing (The readings on the left side back 2 cylinders were much colder but the back left was considerably colder than the rest).

I swapped in a new plug, no change.
I swapped a wire, no change

I did not swap the position on the distributor.

So, where would you guys head next? would you suspect the Cap/rotor or the ignition module? Any way to rule one out? I don't have a compression tester and to be honest I am dreading the thought that it is NOT ignition related!!

Also, just to be certain the plugs are wired correctly does anyone have the layout for a 1970 340. I assume the PO has them in right order but you just never know....

Thanks in advance,
Dennis
 
pop and inspect inside the cap terminals. clean the rotor. switch a wire from a cylinder that is firing. if it is limited to one cylinder not firing, I would suspect a valve hanging open or a dead cylinder
 
Firing order is 1-8-4-3-6-5-7-2

As far as the rest, you have checked the usual suspects. Maybe a dead mouse blocking the intake? J/K

Jack
 
I did switch out a wire but I switched it both at the plug and at the distributor. If I swap it with another position on the distributor (putting it out of time) would I be able to properly tell if it is actually firing?
 
Den's Dart said:
I did switch out a wire but I switched it both at the plug and at the distributor. If I swap it with another position on the distributor (putting it out of time) would I be able to properly tell if it is actually firing?
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all I meant was change the entire wire with one that is firing to find out if the wire is broken / burnt or otherwise. sounds like you did that already. even better if you have a new wire you can put on the cylinder that isn't firing
 
I do it the easy way, by pulling all the plug wires from the distributor cap and just lightly set them back in.
Start the car and pull one at a time until the one I pull makes no difference.
That's the dead cylinder.
Then compression test that cylinder.
If the comp test looks ok, then I change the plug/wire.
If that does'nt do it then I look for a vacuum leak.

I know everyone says "Dont pull a plug wire without grounding it somehow"
but I have never had a problem or caused anything else to fail doing it this way.
EVER, and it makes it really easy to find the cylinder that's not firing.
 
Use a spare spark plug and place it on the coldest cylinder's wire, then start the engine. If you see it firing, then you can suspect a lack of compression. Place your thumb over the spark plug hole in the head while someone cranks it over (remove the coil wire from the distributor first). See if there is a lot of pressure trying to blow your thumb off of the spark plug hole. If not much, then you may have a hanging valve or broken piston rings.

Good luck!
 
TrailBeast said:
I know everyone says "Dont pull a plug wire without grounding it somehow"
but I have never had a problem or caused anything else to fail doing it this way.
EVER, and it makes it really easy to find the cylinder that's not firing.
Click to expand...

that's always fun , ive been shocked more times than I can count lol, but it works

make sure to use insulated needle nose or whatever
 
73AbodEE said:
that's always fun , ive been shocked more times than I can count lol, but it works

make sure to use insulated needle nose or whatever
Click to expand...


LOL, I've always been told that and I still end up like this.
 

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Bad Sport said:
LOL, I've always been told that and I still end up like this.
Click to expand...

Thats why I do it at the distrubutor instead of at the plug. :D

I shut it off to put them all back in tight, because that's when I usually get nailed.

They do make plug wire pliers that are non conductive, but I have never owned a pair so I guess that tells how much I don't mind getting zapped on occaision.
 
If someone can confirm Badsport's diagram I would greatly appreciate it!! According to that diagram, I think the PO reversed 6 and 8. IIRC I am pretty sure it was the centre (closest to firewall) on the cap going to the #8 cylinder. Also it might make sense since both 6 and 8 were considerably colder. Man I HOPE it is something that simple!! I don't mind looking like an idiot on the NET if it cures my problems that easily!!
 
Den's Dart said:
If someone can confirm Badsport's diagram I would greatly appreciate it!! According to that diagram, I think the PO reversed 6 and 8. IIRC I am pretty sure it was the centre (closest to firewall) on the cap going to the #8 cylinder. Also it might make sense since both 6 and 8 were considerably colder. Man I HOPE it is something that simple!! I don't mind looking like an idiot on the NET if it cures my problems that easily!!
Click to expand...

Confirmed
1-8-4-3-6-5-7-2
 
Pay close attention to 5 and 7 also, those are commonly inverted. I've done it myself when in a hurry.
 
I have seen were a hairline crack in the disturber cap would cause a cylinder to not fire.
 
Well, I chased this issue myself recently. After checking compression, started troubleshooting. Replaced plugs. Checked wires, seemed fine contacts were a little green. Checked cap, center button was gone. Had to replace distributor because the bronze bushing was gone and there were shavings all through it where bolts on the underside of the shaft had ground the housing. That is another story.

After I got everything back together, checked and set timing,car seemed fine. Then on the way to work one day it ran like crap. Would stall at lights, rough idle. Back to drawing board.

After checking wires at the distributor (better choice IMHO) found that the ol 340 was running on five of 8. Pulling 1,2,8 did not change a thing. Not good, but God bless Ma Mopar for building something the can run on 5 of 8. Cleaned up the wires with DeoxIT, and car is great again and I have a spare set of wires in the trunk, among other "get you going again" items. Don't be fooled by appearances...you can chase this down.
 
I have a set of plug wire pliers, but I still agree that the timing light is the best and safest way to check for spark. If you have spark, you are going to have to check compression. Do you have a compression tester?
 
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