79 dodge 440 misfiring on cylinders 7&8

[van needs road]

Hey new to this but really need some help. Just a kid looking for some guidance, all input is greatly appreciated. Been working on cars for awhile now but I’m stupidly stumped on this dang 440. Here goes
I’ll try to keep this simple…..
Compression: 120 - 125 psi on all cylinders
New stuff:
Plugs
Wires
Cap & rotor

Went through and swapped some plugs/wires and the misfire didn’t change.

Fuel covered spark plugs for cylinders 7&8

Tested for spark by grounding out and had spark for both

Took both wires out of the distributor and no change to idle

Misfire does not change with load…

Thanks again.

By the way. I’m not sure if this was a good spot to post this so hopefully it gets the right crowd??

Thanks.. Like my name states.. this van needs to see something new other than my dang shed door

 

[493 Mike]

With the two rear cylinders having trouble, I would look for a vacuum leak. With the engine running spray some flammable cleaner around the port gasket areas and listen for an increase in RPM. Any change indicates a leak. Propane will work also.
Mike

 

[Runcharger]

Double check firing order, especially 7+8. Also check the plug lead crimping.

 

[Don Frelier]

How old are the wires?
7&8 are about the longest so if they have high resistance they would be the most likely candidates to misfire.
Did you look inside the cap?

 

[1967coronet]

You have great advice. If its good after checking for a vacuum leak.
Like posted ,dbl check your fireing order / wire placment.
If that's good , I would replace #7 & #8 wires and replace those fuel fouled plugs.
Like posted above 7 & 8 are the long runs. You can be getting spark but not enough compared to the other cylinders.
A couple china plug wires can do that.

 

[oldkimmer]

How old are the wires?
7&8 are about the longest so if they have high resistance they would be the most likely candidates to misfire.
Did you look inside the cap?

Says he replaced plugs, wires, cap& rotor. U may have gotten the wrong rotor. @HALIFAXHOPS have a for sale thread which explains this. Kim

 

[pnora]

79 should not be a factory 440. Is it a motor home? Does it have an EGR valve?

 

[HALIFAXHOPS]

Sounds like the wrong rotor is in there and the shaft is bent a bit. Easy check with a feeler guage.

 

[Don Frelier]

Says he replaced plugs, wires, cap& rotor. U may have gotten the wrong rotor. @HALIFAXHOPS have a for sale thread which explains this. Kim

Not exactly what he said:
Went through and swapped some plugs/wires and the misfire didn’t change.

To me that means he switched around the stuff he had or tried another used part possibly.

 

[van needs road]

Woah… thanks everyone!
First thing first I’ll go ahead and check for a vacuum leak.

I installed a new cap and rotor yesterday as the one I had was getting a big chewed up..(rotor was eating away at the caps points) so I’m sure you’re right about that.

I do have new plugs and wires in this guy (yes…. It’s a motor home )
What I meant and someone said it was I thought the wires were bad, so I swapped #5&7 wires with no change. Cylinder #7 was still dead.

I’ll have to look for a feeler gauge as well thanks!

Oh yeah and it does have an egr valve

 

[pnora]

Woah… thanks everyone!
First thing first I’ll go ahead and check for a vacuum leak.

I installed a new cap and rotor yesterday as the one I had was getting a big chewed up..(rotor was eating away at the caps points) so I’m sure you’re right about that.

I do have new plugs and wires in this guy (yes…. It’s a motor home )
What I meant and someone said it was I thought the wires were bad, so I swapped #5&7 wires with no change. Cylinder #7 was still dead.

I’ll have to look for a feeler gauge as well thanks!

Oh yeah and it does have an egr valve

A stuck EGR will cause poor running and affect certain cylinders. Look at the intake runners feeding the two cylinders. Plug any vacuum ports on them and see what it does. Also make sure you have a reluctor for an 8 cylinder. Seen one with a 6 cylinder reluctor that really ran poor.

 

[Tony Tee]

79 should not be a factory 440. Is it a motor home? Does it have an EGR valve?

Maybe it's a rare leftover 78 or very early 79 440?
Like the real rare 1959 392 hemi truck engine.
The internet indicates that the last year for the 440 is 1978, and the last year for the 392 hemi was 1958 ? If it is ? Nice find. Can anyone else confirm this ?

 

[khryslerkid]

More than likely it has power brakes. Disconnect the hose going to the booster and plug it. A bad booster can be a vacuum leak that's hard to find.

Welcome to the madness!

 

[pnora]

Maybe it's a rare leftover 78 or very early 79 440?
Like the real rare 1959 392 hemi truck engine.
The internet indicates that the last year for the 440 is 1978, and the last year for the 392 hemi was 1958 ? If it is ? Nice find. Can anyone else confirm this ?

78 was the last year made. September 29th, 1978 the last one was rolled out of the Trenton plant.. Some of the motorhome chassis got the left overs and were titled as 1979.

 

[bello78]

Sounds like the wrong rotor is in there and the shaft is bent a bit. Easy check with a feeler guage.

Do you have EGR block plate?

 

[Mackman]

More than likely it has power brakes. Disconnect the hose going to the booster and plug it. A bad booster can be a vacuum leak that's hard to find.

Welcome to the madness!

I just recently had this exact issue. Symptom was weak firing on 7&8.

 

[RemCharger]

I just saw a 79 440 the other day.