A couple years ago it just quit while idling, no drama or noises, I changed the cap, rotor, coil, no result, It's in a bus and eventually 1 1/2 years later had to be moved so I tried taking the plugs out, Big job removing the dog house and every plug hole full of mud, but when done it fired up right away, but doesn't run well. rough and misses badly backfires when revved, barely able to move..... Then it wouldn't start for a long time due to battery and propane fuel problems, sticky mixer ? and eventually I got it going with some pretty dramatic knocking noises, but it starts easily now and sounds close to normal at near idle.

Firing order being 1 5 4 2 6 3 7 8 Now (alternate firing order swapping 2 & 8 and does not work, if not starting, not running any better when swapping when running)
When I originally changed the distributor cap I thought I put the wires on according to how I was taking them off, but when I checked it I thought was wrong by 2 wires (and swapped them) and checking with the order found in this forum and it turning out that in could be either of these two firing orders. but when I checked it again recently, (Way back now) discovered I had 3 wires wrong,but it still ran the same and changed it to the existing order. I think #5 or #4 was out relative to one of these firing orders as well as 2 & 8 but I'm wondering now.

I have the wires numbered left drivers bank Odd, right Even, #1 & #2 opposite sides, Pulling the wires off while running with the idle slightly higher than normal, all with good jumping spark, first tried while engine was warming up and before the compressor kicked out:

1 L- slight decrease in idle, roughness.
5 L- Nothing, though when first tried it, thought to detect a slight decrease in idle, roughness.
4 R- This one being the oddest, when first tried made a slight difference, See end note.
2 R- Nothing whenever tried. Like a dead hole, but still has spark on top of the cap.
6 R- slight decrease in idle, roughness. near stalling.
3 L- slight decrease in idle, roughness.
7 L- slight decrease in idle, roughness.
8 R- slight decrease in idle, roughness.

I having Putt sound when building air that diminished with # 4 out. When first tried the engine smoothed out noticeably. later with the air up, still a less putt sound, but seems to disappear when this plug wire is pulled, Possibly from the engine warmed up, along with less load etc with air up, but appearing to still be tied to this plug.

Swapping 2 & 8 didn't make much of a difference though slightly rougher. Other than noted, No noticeably decrease in other noises. Some normal from day one, others sounding a bit like exhaust and know I have a hole in it under the engine. some valve noise heard on initial start up and while running.

 

I just found the firing order on the manifold under some carb linkage, or half of it anyway and it appears to be 1 5 4 8 6 3 7 2 As opposed to the other #2 & #8 variation common to most Fords.

I should be able to figure it out from there, But am not looking forward to it without knowing for sure what the cylinder designation numbers are without taking the dog house off to take the valve covers off to be sure.

As it sits now it looks like the most forward cylinder Drivers Left side is not #1 and is either #2 or #5 if this bank runs 5 6 7 8
(Which I have as #1 now and I think is one of the few wires that hasn't been moved, It amazing it runs at all and am trying to figure out why before I start moving more wires around)

Elsewhere in the forum it suggested either, and looking like not the norm, forward being #1

 

I believe the cylinders are numbered 1-4 front to back on the passenger (RH) side and 5-8 front to back on the driver (LH) side. See if that doesn't make a difference.

 

Thanks, I ended up lining up the timing mark on the damper and checking the rotor, Which also told me I was looking at the order the wrong direction. But it appearing to closer to #5 (LF) and figuring it out from there. #1 is just before it in order, so figured there as the result of timing and not having the mark on the damper right on.

It turning out #7 & #1 were out according to this, Which seemed to be close to the possible change I made when I swapped caps. so I just swapped them and it started right away. But not without drama.

(It a bit strange that I had the other proper firing order going the wrong direction and using an improper plug # designation.)

It started right away, made lots of backfiring noises and ran at a higher idle than I had it set for previously and smoothed out a bit as it warmed. so I started pulling wires.

Now I have a problem with #2, It won't run with it in, Gets rough, backfires, misses etc and otherwise ran pretty good turning the vehicle around, but haven't tried it driving down the road yet.
It actually idled good with a couple wires out. I think I also had #7 and #1 out with #2 at one time.

This #2 plug being my original #4 (wrong firing order) that when removed earlier also smoothed out or made a change in the idle.

I'd think about swapping it with #8, but I took a closer look at the casting and this firing order should be right now as well as checked many times for crossed wires etc.

So I'm thinking I possibly have some kind of crossing firing going on with a bad cap or wires, Timing? if not some kind of mechanical problem. I'll wait till dark and see if the wires are ok.

 

My '75 shop manual shows a firing order of 1-5-4-2-6-3-7-8 for the 401, 477, and 534 engines. These engines have timing gears and no chain so the cam rotates oposite of the crankshaft. I don't know if the distributer turns the "normal" ccw as you look down on it. Have you cranked it with the cap off to verify rotation?

I'd also compression test all the cylinders to see if you have valve/ring/piston problems.

 

Thanks, I verified the rotation when I was trying to find #1.
The firing order 1-5-4-8-6-3-7-2 is cast into the manifold left side of the carb and under some linkage, and why I didn't see it for along time. (It was also soiled over a bit, but initially didn't look that dirty there till I poked around with a screwdriver)

I was thinking my #5 LF could actually be #1, but I'm sure I never moved that many wires around when I changed the cap. But could have started out of order and have timing problem. But it seems to run ok exception that one plug.

That and it being in a Cab over bus, so with the doghouse around it makes it hard to work on, The spark plugs are difficult to get at and not much easier to get at with it off. It took me over a year to get around to taking it off.

My compressor and power sterring belts are also loose with no visible means to adjust them from below, so that another job I'm not looking forward to, not being able to get at the front of the engine easily or see what's going on.

I'll have to get help to check the timing, Thankfully the timing mark is easy to see under the bus and don't have to crawl very far under it to get close to it. It also barely a timing mark, It looks like 3 punch marks about 1/2" apart, with one that might be a "0" placed right where they pass by the pointer on the front face.

All the spark plug holes were also full of mud so I couldn't get a socket on any of them, otherwise I would have found someone with small arms to do it. A compression test is one of those things that likely wouldn't get done for a while again, But it also looks like I have to take the dog house of to get the valve cover off to check valve action on the right side. (It also tight at the back)

 

FORD 401, 477, 534 SUPER DUTY V8 ENGINES
Looking at the engine from inside the vehicle the right bank is 1,2,3,4 front to back, and the left bank is 5,6,7,8 front to back.
Firing order: 1-5-4-8-6-3-7-2 Counter Clockwise. ( cast into the manifold on the left side of the carburettor under the throttle linkage ).
Distributor is mounted with # 1 socket facing the front of the engine & the vacuum advance unit facing the rear of the engine.
Timing Drive: Geared Type ( Distributor Rotates Counter Clockwise ).
Spark Plug: AR6FS or equivalent
Plug Gap: 0.9MM
Initial Ignition Timing ( B.T.D.C.)
Regular Fuel: 6 Deg. @ 550 RPM
With LPG: 10 Deg. @ 550 RPM