Hi Guys, hope someone can help. The trucks appears to be firing on only 4 cylinders???

I have a newly aquired 56 F250 with a 272, which was running when I bought it 2 weeks ago.

First job I did was to replace dizzy cap, plugs, plug wires and install a Pertronix electronic ignition module with Flame thrower coil.

The motor starts readily but feels rough from insde the cab but smooth from the engine bay. Now heres the thing;

I can remove 4 plug wires and the engine idles with no change at all. If I remove any of the others it runs rough. Its as though its only firing on 2,3,5 & 8 and therefore only missing everyother cylinder - BUT every wire has a good spark.

I double checked all the wires and the dizzy cab, everthing is in the correct firing order. I checked TDC with 10 degrees advance and eveything lines up. I pulled the plugs and can see unburnt gas on those cylinders where I can remove the wires and have no change to idle.

I put shop towls in the plug holes of the 'non firing' cylinders and they pop out with a pop, so imagine I have good compression.

Any thoughts out there? Could it be a miss-alined timing chain or maybe the ignition is off, it has a 57 model year distributer. Should I put the points back in and see if that solves anything?

Any help would be much appreciated.

Oh the exhaust note does not have that typical Y block burble, I guess 'cos its only a four banger????

Paul

It could be a carb problem IF you have a TWO BARREL carb and only are getting gas to one of the two barrels. Much easier to check.

If you have a spark from all the plug wires check your carb. Pete

Pete

Thanks for the suggestion. I just checked and both barrells are giving good fuel.

I would suggest rechecking the plug wires for correct order of installation.Its very easy to mix them up especially if you are using the original sparkplug wire brackets.If you are getting ignition and it runs I think  you can assume the Pertronix replacement ignition kit is working properly.

  

Did it run that way before you replaced those parts? If it didn't I would recheck the plug wires. Sometimes when we check & recheck things we still overlook the problem (dont ask me how I know). If it runs the same way as before you replaced the parts I would look at the carb again. Take a can of carb spray with one of those nozzles on it and try to aim the spray down the carb to one side of the throttle plates and see if it picks up. The cyls you mention that are missing point to a plugged idle circuit in the carb. My .02

Dan      Kingman Az.      86409

well...not to sound too simple, we all know you need spark, compression, and fuel for an explosion...

And from what your original post said, you have gasoline getting to those cylinders that are not firing, and it looks as if you have compression. How did you test for spark?

If it was me, I would get a gauge on test your compression on all 8 cylinders to see what you have.

After that, I would test for spark with one of those spark plug tester gizmos...

If after those 2 tests show all the "explosion" aspects to be true, then you must have a timing issue.

If you have unburned fuel in the cylinders, then you know in that cylinder you either have no spark, no compression, or the timing is way off. Don't forget that the cylinders are numbered 1-4 on the passenger side from radiator to firewall, and 5-8 on the drivers side from radiator to firewall..

hope we can help you. These things are always frustrating. One time I forgot to put all the plug wires in a firing order that went counterclockwise! Talk about a problem...I had the misfiring and towering flames shooting out of the carb until i got that one solved.

Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com

I have had that situation before and it is definately in the carb, one side of the low speed is plugged up, you may still see a squirt on that side from the accelerator pump but the idle circuit below the butterflies is what is plugged. once you bring it up to a certain rpm it will bypass that curcuit and you wont notice it, its only at idle and i could do the same thing, remove 4 wires without change.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Have also seen the same thing when someone added a PCV system and used the connection on the manifold, the extra air leaned out 4 cylinders. Moved the PCV to a carb spacer so it supplyed both banks and it was cured.

Definitely carburetor. With engine off, remove both idle mixture screws and give each side a good blast of air. Replace screws with fingers. Screw them in all the way and back out 2 turns. Should run on all cylinders. If not, repeat. After engine warms adjust to smooth idle.

That last suggestion is a good one.Try it.