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Mr. Asks Alot
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Discussion Starter #1
Okay guys well I just picked up an 82 F250 with a 351 Cleveland in it (yes...it is a 351C), 4spd, 4x4. The motor was rebuilt and has about 100 miles on it (previous owner had it rebuilt and never really went anywhere with it).

Anyways I'm having some issues with it, I noticed it was not running well and was getting some popping (sounded more like a piffff) out of the carb especially after shifting (RPM change?). Pulled some plug wires and realized it was not firing on cylinders 6 and 8. I found the plug wires were hooked up wrong on them.

Replaced distributor cap, plugs, wires, and reoriented them to the correct location. It has a Holley 670 Street Avenger carb on it, the accelerator pump was leaking so I removed the carb and replaced the diaphragm and reinstalled the carb.

After that the motor sounded stronger at idle but when I would give it gas it would bog and hesitate. I pulled the plug wire off Cylinder 6 while running and it didn't seem to make any change to the motor so I still don't think cylinder 6 is firing.

I got a timing light from Auto Zone and could not make it work at all, the light wouldn't flash, tried plug wires 1 and the coil wire and nothing. So loosened the distributor holding bolt and tried playing with it to see if I could get it to run better, idle picked up but I started hearing a tapping metallic sound come out of the carb (not loud, except one time was louder than the others). Killed the motor and said forget it and walked away.

I noticed the distributor top half could move left and right some, opened the cap and it looks like the little plastic piece inside that holds the bottom plastic part in place broke. The distributor itself has no play but the plastic bottom half that the cap snaps too can move left and right some. Can this be replaced individually or do I need a whole new distributor?

I'm stumped. The timing obviously is not quite right, I'm gonna try and get a different timing light and see if I can get that set. I still can't figure out why it would not be firing on cylinder 6.


I have not done much with old trucks in a while (well 8 years), I'm very mechanically inclined I fix and build custom motorcycles on the side. I'm in vet school and picked up this as a play toy/work truck and for nostalgia as I missed my first vehicle (78 bronco). I'm already banging my head on this one.


Any help/suggestions/things to try would be GREATLY appreciated.


Thanks,
Spencer
 

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Mr. Asks Alot
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1,775 Posts
Discussion Starter #2
Okay guys, I had a guy that is pretty familiar with 351 motors come out and help me some today


Update:

Replaced the distributor cap adapter (thanks ctubitis)

We started by playing with the timing, tried it sat to various settings and still no huge improvement

Figured out that I accidentally left the spring out of the accelarator pump, didn't bog/pop as bad after that

The truck still does not run right, it will idle fine and if you accelerate slowly it's fine. But as soon as you mash the throttle it will pop out of the carb. It's not a backfiring its more of a sharper pop sound (no fireballs).

Vaccuum was strong at 20psi

We played around with different cams and air/fuel setting on my Holly Street Avenger 670 and it idled better but still would pop when giving it gas. It has a 6.5 power valve in it, should it be swapped to a 9.5? He said typically you want them to be half what your vaccuum is

We swapped on his 600 Summit Racing carb off his truck and it did the same thing and idled worse (probably not enough fuel/air).

The cylinder that was not firing was 6, we checked the plugs. All the plugs on all the cylinders are BLACK. We are getting spark on cylinder 6, compression is 130 (check 5 too and it was 130).

He says the motor sounds healthy in his opinion

Vaccuum was strong at 20psi

Oil pressure was good (sprayed out like crazy when turning it over with valve covers off)

We found one of the rockers on the right side had been assembled wrong (base/pedestal mounted the wrong way) and fixed that (no change it how it ran).

We tried his coil as mine is the original one it looks like and no improvement.

The cam going bad was mentioned but the motor sounds perfectly healthy other than under accelleration.


I'm stumped and dishearted, and not sure where to go with this. Does this sound more carb related as in I should up my power valve and change my jets? Or does it sound more electrical?

Oh and I was getting good spark on cylinder 6. I stuck a spare plug in the wire and when held against something metal I would get a spark. It didn't spark if it was just the plug wire and plug and not held against something metal.

Also, one thing that I just thought about. When I originally picked the truck up it could be revved up and did not make this popping out the carb. However plug wires 6 and 8 were reversed at this time.

Also, when I pulled the original plugs out all the cylinders except 6 and 8 looked like they had been firing. The 6 especially and 8 looked like they hadn't been very well. That was before everything like plugs, wires, cap, rotor, incorrect plug wire order, etc. were swapped



At TDC rotor is pointing at number 1

Any help would be GREATLY appreicated.


Thanks,
Spencer
 

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What made you think #6 and #8 are reversed in firing order? See diagram above.
 

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Mr. Asks Alot
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Discussion Starter #5
Thanks guys, the firing order is correct (assuming its original cam). I should be able to find out details on motor parts that were used for the rebuild today.

When I got it I found that the previous owner had wires 6 and 8 reversed (going by the known 351 firing order). That is unless the cam is aftermarket with a different firing pattern that calls for 6 and 8 to be reversed (doubt it but I am going to turn the motor over by hand with the valve covers off to confirm firing order).


Thanks,
Spencer
 

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Sounds like ignition system. What type of distributor and coil are being used? What are the plugs gapped at and what type of plugs?
 

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could be a timing chain issue not installed correctly, cam lobes damage by not having zinc in oil and follow correct starting procedure. could be a a lifter stcking, in my opinion for what it's worth go bsack to the basics. pull # 1 plug, make sure engine rotates to tdc. see where distrubtoris at that time. timing could be off i tooth, or more. have seen this many times, including on mine.
on a side note, the clevland motors are not torque monsters like the modiflyed motors, they are a high rpm motor.
 

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Mr. Asks Alot
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Discussion Starter #10
Update, finally talked to the guy that put the motor together, here is what he said:

Motor was fully rebuilt, machined, everything in the top and bottom end was replaced and it has 3000 miles on it and ran great. The guy that owned it let a buddy borrow it and he thinks he missed a gear and over-reved it and broke a valve and scarred a piston up. He said they had it all celaned, freshened, cleaned block replaced the head on that side (right/driver's side). New pistons, rings, rods, and mains were put in it.He said the crankshaft was pinned 0.10 and had 10 valves/rods (I don't know what this means). He said when it was built 3000 miles before it killed that piston that the valves, springs, rockets, etc. were replaced. He said the cam was not stock and was new when it was rebuilt the first time and had 3000 miles on it but was in good shape and reuused the second time. He also said he broke it in properly after the second rebuild when it was at his shop, additives for cam, ran at 2k rpm, etc.

I told him what he was doing and he said it sounded like a cam lobe to him.


Thanks,
Spencer
 

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Mr. Asks Alot
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Discussion Starter #11
Timing was played with and I got no change in it. I did not remove distributor and set it completely only adjusted the distributor.

I have a new MSD 6A box, used MSD distributor, and new MSD coil coming. I'm going to get the timing set right with the new ignition, check and see if I can confirm the firing order with the valve covers off, and then check rockers for movement to make sure everything looks like it is working correctly.
 

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how is the exhaust?
is it kinked anywhere,maybe a collapsed muffler

does it have a cat on it


you cant fart with a cork up yer butt just as a truck cant breath with a restricted exhaust
 

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Mr. Asks Alot
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Discussion Starter #13
trusty rusty, exhaust looked good although I never checked it closely. I'll look again, thanks
 

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Pull the #6 side valve cover. Rotate the engine by hand and watch the rocker movement of #6, compared to the movement on the adjacent cylinders . If there is less up and down, then you could have a bent pushrod, wiped cam lobe, or a mis-adjusted rocker.
 

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A couple of questions for you;

How does it run under load when actually driving?

Is the hesitations still there?

More or less hesitation under load versus just reving the engine?

While accelerating hard during driving (not just reving at a stand still), does it feel smooth (other then the initial bog) throughout the rpm range?

Also while acceleration hard, do you feel or hear any "pulsing" sensation or is it totally smooth?

Last question. Did it run normal before you bought it? Or has this been going on since the rebuild?
 
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