OT-truck engine trouble

[goatchin]

I realize this is a chainsaw forum, not truck engine forum, but I figure this thread will be a little more use full than the "what saw should I buy" threads.

Here goes: '79 dodge power wagon with late 70's early 80's 318 carburetor engine, manual choke, 4 manual speed tranny.

-Starts fine
-idles good but a little choppy
-smokes before releasing choke then fine once released
-will idle for 2.5 minutes before starting to backfire from both sides-each side is on own exhaust system-mufflers
-then continue to backfire once warmed up
-when i rev it quickly it will hesitate/drag/no response. rev it slow=sorta good
-when driving, it has no guts at all

What I have done:
1-new fuel filter and lines good-no leak
2-new air filter
3-exhaust system is all put together
4-new spark plugs (gap at .035")
5-new NAPA wires
6-new NAPA distributor cap
7-new NAPA rotor
8-new fuel pump late last summer
9-carb cleaned, adjusted 2 years ago(????culprit????)

I've asked a couple friends, they are saying to have shop check timing, intake leak, check valve timing. It leaks around valve covers, so needs new gaskets/seals.

any other ideas?

Thanks

 

[sawinredneck]

Check the plug wires for fireing order. It sounds out of time to me.

 

[Work Saw Collector]

IMO rebuild carb with new accelerator pump and reset timeing

 

[TRI955]

Maybe a burnt valve?? Just a guess.....

 

[Fish]

timing chain

 

[stevejr33]

You have an ignition problem some ware. Do you have a spare ignition box that mounts on the fire wall. try that. barrow one if you don't have one because you can't return electrical parts. it could be the coil is worn and over heating also.

 

[brokenbudget]

timing chain

yup. weakest part of those old 318's
remove the dist. cap, and have somebody with a strong pair of hands rotate the crank (use the front pully) back and forth to see how much slack is in the chain. if you can move the crank more than say a couple of degrees either way without the distributer moving, the chain and gears need to be replaced.
cheap and easy fix really.

 

[TDunk]

yup. weakest part of those old 318's
remove the dist. cap, and have somebody with a strong pair of hands rotate the crank (use the front pully) back and forth to see how much slack is in the chain. if you can move the crank more than say a couple of degrees either way without the distributer moving, the chain and gears need to be replaced.
cheap and easy fix really.

Yup. Do that and put a timing light on it too, if it bounces around that's usually a tell tail sign that the chain is worn too. Also the ignition control modules have a bad habit of going bad ALOT, but they ussually just quit running. First thing i'd do is take your gas cap off and shoot some shop air back through the fuel line. Alot of the older vehicals had a "sock" on the other end of the fuel line in the tank as a filter, over 30-40 years they tend to gum up and get plugged. That would explain why it runs fine at first and then as it starts starving for fuel causing a backfire and revving slow. But that's just me.

 

[TDunk]

Pull your fuel filter off too and make sure someone wasn't :censored:ing with you and put sugar in your gas tank too. Had and old international act like that and some one had put sugar in the fuel tanks. That stuff gums up everything.

 

[goatchin]

nobody has has access to the truck unless they've trespassed and gone around on the backside of our cowbarn with out us knowing haha-truck is not currently on the road.

the coil was one other thing that I was thinking of replacing but figured i would go cheapest to $$$. might be able to borrow one from a the shop i'll be prolly taking it to once i get it road-able.

we've already pushed air backwards in the line-no differance.

wireing order is correct.

have to try rotating the crank to check for slack-havent thought of doing it that way.

thanks for the help-i'll check or try everything yall have stated so far. keep the ideas coming

 

[fourfivefour]

Did you foul the plugs?
Very easily done with the manual choke if you don't know what your doing.

When is it back firing?
At idle?
Under load?
On decel?
Is it backfiring out the exhaust or carb?

Does it have a vacuum advance on the distributor, is it working?
Are all the vacuum lines connected.

 

[lugnut]

Like he said ,check timing.

 

[bullseye13]

how about bad lifters/wiped cam? Pushrod failure?

 

[fourfivefour]

how about bad lifters/wiped cam? Pushrod failure?

Would be noticeable on acceleration, more so under load.

 

[goatchin]

Did you foul the plugs?
Very easily done with the manual choke if you don't know what your doing.

When is it back firing?
At idle?
Under load?
On decel?
Is it backfiring out the exhaust or carb?

Does it have a vacuum advance on the distributor, is it working?
Are all the vacuum lines connected.

the old plugs looked to be a bit fouled but not terrible-new ones are fine. starts to back fire after 2.5 min-once it is warmed up and after the choke has been released. will back fire while idleing and decel-none under load, just cant get out of its own way. back fires out of the exaust-get some pretty good length flash/flame in the dark LOL.

no idea what the vacuum advance is. In the middle of the distributor cap there is a black plug/block deal....that it? Its a new dist. cap so no reason it should be bad.

to be honest i'm not that "into" these size of engines so i'm not sure where/what most lines are, but alot of them need to be replace b/c they're dry cracked pretty good, but all lines are connected to something haha.

----------------------------------------------------------------

I have zero clue on the lifters and cams. there is no pinging or rattling when its running.

If I cant figure out the problem then I'll get the truck to the shop so they can do their gig.


Thanks, keep'm coming

 

[rms61moparman]

Any valve train noise?
What do the plug wires look like?

Start it at night and open the hood in the dark. If fire is jumping you will be able to see it.

Pop the distributor cap and look around inside, any moisture, oil or excessive carbon build up on the terminals or rotor?

How many miles on that engine?

I believe you will find the problem to be electrical, however after you rule out ignition/electrical troubles, check the fuel pump pressure.
The pump may be fine but the actuating lobe on the cam in the smallblock mopars wears down and won't work the pump.
A 35.00 electric pump cures that.

But what do I know about Chrysler products?:biggrinbounce2:

 

[Biker Dude]

You have an ignition problem some ware. Do you have a spare ignition box that mounts on the fire wall. try that. barrow one if you don't have one because you can't return electrical parts. it could be the coil is worn and over heating also.

I'm going to agree on this one. Either the ignition module (gold box on firewall with three wire connector) is failing or the pick-up coil in the distributor is bad. I have a friend with an 85 1 ton 318 that showed exactly the same symptoms. He replaced the ignition module, it worked great for 2 days and then burnt out. He replaced the pick-up coil in the distributor and the module again and solved the problem. The old pick-up coil had too much resistance and fried the new ignition module.

 

[Mama Tried]

Either timing or carb. sounds like too much fuel with the backfiring
If backfire threw exhaust its rich or timing is off
if backfire threw intake its lean or timing is off

 

[TDunk]

I'm going to agree on this one. Either the ignition module (gold box on firewall with three wire connector) is failing or the pick-up coil in the distributor is bad. I have a friend with an 85 1 ton 318 that showed exactly the same symptoms. He replaced the ignition module, it worked great for 2 days and then burnt out. He replaced the pick-up coil in the distributor and the module again and solved the problem. The old pick-up coil had too much resistance and fried the new ignition module.

This is why i hate old electronic ignitions, 9 times out of 10, they just quit. But that other 10% can make you pull your hair out trying to figure it out. The only thing that makes me think it might NOT be and ignition issue is that the truck acts up every time, after the same amount of time. Typically an electronic ignition issue will either not start at all one time, and run fine the next time etc......... but not start running like cr@p after 2.5 min. every time. BUT there are exceptions to every rule. Good luck.

 

[propliner]

I had a '78 at one time that often ran like crap. If it has the Lean Burn computer mounted to the air filter housing, that should be your first suspect. This lousy electronic attemp at running an engine leaner than it should be run was a miserable failure. Quite often they ran too lean and burned up valves as well. Also, they caused a terrible idle and black smoke to occur at random.

If you have the lean burn computer on your air filter housing, you can try swapping one from another engine. It should be from the same year and engine size and have the same number of pins on the two plugs. Also, you will want to do a compression check to see that all your exhaust valves are in proper working order. If after changing the computer, it runs somewhat better, consider installing the older points-style ignition and standard carb. I know there was a mod at one time for this but it may no longer exist.