I've been having a backfiring issue with my truck lately. I'm hoping someone can diagnose it. It mostly happenes when changing gears from 2nd to third. Its not a loud backfire, but almost a quiet ticking, like firecrackers. It'll do it like 10-15 times real fast and it sounds like its up front and in the headers rather than in the muffler. Once the truck is back in gear and running it doesnt do it anymore. If I dump the clutch without changing gears it won't do it dont think this is because my timing is too far advanced, I just retarded it last week to reduce a high idle speed. Any ideas what this could be? Any help is appreciated. Thanks.

Brendan
1977 Ford F250 4x4
351M / 4-Speed
33" BFG Tires
www.angelfire.com/ma4/1977fordf250

 

did you do a tune up latley maybe a crossed wire ford has a couple different firing orders depending what motor you have could be a bad timing set , bad valve sounds like to me how many miles on motor im going to say valve get a second opion but i bet the head is bad if it where a timing problem it would do it all the time
lol bad 78 f 250

 

Well the motor is a used motor. It tested OK with a compression test before I bought it. I basically did a tune up on it when it went in, new plugs wires, etc. And I re-did the firing order myself after that I double checked it and had my friend who is a Ford mechanic double check it again. So I dont think it is any of those issues. I'm thinking maybe the exhaust now that someone said it. I couldn't get the exhaust manifolds off this engine, so I had them torched off, and then I drilled out all the bolts. On the drivers side there was one cylinder in which I couldn't get nice new threads. On one of them the tap just wouldn't start, so I drilled up to the next size and tried to tap the next bigger size, I still could't get a tap started. Then on the other side I broke a titanium bit of in the hole. So there is one cylinder that has no bolts holding the header on. Do you think this could be causing it?

Brendan

 

If the exhast manifold isnt leaking out the gasket, or seam where it meets the head, i dont think it would cause the problem. If it is leaking, maybe that cylinder is running hotter, and going lean on deceleration. How about timing chain? It could be that when you get off the gas, it slackens and causes timing problems. If you have an airpump like previously said, that would defintately be the first place i would look. Check for intake manifold leaks such as the base of the carb,hoses or manifold gasket. Double check your mixture too. Basically back firing is cause by excssive oxygen igniting the hydrocarbons in the exhaust. Sort of like blowing on a fire to get it to start.. HOpe you can find the problem..

 

>Well the motor is a used motor. It tested OK with a
>compression test before I bought it. I basically did a tune
>up on it when it went in, new plugs wires, etc. And I
>re-did the firing order myself after that I double checked
>it and had my friend who is a Ford mechanic double check it
>again. So I dont think it is any of those issues. I'm
>thinking maybe the exhaust now that someone said it. I
>couldn't get the exhaust manifolds off this engine, so I had
>them torched off, and then I drilled out all the bolts. On
>the drivers side there was one cylinder in which I couldn't
>get nice new threads. On one of them the tap just wouldn't
>start, so I drilled up to the next size and tried to tap the
>next bigger size, I still could't get a tap started. Then
>on the other side I broke a titanium bit of in the hole. So
>there is one cylinder that has no bolts holding the header
>on. Do you think this could be causing it?
>
>Brendan


+++++++++++++++++++++

I don't think the problem is anything you've mentioned so far; if it was miswired it would have a constant serious miss. The firing order sequence is likely cast into the top of the intake manifold -- is on my M motor.

I'd take a hard look at the carburetor -- my guess is that something like the power valve is ruptured [below the float] -- and while you have the carb off, replace the gaskets above and below the egr adapter.

That egr adapter gasket can rupture to the outside, and it sounds just like an exhaust manifold gasket leak [which is in fact what it is] -- and I guess under the right combination of circumstances might let raw air into the exhaust system.

good luck,
bb

 

What about with a non-EGR system? Would there be the same iissues?

Brendan

 

B,
This is an ignition problem. You've got a bad plug wire or bad plug. Maybe you cracked a plug during installation. Grab each one and shake them. If you feel a click or a little play, you've found your culprit.
A timing chain would give you fits from start up.
A crossed wire is more likely to come through the intake.
What about an exhaust leak at the manifold?
Look for black carbon staining at the block.
Decreased pressure in the exhaust could allow a leak to backfire. This would occur during a shift.
My Way is the Highway,
KingFisher

 

i have the same truck with the same motor and i had the same problem a couple years ago.. i had a fresh motor rebuild with new everything and after hours on this very site and hours in the garage someone suggested a bad plug or wire and by golly that was it.. $1.29 later she ran like a top and still does.. almost like "ve' jadu" all over again..

cheers

99 f250 pstroke 4x4
77 f250 4x4 351m
67 f250 4x4 390