I am working on a 1997 f150 with a 4.2 and it has no power,it back fires when i let go of the gas. Does anyone have a clue of whats going on.

 

it almost sounds like the plug wires are mixed up or the timing needs adjusted, may not be the problem but its something to check

 

I checked everything.I wonder if it is the computer that`s gone bad.

 

First of all, it might help to list what you have done, then somebody will probably have a thing or two to add to your list. Give us some details, how many miles, what you changed, didn't change, checked,didn't check.

 

I checked the timing,spark plugs,spark plug wires,the exhaust system,coil pack,computer,intake gasket,gas pressure,injectors,02 sensors.It seems like the timing is off ,but it`s ok.The truck is a 1997 F150 it has around 232000km on it.

 

TPS bad?
I don't know but it might explain the symptoms. Are you able to rev the motor to high rpms under no-load?

Did this occur suddenly or just get gradually worse over time?
ANY work done just prior to onset of symptoms?

 

We changed the exhaust manifold gaskets,it started after that.It seems to be getting worst everyday now.When i snap on the throttle it the rpm goes up but slowly.

 

What lead to having to change the exhaust manifold gaskets?

An exhaust restriction can cause what you are describing. Any chance something is not right with the gaskets, or something is clogging an exhaust manifold?

And you are certain the plug wires are on the right plugs?

 

The exhaust manifold was leaking. we took the exhaust off ,still the same no power .Yes the plug wires are right.

 

So prior to replacing the exhaust manifold gasket it was running fine, just leaking at the exhaust manifold - correct?

Will it rev up freely in neutral?

Were both sides (gaskets) replaced, or just one?

Are you losing any coolant?

 

Could it be that same problem that came up quite awhile ago. I think it was, Scrimbaby, or something like that. The broken piece around/behind the harmonic balancer. I don't know what it is without looking for that thread. Didn't she have no power at all and changed out around $1000 worth of parts before finding it. I know he mentioned it started after exhaust work, but maybe that's a coinkydink...er coincidence.

I think the thread was called "Bad loss of power".........

Rich

 

Thanks a lot. Found the problem,it was the harmoic balancer that was broke.

 

Good news! (I guess ??)

Thanks for the help Rich. I had forgotten about that thread. Good work!

 

Sure, no problem.

Glad you got it fixed mecanic. What exactly was broken? As best as I remember, there is a "key" or something that shears?????


Rich

 

There is a steel sleave for the crank seal on the damper ,the damper broke at the end of that sleave.