4.0 engine problem

[fes007]

I have a 96 4.0 liter OBDII ranger. For some reason it has been running really rough at idle to the point where it sometimes stalls out and dies. It idles at times around 400 to 500 rpm but very rough. The engine has a tendency to lose power after about ten minutes of driving especially when it is cold. I can start the engine back up and the problem stops. I have replaced the MAF, fuel pump, fuel filter and the air filter. I don't have a scanner and it is not throwing any codes. Since I have put the new air filter in it seems to be running rougher. It is almost like it has a miss to it. Sometimes the idle will surge at a stop hovering from less than 500 to a 1000 rpm. The fuel pressure is fine but this is really starting to stump me. Someone was saying it might be the Throttle positioning sensor but I think it might be the Idle Air Control Valve. Any help would be appreciated.

 

[michowski]

Have you checked your timing recently?

 

[fes007]

It has to be a sensor because it resets itself whenver I turn the engine off and restart it.

 

[07rangersport]

sounds like a vacuum leak to me.

 

[Simple_serf]

So, check the TPS and the IAC...they are both right there in front.

I would still check for vac leaks...... don't forget the EGR and EVAP systems.

Also, check ignition system.

It could very well be a crappy electrical connection.

 

[fes007]

I saw that i had a hose that became unattached when i replaced the air filter. I am still having a problem with a slightly rough idle and the engine still loses power about every ten minutes. I can floor the accelerator and I get all of the power back. I can shut the motor off and then restart it and the problem stops. It hasn't thrown a code for it either. Any thoughts?

 

[todd_351]

That's gotta be a vacuum leak. It can either be a vacuum hose or a bad intake manifold gasket. Take a look around for a vacuum hose that has come unplugged. That's the easy fix. If you don't find one then it's probably a gasket. To find a vacuum leak in the manifold you spray something (like carb cleaner or starting fluid) around the gasket points while the engine is running to see if the engine idles differently (carb cleaner usually makes the engine slow down or starting fluid will make the engine idle higher). When you find a spot where this happens that's where the leak is.

I have a 99 4 liter and I hear the gasket between the upper and lower intake manifold is notorious for developing this problem.

It makes sense that your engine runs good if you floor it. When the throttle is wide open the vacuum is low so the engine doesn't suck enough outside air through the bad gasket. When the throttle is closed the vacuum is high and the engine will suck air through the leak. This air has no gas and upsets the fuel mixture so the engine runs bad.

The hot vs. cold thing makes sense too because as the engine heats up things start to expand so your leak could open up or close down changing the problem.

 

[fes007]

it shouldn't be a intake gasket. It has done it before on occasion when it is cold. I might just go ahead and replace the IAC. I have already replaced the MAF, fuel pump and fuel filter. No codes were thrown. Like I said, i can turn the engine off and then back on and the problem stops. It seems to happen in ten to fifteen minute intervals. Strange.

 

[TayCo 7s]

IAC change it get one at autozone

 

[fes007]

Changed the IAC but still have the problem. I am going to check the OHM's on the TPS to see if there is a flat spot in the resistance. For some reason whatever it is it does not throw a code and it resets itself when i restart the engine.

 

[Simple_serf]

See, that's why I said to CHECK IT!

Don't just throw parts at a problem. Get a book, and follow the proceedures in it! Book will also have the proper testing proceedures for sensors, and will show what they should read when you test them.

Honestly, It would probably be cheapest just to take it to a shop, have them diagnose it, and then you fix it. It would have been cheaper than just replacing stuff.

 

[Bird]

a clogged cat will give many of the same symptoms........................

 

[MAKG]

a clogged cat will give many of the same symptoms........................

But it won't give you "full power" back at WOT.

There are, however, a gazillion things that might. Ranging from a vacuum leak to a hosed computer to a loose battery cable.

 

[Bird]

But it won't give you "full power" back at WOT.

There are, however, a gazillion things that might. Ranging from a vacuum leak to a hosed computer to a loose battery cable.

Agree that there are many other things that could cause the problems, but exhaust restrictions can also have much greater effect on closed loop operation through the O2 sensors and less effect on open loop (WOT) where the O2 sensors are not in the loop - giving the impression that WOT is OK.

As you've said before - a thorough diagnoses would be in order. Too many things can affect closed loop operation.

Bird

 

[almostclueless]

Consider tightening the lower intake to cylinder head bolts....the 4.0 has a rep for intake gasket leaks.


BTW, MAKG, does the 96 have a FPR?


And to the OP, when it starts running rough, is there any exhaust smoke? What do the plugs look like?