I have an 89 F-150 with the I6 engine and 5 speed. It has strange problems. The symptoms are that if the truck idles for a while (about 15 to 30 minutes) it starts to buck and sputter and when you depress the gas it sputters and boggs to the point of stalling. When dirivng for a while (about 15 to 30 minutes) it starts to buck and sputter and when you step on the gas it will sputtter and bog. It even quits entirely while driving down the road. When it quits running, either from idle or on the road, the battery is unable to turn over the engine like the engine is very hot. But it does not smell real hot if you know what I mean. If you wait for a while (until it is cool?) it starts right up with no problem and after a while (aboout 15 to 30 minutes) the problems start all over again.

The temperature gauge never comes above the half-way mark and typically stays slightly below the half way-mark. In other words it seems to be running a bit cool. That is, if the temp gauge is reading right. It has a mechanical oil pressure gauge that shows a solid 50 pounds when starting cold and when warm it is rock steady at 40 pounds at any rpm.

My backyard mechanic friend and I both concluded it was the cats that were clogged. So, we pulled the O2 sensor, started it and let it idle. Same problem.

We put in a new thermostat (in case the old one was shot and the temp gauge was not reading right). Started her up. let her idle and got the same symptoms.

Any ideas out there? We are going nutz!

Thanks

 

When problem starts, is the egr valve hot at idle? What is the fuel pressure? The test fitting is in the back of the motor behind the upper intake on the pass side. Looks like a tire valve on the fuel rail. Hard to see. Pressure for the six cyl should be about 60 psi. You could have a bad fuel pump. I would look into the egr first. Make sure it isn't stuck open, or accidentally commanded on at idle. I.E. the egr regulator bad. If the valve is hot, check for vacuum on the green vacuum line on the valve. If it has vacuum, the regulator is bad. Just trace the green line to the regulator. Hard to figure em out by reading the problem.

Robbie