This one is making me crazy. 2002 F150 Sport 4.2L V6 Shortbed regular cab.

I've found some similiar postings but none that are a match for the trouble I'm having.

I'm having an issue where the engine randomly loses power.

One time, I started the engine and it stalled about 2 seconds later. This was the only time the engine actually died.

Yesterday, I started it and stepped on the gas pedal to rev it up a bit and nothing happened. The throttlebady opened and the idle stumbled a bit but the rpm didn't change much.

Usually what happens is that I reach the top of first second or third gear and the whole thing just bogs down. I push in the clutch to coast and work the gas pedal but get no climb in RPM for as much as 10 seconds. Then, the problem suddenly clears and everything is fine until it happens again. There is no pattern to when it happens as far as moving, stopped, high revs, low revs. It doesn't seem to do it when I'm at steady freeway speeds though.

When it happens in 1st gear its like slamming on the brakes.

So far, I've checked fuel pressure at idle. It was 30psi which is at the bottom end of spec. I haven't been able to have a fuel pressure guage attached when it happens. I've replaced the cam sensor. New fuel filter, super unleaded gas and B-12 chemtool fuel system cleaner.

Some of what I've read here suggest maybe the coil pack is an issue. Trouble is, the engine doesn't stumble like one cylinder isn't firing and it doesn't stall. It just drops to idle and won't do anything until it's damn good and ready.

On top of all this, it hasn't thrown a single code. No warning lights either. The guages stay put like nothing is wrong. I dont have a tach so I can't see what RPMS are really doing.

Thoughts appreciated.

Chris

 

Minor update. I hooked up the fuel pressure guage before I started it this morning. 30 psi to start. At first, I got normal revving when I stepped on the gas a bit. Then my problem showed up. Stepping on the gas made the engine cough, sputter and feel like it was going to stall (though it didn't) and the fuel pressure went up a bit like it should when the throttle is opened and engine vacuum drops.

So, I guess the fuel pump and pressure regulator are doing their jobs. I did notice that if I kept the pedal down a bit while it was sputtering, it would clear after a few seconds and then the RPMS would finally come up like normal. If I just let off the pedal completely it would take as much as 10-20 seconds to clear up on its own. At this point, I'm wondering if the throttle position sensor is intermittantly not working and causing my acceleration issues or if something strange is oing on with the IAT valve.

 

I put the multimeter on the TPS and went for a spin. When the problem showed up, the tps voltage signal was still present and increased/decreased as it should as I moved the pedal. So bad or intermittant TPS signal is out

 

Used the Multimeter to static test the IAC valve. Everything was normal there. I removed it and it was very clean inside.

Static tested the coil pack. Across the connector pins I got primary resistance readings that were slightly above the 0.3 - 1.0 ohms that my Chilton manual specifies. The second time I took readings, they all said 0.9 ohms.

When I measured the secondary resistance across companion sets, two were at the max reading end of acceptable resistance (11.5 Kohms) and one set was at 11.7 Kohms.

I could write off the slightly high readings to minor variance in my multimeter. What bothers me though is that all readings on the coil are right at the maximum allowable resistance. None of them are at the lower limits. I wonder if theis is telling me that the coil needs replacing.

 

I went ahead and installed a new coil, plugs and wires. After two test drives, the problem appears to be gone. I'll wait for a few days of problem free driving before celebrating though.

It does seem to be more powerful, idles more smoothly and the throttle response is crisper.