Hello,
The truck is a 2000 Trailhead 3.0L V6 Flex Fuel. It's been a great truck. I now have about 165,000mi on it and have a few issues. First, the serpentine belt actually slips off everytime I go through a puddle! I'm pretty sure I need to replace the belt tensioner...was really just wondering if anyone else has experienced this. The main problem though, is that the truck has been missing at idle and there is a very noticeable "flat spot" during acceleration. I replaced the plugs and wires and noticed improvement, but it's not right by a long shot. The check engine light is on and the codes are I think 171 and 174, system lean. I cleaned the MAF sensor. I also looked for the EPDwhatever sensor, but can't seem to find one--just an EGR. Does this model have one? I unplugged the air idle sensor (?) with the engine running and the engine stopped, so I'm guessing that works. Should I replace the EGR, or is there a way to test it? Could the acceleration problem be due to a bad coil pack affecting timing? I checked for vacuum leaks with carb cleaner and didn't find any but will check again. Thanks for any help you can offer!

 

If your not certain about the codes, most auoparts stores will scan the computer for trouble codes at no cost, then post All code Numbers as they can offer up good trouble shooting clues.

All that said, it kinda sounds like you may have a flat spot in the TPS sensor, such that the compter does't sense its/the throttle has moved at mid point, so the air/fuel ratio goes lean in that spot. So maybe check the TPS resistance range wth a good quality analog meter, lookng for a midrange dead spot.

 

Thanks for the reply. I should back up a little and tell you that it began running a little rough a few months ago. I put new Motorcraft plugs in and installed new wires and that seemed to help. Today, however, things are worse. Rather than just a flat spot during acceleration, there is a constant miss from idle all through therpm range. The miss is so noticeable that it actually shakes the truck--I can feel it in the steering wheel. It hasn't stalled out, but it feels like it could at any time when I'm stopped. Underway, there a definite lack of power.

I had the codes read at Autozone again and they came up as follows: 171 System adaptive fuel too lean (Bank 1); 174 System adaptive fuel too lean (Bank 2); P0301 Misfire at cylinder 1 detected.

1. Replaced plugs and wires
2. Replaced air filter
3. Replaced fuel filter
4. Replaced MAF sensor (had just cleaned it in the past)
5. Replaced coil pack
6. Replaced EGR pressure differential sensor
7. Made sure none of the new wires was in contact with exhaust manifold
8. Checked for vacuum leaks around intake manifold with carb cleaner

My next step is to get the injectors cleaned, The Ford dealer wants $250 for this and they don't flow test them. If I had an injector problem, would it throw a code? Finally, I priced a throttle position sensor (~$25). I know you suspected that, but now I have the problem at all rpms...any other ideas/advice? I'm beginning to worry about the condition of my valves. A friend has a compression tester I could use...

 

Sounds like a fuel injector is bad/plugged to me... From the looks of it, it's the one for cylinder #1...

 

Listen to the cyl 1 fuel injector to determine if it sounds different than the others.

Adaptive fuel on both banks too lean could be a number of things, from an upstream vacuum leak, low fuel pressure, or low volume delivery over time, lazy O2 sensors, dirty MAF sensor, dirty fuel injectors & the list goes on & on, so you need to do some more diagnostcs, get a positive result, then replace the troubled part. Don't throw more parts at the problem until you get a positive trouble shooting result.

I'd maybe begin with an inspection for a vacuum leak & do a fuel pressure test & post the result.

 

Have you ever replaced the O2 sensors on the truck. If they are gone or even or their way out, that may explain the lean running. If they have never been replaced, with the number of miles on the truck, this could very easily be part of the problem.

 

The misfire did turn out to be the #1 injector. She's running great now. Thanks everyone!

 

OK, good feedback on your fuel injector trouble shoot & repair & to hear all now seems well.