04-FX4

So I was driving home yesterday and coming around a upward curve i gave it a little gas and my truck starting shaking like the tranny was about to fall off or something, so I let off and then got back on it and it shifted and went on its happy way. However the check engine light came on. So i went to Oreilly's to get it looked at and code came to be P0171, Bank 1 Lean. I have a K&N filter and did the gotts mod. I am going to change out the gotts and go stock, and also clean the MAF sensor to see if these things help at all. what else could be my issue. I had the exhaust manifold gaskets replaced about 3 months ago, just fyi.

Also, in the mornings (cold) i will go to start it up and it will turn over but almost die and then like 1 second later it will rev right up and run normal. Do i have someting wrong with getting fuel to the motor, fuel pump, filter etc...? Thanks for all the help!

otto457

Keep the Gotts, it's not your issue. Check your FPDM to start with and cleaning the MAF is always a good idea.

kanga2311

Try tightening you exhaust manifold bolts again. They may not have seated properly the first time.

04-FX4

So i cleaned the MAF and double checked all my manifold bolts. I disconnected battery for a couple hours to delete code, and after a full week of driving, it decided to come back on. In certain RPM (1400-1550) range if i slowly press the gas the truck starts shaking real bad. But if i let go, or give it more gas to shift it will stop shaking and start running normal. Also, if i gas it to pass someone on highway the check engine light will start blinking and then go back to solid. I am going to look at my FPDM and replace if needed, and i was thinking of replacing the VCT solenoid if it would help. Any thoughts on what else i can do or check? Thanks

techrep

iTrader: (1)

Sounds like a mis-fire...(blinking CEL)

VTX1800N1

Clean the throttle body.

When were the plugs last changed? Coils ever replaced? Miles on the engine?

04-FX4

throttle body was cleaned a couple months ago. Plugs i dont think have been changed, or coils. Just bought it about 7 months ago. Has right over 105k

VTX1800N1

Definitely change the plugs. If it were my truck I would put new coils on as well.

04-FX4

Wonderful...I was afraid that was going to be the problem. Would this cause the CEL to come on for being too lean (P0171)? Or is this another problem?

VTX1800N1

Yes, but several things can cause that. A flashing CEL means the PCM is detecting a misfire in real time. Don't continue to drive if it keeps flashing because the unburned fuel (assuming it's not a failed closed or disconnected injector) will damage the cat eventually. A failed open injector can cause a worse misfire because too much fuel gets in the cylinder. That will very quickly destroy a cat and could hydrolock the cylinder, bending rods and requiring a new engine. If the misfire is repeated enough, it will set a hard code and your CEL will light and stay on until the problem is no longer detected for a specific number of cycles or until the code is reset.

A spark or coil that is weak will show up most at full throttle/high torque situations. Cylinder pressures in these conditions are higher, and so it's more difficult to light off the spark. It makes sense then that it's a coil or plug or both that are on the way out, given the conditions that you noticed the problem and your mileage.