00 XLT 4.6 4x4 135k miles - New problem, on accelerating, truck hesitates for a couple of seconds before rpm's pick up. There is no stumble or bogging. It feels like I'm not giving it any throttle at all. And then it kicks in and takes off. It does this from a stop at idle, or at a steady cruise. Its an intermittent problem. No CEL. Air filter and fuel filter are about 3 months old. Haven't done any work to it since. Also, when there is less than a 1/4 tank of fuel, truck sometimes stumbles slightly off idle. Any suggestions? Fuel pump starting to go?

 

Check fuel pressure. Should be about 35 psi.
A faulty TPS could affect acceleration as is also affects fuel delivery to add additional fuel for sudden throttle applications. This is done by the PCM as it monitors the rate of change from the TPS output signal.
Check for a plugup or harness seating issue.
A look at live data with a Scanner can tell a lot about what's going on if the data is able to be interpreted by the user.
As of now you don't have anything positive to go on.

 

Ok, I bought a fuel gauge and hooked it up to the test port on the pass side fuel rail. With key "on" I have 36 psi. With engine running I have 33 psi. I checked the harness going into the tps. It's nice and snug. So does this rule out the fuel pump?

 

Fuel pressure is good.
If the engine still bogs at acceleration,
an ignition timing advance check, performance of the Mass Air signal and other live data observations made to detect abnormal operation.
This requires A Scanner and ability to interpret the data presented.
The program was designed to allow the ability for interactive diagnostics far beyond just code presentation.
Normally the most common consumer grade Scanners will only allow live data observation.
High end and dealer instruments allow interactive system control that normally is not needed for most fault discovery.

Good luck.

 

Well I took it for a ride yesterday and I got about a mile from the house when i lost forward gears. I had to drive home in reverse. Thankfully, I got a 6 month warranty with the truck. I had them come get it. Waiting to see what the problem is.

 

Shop is replacing transmission under warranty. They didn't say exactly what failed in the transmission. I'm hoping my initial complaint was related to the tranny. We'll see.

 

OK, got tranny replaced and started having the same issue, which then turned into stumbling at idle and part throttle. Then quickly escalated to stumbling at all RPM's. Got a SES light and P0308 too many misfires cylinder #8. Pulled the coil pack and I could hear and feel something inside moving around like something was broken. I replaced the coil pack and reset the SES. Problem fixed.