In the last day I started to have a very odd problem I cannot find the cause of...

Here's the deal: While driving at any speed above 40MPH if I take my foot off of the accelerator and coast, then press the accelerator again, the truck will stumble/ping - spark knock three times and then run smoothly again. The truck runs flawlessly otherwise. Idles smooth, has great power, and does not miss/knock below 40MPH. It does this every single time I drive it. It also only does this when the truck gets warmed up and never does it cold. It's a 5.2L.

The truck had a full tune up about 250 miles ago. I replaced the TPS sensor, MAP sensor, and checked cleaned the IAC. Everything seems to check out and there are no CEL lights, or stored codes. I re-checked all of the wires, plugs cap/rotor and everything looks new and I don't see any problems anywhere. I did not replace the crank sensor yet, not sure if that's the problem or not cause that's within spec also. I did a bunch of searches and didn't really see anything the matched the problem I am having. I'm hoping there is something I'm missing that someone could point me in the right direction.

Thanks in advance for any pointers.

 

Test the TPS when hot. Did it do the same thing before changing all that??

 

Will do. Occasionally it would, but now it's very consistent. It's worse now after after the tune up than it ever was before.

 

I checked the TPS sensor after driving for an hour and it checked out perfectly fine. I am going to replace the crank and speed sensor next. I watched it very closely the other day. Literally as soon as it gets over 40MPH is when it acts up. At 39MPH and below, it runs perfectly. I hate to keep throwing parts at it, but at least they are not expensive parts.

Any chance it could be something in the distributor electronics?

 

Sensor in the dist is cam position. Has nothing to do with ignition, just deals with what injector to fire when.

Are you getting any misfire codes? Any pending??

 

OK, Thanks.

No codes at all. So it seems as far as the ECU is concerned everything is good, even when the misses/knocks happen. I also looked around for any shorted wires, missing ground loops, etc. Everything looks great.... It's really odd to say the least.

 

What plug wires did you get? Are they routed per the TSB? (look in the faq section for that.)

 

The last tune up I did I used a full Accel kit that included everything. I think the wires are 8.8MM. I'll look at them again to be sure. Yes, I routed them exactly as the TSB stated. They were painfully wrong at first, which I corrected as soon as I saw the TSB while doing research for this issue.

 

Just out of idle curiosity, does the trans downshift when you step on the gas again? This may be as simple as a TV cable adjustment.

 

No, it stays in O/D with the converter locked. When i press the accelerator again it's just a slight pedal pressure kind of like to maintain speed.