Trying to diagnose a new issue that has developed since performing a complete tune-up on my 89k mile '03 with the V10... Bare in mind there were NO issues before any of this work, I just did it based on mileage.

I replaced all plugs and boots, with the plugs gapped to 0.054". I put in a new fuel filter. I cleaned the throttle body and the MAF with CRC brand cleaners.

As soon as I fired it up for the first time, I knew something was amiss because I now have an idle surge, but only when the A/C is on (defrost or true A/C). Also, I now have a ping under HARD acceleration. Finally, I have greatly reduced towing power, as it will NOT hold OD on even the slightest incline with a trailer on, and my mileage has plummeted from roughly 11mpg down to below 7mpg...

Where do I start?????

 

Checked the fuel pressure:

* 30psi at idle
* 40psi with vacuum line removed from FPR (to simulate WOT)

When I shut the truck down, the fuel pressure slowly rises up to ~37psi after several minutes and holds steady.

Based on the above, I am fairly certain I can rule out fuel delivery issues?

 

I'm dealing with a similar issue, I just bought the truck, so I have no history on how long it's been pinging. I read a lot of topics about it and decided to change the cat, it made a huge difference, pinging is now barely noticeable. Don't know if that was the whole problem, but the original cat was at least partially plugged. I'm still looking into other possibilities that could contribute to it, but I'm happy with the performance now compared to the original cat.

Check out this thread, it's a long read, but read it all, it should cover just about every issue that may cause your problem!!

 

I built an exhaust pressure gauge gizmo and it never registered above 0.5psi, so I don't think the cat is my problem... I'd LOVE for it to have been, not because I want to buy a new one, but at least I would have found a legitimate problem!

 

Was the Map cleaner you used state that it was to be used on these sensors? (a special spray cleaner is made for this purpose). Did you install the same OEM spark plug?