mkatts

I am cruising down the interstate at 70 mph. The engine cuts out for a split second, the doors unlock and lock, the gauges drop and come back. The thing is, once I dropped down to about 50 mph, it was fine. I went up to 70 and it started doing it again. Odd that it's fine around town but when I get on the interstate up to 70 it freaks out.
Dealer has replaced the PCM, the accelerator module and the ignition switch. Also ran all TSB's anout grounds and marginal connections.
Any ideas?

Slammed

Fuel pump ?? maybe even the gas cap causing vapor lock or sumthing how about the coils ??

sorry just shooting ideas

RonH

I know you say you did some checking on connections, but it sounds like a momentary loss of power, like a battery connection. Maybe the engine end of the battery cable or one or more of the engine ground straps is loose/dirty, etc. and engine movement when you accelerate causes it to lose connection.

misonido

I agree with what RonH says, I'd check the connections at the starter as well! Had a similar issue with a 454 motor on our old motorhome and it was power wire at starter.

mkatts

Thanks for the input. I and the dealer have checked all power and ground cables we could find.
The dealer tech was riding shotgun with a scanner connected while it was cutting out and he sees a momentary loss of communication with the PCM when it cuts out. It through a cde one time about loss of communication between the accelerator module and the PCM. That is why they replaced that module. No luck. Then when he saw the loss of comm between the scanner and PCM, he thought it was the PCM. so he replaced that. Still no luck. So he tried the ignition switch. Still no luck. Cables are tight and clean. New batt and terminals. Term at the started are clean. There is a pigtail that comes off the batt into the fuse block right behind the batt. That connection is clean. The + cable goes down to a junction box just below the alternator where a smaller cable comes off the block up to the alternator. Those connections are all clean and tight.
I wouldn't think it'd be the fuel pumo, becasue I don't think the guages would freak out like they do.Plus the doors unlocking and locking.

shawnvw

Have you check the main ground strap at the front frame just behind the bumper? It is on the left side. these truck are notorious for have a bad connection there. I have seen problems in these trucks with only 3000km on it.
That spot had a cable directly form the battery, and is the main ground point for the body

Slammed

no this is a computer issue because he is loseing comunication with the pcm so hmmm what the heck could it be

mkatts

Also I failed to mention in my original post that once the truck warms up, it's fine. And it has never done it when the outside temperature is above 40*. Also around town, going under 50mph, over RR tracks, speed bumps, pot holes whatever, it NEVER dies. Only on the highway above 50mph. I step on the pedal and it stalls out. If I hold the pedal at the point where it stalls, it will not increase in speed after the engine recovers it will stay about 50. If I let off the pedal and ease it back down, I can eventually get it back up to 70 or so. Also once it starts messing up, cruise control no longer works. If I pull over, turn off the engine and restart it, cruise will work fine and the truck will work fine from then on out.

Slammed

hmm what about the throttle body ??

mkatts

Anyway to really test it?