Higher-rev hesitation

[winemaker]

Howdy folks. I run about 6 hours up country on the long weekends and I had a local shop rebuild my tranny and install a new clutch (single mass flywheel) just before my last trip. While he was at it I had him change the oil and the fuel filters, both stock and Racor.

On my way up the Coquihalla Highway, which is a major-league hilly route, I occassionally have to rev out to nearly 3000 before pulling 4th. Never before had this happened, but it happened a few times on this trip: it hesitates near the top of my revs like it's going up against a rev limiter, or like it's not getting fuel for some other reason.

It's not a major concern and the truck runs great (way better fuel efficiency since the new trans/clutch), but I wouldn't mind knowing what could be the issue. My buddy suggested that perhaps not all the air is out of the fuel system after the filter changes. Any thoughts?

Brett

[Robyn]

Lift pump may be on its way down the toilet.
With new filters recently that should be ok.
Might want to check the flow from the lift pump.
Could possibly be the sock in the tank getting skanked up some too and restricting things.

Robyn

[winemaker]

Thanks Robyn. You know, now that you mention the lift pump, here's another symptom:
I had a new IP installed last September. Shortly after that I was coming off a bridge, cruising at about 100kmh, then slowed for the exit. As I down shifted to 4th with my foot off the throttle, the engine cut out. This sounds lift-pumpish, right?
Thanks again. Brett

[Robyn]

Not really. A lift pump that is dyeing will generally show up as poor power and or stumbling when power is demanded.
This could also be the signs of a PMD that is getting ready to go south.
Any codes showing??

[winemaker]

No engine light on, but I haven't checked for codes. The PMD was brand new with the IP.

[Robyn]

Here is a quick trick to test the lift pump
Plug a good new piece of hose onto the water drain up front and hook it to a fuel pressure gauge, make the hose long enough that you can snake it up by the wipers and watch it while you drive. You should see a few pounds even when running.
Even if its only 1 to 3 psi your fine when the engine is working. If it drops off to zero you need a pump or the tank sock is plugged.

Oh once you have the gauge hooked up, turn on the drain valve. :eek:

Did that once and drove off without opening the valve. :rolleyes:

let us know

Robyn

[winemaker]

Thanks again!
I'm loading up the truck as soon as I'm off work today and I'm gone for a week and a half, so I'll have to look at it when I get back. Have a fine week!
Brett