no power at low rpm

[DLang]

I've got a 84 military blazer that has developed a problem where most of the time it has no power below about 5-7 mph, once it gets reved up a bit, it performs well enough to deive on the freeway, but off the line it has no power. By no power, I mean that it can't climb a curb at full throttle, and doing a u-turn on a residential street with a high crown makes me think about having to shift to 4-low or be stuck.

Occasionaly, when it's cold, it will work just fine, but once it warms up again, it's back to no power.

Any suggestions as to what to try? i've had the timing checked and injectors replaced.

David Lang

[Dvldog8793]

Transmission....?

[DLang]

rebuilt a couple months before the problem started.

I'm getting ~17 mpg, if the transmission was having problems that was causing this sort of horrid drag on the engine, I would expect milage to really suffer.

Even when I have the truck in park and rev the engine, it doesn't rev very much.

[Dvldog8793]

Howdy
Sounds like a fuel issue. I would check the filter and lines first thing. Then the lift pump, then the injector pump. Just cause they have been replaced recently doesn't mean they haven't failed.
If the truck has original exhaust it is possible that the baffles have collapsed and is restricting. They came with some pretty big mufflers and also had a restrictive exhaust system(lots of bends) to start with.
Hope this helps...
Good luck

[DLang]

I've experienced fuel supply problems in the past (clogged filters and kinked hoses), that behavior was very different. In those cases the truck would run fine at low power levels, and 'top out' at higher speeds/throttle.

In this case, I'm seeing the opposite behavior, it works reasonably well at higher speeds, but barely moves at low speeds.

I would expect the same type of thing if it was an exhaust problem (i.e. works at low speeds/throttle and tops out early)

On another board the suggestion was made that the IP timing advance could be sticky and not working correctly. That at least sounds plausable as to why it works sometimes and not others, and why power is poor at low RPMs and works better at higher rpms (timing too advanced)

[Dvldog8793]

Howdy
does it rev freely in park?

[DLang]

it doesn't rev up as fast as my other blazer does, so i would say the problem is showing itself there as well.

starts sluggish, then picks up. It's harder to tell in park because the speed at which power kicks in is relativly low (somewhere under 10 mph in 1st gear), and with no load it still gets to that sort of speed pretty quickly.

[Dvldog8793]

I thought I read something similar a while back....
Check this out, might help
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=42745&highlight=low+power

[DmaxMaverick]

If this just started happening over a short period of time, I'd suspect the fuel quality or supply. Check the fuel lift pump. Open the bleeder at idle. It should provide a good flow and not stall or stumble. If you get no flow, or it dies, the fuel lift pump isn't pumping.

[Dieselfume1]

I'd suspect lift pump as well. Your IP may have just enough suction to provide fuel for idle, and low speed operation, and when you wind the engine out on the highway it may pull enough fuel from the tank to have decent power.

Lift pump as D-max mentioned would be my first target.

[DLang]

If this just started happening over a short period of time, I'd suspect the fuel quality or supply. Check the fuel lift pump. Open the bleeder at idle. It should provide a good flow and not stall or stumble. If you get no flow, or it dies, the fuel lift pump isn't pumping.

The truck has had a longstanding issue where it seems to loose power on long (3+ hours at full freeway speeds) drives, but recovered after a short (10 min or so) pause.

This problem did start suddenly, and after I filled up on a trip at a station I had never used before, but the problem has persisted through several additional tanks worth of fuel. This problem started in July on my daily driver.

I would have though that the lift pump haivng problems would cause more problems at high speed than at low speed

[Dieselfume1]

If you think you might have gotten a bad load of fuel, it would be easy to drop the tank and check the sock on the pickup tube. might be plugged up pretty good.