trying to figure out what's wrong with my truck (97 cummins). it seems to run fine at or under about 1/2 throttle, starts fine, idles fine, no smoke. when it needs more than that, ie: in a higher gear going up hill, the rpm's and power just start to drop off until i downshift into a gear low enough that it will go with only 1/2 throttle or less. i have checked the fuel lines, throttle linkage, and intercooler boots and there are no visible problems, but don't have the tools to run a fuel pressure test. from the research i've done, it seems to be one or more of the follwing fuel system components. the commentary is from a mechanic i know.

""Lift pump- can only deliver enough fuel for low
> throttle operation?

Cheap, fairly easy to replace. Most need it by 100k
anyway (especially with running bio)

> Pre-filter/heater - leaking air into fuel and/or
> dirty filter screen?

Pre filter, maybe. Leaks, probably not (would have to
be a BIG leak as it should be pos fuel press and lift
pump would pull enough (~7psi) to see a squirt.

> In-tank intake filter screen -dirty

Probably not. I've pulled the sender units and never
seen enough crap to clog it.

> Fuel shutoff solenoid

Probably not unless the diaphragm came apart inside
the IP. Replacement is about $60 (includes parts/labor
- I get the genuine Bosch SO's cheap)

> Fuel overflow valve

Forget that. That's post flow anyway. Slight chance it
could be bleeding off press pre-IP, but doubtful.""



anyone have any other ideas or know if i can add or eliminate options?

many thanks

 

fuel filter? air filter? I know they're obvious, but sometimes a guy forgets the easy targets first

 

The overflow valve is the one part that wears out more than any other on a 12 valve.
Unless you have access to a fuel pressure gauge setup just replace the overflow valve
You won't find a better price than here.

Precision Diesel Injection and Turbo Inc.
Marty Tompkins
888-734-7349
$35 + $7 shipping and handling.

 

thanks guys,
i should have mentioned that i did change the fuel filter and clean the air filter.
i will try a new ov.