I'm running the stock $32 Carter pump mounted on the filter housing, I know, I know it's not an ideal pump for the QC LWB truck but I just don't have the $400+ to do the upgrade at this time. Anyway what should the pressure be on the back side of the filter going to the IP? During cold weather the truck will ramp up to 1000 RPM but it stumbles almost like a misfire if it were a gasser. This causes it to drop back down to 750 RPM. The only way I can get around this is to use the idle up feature with a cruse control. The truck will still stumble but it stays on high idle. I was thinking maybe the pump was going out again but would like to find a gauge to check it like maybe this. http://www.harborfreight.com/automotive-motorcycle/diagnostics/fuel-injection-pump-tester-92699.html. I know the IP on the 03 and newer trucks will not be damaged by low fuel pressure unlike the older trucks, but I'm sure low pressure can't be good for it also. What things could I be damaging if the FP pressure is in fact low. Also if it's not low what else could cause this, it only does it when it's cold outside. Don

OEM pressure specs (from Bosch) are -5 to +15 psi, but most recommend staying above 2psi. Interesting on the stumble, I doubt its from a fuel issue. It could be any host of sensors, or dirty injectors. But I would start with verifying fuel psi numbers.

I'm running the stock $32 Carter pump mounted on the filter housing, I know, I know it's not an ideal pump for the QC LWB truck but I just don't have the $400+ to do the upgrade at this time. Anyway what should the pressure be on the back side of the filter going to the IP? During cold weather the truck will ramp up to 1000 RPM but it stumbles almost like a misfire if it were a gasser. This causes it to drop back down to 750 RPM. The only way I can get around this is to use the idle up feature with a cruse control. The truck will still stumble but it stays on high idle. I was thinking maybe the pump was going out again but would like to find a gauge to check it like maybe this. http://www.harborfreight.com/automotive-motorcycle/diagnostics/fuel-injection-pump-tester-92699.html. I know the IP on the 03 and newer trucks will not be damaged by low fuel pressure unlike the older trucks, but I'm sure low pressure can't be good for it also. What things could I be damaging if the FP pressure is in fact low. Also if it's not low what else could cause this, it only does it when it's cold outside. Don

10-15psi post filter is fine for an un-modified truck.......usually. Sounds like your Carter doesn't have the "guts" to push diesel thru your FF when it's cold outside!!!! Your last paragraph is not correct. If your LP seizes/freezes, the CP3 doesn't have the ability to pull fuel with that hard of a restriction and damage can occur. AH64ID confirmed this to me last August. I had my LP quit "TOTALLY" on a trip down to KY due to a corroded wire. The pump didn't fail...........the electrical connection/flow did, thus the pump stopped pumping...........my CP3 was able to pull fuel thru the pump because the pump would still turn!!!!! If is seizes/freezes, it's not turning and impedes fuel flow!!!!! If your current pump is stressed by cold weather/fuel, IMHO, you're on borrowed time!! Don't mean to sound like a dickhead here; but, do you have the $$$$$ it'll cost to tow your truck home or somewhere if the LP freezes or fails???

Your last paragraph is not correct. If your LP seizes/freezes, the CP3 doesn't have the ability to pull fuel with that hard of a restriction and damage can occur. AH64ID confirmed this to me last August. I had my LP quit "TOTALLY" on a trip down to KY due to a corroded wire. The pump didn't fail...........the electrical connection/flow did, thus the pump stopped pumping...........my CP3 was able to pull fuel thru the pump because the pump would still turn!!!!! If is seizes/freezes, it's not turning and impedes fuel flow!!!!! If your current pump is stressed by cold weather/fuel, IMHO, you're on borrowed time!!

Correct, you must have flow. The CP3 can draw fuel, but only if there isn't a restriction. One of the design changes on the in-tank was to allow a flow thru when the LP fails, where the engine mounted doesn't.

OK thanks guys I was told that the 03 and newer trucks can run even if the pump dies. Was told it would still run without damaging anything, it just would not start back up. I'm going to pick up that tester from HF and see what the PSI is coming out of the filter also I will have the dealer do an injector balance test. Where is the test port located on my truck?