Engine/Transmission (1998.5 - 2002) Performance

[LAskham]

I bought a used 2000 4X4 extended cab long bed, 3:54 rear end, with 75K on the odometer after having a '92 4X4 that I put 300K on and was still getting 16 mpg (a drop from 20). Hence the switch. The 2000 was getting around 14 to 14-1/2 mpg but with a new fuel filter, K&N filter it went up to 16. Two weeks later the lift pump went out and it went to 10. New pump but it still gets between 14 and 17. I've checked to make sure that the fuel tank vent is not covered or plugged and tightened all of the clamps on the inter cooler hoses, air filter lines, etc. Nothing seems to help with the trucks performance. Slow spool up, poor power (compared with my son-in-law's 98 4X4). A local wrench turner suggested that I might need a new injector pump but that's a lot of money to lay out before I check all of my options. I plan to add a 4" exhaust but don't want to burn the $$ before I clean up the power and fuel milage problem. Any suggestions?



Thanks.



Leonard

 

[cumminspwr01]

Did you try putting a fuel pressure gauge on it to see if the pressure is right. Usually if the lift pump goes to zero and your still driving it its just a matter of time before the vp gives up

 

[Bob4x4]

Is the truck sluggish out of the hole or all the time?

 

[LAskham]

I've only had the fuel pressure checked by the dealer after the pump was installed. Guess that is the next thing to do. I'm assuming that the pressure, at the pump, should be 15 to 16 psi under full throttle. Correct? If not, then what? Another lift pump after I check for a clogged line? And yes, it is sluggish out of the hole compared with the '98 which has much more torc. Did 8. 0 several times in 40 to 60 accelleration test last night. But then the turbo was wound up. And no, I don't have a lead foot. Most of my driving is between 60 and 65 on the highway with a little bit of in-town stuff. Even lightened the truck by taking off the box and putting on a flat bed. Still no change.



Thanks guys.



Leonard

 

[plongson]

You won't see 15 or 16 PSI under full throttle with a stock fuel system. Between 5 and 9 is realistic for WOT and idle at 12+. This is always a real hot topic and everyone has an opinion about fuel pressure. These are the numbers that I have become comfortable with. You might want to invest in a full set of gauges. This is really the best way to monitor the conditions in real time.

 

[Houser]

Houser Here

I picked up a 1. 5 mpg gain by installing a new thermostat. My original one was running a little cold/Hot depending on the grade.

 

[Turbo Tim 1]

Intake Air Temperature sensor! I gained a couple MPG's when I changed mine out. Alot of people say they have good luck cleaning it but I never did so I just got into the habit of changing it every year or two. Here are some threads to read, check out the last one in the search, it has some great information.



Marco IAT Threads



I'm curious how you knew the lift pump went out without gauges, did the truck die on you? If so who knows how long the lift pump was actually out and the damage may already be done to the VP-44. These trucks will run with a dead lift pump most of the time. Also was the new lift pump checked after it was installed to make sure it is good? When my first LP died I was able to do the 40-60 test in 8 seconds, when I put a new one on I was able to do 40-60 in less than 7 seconds and probably closer to 6. Of course shortly there after it got even quicker from hanging around here.