Engine/Transmission (1998.5 - 2002) "NO" voltage to LP

[LKothe]

1. I've noticed the FP being lower than normal for the past few days.

2. I changed the filter and could not get any FP even after filling the filter through a top port.

3. Noticed that there was no noise coming from the pump so figures it had went belly up.

4. Installed new pump, refilled filter, NO pressure/NO noise from pump.

5. Cut old harness and connected the end to a cigarette lighter plug. Pump run and pressured up filter after bleeding air out of it. Reconnected new wiring harness, pump won't run, not even a blip or NO noise.

My question, is there an LP fuse somewhere that I can't find? I removed the relay and could hear it energize when I plugged it back in.

Is there someway that I can run new wires to the LP, bypassing the old ones if there is not a fuse somewhere? Where can I check for that voltage on the ECM, I think that's what it's called.

I tried to start the truck with the pump temporarily wired and it wouldn't start. Do I need to bleed the injectors or?????



Thanks, Larry

 

[tunod_68]

I just posted a similar problem. But I will post to you as well.



if you jump the power wire to 12V and the pump is running open the test port. You should get a bath in fuel. If you do not let it run for a bit. It might take a few seconds to get fuel up there. this will allow you to get most of the air out. Then put the plug back in and hold that wire to battery for as long as you can stand to hold it. mine took a while before it actually cleared all the air out through the pump itself. You will hear the difference in tone when it's returning pure fuel back tot he tank. Then crank away. You shouldn't have to bleed the injectors to get it to sputter / run. I never have.



Of course if you're not getting any fuel out of the test port then your lift pump is probably belly up. They aren't known for reliability! I went through 3 in less than 20k before I FASS'd mine. I left my pigtail wire on the power lead to the lift pump connector for future bleeding. It's a lot easier than turning key on / off / crank / on / off ... blah blah



As for the harness power. It is controled in part by the CPS (Crankshaft Position Sensor $70). I have replaced 2 now. Second time my truck cut off 5 feet from the lift so I jumped by pigtailed wire to the battery and it started right up! Check the codes for this one. It is simple to replace just try not to break the old one getting it out!



Hope this helps.

 

[Lonestar]

There is no fuse for the lift pump. It is controlled directly from the ECM from what I understand. A buddy of mine had the same issue. I thought it was a bad lift pump, so we bought a BD bypass pump. Turns out the harness had no juice, so we just wired the new pump through a fuse that powered when the key was on. Not the way I would like to have mine work, but we were on a time and money crunch. Truck has about 20k on that setup, and it is working flawlessly.



KEEP ON TRUCKIN'

Lonestar

 

[mhenon]

There is no fuse for the lift pump. It is controlled directly from the ECM from what I understand. A buddy of mine had the same issue. I thought it was a bad lift pump, so we bought a BD bypass pump. Turns out the harness had no juice, so we just wired the new pump through a fuse that powered when the key was on. Not the way I would like to have mine work, but we were on a time and money crunch. Truck has about 20k on that setup, and it is working flawlessly.



KEEP ON TRUCKIN'

Lonestar

I've been suspicious of the ECM for years now (in regards to operating the LP anyway) and run my LP from a relay and right off the battery. I still let the ECM throw the relay (very low draw) but can bypass that easy enough if it acts up. Remember the ECM is just a computer. Ever had problems with your computer? Thought so!

Mike

 

[LKothe]

Thanks to you both. I went ahead and straight wired the new pump and bled the filter till no air was observed. Took the truck out for a short drive, the FP is back up to 12 1/2# at speed and goes to about 10 1/2# WOT. Pretty much the same as it was up to a couple weeks ago. Disconnected the jumper and rehooked the wiring harness.

Lo and Behold, the pump operates like it should with the exception of the check engine light is now on. Getting cold out there so I'll read the codes tomorrow and see if it indicates the CPS had problems. Probably ought to change it and the starter brush's too. Got 125k so I'm guessing it's time for both. At least I found that I could jumper it and get home if the CPS die's on the road...