Lift pump doesn't run when key is ON

[Dunedain15]

Here's my sad tale:

My mileage dropped significantly during my last tank (15.5 down to 13.4). I've had some other performance issues that point to the IP, but I didn't want to replace it while I had the stock lift pump/fuel filter sock. So, I ordered the Walbro lift pump/NAPA fuel filter from LeroyDiesel.com. That was last Friday. On Saturday, I was helping my aunt move and was pulling a small trailer. I was about to turn left at a light, and, when I hit the gas, the truck shut off. I cranked and cranked and cranked, but there was no fuel getting to the engine. We got to the side of the road, and I loosened the cap on the fuel filter while my wife turned the key to the ON position. This has always activated the lift pump previously. No fuel came out. "Great," I thought. "That part's already on the way. Good time for it to die." Got it towed, put the new filter and lift pump on last night, and the pump still doesn't run when the key is ON. I ran 12V straight from the battery to the lift pump, and was able to bleed the air out of the system that way. Fuel came out of the FFM. Plugged it back into the harness, and nothing.

So, what do I check next? It's my understanding that the ECM controls the LP until the engine is running. With that in mind, I'll be picking up a fuel pump relay on my way home today. But I wanted to see what else you guys thought. Truck details are below. Thanks in advance.

 

[THEFERMANATOR]

Check the lift pump fuse and relay. On OBD II trucks the ECM triggers the lift pump for about 5 seconds when the key is turned on, and then turns it on when the engine is running. The OPS also powers it as sort of a back-up fail safe. Most likely the relay is bad or the fuse is blown from a bad lift pump.

 

[Dunedain15]

Awesome. Those are both easier than the OPS. Thanks for your reply. Since you mention it, how do I know if I have OBDI or II? Is it year specific? Thanks again.

 

[THEFERMANATOR]

96+ is OBD II, 95- is OBD I.

 

[hookedup50]

If its a 98 its obd 2. I think 96 was first year of obd2, but don't hold me to that as my 95 gasser is obd1. When my relay went out on my 97 the pump not run for 5 seconds when shutting truck off, but powered up during glow cycle. There is also a female plug right near the engine bay fuse box that I have jumped to EBFB to bleed system on my 97. If its OPS get AC Delco only. Hopefully its fuse.

 

[Dunedain15]

So, I put in the new fuel pump relay, and that didn't do anything. I put the old one back in and kept the new one for a rainy day. I saw another post about a similar issue that showed a fuse on the wiring harness feeding the lift pump, but I was unable to find something like that under my hood. So I just started pulling fuses in the box under the hood. When I got to a 20A fuse labeled "ECM-B", it was blown. Put a new one in, and it fired right up. Hooray!!! Thanks for all your input.

 

[Burning oil]

Hey good to talk to you today. Welcome to TTS. Now we need pictures.

 

[GM Guy]

Allways check fuses first. I skipped this a while back, and changed a GP controller and a WG solenoid. neither worked, so I checked fuses. changed the blown ENG-I fuse, disassembled, put original stuff back on, kept the other stuff for a spare. luckily it was used stuff off a parts motor, but still, I wasted a bunch of labor that i didnt need to.

welcome to the site!

 

[JMJNet]

Another fuse is ECM-B.

 

[Dunedain15]

Hey good to talk to you today. Welcome to TTS. Now we need pictures.

Gentlemen, sorry for the delay. I have no idea how you guys managed to cram all this stuff up into the area where the stock lift pump is. I couldn't get mine to fit, so I moved it behind the crossmember on the frame. My setup is just below the passenger door. I had to extend the plug, but I have an electronics background, so soldering was the easy part. Here's the pump and filter. I used slotted angle iron from Lowes. One piece bolted to the frame, and then one for each of the components bolted to the first one. I think it came out pretty nice:


Here are the connections to the fuel lines:


Thanks, again, to everyone for all your help.

 

[bison]

Check the lift pump fuse and relay. On OBD II trucks the ECM triggers the lift pump for about 5 seconds when the key is turned on, and then turns it on when the engine is running. The OPS also powers it as sort of a back-up fail safe. Most likely the relay is bad or the fuse is blown from a bad lift pump.

Don't agree with you on this Ferm.
On my 98's ,..Key on only powers the LP during the entire glow cycle,..on and off in cue with the glowers.
Only the OPS powers it when engine runs, same as all the other models.

 

[Will L.]

Got it well tucked up, good job. I always panic over anything hanging below the frame.

It did solve the problem, right? Somebody clue me in here on something... He said engine died when he hit the gas at the light & turning... What happened to flow on fail? Ip should have sucked fuel straight through and kept running. With this in mind i would make sure of new filter, clean screen. If both of those are good how is pickup tube and ip health?

 

[Will L.]

Sorry, disregard that. I thought I said I was gonna quit posting after 18 hour shifts and on my way to sleep. ECM-B fuse i glassed over it thinking he said the lp fuse.

 

[Burning oil]

Gentlemen, sorry for the delay. I have no idea how you guys managed to cram all this stuff up into the area where the stock lift pump is. I couldn't get mine to fit, so I moved it behind the crossmember on the frame. My setup is just below the passenger door. I had to extend the plug, but I have an electronics background, so soldering was the easy part. Here's the pump and filter. I used slotted angle iron from Lowes. One piece bolted to the frame, and then one for each of the components bolted to the first one. I think it came out pretty nice:
View attachment 39414

Here are the connections to the fuel lines:
View attachment 39413

Thanks, again, to everyone for all your help.

Thanks for the pictures.