97 40th Odd Fuel Pump Issue - SOLVED (1 Viewer)

[mtrdud]

Ok, I have a 97 40th with a brand new OEM fuel pump installed right at 1k Miles now. About a week ago I took it about 10 miles to the gas station and was running great. Shut it off, pumped some gas and it wouldn’t fire back up. Had the get it pulled back to the house. As I’ve diagnosed it all fuses were good. Relays good. I haven’t took the relay on the firewall apart but did “tap” it as read in some forums. Yesterday I took the fuel pump out and when I initially checked the pump with a battery it didn’t seem to come on. Shortly afterwards it did. I’m not 100% sure I was making good contact though. I put it all back in and it fired right up. Drive it a few miles and parked it by my shop. After it sat a coupe hours I tried to crank it again and no go. I checked fuses and swapped relay in the under hood box again. Nothing. I then tried to run the pump while in the tank with a battery and couldn’t hear it. Removed the pump again and tried to run it with a battery and it runs well so I put it back in the tank and it fired up. WTF is going on? It seems like I have to coax the pump outside the truck and then put it back in and it’s fine. Anybody run into anything like this before? Could the pump be going bad? Something else?
Thanks.

 

[ajax1]

Maybe harness plug is corroded, there is also a resister on driver side of fender under the hood by the fuel relay you can test

 

[BILT4ME]

What brand of fuel pump?

 

[mtrdud]

What brand of fuel pump?

Denso. My statement of an OEM pump may not be totally correct.

 

[ppc]

Maybe harness plug is corroded, there is also a resister on driver side of fender under the hood by the fuel relay you can test

At startup the fuel pump is supplied with full voltage so the resistor is is not in the circuit.

 

[jonheld]

There is also a pesky connector under the left side c pillar that feeds the fuel pump. It is exposed to the elements and can cause issues.

 

[mtrdud]

@jonheld i will check that. Is that under the truck or underhood? Also I cranked it successfully all thru the day yesterday with no problem but I'm paranoid about driving it very far.

 

[jonheld]

Under the truck. Left side. C pillar.

 

[mtrdud]

Still is starting up ok but I’m leery about driving far. I still haven’t nailed this down. Anybody else experienced this?

 

[mtrdud]

Update- relays and resistor replaced, swapped in another fuel pump, it initially didn't want to start. Eventually it fired up and ran well but eventually started the same BS up again. I removed the assembly out of the tank and ran direct power to the pump and it works. I put the assembly back in the tank and the truck fired up and runs well. WTF!
I have done this a few times when it won't run and every time after I take the assembly out of the tank and power it up and put it back in, the truck runs. Does this make sense to anyone? Oh, I checked the connection under the truck and cleaned it up. It appeared ok.

 

[mtrdud]

I thought I would provide the resolution to this. I found out that my fuel tank was pretty rusty from sitting while I had the motor torn down and when I finally got a new motor swapped in (started with brand new OEM shortblock). Basically the rust stopped up my fuel filter and it would not run. I swapped in ALL new OEM tank and inside stuff. All is good now and I should be good for years to come at least in that area.

 

[mtrdud]

 

[Landseer]

Did you check the Circuit Opening Relay thats inside the kick panel just to the left of the brake pedal?

 

[mtrdud]

I replaced that too. I replaced all weak points or possibilities in the system with brand new OEM parts. Basically I did all of that prior to the tank. When I pulled the filter at the time I replaced the tank I was shocked at how much crap that I bumped out of the “in” side of the filter which had about 1000 miles on it. In other words it was obvious what the problem was, however I’m glad I replaced it all and I have spares now also.

 

[Cruzilla]

Where did you source the new fuel tank? I was under the impression they were NLA.

 

[mtrdud]

They are readily available but pricey. Your only options for new is OEM or one of the new extended range tanks. There is no cheap route for new. Trust me I read the threads here and searched.