Fuelpump Quandaries

I replaced the fuelpump 2 years ago on my 1998 Tacoma Ext. RWD, and it would only run with starting fluid. I tested the fuelpressure and it was 0.

I ordered another pump to minimize downtime, and after pulling the sending unit, I found a hole in the hose, that connects the fuelpump to the assembly.

I was relieved, that I found an obvious problem...

Got it all together, tried to start it, and the fuelpressure was still 0, which baffled me, since I replaced the hose.

I tested the blue wire from the fuelpump relay under the dash, and I have continuity.

I then plugged the relay back in, and I have 12v at the fuelpump, but only when I crank it, and not when I let go of the key, or if I just set the key to the run/on position to cycle the fuelpump.

I really don't want to add a relay, and trigger it off the ignition, but I'm at a loss.

The truck was hard to start before it quit all together, and I had to crank it for 4 or 5 seconds, and I'm thinking that was caused by the slit in the hose.
I connected the 2 wires going to the clutch switch to eliminate it, but it was still hard to start.

Any ideas?

Thanks in advance!

 

Welcome to TW...you sure the fuel pump is good?

 

Assuming the pump runs while cranking, when "you have 12v at the pump".
A "start" signal to the ECM energizes the pump the instant the starter comes into play. When the crankshaft gets turning a signal from the crankshaft position sensor then maintains pump operation when the key is released to the run position. This set up allows the pump to run only when the starter is cranking and/or when the crankshaft is turning (engine running).
At the get go, I would be troubleshooting those circuits.

V6 below, 4cyl is same but uses the camshaft position sensor instead. No other sensors have anything to do with fuel pump control.

 

I'm not, and I was going to test it with one of my M12 Milwaukee batteries.

I'm trying to confirm, and find out why I don't have 12v in the on position, since I thought it should.

 

I appreciate that!

Thanks for explaining the circuit!
I'm more familiar with A1 VWs, where the fuel pump relay runs off of the coil.

It sounds like the electricals are fine then, and the pump might be bad.

I will test that next with the M12, and report back.

Thanks!

 

I hooked the pump up to the battery, and it works fine.

The cable that connects the pump to the assembly has an intermittent connection, as I manipulate it, it goes from 0 to infinite ohms.

I'm just glad I finally figured it out.

I'll confirm once I get it all together.

Thanks!

 

I replaced the bad wiring, tested it off the battery and the pump ran. Put it all back together, and it still has zero fuel pressure and wouldn't start.

 

I'm changing out the sending unit/fuelpump connector today.

The fuelpump ran with the new connector, when I tested it at the battery.

BTW, the Standard connector had thicker gauge wires, than the $12.99 connector Amazon sells, and it came with crimp connectors.