Hi all, bought a 1994 Dakota extended cab SLT with the 5.2 in it. Originally had no spark and wouldn’t start, chased that down to the known bad splice on these trucks and repaired it properly. Next was the old fuel in the tank which I removed along with the pump to thoroughly clean and dispose of the ancient varnished gasoline. After reassembly and hooking it up, the pump doesn’t run. Not with the key in the on position or in start position. Wondering what the problem could be? Below are some symptoms/observations noticed.
1. Only 0.2ish volts at the green power wire for fuel pump
2. Pump didn’t run before I removed the tank, had same problem but i needed to clean before diagnosing.
3. ASD and fuel pump relays have appropriate voltage at the 30 and 86 pins with key on and off

 

PCM will only turn the pump on for about 3 seconds at initial key on, after that, only if it sees the engine turning. (crank sensor) If you are getting spark, crank sensor is fine. See if you get that initial jolt of power to the pump, from the sounds of it, very good chance the pump is just toast.

 

Tried all the pins with a multimeter while a friend cycled the key, nothing more than 0.4 volts on the dark green positive wire going to pump. Probably gonna end up replacing the pump anyways, but shouldn’t there be +12 volts there constantly with the engine cranking/running?

 

Yup. Should see battery voltage there for about three seconds, unless the engine is actually turning, then it should be constant. Are you getting spark?

 

Getting great spark, truck runs good on fuel poured directly into the intake.

 

Test and see if the PCM is actually controlling the relay.... put a test light across pins 85 and 86 in the relay socket, turn the key on.... Should light up for a few seconds.

 

My test light does shine when turn the key on across these terminals, but only for about 2 seconds. The CEL doesn’t even finish its cycle before the test light goes dark. Bulb seemed dim, verified by a multimeter, only 10.51v across the fuel pump relay when cycling the key.

 

Another thing to note is the fuel pump is known good, I removed it to clean and wired it directly to 12v which made it spin and work great. Just no power going to it, which if the relays are working like they are supposed to it must be a break in the wires somewhere?
Any idea where the hot wire connects to under the hood so I can test for continuity?

 

Should run in the rear harness loom. Always fun trying to trace wires. You can test continuity by jumping power and ground at the fuel pump connector, (unplugged....) then test from pin 87 at the relay socket, to a good ground. Should be very little or no resistance.

 

Thanks so much for the replies HeyYou!

I made a jumper between the positive and ground wires on the fuel pump connector then checked for ground on terminal 87 of the fuel pump relay. There is no continuity to ground in any ignition position, what could this mean?

Plugging back in the relay and putting a multimeter between the positive and ground wires on the pump connector instead of the jumper shows the following:
Key off: no voltage
Key on: spike up to 1.53v then back down to 0v after one second
Engine cranking: spike up to then constant 1.53v while engine is turning over