Parked my 95 Ram the other day, came back 5 minutes later and it wouldn't start. At first it would turn over, idle rough, and die whenever you touched the gas pedal. After sitting a while and a few more attempts, it wouldn't start at all. I went and got some starting fluid and got the truck to stay running spraying that into the throttle body so the issue is with fuel delivery.

Tried the test valve on the fuel rail and there's no fuel pressure.

I towed the truck home and used a multimeter to check voltage at the fuel pump connector, it momentarily (1second or less) shows 12V when the key is turned to on but I couldn't hear the pump run.

I assumed it was probably a pump issue so I dropped the tank. Before buying a new pump assembly I connected the pump to a battery and it turned on and started pumping fuel.

Went back and checked the relay, ohms normal (~75) and pin 87 has 12V. Pin 86 gets 12V when key is turned to on. When 87 and 30 are jumpered the fuel pump connector reads a constant 12V.

So, I guess where I'm at is I think that the fuel pump isn't seeing 12V long enough to prime when the key is turned on. What would cause the relay to open the circuit so quickly? As I said, the pump connector only sees 12V for a second or less. Is it a bad PCM? How would that go bad?

Thanks for any help, I'm running out of things to try.

 

Pulled the relay and checked that pin 85 is grounded when key is turned to on. It grounds and stays grounded, but then when I put the relay in it ungrounds. If I pull the relay and check continuity again between pin 85 and the negative terminal (with relay out) it shows continuity and stays that way after the key is turned on.

 

You can download the service manual with wiring diagram in the FAQ/DIY section. You can trace it from there.

 

That is actually a normal condition. The relay only activates with initial key on for a few seconds then shuts off. Once the key is turned to the start position the relay is suppose to repower constantly. The pump should bring the fuel rail to pressure almost instantly. If not the pump is no good or another issue may exist
(clogged fuel filter)(Or a problem with the line). Check the pressure at the valve on the fuel rail to see if enough pressure is being produced on the prime.(dont know spec 35-45psi should be close) Then check for constant power at the pump during crank after initial key on signal.

 

The voltage at the pump connector is more of a spike than a momentary on. I'm not even sure it sees 12v for a full second. Luckily I have a decent multimeter that can refresh that quickly.

I'm going to reconnect the pump and jumper the relay and see if the truck runs then.

Tested the relay by itself and it clicks when pins 86 and 85 see positive power and a ground.


Also - did test pressure and there was nothing at the rail, that was one of the first things I checked.

 

Replace pump.

 

just a thought maybe when u took the pump down it got bumped just right and it allowed it to come on one more time. when mine went out, i got towed, got home and tried it for fun, and it started, went to the gas station, and then nothin AGAIN. replaced the pump and was all good.