Fuel pump not kicking on

[mohawkman94]

Hey guys,

Just the other day I replaced the a/c system on my 87 gn and went for a drive. on our way back the car died and didn't start and we had to get towed home. W figured out that the fuel pumps not kicking on so we replaced the fuel pump relay for the pump and the hot wire kit and still doesn't start????? What could it be I have heard some stuff about the ecu but need lots more info

Anything helps thanks!!!!!!!!!!!!!!

 

[PSID6]

Is the pump working after you replaced the relay? You might not have enough pressure out of the pump. Put a gauge on the fuel rail and see what ya got.

 

[mohawkman94]

The pump works we connected a wire from the battery to the pump and it turned on.

 

[TurboBuRick]

You said it has a hot wire kit? Check fuses?

Verify battery power at the hot wire relay. Red wire coming from front of car.

 

[GNRick]

Crank sensor? Ignition module?

 

[mohawkman94]

Crank sensor? Ignition module?

But it died on us at a stop light what would that have to do with the crank and ignition module?

 

[GNRick]

Everything has to die sometime. If one of them died at the stoplight then your car won't run.

 

[aminga]

check engine light come on KOEO?

 

[captndave737]

I had the same thing happen last year. I got the car home and it started. It was one of the female terminals that the hot wire relay plugs into was loose and making a poor connection so the fuel pump would come on tntermittently. Tightened the terminal and never had a problem again.

If the fuel pump runs when you connect it directly to the battery and not when you turn the key on its in the wiring in the fuel pump circuit. It's a pretty simple system.

 

[vader87]

Ok there are a few reason the fuel pump may not be working. Oil Pressure switch and/or harness maybe bad, yes your new relay maybe bad, ecm may be faulty.

To test the ecm, unplug the relay, throw a multimeter on the green wire, turn the key to the run position and see if you have voltage for a few seconds. If so, your relay is getting signals from the ecm.
Reconnect the relay, put your finger on it and have someone turn the key to the run position. You should feel a slight "click". If not, bad relay.
Check the oil pressure switch located on the lower front of the engine. Will have 3 wires. Check the connections and wiring. They tend to get brittle from heat.


I had the same issue and it was my pump. It runs for a while then gets hot and stops. After it cools, it works again.

 

[captndave737]

The Hotwire changes this a little. Instead of the fuel pump relay powering the fuel pump it powers the hot wire relay. I'd start by putting 12v on the fuel pump prime connector (gray single wire on the drivers side) if the fuel pump comes on it's a problem between the fuse, ignition, ECM and fuel pump relay. If not then it's downstream.

Second, if the fuel pump does run when 12v is applied to the FP Prime connector but not when the ignition is turned on I'd pull the FP Relay and check the voltage to terminal D with the ignition on. If there's voltage then jump terminal D to B. If the fuel pump runs with those terminals jumpered I'd check the voltage at Terminal A.
You will ONLY have voltage there for a few seconds after turning on the ignition. If there is voltage there check terminal C for ground. If there is voltage at A and ground at C either the FP Relay is bad or there is a bad or intermittent connection or broken wire somewhere.

A broken wire is unlikely but a bad connection on a 29 year old car is EXTREMELY likely. I've posted before that almost every electrical problem I've had on my car has been just that. The only sensors I've ever had to replace is the MAF and O2 sensor. Every other one is original. In theory the Crank sensor should never fail electrically, same with the Cam shaft sensor except the shaft or gear can wear on that cause problems.

 

[TurboTGuy]

I know it sounds dumb, but is the hot wire kit connection at the alternator secure?

 

[captndave737]

Ok there are a few reason the fuel pump may not be working. Oil Pressure switch and/or harness maybe bad, yes your new relay maybe bad, ecm may be faulty.

To test the ecm, unplug the relay, throw a multimeter on the green wire, turn the key to the run position and see if you have voltage for a few seconds. If so, your relay is getting signals from the ecm.
Reconnect the relay, put your finger on it and have someone turn the key to the run position. You should feel a slight "click". If not, bad relay.
Check the oil pressure switch located on the lower front of the engine. Will have 3 wires. Check the connections and wiring. They tend to get brittle from heat.


I had the same issue and it was my pump. It runs for a while then gets hot and stops. After it cools, it works again.

The fuel pump will run with a bad oil pressure switch. I had mine disconnected for years, If the FP Relay is bad and you crank the engine long enough to get 5psi of oil pressure then the oil pressure switch will close and the fuel pump will run.

 

[Turbogarage]

Hey guys, just a quick update to say thanks for all the help. I worked with Mohawkman94 this weekend and we were able to identify the issue. After checking the crank sensor and relays again, we decided to double check the fuses one more time. Turns out we had missed one and the FP fuse was in fact blown. What was more interesting is why. The fuel pump hot wire kit had one wire that was a tiny bit frayed and was occasionally grounding out and blowing fuses. We were able to track this down thanks to captndave737's diagram. Just wanted to say a big thanks to everyone. You guys are awesome and have made this GN project car a blast to repair.