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Old 04-30-2012, 01:42 PM   #1
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Fuel pump relay issues (93 5.0L)

I'm having some issues getting power through my fuel pump relay. The pump doesn't prime when I put the key on ignition and it doesn't prime when I touch the ECC test connector to ground. The power isn't going through the relay and I'm not sure why. The red wire coming into the relay has 5V and the wire on the other side of the coil, the light blue/orange wire leading to the ECU and ECC test connection has 5V as well. The relay doesn't throw so no power is going to the fuel pump. I can manually short the relay and power goes to the pump just fine.
I don't know why the relay won't close to send power to the pump. Could it be an ECU issue?
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Old 04-30-2012, 02:06 PM   #2
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Looking at the '92 EVTM...


The Red wire should have battery voltage (12 VDC). It gets power via the ECC relay which energizes when the ignition is in RUN. Power comes from Fuse Link G (20 ga Dark Blue) to the ECC Relay and when the relay energizes power goes to the Red circuit. The EEC supplies the ground to the Fuel Pumpp relay via the LB/O wire.


How The Circuit Works


The Electronic Engine Control System uses an Electronic Engine Control (EEC) Module to control fuel flow, exhaust gas recirculation (EGR), ignition system functions, evaporative emission, idle speed, A/C cutout, engine cooling and air management.

Fuel Flow
Fuel injectors, mounted in the intake manifold at the intake port, meter the flow of fuel into the engine. The EEC Module fires the injectors.

Fuel is supplied to the engine by an in-tank Electric Fuel Pump. When the Ignition Switch is turned to the RUN position, voltage is applied to the Fuel Pump Relay Coil. The Coil is grounded by the EEC Module and the relay contacts close. Voltage is now applied to the Fuel Pump.

When the Fuel Pump Relay is grounded by the EEC Module and the Inertia Switch is closed, power is supplied to the Fuel Pump. Fuel flow is produced by the Fuel Pump, and fuel pressure is built up in the fuel delivery system. Fuel Pressure is controlled by a fuel pressure regulator.
NOTE :If the engine does not operate after a collision, it may be that the Inertia Switch has opened. To reset the switch, put your finger through the hole in front of the trunk trim line and push down on the plunger.

WARNING :
If you see or smell gasoline, do not reset the Inertia Switch.
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Old 04-30-2012, 02:37 PM   #3
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Is the red wire supposed to be 12 volts? I am only getting 5V for whatever reason... Maybe there is some resistance upstream that is causing that to be only 5V, I'll trace the wire down.
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Old 04-30-2012, 03:21 PM   #4
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PM me your email and I'll send you the circuit diagram from the EVTM.
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Old 04-30-2012, 05:43 PM   #5
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After looking through the diagrams you sent me it seems the red wire should be 12 Volts but I am only seeing 5V. I tested my grounds and they seem to be ok. So some where, this red wire is losing voltage and I can't figure out where. I hooked a switch up to the fuel pump and tried starting the car and it won't start. My guess is because that same red wire sends power to all the injectors as well and if they aren't getting 12V they won't work right. I'm not sure if that's true or not though. I'm not sure where to start looking as to why I am only getting 5V instead of 12.
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Old 04-30-2012, 06:10 PM   #6
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Check for 12 Volts at the EEC relay input (hot at all times) and output (hot with ignition in RUN) and back to the fuse link G.

The EEC Relay is "Behind RH cowl panel, on bracket, above electronic engine control (EEC) module (A6)"
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Old 04-30-2012, 07:41 PM   #7
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I checked that and 12V come in (yellow wire) and 5V go out (red wire). Napa will have a new one in stock tomorrow morning so I will try that. There was some corrosion inside the relay. Must be a corroded connection inside causing enough resistance to cause a voltage drop.
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Old 04-30-2012, 08:29 PM   #8
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Check the voltage at the EEC Relay with the EEC disconnected.
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Old 04-30-2012, 08:37 PM   #9
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Here is a thread with the same problem EEC Power Relay Problem

Fix as stated by the OP...

Yes, it's true, I fixed it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I checked the voltage for all the wires at my ignition switch and everything stayed the same, before and after it dies. I was then in the process of looking at my alarm that I no longer use due to me painting over the password for it years ago (the company doesn't exist anymore as well) but it is still hooked up. While I was checking the voltage at the EEC relay, I remembered that the red ignition wire also goes to the fuel pump relay and it was at this point that it occured to me that if the relay for the EEC was corroded inside, why couldn't the fuel pump relay? So I put one in that I got from the wreckers and...IT WORKED!!!!

I am sooo happy now. All I have to do now is rewrap the wiring and put everything back together


thanks for offering to help Reaper, but I have it under control, but I will keep you in mind next time.
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Old 04-30-2012, 10:24 PM   #10
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Very common on the cars with the relay in the engine compartment.

My 86 still has the org under the seat. Did a car for a guy and it sat in his garage for a year spend a couple months at my house putting the car together and the relay was bad.

took one out of my scrap bin and it worked perfect

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Old 05-01-2012, 08:23 PM   #11
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Just an update, it was the PCM Power relay that was bad. I replaced it and the car fires up no problem.

Thanks for the help!
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