No fuel

I have a well maintained 94 Explorer with 160,000 miles.

The truck runs great but simply stopped running while backing out of the garage (it could have been much worse).

When I first turn on the ignition you typically hear the fuel pump pressurize the system, but it no longer does.

Using this site I dropped the tank and replaced the fuel pump. Not a problem but it still won’t start and the new pump does not energize with the ignition on.

I had already checked the fuses and the inertia switch, but all check fine. I then scrapped away the insulation of the hot wire at the pump and get no voltage with the key on.

In fact, I checked and get no voltage at the inertia switch with the key on.

Is this a computer controlled signal?

Welcome to this forum! There are 2 relays which control the pump. The main one is the fuel pump relay, and the second one is the PCM (computer) relay. If you don't see a check engine light when you turn the key to the accessory position, then it's the PCM relay. Try the fuel pump relay first. I suspect that the old pump was good.

Hello Brian, welcome to the forum.

Unless something totally bizarre like a busted wire is in play, BB has narrowed it down to the most likely players.

To answer your question, yes it is a computer controlled signal. If you put a paperclip into the bypass switch connector, you should read about +6 VDC assuming you have a digital voltmeter. That's the bias voltage from the input to the computer. When you turn to run, not start, you should read +12 VDC for a few seconds, then back to +6VDC.

For a reasonably good set of diagrams:
http://www.explorerforum.com/forums/showpost.php?p=1655246&postcount=22

FINALLY SOMEONE WHO IS GOING THROUGH THE SAME PROBLEM AS ME!!!!

The truck i got was going through the same problem while it was at the shop. There fix was to cut into the fuel pump wiring and hack it into getting power But they did a damn bad job.

They took a thin wire, wrapped it around a fuse from the fuse box under the dashboard and that how it was started but you had to keep turning the ignition to build up pressure for the fuel pump to start which sucked.

So my fix was to take out that then wire and wrapped a new heavy wire around a fuse that had power to it constantly even when the truck is off, so i put a toggle switch on it to turn the pump on and off. So in order to start the truck i gotta turn the switch. But i tried replacing the fuel pump relay but that didnt work. I didnt try replacing the pcm. I will try that soon.

Thanks for the help and sorry to bother again. My 94 has a total of six relays above the right fender well. These include the heater blower, ABS elec cntrl, ABS hyd cntrl, A/C WOT relay (?), Fuel pump, and EEC power.
I called Autozone and they told me their system didnt call for a PCM relay. I swapped the fuel pump relay with the A/C WOT and still didn't energize the fuel pump. I'm going to review the diagram from Shamaal but wanted to get back to you.
Thanks again,
Brian

Put that relay back in for now, and try to swap the PCM relay with the A/C relay.

A clarification the OHV calls their computer the EEC, the SOHC calls theirs the PCM. Either way it's the computer.
I believe Mr G has the OHV in his 94. Correct me if wrong.

Also the inertia switch and the bypass switch are the same thing.

I thought that it was called the ECM for the EEC-IV or OBD-I. The newer systems are known as EEC-V or better known as OBD-II.

Just going by the Haynes, it doesn't seem right to have two computer names for the same engine/computer. EEC- OHV; PCM - SOHC & V8. But I could be wrong, Haynes is not by any means an authority.

What prompted the clarification was a request for a PCM relay at an auto parts store for a 94 came up empty, it's listed as an EEC relay.

Brian again,
First I can't tell you folks how much I appreciate your assisatnce, this is an incredible site...i jsut wish my truck ran as well.
I actually cut out the inertia switch to be certain it was not the issue. In this condition and with a fully charged battery I checked the voltage at the hot wire and read zero with the key in run position. I then watched the digital meeter as I turned to start and with solid starter engagement continue to read zero at all times.
Totally frustrated in Tulsa

The relay isn't applying the power. Either swap another relay into it, or bypass the relay connection to test it. Check all of your fuses in the process just in case you might have blown one out during all of this troubleshooting.

Still no fuel

Both BrooklynBay and shamaal were right regarding the EEC fault. The EEC and all other relays were fine, but after another round of frustration, I checked each of the fuses with an ohmmeter and found the EEC 30A fuse was blown (I missed this the first time). I replaced the fuse, hooked up the battery turned on the key, and the fuse blew again.
I saw there was an EEC test block at the rear of the fuse box in the engine compartment. Would you recommend I have this tested or should I simply try to find a short in the wiring??
Thanks again,
Brian

I'm not trying to hijack this thread, but I have the same problem in my 1991 4x4 Explorer XLT.

The EEC fuse keeps blowing, shutting off fuel supply. I replaced the relay and put in a new fuse, but still the same problem.

So, like Brian, I'm wondering where to go next.......... Should I begin looking for a short in the wiring? Where would the most likely place to start be? Will this show up as a code? The EEC fuse blowing shorts out the "Check Engine" light.......

Oh man! There's a mess of stuff this could be. Get yourself a mess of fuses. Avoid temptation to jumper fuse and look for smoke. Wiring harnesses are expensive. A resistance test may help but I don't know what the values should be, although a short like this should be obvious.
Below pic shows our fuse and its first circuit. Power comes from fuse and goes to relay and EEC. Relay output goes to schematic D.


now the fun begins, when the key is turned on the EEC relay energizes and brings power to splice 123 (S123). From there it goes to:
*B - Mass Air Flow Sensor
*C - Fuel Pump Relay
*G- Electronic Distributorless Ignition System (coil pack)
Wire 361 R - Canister Purge Solenoid & A4LD Automatic Transmission Solenoids & EEC
* Connector C112 - Fuel Injectors.


First thing I would do is unplug the EEC. On the 91-94 it is located behind the right side kick panel on the passengers's side inside the cabin. Try test again, if it doesn't blow, things don't look good for the EEC. I think it still will though.

From now on it's a matter of disconnecting everything you can until it stops blowing then back up. All this assumes that there is a bad component and it isn't a chafed wired.

Leave the EEC out and the EEC relay in, pull the WOT and Fuel Pump relay, disconnect the MAF and coil pack, disconnect Idle Air Bypass valve (no idea where that is, down on the intake plenum I imagine), disconnect canister purge solenoid. Follow the injector wires to the connector (C112) and seperate it (I don't recall where this connector is). Everything should be disconnected but the transmission solenoids (way out of my league). Disconnect what you can get to and try the test again. If it doesn't blow, connect one at a time until the faulty path is determined. If it still blows, problem is in components you did not disconnect (auto tranny solenoids) or in wiring.

FWIW I'm betting injectors, MAF, EEC, coil pack in that order is bad. If you have cleaned the MAF lately I'd move that to the top of the list. The wires are brittle on these cars, take care disconnecting and if you can't get to a component remember it in the troubleshooting sequence.

Ask questions.

I saw another thread about some faulty internal transmission wiring harness blowing the fuse. It's simple to test the transmission solenoids in an A4LD. There is a 3 wire harness on the driver's side of the transmission which is a vertical connector. It connects to 2 internal solenoids (overdrive, and the torque converter clutch). One has constant (+) from the fuse. That is the center wire. The other 2 are computer controlled ground connections. The solenoids have a resistance of 25-40 ohms.

Ok, thanks guys. I think it's my tranny solenoid, because I was going to take the Explorer into the shop with problems going into overdrive.

Brooklyn, I think I read that post - Guy was from Wilkes Barry, PA.

It's all good advice tho from you and Shamaal. I'll tackle the procedures posted after I check the transmission.

I hope Brian is having good luck.

Jim

PS: What's - WOT

Manners said:

PS: What's - WOT

Click to expand...

Wide Open Throttle. When the computer detects a WOT condition from the TPS sensor, it opens the AC WOT relay to cut power to the AC compressor.

So I disconnected my A4LD transmission solenoid and the Explorer runs fine. I'm going to pull the valve body and clean/rebuild it as per these excellent How-To columns from Glacier991 and TN_Explorer.


http://www.explorerforum.com/forums/showthread.php?t=126461

http://www.explorerforum.com/forums/showthread.php?t=101571&page=3

It gives me a lot of confidence knowing this information is here. Thanks to everyone who contributes.

Jim

I have finally had a chance to get back at my problem, and have followed the suggestion of shamaal by doing the following:
Disconnected the following; EEC connection pulled, Fuel pump and A/C WOT relay pulled, MAF disconnected, and plenum harness pulled.
Turned on key and immediately heard fuse blow.

After a trip to Autozone for more fuses, did the next steps:
Disconnected the coil pack, as well as both harnesses to the tranny (one was a three wire harness the other a five wire harness....same results, blown fuse.

The last step was to disconnect the A/C wiring harness, as I recalled that I previously had a leaking heater valve switch located directly above this connection, also disconencted the fuel injector leads, and found what looked to be two of the primary harness connections located on the passenger side between the air cleaner box and the intake manifold. some of the wires from this went to the injector leads. I disconnected the top one of the two bundles, but to no avail, fuse blown when key turned on.

I consider myself quite capable mechanically, but the electronics side is not my strong suite.

Signed, still needing the help from my forum friends.
Brian

This is nasty, assuming everything pulled is correct, the problem appears to be a wiring short, rubbing against the chassis perhaps. I didn't see the purge solenoid in your list. That's the doodad with the connector and a hose that goes to the carbon cannister near the left front of the engine bay.

To confirm, remove the EEC relay (all the other stuff is still disconnected) and turn on again. Fuse should not blow. Also, we are talking about fuse 4 in the power distribution box, correct?

Mine's a 91 and the relays and PDB are on the passenger side of the engine bay with a different fusing configuration. So the wiring harness is different than the 94s.