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1991 explorer need help


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January 21, 2007
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1991 explorer 2wd xlt
I love my truck but it's driving me crazy. right now it is the only source of tranport for my family and me need help. The truck had been getting very low gas mileage and had a loping idle. I purchased some injection cleaner, air filter and new plugs at Advance Auto. On the way home stopped at the gas station poured injection cleaner into the tank topped it off with gas and the truck ran for about 2 miles and lost power and came to a stop. I was able to get the truck home and changed plugs thinking maybe they were fouled by the injection cleaner changed the air filter hopng this would solve the problem.
No such luck. We ran the diagnoisic test after clearing the pcm of all the codes. We keep getting codes 31 and 33 with ingnition on engine off uable to do ant more test because the truck will not run. Started looking for the EGR valve and we can not locate it. PLEASE HELP

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No EGRs on 91s; that started on some 93s.

sorry not a 1991 but a 1992 explorer not sure the egr is the problem any help would be great nee a the input I can get

Welcome to Explorer Forum! Have you checked your plug wires?

No EGRs on 91s; that started in 92.

My mistake, after some research the EGRs first went on the Cali models in 1993. There was no EGR on the 91s and 92s near as I can tell (I have a 91). Anyone with a 92 that's different, say something and I'll stand corrected.

For those still looking, a pic (courtesy Dogfriend) below.

Sorry for the confusion.


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I have changed the plugs, checked the wires, changed the fuel filter, replaced the air filter, checked to see if the injectors are leaking, replaced the fuel pressure regulator, replaced the PCV valve, checked the vacuum lines, pressure tested at the fuel rail and not seeing a good pressure. But....I am not so sure the gauge I was using is accurate. I am getting a good surge of fuel coming from the fuel pump. I finally got it to start up and idle ok after changing out the FPR but still can not get it to run once I shift into gear. THIS THING IS DRIVING ME NUTS BUT I AM DETERMINED NOT TO LET IT GET THE BEST OF ME!!! My husband posted on here a few days ago and has just about lost his mind trying to figure out whats wrong.....so now its my turn. I really really could use any advice you've got about what to try next. I suggested the O2 sensors or maybe the cat.conv. may have something to do with it....but my husband just keeps telling me that its not possible for those things to be causing this. He insists that it is fuel related.
Help me....please!!!!

1st thing, double check the results of your self-tests. A '91 can't output EGR codes, because a '91 doesn't have EGR. A '92 should output 3 digit codes, so make sure you aren't simply seeing 111.

2nd thing:
pressure tested at the fuel rail and not seeing a good pressure.
How much pressure? Why don't you think the gauge was accurate? If you need to, get another gauge and try again. If you can't trust your diagnostic equipment, you're going to have some difficulty.

When I did the pressure test the gauge stayed at 10 the entire time....saw no variance when I tried turning key on without cranking, when I cranked it or when it actually started. It kind of made me wonder if its my truck or if the gauge may not be working correctly. When the pressure valve is pressed on the gauge it did reset itself to 0, but never fluctuated from 10 other than that. I'm going to see if I can test it with a different gauge today...not sure what else to do. Could the AIC be causing any of this? Have thought about taking it off and cleaning it...but need to get a gasket first. After trying about 6 times today it cranked up and is idling fine but cuts out just as soon as I shift it into drive. Have dbl checked the inertia switch and it seems fine, have dbl check all my fuses and they are fine. It has a full tank of gas, which we checked yesterday to make sure there was no water mixed in it and that was fine. Any further suggestions???

And, btw, my husband posted this as a 91 but it is a 92 (not sure why he has trouble remembering that).

It could be a dirty AIC. It's pretty easy to remove the AIC, shoot it with some throttle body cleaner, and see if it looks ok.
But your fuel pressure gauge only showed 10 psi? If it were me, I would be looking into that. In the absence of a known good gauge, Do you have another, known good vehicle, to hook the questionable gauge up to? 10 psi is not enough pressure to run your engine off of.

First of all, Thank So Much!!! for all your help and suggestions. Next, I wanted to let you know that I did check my gauge on my Brother in Law's F150 and my gauge is fine. His truck has perfect pressure and the gauge worked perfectly.....so now I know it's my explorer. I realize it sounds strange that I'm getting 10psi....but that's all. Even Stranger....the truck is cranking and idling beautifully now (with just a little loping), we have driven it a few miles down the road and back but is still cutting out and loosing power.

Since I last posted, we have cleaned the AIC, replaced a vac line and rechecked the pressure at the rail. We turned the key on and got an initial reading of approx 15 psi and no variance when we started the engine. Rev engine made the needle on the gauge bounce between 10 and 30. I don't understand why I am able to crank and run it when everything I have read and heard tell me that I should not be able to do either with a pressure of 10-15psi....but I can.

We decided to dbl check the electrical circuits to the fuel pump and had another really strange thing happen. We replaced the fuel pump relay...as a just in case kind of thing. While the truck was idling....my husband reached over and unplugged the relay....nothing happened, no change at all. Am I correct in thinking that when the relay was unplugged, the fuel pump should have lost power and stopped sending gas to the engine? When the fuse was pulled out, that's exactly what happened. I'm not sure why the removal of the relay had no impact on the fuel pump.

Does anyone know of any way to test the power being received by the fuel pump without having to drop the fuel tank. We had just filled up when all our problems started happening....the tank has about 16 gallons of gas in it. It's not gonna be fun!!!

It depends on how close to the fuel pump you feel you have to be to check the power the pump is receiving. On my '92, there's a connector for the fuel pump/fuel level sender (4 wires I believe) near the driver's frame rail, just behind the fuel tank, near the axle/spare tire that you can access without dropping the tank.

A few observations:
1. Pic FWIW,
2. Fuel Rail Specs (at idle):
Vacuum hose attached - 30 to 45 psi
Vacuum Hose detached - 40 to 50 psi
Fuel system hold pressure (after 5 minutes) - 30 to 40 psi
Fuel pump Pressure (maximum) - 65 psi
3. To answer question - a good place to read voltage going to pump is to put a paperclip in the inertia switch connector on the floorboard behind the top of the carpet on the passenger side. Reading should be around six volts (depending on meter) rising to +12 volts for two seconds when key turned to run and not turned on. Staying at +12 volts if engine is running.
4.FPR and fuel filter, which you changed, are most likely culprits. Generally speaking pump dies or wiring deteriorates, I suppose it's possible that the pump filter is clogged. Check connections again for tightness, particularly fuel filter, it should not pull free by hand. Removal of fuel pump will require same fuel connection tools used during fuel filter removal.
5. There's a set of schematics floating around if interested, but I doubt if problem is electrical. See figure 7.

Good Luck!


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Got My Explorer Fixed!!!! Thank you so much to Mr. Shorty & Shamaal for all your help and suggestions. It ended up being the fuel pump. After replacing it with a new Bosch, my pressure came back up into normal limits, and the truck is running great. Pump was the last thing I thought it would be. After spending quite a few years in the car business, I had never seen a fuel pump linger that way...had always know them to just die. But I guess stranger things have happened, although I'm still not sure that it was bad... maybe it was just clogged up. The sock was really dirty. Hopefully I'll at least get some better gas mileage since I replaced all the other stuff as well!!

Worst part of all.....Now I have to admit to my husband that he was right all along : (