Hello folks,

New to the Forum please go easy.

Vehicle:

1991 Ford Explorer XLT, 4X4, 4.0L push-rod motor, 315,000K

Problem Part 1: Excessive fuel consumption

Codes for O2 sensor, system lean, some black smoke, unburnt fuel smell, some slight hesitation when accelerating from a stop

I replaced the 02 sensor, replaced the IAC, cleaned the MAF, replaced the coil pack, replaced the plugs, replaced the plug wires, replaced fuel filter, replaced air cleaner, replaced the PVC valve changed brand of fuel, checked tires and "brake binding" - NOTHING. Truck ran "fine" other than excessive fuel consumption. I decided to replace the fuel pressure regulator and before I could get to the parts store we have...

Problem Part 2:

Truck begins to lope along like there is one bad cylinder. It sometimes "fixes" then comes back (all this over a period of 3 days).

Day 4 it's dead - no strart.

The motor cranks, the fuel pump "pumps" 3-5 secs KOEO fuel line is clear, return line is clear, filter is clear. There is fuel at the Schrader valve (do not know pressures) and the electrical system seems OK (sparks to all 6cyl). I believe the crank position indicator is OK because the CEL is on KOEO but goes out when cranking. I have no codes because I needed to remove the battery to re-charge. Fuel pump fuse is OK.

Only other information that may (or may not) be relevant is that lately it is slow to heat up. It does not come off "cold" (for the last 4 days). Maybe it's the thermostat or temperature sending unit? Maybe it's because its -30C here. It heats up fine if I block the airflow across the radiator (the old carboard solution).

Vehicle should still fire up even with these coolant issues though (right?).

I have not checked the relay. Does anyone know where this unit is on the 1991?

Any other suggestions? Don't say fuel pump. I don't have the money.

 

I had the same problems you described in problem part 1,with my 91 EB explorer and a new fuel pressure regulator fixed it.However,The other things you describe in problem part 2,I cant help you with....sorry.

 

Thank-you for your help.

I think I will replace the FPR anyway as you suggest (regardless of my bigger issues). It can't hurt my situation and when (if) I get her running I think my MPG will improve with the new FPR.

My fuel economy is great right now. I haven't spent a dime on fuel in over 2 days!

 

I'd start by getting a pressure gauge and seeing if the pressure's where it should be.

 

I believe you're right. I need to get a guage when I pick up the FPR. Will have to wait until the weekend. It's only about $50.00 so probably a good investment.

Both this morning and this evening it showed signs of life. Kicked over and ran (very poorly) for 10-20 seconds then dead again.

The saga continues.

Thanks MS

 

My responses are in bold below.

Problem Part 1: Excessive fuel consumption

Codes for O2 sensor, system lean, some black smoke, unburnt fuel smell, some slight hesitation when accelerating from a stop

I replaced the 02 sensor, replaced the IAC, cleaned the MAF, replaced the coil pack, replaced the plugs, replaced the plug wires, replaced fuel filter, replaced air cleaner, replaced the PVC valve changed brand of fuel, checked tires and "brake binding" - NOTHING. Truck ran "fine" other than excessive fuel consumption. I decided to replace the fuel pressure regulator and before I could get to the parts store we have...

I think you're on track with the pressure regulator. After the engine has been running, shut it off, find and pull the vac line leading to the pressure regulator, pull it and look for and sniff for gas. There should not be gas in the line.


Problem Part 2:

Truck begins to lope along like there is one bad cylinder. It sometimes "fixes" then comes back (all this over a period of 3 days).

Same reply as for #1 above

Day 4 it's dead - no strart.

The motor cranks, the fuel pump "pumps" 3-5 secs KOEO fuel line is clear, return line is clear, filter is clear. There is fuel at the Schrader valve (do not know pressures) and the electrical system seems OK (sparks to all 6cyl). I believe the crank position indicator is OK because the CEL is on KOEO but goes out when cranking. I have no codes because I needed to remove the battery to re-charge. Fuel pump fuse is OK.

Only other information that may (or may not) be relevant is that lately it is slow to heat up. It does not come off "cold" (for the last 4 days). Maybe it's the thermostat or temperature sending unit? Maybe it's because its -30C here. It heats up fine if I block the airflow across the radiator (the old carboard solution).

Vehicle should still fire up even with these coolant issues though (right?).

I have not checked the relay. Does anyone know where this unit is on the 1991?

If the Explorer is the same as my 94 Ranger 4.0L, then the EEC relay is in the PSD box, which is located above the LF wheelwell under the hood. BUT, since you got spark, I tend to doubt the EEC relay is the problem. So far, it really sounds like a bad pressure regulator, so I'd take care of that first and see what happens. Assuming that it runs after replacing it, erase all your codes and drive it for a bit. Come home and check to make sure there are no codes.

Yes, the rig should still fire up with the coolant issue; take care of that one after it's running right. It sounds to me like you may have a thermostat stuck open or partially open.

Don't say fuel pump.

Although not as accurate, you can use a tire pressure gage. It works; I've used one myself to rule out low fuel pressure. I would not try this on a hot engine. This gage will give you a gut feel for where the pressure is at before you spend $50 on the "good gage". From what I've read in the post, I really don't think it's a bad fuel pump. Generally, they are a go/no go but I've seen a couple intermittent problems. In that case, it tends to happen when they are warm.

Hope this helps.

 

Thank-you very much for your response CB9Mile.

I put a line on the Schrader valve at the fuel rail (from an old bicycle pump) last night and fuel flew out like a fire hose. FYI, I drained it into a can for safety. I can hear the pump running like mad in the tank. So I think you're right about the pump although I will check the pressure on the weekend (mrshorty).

I will also replace the FPR.

Two questions: (the first one may seem simple).

1. I have a Haynes Guide but it is not specific for 1991 (it covers 1991 - 2001) so ALL the details are not in the book. Does my truck have a fuse AND a relay in (around) the PDB? I'm looking at a green 30A plastic thing that looks like a large fuse. I expected a relay to have three or four leads within a sealed unit.

According to the electrical diagram the vehicle has a fuse AND a relay (fuel system). Am I looking at a fuse a relay or both (the green thing). I pulled the PDB up and saw three sets of wiring going to the underside of the PTD harness but nothing that looks like a relay as I know them.

2. If the FPR was jammed closed (no fuel return) would that be enough to continuously "flood" the engine and prevent start? Next time I crank it I'm going to pull a plug and check condition.

 

P.S. pulled 2 plugs after cranking - soaked with fuel

Next time I'll try a pre & post (look for dry/wet)

 

The fuel pressure regulator has a rubber diaphragm between the fuel and the vacuum line. When this leaks it can dump large amounts of gas into the intake manifold. It is easy enough to pull this rubber vacuum line off to see if there is fuel in it. The FPR can create a number of strange problems that are hard to diagnose. Excessive fuel is not one of them that has to be proven by replacement. Incidently about 80% of the fuel pumped is returned to the tank by the FPR. If you measure pump current it should be approximately 5A.

 

Replaced the FPR today. Fuel pressure is 40psi at the Schrader valve KOEO. Obviously can't tell the idle pressure yet.

It coughs a little but won't catch.

Probed the coil pack and wires all within spec.

I'm through for tonight. Need to recharge the battery to get full cranking power for tomorrow's activities.

Time for a beer(s).

I guess I have to WALK to the beer store, brutal.

 

This may be really stupid, but are you sure you don't have contaminated gas?

 

After all of this flooding, I have to wonder what the condition of your plugs is like. Excessive carbon deposits work like resistors, lowering spark voltage by drawing current away from the actual spark plug gap. It's hard for me to judge this since I can't see them, but from my experience the heavily baked on carbon with sort of the apperance of spatters in the kitchen oven from cooking a roast are a bad sign. Light fluffy black isn't great, but should not be a show stopper. It's also a fact that it's harder to fire a cold spark plug that it is a warm one. Maybe pull a plug and have a witness crank the engine while you check for reasonably strong spark.

BTW, you found 2 plugs soaked with fuel; this is a major piece of evidence in solving the mystery. They should not be soaked like that.

As for the fuse + relay, I can't confirm that but logically it would have both. If you look under the "lid" for the PSD box is may/should identify what is in each socket, assuming it's not printed next to the fuse or relay on the lower PSD. The relays will have a steel cap on it and the fuse is plastic.

 

at -30C (-22F), i would dump a .59 cent bottle of HEET in the tank. cheap insurance. do you have a block heater? can you plug it in? i know this is getting away from what the other guys are thinking, but sometimes it helps to get a different perspective on the subject. good luck.

 

Good morning gents.

I believe the fuel flow is OK I checked this morning KOEO and while cranking and it maintained 40psi. Fuse, relay, pump and pressure all check out OK. I dumped 20L of 94 octane fuel in the tank (every little bit helps).

As suggested I pulled all 6 plugs cleaned and dried them re-gaped and re-installed (one at a time by the way). It ran for about 30 seconds VERY roughly. It now coughs but won't catch. Coil and wires check out OK. Seems to be sparking OK too. I'll replace the plugs with the highest rated replacement plugs and try again.

I would like to get the block heated up but not possible.

Any plug recommendations? I have platinum tipped NGK TR55GP in her now (installed by professional shop).

Any other electrical suggestions?

Thanks fellas. I appreciate the help.

 

Squirt some ether/starting fluid into the intake. If it runs on that, then your problem is fuel related. If the plugs have been getting wet, then it's getting fuel. You could have a gas contamintation problem.