94 Explorer hesitation/bogging down

[Fernando Uribe]

You said you replaced the pump in your second post?

Whatever the case, we are nowhere near replacing the pump yet... the reason why is that highway driving consumes more fuel than idling, so that doesn't quite make sense. We may end up there anyway, but here's my thing:

Lean condition means not enough fuel or too much air. Fundamental. A fuel pressure reading with the problem occuring allows us reduce the potential problems without replacing parts.

Here is what I want you to do, and again, I am not really chasing a fuel delivery issue, I want to rule it out:

1. Buy or borrow a fuel pressure test gauge, such as this one: Amazon.com: Actron CP7818 Fuel Pressure Tester Kit,Black: Automotive you may find one like it cheaper somewhere else, that's fine... stores like O'Reilly's will loan it to you free with a deposit.
2. If you have run the engine, then stop and allow it to cool to COLD.
3. Connect it to the port. The port looks a LOT like a metal tire stem... you were near it when you changed the pressure regulator, it's on the fuel rail just behind it. You may have some gas spurting/leaking when you do this, so be prepared.
4. Turn the key to ON, but do not start. RECORD THE READING
5. Repeat step 4, and again, record the reading
6. Start the engine and immediately record the readings as it goes from high idle to your rough idle. At least 3 readings for this, please.
7. Allow the engine to warm up. If the pressure changes in any way, please describe it.
8. As you can, with assistance as needed, open the throttle to 1,000 rpm, then 1,500 rpm and 2,000 rpm. Record the pressure for these 3 conditions.
9. Return the engine to idle and record that reading.
10. Shut down the engine.
11. With the engine off, record the pressure immediately, then after 10 seconds, 30 seconds, 1 minute, 5 minutes, 1 hour and if you can, the pressure remaining overnight.

The ideal readings are 35 PSI at idle, as high as 40 PSI when revving the engine, and pressure maintained overnight.

If you do this and report all the readings in detail, I can rule in/out the fuel system and if there is a problem, I can most likely give you fairly precise troubleshooting.

For example, if your idle pressure is lower than 35 PSI, I'm going to be thinking about the fuel filter, then the pump.
If the pressure does not rise when revving, I'm going to be thinking about the pressure regulator.
If the pressure drops off after shutting down, I'm going to be thinking about the fuel pump or the injectors.

This is a lot of work, but it will conclusively rule in/out and the time will be well invested.

I imagine there are many videos online on fuel pressure testing, so you might want to look at a few of those.

I would also like you to remove that plastic tube between the MAF and the throttle and inspect it carefully for any cracks that might open up if it is flexed. This is a classic cause and I would like to rule that in/out.

If you find yourself with more time, I'd like you to test the MAF as per this website: Part 1 -How to Test the Ford Mass Air Flow (MAF) Sensor

I think if you do all these things and report readings and results... please... I spent a lot of time thinking and typing this out. Please do not tell me: The pressure is fine. Please give me the details I am asking for. Ok, I'll check back later this weekend, good luck!

Whoops, I cant believe myself I said I didnt change it....I'm getting old.

Well things changed. So I was on my way to the auto parts store to get the fuel pressure test gauge and I noticed the car worked perfectly fine. I decided to drive for a bit in the highway and the Explorer seemed okay. After 30min of driving, I pulled into a Burger King drive thru to see if the car will stall on me.

Surprisingly...nothing!

The only thing I did was remove the fuses, diodes, relays and clean out the contacts. I then cleaned out the Ignition Control Module (it had white stuff all over the pins) and then the ECU (it had a thin brown fluid on some of the pins).

It's been working pretty great since! I guess it wasnt the fuel pump or fuel pressure.

 

[Roadrunner777]

Whoops, I cant believe myself I said I didnt change it....I'm getting old.

Well things changed. So I was on my way to the auto parts store to get the fuel pressure test gauge and I noticed the car worked perfectly fine. I decided to drive for a bit in the highway and the Explorer seemed okay. After 30min of driving, I pulled into a Burger King drive thru to see if the car will stall on me.

Surprisingly...nothing!

The only thing I did was remove the fuses, diodes, relays and clean out the contacts. I then cleaned out the Ignition Control Module (it had white stuff all over the pins) and then the ECU (it had a thin brown fluid on some of the pins).

It's been working pretty great since! I guess it wasnt the fuel pump or fuel pressure.

Contact corrosion, fuel pump relay most likely... well good! The stuff on the pins could be contact grease from factory. If this were to return, I would replace the fuel pump relay with new, but for now, I guess we will call this done!

 

[Fernando Uribe]

Contact corrosion, fuel pump relay most likely... well good! The stuff on the pins could be contact grease from factory. If this were to return, I would replace the fuel pump relay with new, but for now, I guess we will call this done!

Thanks! I noticed the diodes had some sort of green coating on them. It wasnt noticed up top, but i took apart the fuse box and used a toothbrush to clean since it was more at the bottom. I used a whole can of this guy and air dried everything since it tended to create moisture.

Other than that, its working really good. Thank you for the help!

 

[Roadrunner777]

Thanks! I noticed the diodes had some sort of green coating on them. It wasnt noticed up top, but i took apart the fuse box and used a toothbrush to clean since it was more at the bottom. I used a whole can of this guy and air dried everything since it tended to create moisture.

Other than that, its working really good. Thank you for the help!

Any time...

 

[ddenton749]

To recap, we have codes indicating lean condition and bad voltage to the fuel pump. Idle is good momentarily, then gets rough. Good while driving. It has been like this since the Lucas treatment, even though you have replaced: Fuel pump, filter, injectors and pressure regulator, MAF, and air filter, plus 02 sensors, IAC and TPS.

The codes lead me to a fuel delivery issue. I would check this with a fuel pressure test while it is idling badly.

The symptom... idle is initially high, as part of the computer programming, and then it starts using the MAF to measure air intake, sending an output to the IAC. This forms a closed-loop idle control. This leads us to the MAF, which is well known for this symptom, or.... there may be a crack in the plastic tube between the MAF and the throttle body. It's the black plastic accordion part. A leak there would allow air into the engine that is unaccounted for by the MAF, causing lean condition and rough idle.

I think I would test fuel pressure while it is failing. If it's ok, I would take that plastic tube off and do a very careful inspection. If that's ok too, then I have to go back and consider if there is something wrong with the recently replaced MAF, IAC, or... maybe the engine control computer itself, but I would take small steps, fuel pressure test and inspect that tube.

I had a similar problem with my 93. It started suddenly driving down the road. It ran extremely poorly. First, remove the plastic air tube between the MAF and the throttle body. Turn it over and look for cracks in the accordion parts and check the rubber seals. Damaged seals and holes in the plastic will give you a big vacuum leak - unmetered air. The car will run better when cold because the fuel is rich for cold start. It makes up for the vacuum leak. Buy a good one. There are some cheap replacements out there.

Try unplugging the MAF and see if it runs better. (It will give you a CEL code.) Clean the MAF plug with electronic/electrical cleaner and check to make sure the rubber seal in the plug is in the correct place. My 93 had problems with corroded electrical connections. It doesn't take much corrosion to degrade signals to the PCM. I also had a corrosion problem at the fuel pump fuse and relay.

Check your grounds. If your negative battery cable is falling apart as they typically do, replace it in its entirety. Clean the frame connection and the body connection. They are about $20 at Rock Auto.

I replaced my MAF with a good used OEM part from Ebay. Two non-OEM replacements didn't work. That solved my issue.