94 Explorer hesitation/bogging down

[Fernando Uribe]

So I just changed out my O2 sensors on my 94 Explorer and after a 30min drive - everything was fine. The very next day, the engine bogs down and sputters like crazy. I have to floor it so it can accelerate! It's never done this before and now it caused my transmission to hard shift.

When I'm on the highway, it works fine. But when its stop and go at lights or intersections, it's at its worst. Anything I can do to fix it?

 

[Roadrunner777]

It's odd that it drove fine after the O2 change, and then overnight just on it's own started having problems... I'm going to put that aside and just consider the current symptoms.

I think a vacuum leak is possible, perhaps the line to the transmission modulator. That's the only thing I can think of that would have any relation to what you were working on.

Unrelated things might be a fuel pressure issue or the temp sensor for the computer, maybe the MAF.

Check engine light?

Actually, I could see where you were moving wiring harnesses around to do the sensors and one of them ended up too close to a hot pipe and melted to cause a short of some kind, that would account for the delayed failure, a connector that came loose because of vibration.

I think you might go back into where you were doing the work and see if anything is wrong there.

 

[Fernando Uribe]

It's odd that it drove fine after the O2 change, and then overnight just on it's own started having problems... I'm going to put that aside and just consider the current symptoms.

I think a vacuum leak is possible, perhaps the line to the transmission modulator. That's the only thing I can think of that would have any relation to what you were working on.

Unrelated things might be a fuel pressure issue or the temp sensor for the computer, maybe the MAF.

Check engine light?

Actually, I could see where you were moving wiring harnesses around to do the sensors and one of them ended up too close to a hot pipe and melted to cause a short of some kind, that would account for the delayed failure, a connector that came loose because of vibration.

I think you might go back into where you were doing the work and see if anything is wrong there.

Hi roadrunner,

You could be right, I'll check it in a bit.

So I went ahead and disconnected the battery for a while and hooked it back up.

When I start up the explorer, it sounds perfect! But give it a minute and it begins to sputter. After it sputters for another minute or two, it suddenly accelerates and stabilizes back to normal. Then it repeats the sputtering again. Kinda like some cycle.

The fuel pressure regulator, filter, pump and even injectors were replaced new by me a month ago after pouring some Lucas made my injectors stuck open.

The MAF is also new too including the air filter but I'll check that too.

 

[Fernando Uribe]

So I borrowed a buddy of mines OBD reader and it popped up these codes

172
176
181
536

His reader doesnt indicate the meanings of the codes but after disconnecting the battery and restarting the car, the same symptoms re emerged

 

[Roadrunner777]

So I borrowed a buddy of mines OBD reader and it popped up these codes

172
176
181
536

His reader doesnt indicate the meanings of the codes but after disconnecting the battery and restarting the car, the same symptoms re emerged

172 Oxygen sensor not switching – system is or was lean – Single, Right or Rear HO2S – Fuel control
176 Oxygen sensor not switching – system is or was lean Left or Front HO2S – Fuel control
181 Fuel system was lean at part throttle Single, Right or Rear HO2S – Fuel control
536 Brake On Off open or shorted to ground – BOO

Decoded from Ford OBD/OBD2 Codes – TroubleCodes.net

Add this to poor acceleration... ok. Lean means too much air (vacuum leak) or not enough fuel (fuel delivery issue).

I would go back over vacuum lines and do a fuel pressure test. I appreciate (more than you realize, probably) that you changed out new parts in these systems recently, but sometimes they go bad.

It would be helpful to have a complete history starting with the Lucas additive. Chronologically, what symptom, what you did to address it. I'm kind of thinking some residual Lucas stuff was in the tank and has come back to cause you problems again. That's just a guess. If I could do any one thing at this point, it would be either a fuel pressure test or to go through the vacuum lines depending on the equipment and time I had on my hands.

 

[Fernando Uribe]

172 Oxygen sensor not switching – system is or was lean – Single, Right or Rear HO2S – Fuel control
176 Oxygen sensor not switching – system is or was lean Left or Front HO2S – Fuel control
181 Fuel system was lean at part throttle Single, Right or Rear HO2S – Fuel control
536 Brake On Off open or shorted to ground – BOO

Decoded from Ford OBD/OBD2 Codes – TroubleCodes.net

Add this to poor acceleration... ok. Lean means too much air (vacuum leak) or not enough fuel (fuel delivery issue).

I would go back over vacuum lines and do a fuel pressure test. I appreciate (more than you realize, probably) that you changed out new parts in these systems recently, but sometimes they go bad.

It would be helpful to have a complete history starting with the Lucas additive. Chronologically, what symptom, what you did to address it. I'm kind of thinking some residual Lucas stuff was in the tank and has come back to cause you problems again. That's just a guess. If I could do any one thing at this point, it would be either a fuel pressure test or to go through the vacuum lines depending on the equipment and time I had on my hands.

Alrighty so the history began when I added the Lucas High Mileage Fuel Injector Cleaner. It caused my injectors to be stuck open and spew tons of white smoke. I replaced the injectors, fuel pressure regulator, filter, O2 sensors and spark plugs.

On the other note, the MAF sensor, IAC, TPS and air filter were replaced too!

I went all out on replacing this stuff lol, its basically a project car for me.

Heres a rather odd note: after all that, I noticed that if I fill the Explorer with regular unleaded, it stumbles. When I add Super Unleaded, it seems alot better.

Thanks for the codes! I did check the O2 connections and sensors, but everything is good.

I'll check out the vacuum lines too, I dont hear any hissing but rechecking wont hurt

 

[Roadrunner777]

Alrighty so the history began when I added the Lucas High Mileage Fuel Injector Cleaner. It caused my injectors to be stuck open and spew tons of white smoke. I replaced the injectors, fuel pressure regulator, filter, O2 sensors and spark plugs.

On the other note, the MAF sensor, IAC, TPS and air filter were replaced too!

I went all out on replacing this stuff lol, its basically a project car for me.

Heres a rather odd note: after all that, I noticed that if I fill the Explorer with regular unleaded, it stumbles. When I add Super Unleaded, it seems alot better.

Thanks for the codes! I did check the O2 connections and sensors, but everything is good.

I'll check out the vacuum lines too, I dont hear any hissing but rechecking wont hurt

Did you replace all those at the same time? If not, please... what order, what worked, what did not.... I'm sorry it will take some time and typing, but I'm starved for clues.

 

[Fernando Uribe]

Did you replace all those at the same time? If not, please... what order, what worked, what did not.... I'm sorry it will take some time and typing, but I'm starved for clues.

After the Lucas stuff it was
The filter and pressure regulator were first immediately
A week after it was the injectors
Two weeks later it was the O2 sensors

All the other items not involving the fuel stuff were done months before.

 

[Roadrunner777]

After the Lucas stuff it was
The filter and pressure regulator were first immediately
A week after it was the injectors
Two weeks later it was the O2 sensors

All the other items not involving the fuel stuff were done months before.

Thanks, how did it run as you changed those parts?

 

[Fernando Uribe]

Thanks, how did it run as you changed those parts?

After the Lucas, it ran like CRAP! lol but as the parts were replaced, it ran more normal

 

[Roadrunner777]

After the Lucas, it ran like CRAP! lol but as the parts were replaced, it ran more normal

I think I would run a fuel pressure test, ideally in some way where you can see it while the problem is occuring.

 

[Fernando Uribe]

I think I would run a fuel pressure test, ideally in some way where you can see it while the problem is occuring.

I appreciate it! So I ran my buddy's DTC code reader and this now came out

 

[Roadrunner777]

I appreciate it! So I ran my buddy's DTC code reader and this now came out

This means the Powertrain Control Module (PCM) is not sensing correct voltage coming out of the fuel pump relay. The most common cause for this is a bad fuel pump relay, and that's easy to check - just swap it out for a known good one, such as the blower relay. There is also a fuse that feeds the relay, that could be intermittent, loose, corroded.

There can be other causes. The fuel pump relay is triggered by +12V from the PCM relay and ground from the PCM itself. That is a fairly substantial troubleshooting tree, which I
can guide you through if it comes to that.

Here's a wiring diagram for that circuit. Hopefully it's just the relay, but if not, the diagram should carry you forward a little bit. You can see '238' between the PCM and the relay, that's the sense wire that is causing the code. So, if you go upstream, there's the relay itself, a fuse that feeds it, and then the stuff that drives the relay coil, the PCM Power Relay and so on. It's the relay 90% of the time... here's hoping!

 

[Fernando Uribe]

This means the Powertrain Control Module (PCM) is not sensing correct voltage coming out of the fuel pump relay. The most common cause for this is a bad fuel pump relay, and that's easy to check - just swap it out for a known good one, such as the blower relay. There is also a fuse that feeds the relay, that could be intermittent, loose, corroded.

There can be other causes. The fuel pump relay is triggered by +12V from the PCM relay and ground from the PCM itself. That is a fairly substantial troubleshooting tree, which I
can guide you through if it comes to that.

Here's a wiring diagram for that circuit. Hopefully it's just the relay, but if not, the diagram should carry you forward a little bit. You can see '238' between the PCM and the relay, that's the sense wire that is causing the code. So, if you go upstream, there's the relay itself, a fuse that feeds it, and then the stuff that drives the relay coil, the PCM Power Relay and so on. It's the relay 90% of the time... here's hoping!


View attachment 179379

This is awesome! For starts, I'll take a look at the fuel pump relay but what fuse do I need to look at though?

 

[Roadrunner777]

This is awesome! For starts, I'll take a look at the fuel pump relay but what fuse do I need to look at though?

Fuse #18, it's 20A from the factory, sorry for the rough image, but in the group of 2 x 4 small fuses, it's the upper right corner.

 

[Fernando Uribe]

Fuse #18, it's 20A from the factory, sorry for the rough image, but in the group of 2 x 4 small fuses, it's the upper right corner.


View attachment 179404

Thanks! Well I swapped the relay and fuse...and it didnt help :/ itll fire up smoothly for a minute and then back to stumbling again then repeat the process.

This time though, I drove on the highway and it works perfectly fine. So it's only when its idle.

 

[Roadrunner777]

Thanks! Well I swapped the relay and fuse...and it didnt help :/ itll fire up smoothly for a minute and then back to stumbling again then repeat the process.

This time though, I drove on the highway and it works perfectly fine. So it's only when its idle.

Thanks! Well I swapped the relay and fuse...and it didnt help :/ itll fire up smoothly for a minute and then back to stumbling again then repeat the process.

This time though, I drove on the highway and it works perfectly fine. So it's only when its idle.

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.

 

[Fernando Uribe]

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.

Oh not the fuel pump. Everything else has been replaced EXCEPT the fuel pump lol

 

[massacre]

Roadrunner is right on
I ended up buying the fuel pressure tester, they aren’t too expensive and can tell you a lot about these engines.

 

[Roadrunner777]

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!