Lean codes and a mystery O2

[fridgeulator]

Hi all, i've got a '96 XLT with the 4.0 OHV V6 engine. ive had an issue where, despite running mostly ok the rest of the time, the car will stall immediately after starting if the engine is warm. Every so often mashing the gas pedal for a few seconds will get the engine to pick up. I can send videos if this vague description is insufficient.

Ive replaced the EGR and all of the o2 sensors, and the codes P0171 and P0174 (Cylinder banks lean one & two), and my downstream (?)(Bank 1 sensor 2) O2, that ive replaced, seems to be not reading. ive sunk quite a bit of money into this thing and it's really starting to stress me out, any help is appreciated.

 

[C420sailor]

Downstream O2 just measures catalytic converter efficiency. Truck will run just fine even if it’s bricked.

These are classic fuel pump symptoms. How old is yours? What’s your fuel pressure while this is happening?

 

[fridgeulator]

Downstream O2 just measures catalytic converter efficiency. Truck will run just fine even if it’s bricked.

These are classic fuel pump symptoms. How old is yours? What’s your fuel pressure while this is happening?

havent gotten around to measuring my fuel pressure but the pump is factory, and this thing's pretty high mileage. ODO broke but its probably almost at 200k.

 

[C420sailor]

Pump is probably on its way out.

Just make sure you check the pressure before firing up the parts cannon

 

[DintDobbs]

Post #34 and downward.

Getting the most out of what I have

now that winter is in full swing, starting to work on this a bit! got the LEDs installed in the instrument panel, feels like i'm driving a spaceship now. installing new brakes within the next week or two, probably going to do it with my dad the weekend before Christmas :) i'm just glad i can see...

www.explorerforum.com

Besides the fuel pump, you might consider cleaning/replacing the injectors. I've got two 2nd-gens, one around 225k and one just hit 195k, and have seen and heard of others even higher with the original fuel pump still going strong. When the fuel pumps quit, they usually quit without warning, so replacing it wouldn't be a bad idea either way, if you're going to keep the vehicle.

I dealt with those two codes on my Sport (SOHC), but a faulty sensor reading lean was the culprit. In your case, you said that your new downstream O2 might not be reading; do you suspect that you've received a faulty downstream O2 sensor?

Also, this is probably a no-brainer, but you didn't mention having done it, so I have to ask - did you erase the codes after you replaced the sensors, and the codes came back, or did you not clear the codes and they didn't go away? You can clear DTC's with an OBDII scanner (preferable) or by disconnecting the negative battery cable for about 30 seconds (resets the entire PCM).

 

[fridgeulator]

Post #34 and downward.

Getting the most out of what I have

now that winter is in full swing, starting to work on this a bit! got the LEDs installed in the instrument panel, feels like i'm driving a spaceship now. installing new brakes within the next week or two, probably going to do it with my dad the weekend before Christmas :) i'm just glad i can see...

www.explorerforum.com

Besides the fuel pump, you might consider cleaning/replacing the injectors. I've got two 2nd-gens, one around 225k and one just hit 195k, and have seen and heard of others even higher with the original fuel pump still going strong. When the fuel pumps quit, they usually quit without warning, so replacing it wouldn't be a bad idea either way, if you're going to keep the vehicle.

I dealt with those two codes on my Sport (SOHC), but a faulty sensor reading lean was the culprit. In your case, you said that your new downstream O2 might not be reading; do you suspect that you've received a faulty downstream O2 sensor?

Also, this is probably a no-brainer, but you didn't mention having done it, so I have to ask - did you erase the codes after you replaced the sensors, and the codes came back, or did you not clear the codes and they didn't go away? You can clear DTC's with an OBDII scanner (preferable) or by disconnecting the negative battery cable for about 30 seconds (resets the entire PCM).

Sorry about the huge wait! Cleared the DTCs, they came back. Been doing some reading about possible leaks from the upper/lower intake gasket as well. Worth checking and seeing if that sensor is bad though, will report back. Really hope its not the injectors, would i be able to tell by seeing if the fuel rail holds pressure when the car is off?

 

[410Fortune]

Injectors are not difficult or expensive

96 ohv w 200k needs intake gaskets upper and lower
While in there install new injectors and o rings

I do this All The Time!
The ethenol in our fuel dries out your intake o rings
The lower intake gasket is only one more step
Don’t forget to replace the egr o ring
Injectors on eBay under $100 for 6 reman
Gaskets are about $30-60

You will need an e7 socket for the fuel rail hold down studs
Also check your fuel pressure before doing this to ensure you do not also need a new pump strainer and filter

 

[fridgeulator]

Injectors are not difficult or expensive

96 ohv w 200k needs intake gaskets upper and lower
While in there install new injectors and o rings

I do this All The Time!
The ethenol in our fuel dries out your intake o rings
The lower intake gasket is only one more step
Don’t forget to replace the egr o ring
Injectors on eBay under $100 for 6 reman
Gaskets are about $30-60

You will need an e7 socket for the fuel rail hold down studs
Also check your fuel pressure before doing this to ensure you do not also need a new pump strainer and filter

Checking my pressure is first on the list, after that i'm doing the gasket/injector/o-ring job like you suggested. Ive had a feeling that it may be fuel tank/filter/strainer related as i tend to hear a pretty large amount of suction pulled into the gas tank when i fill up.

 

[410Fortune]

Ahhhhh so when you release gas cap and you hear vaccuum this is an indication that your Evap system is having issues. The canister purge valve may be stuck open causing the intake vacuum to be sucking vapors from the fuel tank all the time instead of only once in a while as intended

This can put strain on the fuel pump

 

[fridgeulator]

Ahhhhh so when you release gas cap and you hear vaccuum this is an indication that your Evap system is having issues. The canister purge valve may be stuck open causing the intake vacuum to be sucking vapors from the fuel tank all the time instead of only once in a while as intended

This can put strain on the fuel pump

i'm assuming replacing the canister in its entirety would remedy the issue?

 

[fridgeulator]

Update, did some more fooling around and i'm more sure its CPV or fuel tank related, as it pulls vaccum in the tank a LOT. going to replace my canister purge valve today, will update if that fixes the issue.