97 4.0L SOHC fuel trim & O2 sensor questions

[djt294]

All,
I'm new to this forum and to Ford (last Ford was a 95 Windstar). Me and my son just picked up a 97 explorer XLT 4.0 SOHC. The vehicle had some issues when we bought it. We were told it had thrown a code for P0171, P0174(?) for lean conditions in bank 1,2. The vehicle is idling rough and does not feel like full power to me, but then again I have never driven an explorer before. The previous owner said they had the MAF, IAC, injectors and EGR valve as well as the ECU replaced. I am not in the position to just throw money at the problem. We tested for a vacuum leak using both propane and carb cleaner but did not find anything ( we are novice wrenches, done the usual maintenance stuff, including timing belts). We reset the ecu and took a test drive. The long term fuel trims were at -100.X and the O2 sensors were reading 0V at operating temperature. We stopped at that point. Any suggestions on how to proceed?

Appreciated

 

[anti eloi]

Lower intake manifold gaskets....

they are o-rings and shrink over time.
You have a vacum leak.
Do a search for the DIY.

 

[djt294]

Ok, thanks. My only concern was that I did not hear a change in rpm when I used the propane to find the leak. Also the fuel trims and O2 readings threw me off


Appreciated

 

[anti eloi]

The carb cleaner/propane trick....

Has never worked for me.
I am begining to wonder if it is an urban Legend.
I guess it would work for a massive leak though.
Anyway...the lower intake gaskets are a well documented issue with the 4.0 SOHC and have cured many a lean condition in both banks.
It is not that difficult and there are a bunch of DIYs here on the forum.
I use a little Hylomar along with the new o-rings just for added insurance.
You could probably use RTV but it isn't fuel resistant.

My second guess would be another vacum leak somewhere in the lines.
My third guess would be low fuel pressure.
If your SOHC has never had the lower gaskets changed I would just start by doing that and then go from there.

 

[anti eloi]

One last thing about fuel trims etc.

I have a 1998 and the OBD II is not supported for fuel trims on my Harbor Freight OBD II scanner so yours may be giving you false readings.