Hello and Help!

[cvance]

Hi Everyone,

I've got a 97 Explorer Sport with 104k miles on it and have noticed it was idling rough and was "hesitating or bucking" between 40-55mph. This happens regardless of whether cold or operating temp. At lower or higher speeds the truck seems to run just fine, and starts fine as well.
I had the coils, plugs, wires and fuel filter changed with no luck. We checked ALL the wires and when we hooked up a scanner, we got a flat line reading (Nothing) from ALL the O2 sensors. We also cleaned the Air Flow Meter.
Weird.
We tried a good scanner and a high end scanner- same results, so we checked the sensors and each of them worked when tested. We then tried both scanners on a different vehicle to verify it wasn't the scanners, and both worked fine.
We then removed the ECU and replaced it with another one with no luck.

Has anyone experienced this and if so, can you offer a solution? This is driving me nuts.

Thanks!

 

[Rick]

Just guessing, but possibly a bad throttle position sensor?

Maybe someone else could offer more insight.

Welcome to the forum:chug

 

[swshawaii]

Welcome! OHV or SOHC? Both are known for leaking intake gaskets, particularly the earlier SOHC's. The upper and lower gaskets shrink with age causing lean issues, especially when cold, but usually throw p0171/174 lean codes. Unlit propane, starter fluid, or carb cleaner are often used to test for idle speed changes when running. Most often a rough idle is caused by some form of vacuum leak or leaks. GL

If SOHC

http://www.explorerforum.com/forums/showthread.php?p=2364255

 

[1Aauto]

Welcome to the site

Tony:wavey:

 

[cvance]

Hi,
I wish I could get codes but I am getting nothing from all the 02 sensors. Weird. Have also cleaned air flow meter and checked for vacuum leaks.
-nothing

 

[FR-425]

hhmmmmmm?

 

[FR-425]

Ummmm....aaaaa check the main engine harness for damage particularly the o2 wiring.

If I'm understanding this right ... You have an engine that runs .. No o2 data getting to the ECU ... o2's test ok.....gota be wiring, yes?

 

[2000StreetRod]

open or closed loop?

As I recall the PCM totally ignores the O2 sensor outputs when in open loop. Did you state whether OHV or SOHC V6?
What were the diagnostic codes, if any?
I suggest using the scanner to determine if the PCM is staying in open loop.

 

[cvance]

Yes, the engine runs- but idles rough and rough between 40-55mph. Where exactly is the main engine harness located?
It's an SOHV V6. We got NO codes at all- no reading from any O2 sensors. Sensors were independently checked and we used two different scanners- and even verified they worked by checking them on another vehicle.

 

[2000StreetRod]

engine main wiring harness

I assume you meant SOHC V6 instead of SOHV V6.
The engine main wiring harness is located mostly on top of the engine.

It looks like this when removed.

Ignore that some of the wires have no looms as I was modifying mine when the photos were taken.

Read the fuel trims or some other parameter to make sure the scanner is communicating with the PCM via the OBD-II port. I seem to recall some incompatibilities between the 1997 PCM and certain scanners. I suggest again that you read the open loop flag. If the value is 0 the PCM is in closed loop, if it's 1 the PCM is in open loop and probably not reporting the O2 voltages. Don't start tearing apart the wiring until you determine if the data you've read (no O2 output voltages) is valid.