Need diagnosis help for a '91 Explorer

Ok, not XJ-related, but I would really appreciate some help. One of my friends at work (who can't afford to keep spending money at an auto garage, especially after they just charged her a bunch of money to clean the throttle body) has a 1991, Ford Explorer, 6-cyl, auto, 4wd. She says it is idling rough but gets a little better when it warms up. Also when it warms up, the check engine light comes on and the code reads that the O2 sensor is bad. They replaced the O2 sensor with no help and the same code reading. In addition to it running rough, her mileage has dropped to 84 miles per 3/4 tank (sorry, but I don't know her tank capacity, so I couldn't calculate her MPG).

Any thoughts guys. How about you EcoMike, this sounds like it might fall under your area of expertise?

I'm going to pick up her vehicle tomorrow and see if I can find anything but I would sure appreciate any ideas you might have that could focus my time.

Thanks in advance!

Plugs, clogged or malfunctioning fuel injector.

What specifically is the code? It would either read too lean or too rich, not "Bad O2 Sensor".

Too rich (and thanks).

I have had 3 Exploders in the past. In my experience the rough idle is a result of a dirty throttle body/butterfly. The dirty TB is causing a rich idle and throwing the O2 out of range=CEL

Clean the TB with Seafoam Deep Creep and an old tooth brush(engine off) scrub it good. Start it up and keep spraying it down with a 2 second burst of cleaner every 10-15 seconds

Try that and see it it helps

I will say it is either the EGR or Cat getting plugged. the 1991 Exploder is the b@stard child same as the 1991 Wranglers. The 1991 exploder uses the dual inline cat converter. But my money ois on a stuck open EGR, which will cause a VERY rich condition . Hal

Good luck KJ

arty: MISS YA'

copper204 said:

I will say it is either the EGR or Cat getting plugged. the 1991 Exploder is the b@stard child same as the 1991 Wranglers. The 1991 exploder uses the dual inline cat converter. But my money ois on a stuck open EGR, which will cause a VERY rich condition

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I agree with all of that except there is no complaint of the Ford being any lower on power than they already are in the original post.

If she is complaining of power loss and poor mileage, then yes its most likely the cat(s) but for a quick cheap fix try cleaning the TB real well.

Also check the vacuum lines at the rear of the intake and make sure they are connected and are in good condition.

I bought a 91' 2-door sport in 93 with 30k on it for only $10,000. The car lot that was selling it said that it had a burnt valve, the only thing that was wrong with it was the vacuum line had fallen off the "T" fitting at the back of the intake causing a very rough idle and low power/poor mileage. I plugged the line back in and drove it for 4 trouble free years!

I sold the vehicle in 97' with 90k on it for $14,000!

I had a '93 F150 Lightning that gas mileage went to hell, and actually ended up fuoling out the plugs. It was the vacuum controled fuel pressure relief valve near the fuel injector rails. Made too much gas blow through the injectors at low speed.

OK, I got the vehicle and drove it home. It is loud because of a hole in the muffler and other than a little bit of a surge in the idle, it is mainly just running VERY rich. After about 3-miles, the check engine light came on with no real difference in performance.

My best advice is to start with the simple stuff first, clean the TB, check all of the vacuum lines, check the wire harness to the O2 for damage, check the EGR for proper operation(should move in or out on acceleration, it could be stuck open) and pull a couple of the "easy to get too" plugs and look them over.

KJ

Dr. Dave says it is probably a blown diaphgram in the fuel pressure reg. This causes it to rum rich and throw a rich condition for O2 sensor causing piss poor mileage. Same thing he says happens to our Crown Vic's.

Hal

P.S. I still need your phone number TURKEY

arty:

You are THE MAN! Tell Dr. Dave hello and I'll shoot you an e-mail with all of my info. It sure was easier (and more fun) to work on these things with you closer by.

KJ