97 Jeep Wrangler TJ 5spd Faulty O2 Oxygen Sensor Issue & Chipmunk Long...
 

This is general information about what happened with my 97TJ 4.0L 5spd.
About a week ago I noticed that under acceleration (between idle and wide
open throttle position on the TPS Throttle Position Sensor) my jeep was
stalling and power totally dropping out except at idle or wide open
throttle. As long as you kept it floored (don't recommend in the rain with
lockers) you could limp it home. I was getting a check engine code of 21
(bad O2 sensor) and 55 (end of codes).

Now the chipmunk effect (I thought). My dog had been sniffing around the
back finder wells of my jeep really after something. With the stalling I
thought, stalling + critter = chewed wires. I dug around the drivers side
first and there it was, enough moss and sticks to build a bonfire! I pulled
out enough to fill a laundry basket! Cleaned that all out, washed it well
and let dry (I do recommend BBQ tongs so you don't have a critter running
down your arm!).

I traced the wires back to the fuel pump and unfortunately they were no
where near the "worlds largest chipmunk nest". I cleaned off all the wires
and connectors and felt for any nibble marks etc. Nothing. I put my meter
on the wires to check for short to ground and nothing there either. All
perfect. So much for the chipmunk theory! Nuts!

Then I thought it was a bad fuel pump. I put my fuel pressure gage on the
test port of the fuel rail and because I have a long enough hose (fill in
your own joke here) I routed it up and onto my cowl vent area so I could
watch the pressure as I drove. Perfect 49psi even when the engine stalled
and sputtered. It had to be somewhere else and electrical.

With the fuel pump eliminated from the formula, I went back to the strange
action of the throttle position sensor. I thought that maybe it was going
out intermittently, not enough for a code, but just enough to mess up the
fuel mixture to trip the O2 code. Makes sense?

So I removed the two torx screws holding in the TPS and took a closer look.
With my trusty Fluke, I checked it in all positions and had a perfect sweep
of resistance all the way from closed to wide open. I cleaned it out with
WD-40 and an air hose and double checked. No problems. Double triple
checked, still perfect. I put everything back together and took another
test drive, still stalling out...

At that point I thought, "...well better clean every connection and apply
WD-40 to everything". Several hours later after cleaning everything I could
find, battery post, grounds on block, all connections to computer,
injectors, CrankSP sensor, CamSP sensor, both O2 sensors, the works. Test
drive and it ran better! I thought good 'ole WD-40 once again saves the
day. I gently placed my can in it's sacred location with pride.

Next day...

Sputter Sputter..... Bang Backfire.... limp limp x 100 from what it was
before! I thought holy heck batman now what in the world is going on? As
much as I liked keeping it to the floor, this was getting old and a bit
dangerous! Back to the garage at home for more brainstorming.

The kicker was the action of the TPS. I kept thinking it had to be in there
somewhere. Took it all apart again, cleaned, metered perfect and reinstall.
Still chitty chitty bang bang. Darn.

At this point I figured I could do two things, start replacing everything
until it stops OR suck it up and crawl down to the local shop and put it on
the test machine. I called a few places and found one that I trust that
would check it out for $80. I know what your thinking, DON'T DO IT MAN!
IT'S A SCAM! Don't suck up to the modern electronic overlords and beg for
help! I admit it did hurt, but I did it anyway. Why? Cause I wanted it
fixed right, and do not want a failure out on the side of Mt. Rainier.

I took it to the shop and about an hour later I got the call. Shorted out
O2 sensor upstream. Because of the way it shorted out internally it put
power into the ground lead causing it to send 12 volts to the TPS on both
the hot and ground wires! Because of the short they said it could have
damaged the computer causing the 12 volt short. I couldn't believe them at
first because that seemed just to (seemingly) simple of a problem. So I
reluctantly let go of my $80 and went home to fix as reported all the while
hoping it was only the O2 and not the computer as well.

For grins, I just did a simple unplug of the upstream O2 sensor,
disconnected the battery for a quick reset and took it for a quick test
drive. It ran so much better! No sputter or back firing. TPS worked
perfectly, though performance was a bit doggy and I did get a solid Check
Engine Light. Off to NAPA I went for an O2 sensor. As it turned out the
Bosch sensors had a $10 gas card rebate on them. I had a local discount
card that knocked off another $10 getting me my sensor for $47 bucks! Not
bad!

Got home and installed, plugged everything in and test drove. Ran
perfectly! I have to say I'm glad I paid the $80 for the analysis and I was
still able to wrench it the rest of the way to a fix. So I now owe two
apologies. First to the chipmunk who I assumed had chewed up my wires
causing issues (can't blame 'em for making a nest in a Jeep can you?) and
another for the computer tech who I swore would be an idiot and have no idea
of how to tell me what was wrong. Sorry Chip and thanks Randy for a great
job!

Tqm
97TJ