Diagnostic nightmare

[Maytag]

So I've got a 97 cherokee government edition 4.0 auto, 126000 miles, and it's been giving me some problems the last few weeks, the engine is essentialy stock except for a replacement header and a Jet chip (removed for diagnostic)...and 2 days before when I filled with gas I put some injector cleaner in the tank

It started as I was leaving for a road trip (doesn't it always) once the XJ got hot, when I would go to pass someone, the tranny would downshift, and a plume of black smoke would come dumping out

At first it didn't seem to be an issue, but as I got farther it got worse, the engine started missing and stuttering

Checked codes...got nothing

We thought it was an ignition problem at first, ended up my cap and rotor was kind of munched up, found a napa and replaced that. Better, but not fixed, so I checked the plugs, all black, put new ones in...and one of my wires looked a little cooked, so replaced them too

Ran like a top so we continued on our way...about a mile down the road it started again

Also sucked down Gas like a gold digger drinks Cristal

So after driving home from my trip early (worried about getting stuck somewhere, and had to keep full throttleing it to clear out the cylinders of fuel) I brought it to my local shop...

Ran a scan tool, #5 and #1 misfire 90% of the time, O2 sensor sees way rich, computer running it very lean to compensate for seeing major rich, fuel pressure checked out ok

Reading through the TSBs it recomends replacing everything except the rear bumper

figured injectors gummed up and letting fuel dump in, you can't clean Chrystler injectors so replaced them all (after pulling them we could see #5 injector clearly clogged) reset the ECU, cleaned plugs, started it up...ran perfect...warmed up...ran like shit

kept digging, checking all sensors, everything tested fine but still saw rich at O2S...checked distributor again, found plenty of shaft play, replaced it out too, cleaned the plugs again, ran perfect

driving it home drove it hard to test it...still fine...got stopped in traffic and crawled along...started stuttering again, then black smoke again

mostly runs fine, but when hot, then driving slow it starts up again

Maybe ECU? O2S? God Smitting me?


so far I've only replaced things that for sure needed it, but now I'm out of ideas

[jay diemme]

whats your fuel pressure at?

[thedownlow]

if it has a vaccum operated fuel reg pull the vac line off and see if it is dumping fuel pas the diaphram chevk it right after it acts up. this would cause it to dump liquid fuel straight into the intake deviding the rich mix amung all the cyl, but it is worth a shot

also the injectors in 1 and 5 may be cracked, when they get hot they might expand causing them to leak fuel. I haven't heard of this but its posible

[Maytag]

I believe 49 at idle

[TJP]

I would be checking out the upsteam O2 sensor and the coolant temp sensor readings. Either one can cause the problems you have.

Oh ya...

[Maytag]

thedownlow - it's a returnless fuel system, so no fuel pressure regulator at the engine, only in the tank area

TJP - I'm going back tommorow and will check both of those out...although they test fine on a scan tool

and yes...I have been ing the XJ quite frequently lately

[olivedrabxj]

whats the map reading at idle?
what is the actual vaccum? should be within 1in of the map reading.

[Goatman]

Make sure the plastic line from the throttle body to the MAP sensor isn't cracked or plugged up, this will throw the MAP off and can cause it to run rich. I'd think a shop would have found that, but it's something to check.

[olivedrabxj]

the map on a 97 is mounted directley to the tb if your seeing more than about 1.3 volts at idle pull it off and make sure the port in the tb or the map itself is not plugged up with junk.
the 3 wires on the connector from left to right with the release clip on top are 1-ground from pcm,2-sensor signal to pcm,3- 5 volt supply from pcm
hope that helps

[bigindyxj]

have you tested the ect, a buddy of mine had the same symptoms that you have. he would replace the spark plugs every time he filled it with gas, turns out the ect wires were shorted... my 2 cents

[Maytag]

Thanks for the help so far guys...it's been better, but still giving me problems

My new 50+ mile commute each day is getting hard at 10 MPG

I've been to the shop so many times they don't even charge me to try things anymore, and call me to check something when they have an idea

Every connector in the engine bay has been unplugged and packed with Dielectric Grease, I've had a Scan Tool on it recording everything when I drive for 2 days just to see if there are any anomolies that show up. All we see is that the O2S see very Rich, but the ECU thinks it's Lean, so it continues to spit fuel in...And it's so fouled up it missfires almost half the time (although it still runs suprisingly smooth)

I'm going to replace all of the vacuum lines just to be safe, and I will Re-pipe clean every port again

I'm almost down to swapping the ECU or Wiring Harness


bigindyxj - I feel dumb not knowing what you mean by ECT, but let me know...I'll check it if I haven't already

[TJP]

ECT = engine coolant temp sensor.

[Maytag]

Ah...I always called that the Coolant Temp Sensor....CTS....Tomato...Tomato (add your own accent )

[Brink_]

Updates?


I'm having troubles like this.

[Maytag]

well...

the last things I replaced were the Cat and both O2Ss, after so long of having fuel spitting out the back they were totaly killed...which seems to have the same symptoms as everything else that was giving me issues

before that, I also repaced my Coil with a higher power coil, to make sure I was getting a spark even with all of the carbon build up in the combustion chamber (at the same time did another new cap and rotor, plugs, wires and already had the distributor replaced)...so the ignition was totaly up to new

I also replaced the ETS (coolant temp sensor ) and the Crank Position Sensor, even though they tested fine...I didn't want them to be an issue later on




now the real kicker...through all of this...my Check engine light was actually burned out, so I don't know exactly when my O2Ss died (time for a guage cluster without the idiot lights)





Honestly, I have no idea what was really the problem...one shop says it was probably the O2S being dead all along...another says it was probably the coil going out...another says that my Cat was just clogged and sending mixed signals to the rear O2S...

but now...I'm getting 25-26 MPG with 30" tires



hope it helps, and let me know if you have more questions...I spent a lot of time researching things on this topic

[Brink_]

Hmmmmm.......

Mine is in a TJ.

50000miles. Trail only now.

It's been losing power more and more for this whole season. Then it started to shoot a bit of black smoke when I'd shift from 2nd to 1st under throttle. Also lost a ton of power most noticable under load (spinning in mud or climbing ledges). I put it in neutral yesterday and revved it up and at about 4000RPM I got a huge cloud of black smoke out of it. It's been smelling very rich for a long time now. At the end of the trail yesterday I had so little power that I couldn't run it in high range 2nd gear to get it back to the trailer. It's thrown a code for being lean (which my nose would argue) which I cleared before yesterdays run. Now it's throwing one for a grounded O2 sensor.

Thoughts? The O2 sensor came on for the first time this time.

[jp4lo]

but now...I'm getting 25-26 MPG with 30" tires


Damn, I need to let you work on my jeep.

[Maytag]

well....if you think about the fact that the O2S is giving a lean code, the computer thinks the engine needs more fuel, so it spits more in

since you are obviously getting to much fuel, my guess is that the O2S is dead and stuck on a lean reading...and If you have a cat, it's probably plugging up as well from all the excess fuel, causing the loss of power (since it's a trail rig you might not need one...but they can be had for as low as $45 at Napa...keeps the forest green ) I learned that even if it doesn't carbonize, the unburned fuel likes to bond to the Catalyst in the Cat hindering airflow and limiting your power

what I learned to look for (after many days of scratching my head) is that just because the O2s is reading, it might not be reading properly



Hope this helps...not too expensive of a fix at least

[Maytag]

Originally Posted by jp4lo

but now...I'm getting 25-26 MPG with 30" tires


Damn, I need to let you work on my jeep.

Just replace everything electrical like I did $$ $$ and it works great

[f250rollinon37s]

never belive an o2 - i have seen many fail - do you know that bosch recomends replacing 02 at every tune up or 60 k ? you should have been able to look at the rear 02 and compaired it to the front - if the rear is switching ok then suspect the front ( it will be slower - post cat )


if your running rich and have checked you fuel pessure - unplug the 02 and drive with it unpluged ( ecm will go into bypass / limp mode - run on pre set # ) also the 02s do not fucntion when the engine is cold - the ecm controls the a/f ratio - then the 02s will pick it up after the engine warns up or the rpm is raised

[Maytag]

Any luck Brink?

[mdd0127]

I've had four different vehicles(500 CID Caddy, 91 Talon, 86 D50, and 91 Prelude) do the exact same thing. Run rich as hell, misfire, replace everything electrical, run a little better, then run like crap again, then magically start getting awesome fuel mileage and power, then run like crap again, and all four blew the timing chain/belt shortly there after.

[Brink_]

Originally Posted by Maytag

Any luck Brink?

Took it to the dealership to have them run codes on it. It's throwing codes for both 02 sensors on one side (before and after the mini cat in the header)

I'm gonna replace them soon as I can and see what happens.

I'll report back when it's done.

[jeepcrazie]

Originally Posted by Maytag

now the real kicker...through all of this...my Check engine light was actually burned out, so I don't know exactly when my O2Ss died (time for a guage cluster without the idiot lights)

I am surprised they missed something this elementry. This is a very simple thing to check and is helpfull in determining how quickly a problem recurs from the driver seat.

o2 sensor sounds like what your problem was all along.

Brink, try swapping the sensor to the other bank(if you have one) and see if the codes follow. Good luck.

[Brink_]

Originally Posted by jeepcrazie

Brink, try swapping the sensor to the other bank(if you have one) and see if the codes follow. Good luck.

Good plan. I'm on it tomorrow.