98' XJ 4.0 AW4 with 155k on it. An on going issue for the last couple of years. Running rich to the nose yet occasionally throws a running lean code on bank 1. Now it runs rich to the point of spitting droplets of gas out the tail pipe and stalling at stops after it has warmed up. Goes down the freeway fine however.

I replaced the upstream O2 sensor a couple of weeks ago, with no noticeable difference. Looking for ideas on a fix. I have had a couple people guess a bad computer....

With Innova scan tool I get this info

Cold (initial start up)
upstream read .4 - .75
downstream reads .76

Engine at 192
upstream reads 0.00 - .88 (jumping quickly with nothing in between)
downstream reads 1.0 solid (way rich)

STFT remains -4.7 to 0 hot or cold
LTFT remains 6.0 hot or cold

A couple other odd things I noticed. Even when warmed up it remains in CL (closed loop). Shouldn't this have changed to open loop?

Also the TPS reads 15% even at idle. That doesn't make much since, but I have gotten that reading for a couple of years. Is this correct or another source of trouble?

 

Check what the tps says with key on engine off, mine used to say 10%, replaced with mopar sensor and now it reads 0%. Steer clear of Non mopar sensors, they just don't work out as well, been there done that!

 

I just went out and checked mine again. It is actually the same, Key On Engine Off 14.9% and engine at idle is also 14.9%. If I give it light throttle it does go up to 20% so I know it's working, but apparently not giving the right info.

I replaced the TPS a couple of years ago. Can't remember how soon after that my running rich problem began but makes me wonder if that is the original cause.

I am also still curious about the Closed/Open loop. I thought they start in Closed Loop going of long term stored data. Then once the engine is at temp they switch to Open Loop to adjust the engine for real time info. Am I right or wrong with this. If I am correct then why would my rig stay in Closed Loop?

Also any idea what the MAP should read? It showed 28 (inHg) engine off and drops to 14.3 at idle.

 

Open loop is when the ecm is ignoring the o2 sensor data (not at operating temperature). Closed loop is once the sensors are warmed up enough to read efficiently. The ecm should be in closed loop almost all the time.

The map sensor seems normal. Should read absolute atmospheric pressure with key on engine off, 28-31 in/hg.

 

He's right open loop until everything gets warmed up then switched to closed loop. Also make sure the throttle isn't binding and holding the butterfly open. Really the main sensor that is in charge of air/fuel ratio is the o2

 

Ok, interesting that mine is always in Closed Loop even on a cold start up at 50 degrees. However being in the proper loop while driving is what's most import so I won't over think that one.

 

have you checked the coolant temp sensor. i understand that works with the intake air temp sensor to control fuel mixture. just a thought.

 

Yes it is good. Actually replaced it last summer out of frustration just to see if it would change anything. It was cheap enough, but no change.

 

What brand O2 did you use? Are you positive the circuit for the front O2 isn't malfunctioning?

 

It is a Bosch. I have only assumed the sensor itself is working correctly. I do not know how to easily test the wire.

 

Did you change the TPS yet?
I'd also take a look at the rear O2 sensor and visually check the wiring for both sensors. Make sure it isn't broken, burned, abraded...also the O2 sensor grounds.

 

I just bought a new TPS. My current TPS is showing to much voltage at idle and to little at WOT. So I am about to go out and swap them, see what numbers the new one gives me.

The downstream O2 seems to be working right. .76 or so when I first start it, with little fluctuation. But then will go as high as 1.0 when it's loading up with fuel and running rough.

 

All this chatter about the TPS is BS. Using a quality Voltmeter, measure the voltage at the TPS connector Orange wire with the ignition switch to ON, without starting the engine. Record this voltage. Spec is 5 Volts, +/- .5 Volts.

Multiply the % reading you get on your scanner X the voltage reading you recorded. That's the TPS output voltage.

TPS output voltage is: At idle, it shold be greater than .26 volts but less than .95 volts. At WOT, the TPS output must be less than 4.49 volts.

BWD TPS' are crap. Use only OEM TPS'.

As far as running rich and fuel puking out the tailpipe, consider this: If you are seeing a negative (-) STFT correction the problem could be a defective MAP sensor, high fuel pressure, leaking fuel injector(s), defective O2S sensors, an exhaust leak/pinholes before the upstream O2S, a defective ECT sensor, or engine issues, such as a defective Camshaft Position Sensor.

First order of business is to una$$ that Bosch O2S and install two new NTK O2S (upstream P/N 23151, downstream P/N 23099).

If no change takes place with the new O2S', consider fuel injector(s) leaking or MAP Sensor going South.

 

Alright, new info. I bought a new TPS today and installed it. While I was at it I checked the voltage readings of the new TPS and what my scan tool said. And everything was the same. No difference with the new Mopar TPS. I also thought I might have a 180 thermostat so I went to change it back to the factory 195. When I popped open the housing I found that I did have a 195 in it already. So running temp has nothing to do with it.

After it warmed up and started running rich and poorly I decided to unplug 1 injector at a time to kill each cylinder and see if I could tell if there was a particular cyl giving me grief. Each time I unplugged an injector the engine would stumble a bit, then the computer would blip the throttle and it would smooth out and idle surprisingly well. I would plug the injector back in and move to the next cyl. etc. What I found out was that by unplugging any injector, letting the computer do it's thing and then plugging it back in my engine would then idle smooth and lean out. The Innova showed my O2 changing from the .8 to as high as 1.0 before, down to .02-.08 after. My STFT and LTFT would go from the low 30's each, to 0.0 and instead of showing CL or OL it just showed NA.

I don't quite understand what was going on. All I know is that the engine would run perfect for as long as I let it run after pulling and then reconnecting any injector. If i turned off the motor and started it back up, it would again go back to running rich and stumbling.

Can anyone explain why this might be?

 

With both the 3rd party and the new Mopar TPS I have 5 volts in and .95 - 1 volt at idle with 4 volts at WOT. This is also on the installed bored over TB.

So I tried both TPS on my original TB just out of curiosity. The idle went up a little 1.1-1.2 volts and I still got 4 volts at WOT