JstGtnStrtd85

Ok so my 97 ZJ 273xxx mile jeep has been running like **** lately. I did the key on key off trick and got code 12,43,21, and 55. Im just trying to figure out what repairs i need to do to fix these issues( poor gas mileage,rough idle, missing, loss of power). Also i noticed the transmission mount was completely hollow. Would this contribute to vibrations when in low gear. Once i put my foot on the gas its fine, when i take my foot off the gas its fine. It seems to vibrate pretty bad between 50-60 mph and floating the throttle. I have had the tires rotated and balanced with no luck.

Any help would greatly be appreciated...

Thank you

Aaron

dave1123

Okay; 12 is a "battery has been disconnected" code. 43 is a "cylinder misfire" code. 21 is and "02 sensor shorted" code, and 55 is "end of test".

The codes can get more specific if you use a scanner.

The transmission mount can cause a lot of vibration because every little bit of imbalance is transmitted to the frame. If the trans mount is broken, check your motor mounts also. A broken trans mount can also cause transfer case shifting problems with the '97 because the linkage is mechanical instead of the later cable.

Which engine do you have?

JstGtnStrtd85

Oh great thank you!!! I have the 4.0L, with the o2 sensor i know the on in the cay is not there( thank you junkies who wanted to make a quick buck) but from what i read it only monitors the temp of the cat and doesnt effect air/fuel ratio if that is correct?

dave1123

It measures the cat's efficiency, but it could be the wire is shorted somewhere. No, it doesn't modulate air/fuel ratios.

The upstream 02 sensor's wires are held in a clip on the side of the oil pan and can get burnt by the exhaust if they come loose. My '97 ZJ had them held by a cable tie because they HAD come loose.

JstGtnStrtd85

Ok cause I'm not running one in the cat at the moment so I'm assuming i should check the upstream wiring and possibly replace both since I've had it for 7yrs and haven't replaced any of them. Also with the misfire would the O2 be a culprit or would it be somewhere along the lines of ignition coil?(since I've replaced the plugs,wires,distributor cap)

dave1123

I hope you replaced the rotor too.

I would look at the throttle body. Clean it and the IAC , TPS, check the hose to the MAP sensor. Put a good injector cleaner in it and see what happens.

JstGtnStrtd85

Oh yeah i did replace the rotor.. Its been a bit since cleaning the Throttle body and things.. I also run restore fuel injection cleaner every couple fill ups. Ill look at the MAP hose later today and get back with what i find

JstGtnStrtd85

Hey dave so i checked the MAP sensor and i dont see a hose. Theres a plastic tubing that covers the wires but no physical hose. I also got the jeep scanned and its a P0300 misfire in P0303 cylinder 3 and P0304 cylinder 4. Also said that there is an issue with o2 circuit/voltage. Ill seafoam the **** out of her this weekend any suggestions on how to get really deep and clean the TB

dave1123

To tell you the truth, I've never had a MAP sensor off on my 4.0, but my book says it's mounted on the TB and to remove the screws and the hose. Maybe it's a short piece behind the sensor? IDK.

JstGtnStrtd85

Oooh lol. That i can look into than. Thank you

JstGtnStrtd85

Sorry its been a while been extremely busy. So i took off the Map Sensor and checked the hose the hose looks fine.. I did notice on the intake manifold the vacuum hose going to what appears to be an EGR canister( not completely sure what it is, but is on the driver side where the air intake is) appears to be dry rotted on both ends of the boots. I also picked up a new tranny mount and downstream o2 sensor to install. My question is I've read mixed things about the purpose of the downstream sensor. What is it really for other than monitoring the cat?

dave1123

That's your fuel vapor recovery canister. The hose connects to the purge solenoid and sucks the canister dry on start-up. My WJ makes a clicking sound every morning when I start it up. If that hose is dry rotted, it will cause a vacuum leak and that's precisely what I was looking for. That's the probable cause of your rough idle and poor fuel mileage. Also check your CCV valve and hose. The CCV valve is nothing more than a CONTROLLED vacuum leak. The internal plunger is controlled by vacuum and if it's dirty or plugged can cause the same thing.

I have an interesting story about PCV/CCV valves. I had some rough idle and poor fuel mileage problems with my Chevy truck. I worked PT at Valvoline at the time and my boss asked me when I had changed my PCV valve last. I told him I hadn't because it seemed to function when I put my finger over it. He said "Change it!" I did and my problems were over. Ever since then, I change them regularly.

JstGtnStrtd85

Awesome!!! Ill run buy the auto store and grab a couple elbows.. Also where is the PCV/CCV valves? And when I'm changing my transmission mounts do i need to remove the skid plate or should i be able to slide it in or out?

JstGtnStrtd85

Ok so i replaced elbow, cleaned throttle body,IAC,downstream o2 sensor, and reset the pcm... Now it seems my gas mileage has dropped even more... What else should i look into?