94Crawler

Hello,
Thank you all for reading this. If I have mis-posted please tell me so I can change the location of this thread. For the veterans that are tired of reading the same old questions, I hope this is different....plus, I have a video

BACK STORY

My wife bought a 1995 Jeep Grand Cherokee 4.0 a month ago with 209,000 miles. To date, I have replaced the water pump, shocks, and oil. I am going to name this project leaky because everything has a leak in it. I have plans to fix the T-case, differential, rear main, and auto trans leaks. I just replaced the down stream O2 Sensor and vaccume hose between the air intake and rear PCV Valve.

Pictures of recent work:







Current Issue

Last week, my wife said the Jeep was sputtering after stop lights, and occationally when she was driving. Her description sounded like bad gas. I only use 91 octane in my Jeeps, but that is a different story of why. She filled up the gas and said the issue went away.

The issue came back today, with a vengance. She said she would just be driving and the power would go down. She would mash the gas pedal, but the RPMs would stay around 300. At stop lights, the RPMs go between two distinct levels: 300, and 900. I have a video of this. It seems vacuum related so I have been checking for leaks. Last week, I thought it was due to the one hose I replaced. The video is after that hose was replaced.

Link to Video:

http://www.youtube.com/watch?v=eSXcn...ature=youtu.be

Negative Rationalization

To help you, help me, Let me cover more information about this vehicle:

- Inconsistant idle has always been there, but not to this level

- The car came from the North East

- There are NO error codes

On this model, error codes include the following:

Code 13 MAP sensor pneumatic signal

Code 14 MAP voltage too high or low

Code 24 Throttle body position sensor

Code 25 Automatic Idle Speed motor drive circuit

Code 26 Injectors 1,2,3

Code 27 Injector control circuit

Code 35 Idle switch shortened

Code 43 Ignition control circuit

Code 51 Air/fuel at limit

Code 77 Speed Control Relay


My Opinion

Because it loses power randomly at speed higher than idle, we can deduct the idle position sensor. The MAP and injector systems appear to be a Code that would be shown. I have traced all vacuum hoses and found they are all connected and do not appear to have any leaks.

The Throttle Position sensor may be a likely fit, except the issue also appears at speads above idle.


Smells and Exhaust

There is no extra fuel smell. There is a minimal backfire feeling from the exhaust and feels like a double miss, then back to normal idle.

Fuel Pump

I bought the Fuel pressure guage at Checkers to see if it is the fuel pump. In my experience, the pump usually just goes out. It may have these symptoms, but does not last as long. Also, the idle, as you can see in the video, is a constant jump between two different RPMs. This leads me down the vacuum sensor or pressure road. Does any one have any guesses? I am not offended at anything off the wall.

Thank you for reading!

Bustedback

You don't have a 95 ZJ, it's a 96. Does the idle surge only when you step on the brake? A failing fuel pump can cause the idle to hunt, a bad TPS can cause issues no matter what the RPM is. I would suggest having a shop look at it, it may save you money in the long run.

94Crawler

Bustedback,
You are correct. The manufacture date says 10/95 but I forget that is is considered a 96. The idle surge/low/surge/low pattern is there regardless of the brake being pressed. When in Drive or Reverse, the same ratio of surge/low/surge/low is present, however the RPMs are lower and the vehicle almost stalls.

I bought a fuel pressure test, and can find the pressure tonight. I also was looking at replacing the TPS before taking it to a shop. Shops in Colorado are rediculous, as I'm sure they are in other places as well. Thank you for your info! This direction is better then me taking shots in the dark! : )

94Crawler

This post will be updated Friday or Saturday, June 29th or 30th. At that time I plan on replacing the TPS and checking the fuel pressure. Pictures and video will follow. I hope to have an end resolution so this can be turned into a troubleshooting forum.

gmv93

i watched video. it reminds me a problem i faced on a small French made car. MAF was problematic on that car. hunting idle. On 4.0 MAP can be problematic too. if no exhaust smell after warm up at back of car, o2 sensor is ok.

Plus, all grounds must be securely attached to body of car and on ECU or whatever we have on those engines.

Did you try to reset ECU by removing battery - for few minutes?

pwb

Bosch o2 sensor?

http://www.jeepforum.com/forum/f13/w...ensor-1049729/

"when i bought my 98zj, i went through it updating sensors and more. i chose to go with bosch because they worked great in my mercedes. Only a few months later, my jeep was experiencing hesitations and rough idle. The bosch O2 sensor had failed and i found myself replacing it with a mopar sensor."

zjrog

Great, just but a Bosch O2 sensor in... Guess I'll buy a Mopar for when the Bosch fails.

94Crawler

GMV93,
I did indeed take the battery off line for a little bit. I did that when I replaced the 02 sensor. : )

94Crawler

PWB,
The Bosch was the only one they had. It was $10 more than what OEM would have been. I do buy the 4 prong bosch spark plugs, but other then that I prefer to stay away from that brand. I used to work on Mercedes and I will agree that they work well for that eye sore of a car. For everything else, I try to stay away. : )

94Crawler

ZJROJ,
One of my dogs is an Argentine Mastiff (Dogo Argentino). I like your quote. : )

94Crawler

To all who have followed this,
When I first posted, Bustedback told me to check my TPS. I went to Metal Movers today and grabbed the best conditioned TPS I could find. On a side note, I love Metal Movers. I got a shift **** off a Camanche, a TPS, TPS connector, and idle sensor for 10 bucks. They also opened early because they saw me waiting to get in.

Any-who, threw the used sensor in the Grand Cherokee and without removing the battery, the idle problem was fixed. Due to the high speed chase this morning, Santa Fe and Dartmoth were blocked off so I had to find a different street that had lots of stops, plus speeds of 45+. Therefore, I drove up and down Logan Street until I was satisfied with the fix. My wife drove the Grand Cherokee over to Smokey Hill and it did just fine for her too.

Thank you all for your support. I learned that I should rely on the ECU to throw an error if a sensor was out. With that type of thinking, I almost bought a new fuel pump. I also learned that a TPS can feel like a fuel problem. This was a quick test that didn't cost alot of money and didn't put me behind too much. Bended back helped me through this one, but all of your recomendations were helpful!

94Crawler

Team Cherokee,
My wife told me that right when the Jeep went to one-quarter of a tank, the idle dropped and took a minute for it to accelerate from a stop light. She filled it up and the problem went away.

I hooked up a Fuel Pressure gauge and found it was at 50 PSI before flow, and flowed at 15 PSI. This is the standard operating range, however I did this with a full tank of gas.

I plan on draining the gas out then trying the pressure test again.

I also took it on a test drive on a loop from Santa Fe to C-470 and around to 285. It took 1/8th of a tank for the 25 miles driven which is a huge sign of a fuel pump issue. If the pressure test points to a bad fuel pump, I will be replacing the OEM with a Spectra. Not really thrilled about Spectra, but can't beat the price of $266 at Advanced Auto. That is cheaper then O'reilly right now. Also planning on price checking Clutch Doctor which has comparable low prices.

94Crawler

Team Cherokee,
I bought a used fuel pump from a guy in Conifer and a fuel tank for $100 together. Replaced my old pump, which lookes like it was replaced once before, and that fixed the issue! Now it's driving nice and smooth.....now to find a buyer for my old fuel tank.