I recently bought a 1989 Cherokee with the 4.0, it had been sitting for several months before I got it. The last owner said he had installed new injectors, spark plugs, and air filter. It idled rough and had a hesitation when accelerating. It would hesitate at first, shake very badly, and then surge forward.

I have confirmed that the spark plugs and air filter are new but I have not taken the injectors out. Since buying it I have replaced the distributor cap and rotor button, gapped the spark plugs to .035, installed a new crank position sensor and that didn’t change anything. I also changed the clips and o rings to the hoses on both ends of the fuel rail. I checked all the vacuum lines and found a cracked one that was leaking. I replaced all the vacuum lines that are connected to the “vacuum harness.” All the other vacuum lines look good. I have also checked the EGR valve, its working properly, and cleaned the Idle Air Control Sensor. IAC i think its commonly called.

I replaced those vacuum lines today and took it for a drive to see if it made a difference. When I started it, it idled fine and drove like a champ until it got to about 200 degrees then it started bogging down again and idling rough. It would bog down then after several seconds surge forward. I was driving up a large hill about ½ mile from the house, it just about didn’t make it up the hill and I started smelling a strong smell of gas. When I got home a checked under the hood and discovered the front fuel line attached to the fuel rail had pooped off.

This is my first Jeep and I have a “little better that novice” mechanical knowledge. Any help you guys can provide would be greatly appreciated as I stumped.

 

I forgot to mention it also backfires through the mintake when it boggs down

 

Check the fuel pressure.

 

^X2^....Welcome! I know you checked...but. That little tube from the inside of the throttle body to the MAP sensor there up on the firewall is "uncommonly important". Any crack, flaw or if it's plugged will make your Jeep fun ****ty rich. Not sounding like your problem, but good to check that on GP.

There is a supper easy test to double check that new CPS if you have a digital volt meter. I guess you know that, that, and it's connector are supper important.

Also when it's screwing up, try putting your foot in it, (past 70% throttle), see what that does.

 

How about your fuel filter and your fuel regulator?

 

I just pulled off the hose from the MAP to the side of the throttle body its not cracked or damaged at all. I blew it out with carb cleaner just to check it flowed through np.

When its screwing up I have to floor the pedal just to get any response at all, way past 70%. And i have a volt meter not sure how to check the senor ill have to look in my Haynes manual. I also failed to mention i cleaned all the eletrical connectors under the hood with electictonic connector cleaner right after i bought the thing.

As for checking the fuel pressure ive gotta rent a fuel pressure tester from AutoZone on my next day off, Sunday.

Like I said before this is my first jeep. What a pos!

 

I did change the fuel filter right after I first got it. Sorry i forgot to mention that, kids are running around distracting me. The old one was nasty as !@#$. I haven't changed the fuel pressure regulator.

 

Where are you? This almost sounds like something where you're going to want someone there to help - the problem is just goophy enough that nuances are likely to be "lost in translation" when you type them out (not because you're lacking skill, but because you're not always sure what's important when conveying information. Don't worry about that - we all do it.)

 

Surprised Cruiser hasn't showed up (Yet). Forget the book for this. Here's a wrightup from Cruiser on the CPS. Again not saying that's your issue but easy to rule out. Got a nice crisp blue spark? So till you can get to the fuel pressure, here it is;

Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
　
Revised 11-29-2011

 

There is a link that tells you how to check all the sensors. I am on my phone so I can post it. On the renix each sensor is very important. Check each one. Each out the TPS make sure its good and adjusted properly. Also since it has sat for awhile before you got refresh all your grounds. I did the ground refresh/upgrade on my 90. Made a big difference. I know cruiser54 has the write up for it. I highly recommend the grounds to start. Good luck. I know it gets alittle frustrating to understand the renix. I wouldn't trade mine for anything.

 

quick google, i have ti bookmarked too ^_^

http://www.lunghd.com/Tech_Articles/...iagnostics.htm


that site is great!

 

O2???

Fuel trims are based on O2 feedback until 80% - WOT. Then fuel trim is based solely on MAP feedback.

 

Thanks. Wish this phone would do that. It gets frustrating sometimes.

 

I'll also note that below operating temp your fuel trims are based on MAP and then switched to O2 when operating temp is achieved.

More evidence that O2 is the culprit.

 

^^Agreed^^ Was thinking some basics should be ruled out first.
http://www.naxja.org/forum/showthrea...ht=sensor+test