Surging,missing when warmed up

OK , I have did searches amd looked these boards over since a buddy turned me on a while back .I see similar problems , but not EXACTLY the same . Anyway , here goes ...

I have a 93 Country with the 4.0 HO motor . When I bought it , it would "stutter" ever so slightly at idle . Nothing bad , really , just noticable . Well , I would put fuel system cleaner in , and it seemed to help , until I would get gas again . (I don't get gas at the same place all the time , so not bad gas I don't think)

Last weekend it got to doing it again . I figured the fuel filter , so I changed it , no problems . When I started it , it ran worse than ever!
I barely limped home , but it would run GREAT every so often .I have drove it around town a few times since , and it runs great when cool , but when it gets hot (210) it will start doing it intermitently .I will be driving along at speed and it just cuts out real bad , almost wanting to backfire . It may do this a few minutes then run fine for awhile. There is no pattern to it it seems , it's just off and on .

I've read about the TPS and a few other things , as well as the CAT . I am no mechanic , but would like some ideas to throw at him when I take it in if any of you guys have any suggestions .

Thanks for any help ,
Steve

did you clean the carbon off the iac?

Jess said:

did you clean the carbon off the iac?

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I'm a N00B. What's the iac ?

shutter

If you didn't replace the rubber hoses from fuel tank and in front of fuel filter, they tend to crack and suck air instead of supplying gas. This fixed mine.

How many miles? When was the last time a tune up was done? Are the plugs good? I have bad blow by and when the plugs get nasty it runs really bad. Also look at plug wires. Definitely sounds like a fuel and spark problem. Also if the O2 is bad it may cause it to stumble but I thought that was more on the new ones than the older.

It has 114,000 on it. Holds great oil pressure (60 pounds cold , 40+ warm) . Not sure on the plugs and wires , and the rubber hoses have not been replaced .

Would this cause an intermitant problem ?

Thanks for the replies , it's really appreciated !

Change the hoses on either side of the fuel filter first, then look at the running engine in a very dark place and see if you see any spark jumping on the distributor side on engine. If yes change the cap, rotor plugs,and plug wires.
That should do it. If that does not cure it we are then talkin sensors, TPS, O2,MAP etc.....

Re: shutter

gtaylor1 said:

If you didn't replace the rubber hoses from fuel tank and in front of fuel filter, they tend to crack and suck air instead of supplying gas. This fixed mine.

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How are they going to suck air when they are under pressure? The fuel pump is in the gas tank, the fuel lines and fuel filter are under pressure?

Sounds to me like he needs a tune up, new spark plugs, spark plug wires, and a new rotor and cap on the distributor. Also sounds like it has not been worked on or serviced since he bought it used. Could be the original wires and plugs on it.

Re: shutter

Ecomike said:

How are they going to suck air when they are under pressure? The fuel pump is in the gas tank, the fuel lines and fuel filter are under pressure?

Sounds to me like he needs a tune up, new spark plugs, spark plug wires, and a new rotor and cap on the distributor. Also sounds like it has not been worked on or serviced since he bought it used. Could be the original wires and plugs on it.

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You are correct. I havn't did a tune-up on it since I purchased it .I did lose a water pump and had my mechanic look it over . He said nothing out of the ordinariy .Only thing that doesn't work is the cruies control , which I can live without . It's a DD , so I would prefer to have it , but hey , I'm not picky .

I think I will start there. I can do that myself , (I'm not a total dumb-ass) but I wanted some opinions. It sure won't hurt to do all that anyway , so it's not really "wasted money" .

Thanks again , and I'll keep ya posted .
Steve

OK..I did a tune-up on it today . It seemed like it was gonna run great until I hit the highway . It wanted to fall on it's ass whenj I did, and the more I drove it , the worse it got. I triple checked the plug wires and the firing order .All good .

It seems like it wants to just "cut-out" when I romp it , and it did backfire a few times through the exhaust . Not REAL bad , but some. It just has no power under a load now .

Anything else ?

Steve_Moore said:

OK..I did a tune-up on it today . It seemed like it was gonna run great until I hit the highway . It wanted to fall on it's ass whenj I did, and the more I drove it , the worse it got. I triple checked the plug wires and the firing order .All good .

It seems like it wants to just "cut-out" when I romp it , and it did backfire a few times through the exhaust . Not REAL bad , but some. It just has no power under a load now .

Anything else ?

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Mine did this... I changed the O2 and Knock Sensor and it ran well again.

That fact that it runs bad after warm up makes me think O2 sensor.

Where's the "knock sensor" ?

Steve_Moore said:

Where's the "knock sensor" ?

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93 models don't have them. It was a Renix 87-90 item.

ratherbcamping said:

That fact that it runs bad after warm up makes me think O2 sensor.

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I see where it's at , is it just unscrew and plug the new one back in ?

Disconnect the O2 sensor and drive it on the freeway hot and cold. If the problem is gone with the O2 sensor disconnected, then change the O2 sensor. If the problem is still there, unchanged, I would look elsewhere for the problem.

Somebody correct me if I am wrong, but this test should work on the OBD-1 93 models, yes? I know it works on the 87-90 models. It might, or should throw a code with the O2 sensor disconnected but it should run in the open loop mode allowing him to determin if it is, or is not the O2 sensor.


I would have them test the fuel pressure to test the fuel pimp and fuel pressure regulator. Also check under the hood when it is dark and look for any high volate arking. Sounds to me like a high temperature insulation failure in the plug wires or one of the other ignition wires.

Check some simple things first like the battery clamps and posts. If they are corroded and or loose, they cause this problem too.

my first xj did this after i cleaned the throtle body w carb cleaner(aparrently a bad idea)
i replace EVERY sensor on this thing and it still did it for about a year untill a buddy of mine told me to change the pcm
80 bucks at kragen and the jeep ran great... it was an 87 4.0 5 speed
dont know if this helps but good luck

xjpheonix said:

my first xj did this after i cleaned the throtle body w carb cleaner(aparrently a bad idea)
i replace EVERY sensor on this thing and it still did it for about a year untill a buddy of mine told me to change the pcm
80 bucks at kragen and the jeep ran great... it was an 87 4.0 5 speed
dont know if this helps but good luck

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Ok...whats the pcm ?

pcm, ecu, dont remember exactly what jeep calls theres but its the computer the brain

xjpheonix said:

my first xj did this after i cleaned the throtle body w carb cleaner(aparrently a bad idea)
i replace EVERY sensor on this thing and it still did it for about a year untill a buddy of mine told me to change the pcm
80 bucks at kragen and the jeep ran great... it was an 87 4.0 5 speed
dont know if this helps but good luck

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You are the first one I have heard of to have a bad Renix ECU (1987-90 was a renix ECU)!!!! Do you still have the old one, if yes I am sure 5-90 would like to get his hands on it.

I would look at a number of other items before bothering with the PCM (called a PCM since 1991), especialy since he says it runs perfectly at times. Sounds more like a loose, damaged or corroded electrical item or a fuel pressure/flow problem (intermitent), or a loose Cat.