Same Jeep different problem

[SpinnerBait_Nut]

First a little background on my Jeep.<br />It's a 1996 Cherokee with 130000 miles on it.<br />It is used ever day on a 90 mile stop and go run.<br />It is used to deliver the mail in my area.<br /> <br />I have had it since October and after I first got <br />it, it had a problem with wanting to miss and act<br />like it was running out of gas.<br />It would only do this after about 80 miles or so.<br />I took it back to the dealer and he had his mechanic<br />drive it till it started doing this and then he hooked<br />it up to the computer and found nothing, no codes<br />were on there.<br />He then took it to another place to put it on their computer<br />with the same results. No codes.<br /> <br />So, he put a fuel pump on but not the pressure regulator.<br />New cap, plugs, wires, rotor, even a distributor.<br />No good. Same thing. After about an hour and a half into the run, start acting the same way.<br />I talked to some people and after that, I put an 02 sensor on and it ran great up till 2 days ago.<br />Now, it is doing it when you go up a grade.<br />It is like you have the gas pedal pushed down and then let it up and then back down again.<br />A surge if you will. No missing, no acting like it's running out of gas, just the surging.<br />Not on flat ground, just when you are going up a grade.<br />I am at my wits end with this thing.<br />Has anyone got any ideas?<br />Could the fuel pressure regulator be doing this and if so, why wait so long before it starts?<br />How about the TPS. Could this do it?<br />Thanks in advance.

 

[Spidybot]

Re: Same Jeep different problem

Your engine is run by a computer which, in it's turn manages the thing based in reading from sensors around the engine.<br /><br />Signals are picked up on air intake, temp, exhaust, cranck/flywheel. At least.<br /><br />I'd suggest a thorough looking over wires, connectors and joinings. Then a systematic troubleshooting of sensors.<br /><br />Fault codes are stored only when values outside certain limits are recorded - and very often a fault in another part leads to the lambda/oxygen sensor recording 'off limit' values pointing all errors to this item.<br /><br />Unfortunately a set of weird values that are each within the limits may result in a hardly driveable mix thus not storing any fault codes.<br /><br />If you're outside warranty and/or want to talk to someone beside the dealer, look up one of those garages who make hi-perf cars ('chip-tuning' or aftermaket EFI's). They have the experience on where to look for such 'ghosts'.

 

[mellowyellow]

Re: Same Jeep different problem

howdy SBN, this is a shot in the dark, but I had<br />exact same problem in an old van. took forever<br />to finally figure out that there was some crud<br />floating around in the gas tank and when I really<br />stepped on it, it got sucked into the feed and<br />would almost die. after engine was turned off the<br />small piece of carpet in there would release and<br />it would start right up and run fine. how a piece<br />of carpet fibre got in there, god only knows.<br />again, shot in dark, but u never know.<br />good luck,<br />M.Y.

 

[jinx]

Re: Same Jeep different problem

Here's an easy check out that could cause it.<br /><br />On the Cherokee the vaccuum reservoir is located just behind the front bumper, sort of tucked into the bumper, on the right side. Check your vacuum lines back from it. I've seen them get pulled off at the reservoir or sustain damage where they go past the battery.<br /><br />Vaccuum leaks can cause all kinds of oddball problems. I hope yours is this easy.<br /><br />Good Luck,<br /><br />Jinx

 

[Boomyal]

Re: Same Jeep different problem

A Chrysler dealer has a diagnostic tool called, I think, the Co-pilot. They hook it up and leave it in the car. It continuously moniters every function/sensor in the vehicle while retaining an approximate 10 second memory stream. When you get an occurrence you push a button and it saves the data stream from the 10 seconds b4 you hit the button to 10 seconds after you hit the button. It will record 3 such episodes. You take it back after the 3 recorded episodes and they download onto their computer and read the data.<br /><br />It's probably the main computer.

 

[jimchere]

Re: Same Jeep different problem

If this is happening only under load, then knowing everything else is good, I would check the MAP (Manifold Absolute Pressure) sensor. It has a vacuum line to if from the intake manifold and based on vacuum demand alters the timing and mixture. Typically mounted near the rear of the valve cover or on the firewall. It relys upon a diaphragm, which may be going bad based on the age and mileage of the vehicle. But first, check the vacuum lines to the MAP sensor closely, along with the electrical connector and make sure the contacts are all clean. Could very well be a cracked/bad vacuum line, leaky diaphragm in the MAP sensor or a cruddy electrical connection to it. The MAP sensor is one of the things that puts big inputs to the PCM only under load.

 

[DJ]

Re: Same Jeep different problem

SBN,<br /><br />Two words. Fuel Filter.<br /><br />That is one of the most neglected items on a fuel injected engine. Out of sight, out of mind.<br /><br />Everyone is FAR too quick to start blaming expen$ive electronic components.

 

[JasonJ]

Re: Same Jeep different problem

I feel your pain. My Jeep is running good now, but only after an $1100 ECM was installed. I recommend you go to Jeepsunlimited.com, and choose the appropriate forum. They should be able to hook you up. BTW, my ECM never showed any fault codes, that is one of the symptons of a bad ECM, is that the vehicle runs like arse but no codes are thrown. I hope it is simple and cheap for ya....

 

[DJ]

Re: Same Jeep different problem

SBN,<br /><br />Another thought.<br /><br />Your changing the O2 sensor and getting the rewsults you noticed makes sense.<br /><br />A new o2 sensoer will tend to make an engine run leaner, thus use less fuel.<br /><br />Now that the O2 sensor, has some miles on it, you're back to your issue.<br /><br />I'm convinced that you are starving it for fuel.

 

[snapperbait]

Re: Same Jeep different problem

I dunno diddly squat about chrysler/jeeps efi, so...<br /><br />doubt seriously that the fuel pressure reg would cause that specific problem..<br /><br />TPS could cause the problem.. They do get dirty inside.. <br /><br />Maybe carbon build up in the EGR valve, or a funky EGR valve vacuum switch.. Pull the vacuum line off the EGR valve and cap off the vacuum line... That'll keep it closed.. Run it and see if the problem persists..

 

[LubeDude]

Re: Same Jeep different problem

Id change the o2 sensor again, if that doesnt do it, there is always the posability that it may be a transmision, torque converter problem with that many miles of stop and go driving! Change fluid and put in a bottle of trans fix!<br /><br />LubeDude

 

[SlowlySinking]

Re: Same Jeep different problem

SBN, seems to me you can read Chrysler (Jeep) computer codes without any equipment, simply cycle the ignition key ON/OFF 3 times (or is it 5) and stop on ON, then count the Check Engine Light flashes, the flashes are equal length, you need to look at the spacing between flashes to read the code numbers, you can then check online for the codes. You may have to do this several times to see the sequence and accurately read the codes, but it's free, each time I do this it saves me about $100 that the dealer charges to read the codes. Good luck

 

[SpinnerBait_Nut]

Re: Same Jeep different problem

Thanks guys.<br />Have put new filter on it along with new pump.<br /><br />Also, this engine has no EGR valve.<br />Something they done away with.<br /><br />SS, I did pull the codes that way and all I got was a 12. Battery cable disconnect.

 

[SpinnerBait_Nut]

Re: Same Jeep different problem

Let me add a side note here.<br />Don't know if it will help or not, but it will do it more as the outside temperature goes up.

 

[Stratosfied]

Re: Same Jeep different problem

I had a problem similar to this once and it was the catalytic converter being worn out. Changed it out and everything ran normal again. I don't really know of any way to diagnoise(sp) this problem other than to hook to a exhaust monitor. Just a suggestion..

 

[SpinnerBait_Nut]

Re: Same Jeep different problem

Thanks Stratosfield. The cat is new along with the 02 sensor in it.

 

[Pete30]

Re: Same Jeep different problem

I had an 88 cherokee with about 120000 miles that would do something similar, I never did get it fixed, but if you shut of the ignition, pumped the gas pedal 5 times, and counted to 5 it would idle and run like a champ. No lie.

 

[Skinnywater]

Re: Same Jeep different problem

Sounding like a Mass airflow sensor to me.

 

[JHOLE]

Re: Same Jeep different problem

Just a thought here. 90 miles a day of stop and go.<br />

It is like you have the gas pedal pushed down and then let it up and then back down again.<br />A surge if you will. No missing, no acting like it's running out of gas, just the surging.<br />

At 130k, maybe a look at the trans?

 

[SpinnerBait_Nut]

Re: Same Jeep different problem

The RPM's are going up and down.<br /><br />I drove it myself just now on a 6 hour run I do ever morning and I took it instead of the one I normally drive.<br /><br />At first everything is fine.<br />Runs like a champ.<br />Could not ask one to run any better than it did and I got on it pretty hard at times.<br />Nothing, just kept on keeping on.<br /><br />Then when I got off the interstate and started to the house on the back roads, the first grade I went up, it was just like you was playing with the gas pedal, pushing it down and letting it up, like maybe 300 or 400 rpm range.<br /><br />Beats me what it is, but it's driving me and my driver nuts.<br /><br />Thanks everyone for your help.<br />I will let you know what I find out, if and when I do.