somethings not right Part II....

[JDusen4211]

This was in another thread but I thought I would clean it up a bit for an easier read! Thanks,
John

i still haven't had any luck getting my 97 cherokee 4.0 to run right... it runs rough at idle and surges about +/-100 rpm. it also misses/stumbles a little at higher rms. For example, if you have it in park or neutral and hold it on, say on 2000 rpms, you can kinda hear it stumble ever so slightly. 3 times in the past 2 months it has hesitated when accelerating, like it wanted to cut off but didn't. after i pushed the petal down it stopped bogging down and took off like it should. Any time you take off, full throttle or normally, there is usually nothing noticably wrong.

ive replace the plugs, wires, cap, rotor, iac, TPS sensor, MAP sensor, O2 sensor, added injector cleaner, checked timing, checked for vacuum leaks, checked fuel pressure, cussed at it and it still runs the same. I rechecked the plugs after a few thousand miles and they look good as new.

I am still going to replace the crank position sensor and drill a hole in the cat like some of yall had recommended. Any other thoughts??

[sector95]

Drill a hole in the cat???? No, I don't think so.... if it's plugged then it needs to come out and a new one put in.

Most fuel injector cleaners you dump in the gas tank are not gonna fix six crapped up injectors. In fact most are pretty much a waste of money. The only stuff that *might* help is an *ample* dose of Chevron's Techron (by ample I mean at least double the dose on 1/2 a tank of gas). At nine bucks a bottle this will get expensive quickly and still may not fix your problem soooo....
Take it to a reputable shop and have a thorough intake track/injector cleaning performed..... probably run upwards of $75.... then at every 3k oil change, drop in a bottle of the Techron.... this stuff *does* work and it will keep your injectors clean.

mike

[JDusen4211]

so how exactly do you know if the injectors are actually dirty and need cleaning? any good waay to diagnose this?

[JDPascal]

If the cat was the problem, the noticeable thing would be a lack of power to move the vehicle. It would likely idle well but try to go more than 30 or to pull a hill or slight incline and you could push it faster.

I once had a truck with a broken cat ceramic honeycone. it would float around and randomly block the exhaust. When that happened, it wouldn't go over 25-30 mph at all.

You said there was a dent in the exhaust pipe. sometimes exhaust pipes are double layers and the inner one buckles inward and blocks the pipe. Then again, some exhaust pipes have the dents from the factory.

You also said it boggs out and then takes off like it should. That doesn't sound like a blocked exhaust to me


If you still want to check the converter, take the exhaust off at the manifold. Drilling a hole is not going to tell you much at all.

Get someone with a scope to do a cylinder balance test and read the scope patterns. Isolate individual cylinders to see which one is the weak one causing the stumble at idle. Quite likely the same one is the problem at higher speeds.

Try disabling individual injectors in turn. the ones that makes the least difference are the problem ones.

Have you checked the compression? That would cause an idle problem and miss at speed too. Possibley a burnt valve?? or maybe cam wear. (now we're getting into the unpleasent stuff!)

JD

[JDusen4211]

well it is def. not lacking power because it has awesome acceleration. i checked the injectors by unplugging them one at a time and they all made it run worse about the same. however, the way in which it seemed to get worse seem to be the same as how it has been running. if that makes any sense. i checked the fule pressure again ant it was about 48psi. not sure what to make of that???

i will try checking compression this afternoon. what should the compression be? about 90psi? i hope it doesn't have anything to do with the internals, but... that would be just my luck...

one other thing to mention would be that sometimes it idles worse than other times, sometimes it is only noticiable because i am looking for it while other times you can feel it shake the jeep a little when it fluxuates +/- 100 rpms.
i was thinking thinking it has to be something in the ignition system still. the plugs still look great after a few thousand miles, 2 sets of new wires, cap and rotor look fine. i did the "spray water test", like someone suggested and i didn't see any faulty areas. what are some other things i can check for?

[myjeepsux420]

Did you say that it idles @ 2000 rpm? How did you verify you don't have a vacume leak? Perhaps you have an intake gasket leak? I think if you had an intake leak it would affect the MAF sensor. This one is going to be a paint in the ass to fix. Keep us posted.

[Ray H]

Fuel filter!
In your last post someone suggested fuel filter and you said you had changed it then that you hadnt changed it. People tend to jump through hoops when troubleshooting when its generally a simple, common, problem they overlook.

[JDPascal]

This is getting way to complex.

Suggest that you make a check list of all the advice and everything you have done with the settings/adjustments made and results of any tests.

Compression should be even with less than (15-20%) between cylinders. Right now I don't expect that there will be anything out of the ordinary here.

With the randomness of the miss, I would tend to think injectors. Dirty fuel or diposits causing them to stick or it could also be in the computer because that is where the control is made thru pulsing the ground circuit.

Check the computer connectors and the ground contact from the module to the body/frame and back to the battery.

(I didn't see you saying that it idles at 2000, only that when you hold it at 2000, there is a miss......)

JD

[Ray H]

Agreed,

Intermitant "stumble", surging, intermitant lose of power:

Dont waste you time on compression, vacuum or exhaust. None of those will cause an intermitant miss or "stumble". Its either spark or fuel related.
Theres no reason a missed spark would cause the "surging". That leaves fuel.
The computer controls fuel and spark but very seldom does the actual computer go bad, generally its the sensors that go bad. It looks like youve replaced most of the sensors. Could be the wiring from the sensors to the computer. If there hasnt been any trauma to the vehicle, why would the wiring spontaniously and intermitantly be bad? Its unlikely.
Concentrating on fuel delivery. You have the filler cap, tank, fuel lines, pump, filter and injectors. Lets eliminate the filler cap, tank and fuel lines. Again, why would there be a problem with them, short of some kind of trauma. If the only problem you have is "surging" I would suggest looking at the filler cap but that wouldnt cause a miss.
This leaves pump, filter and injectors. Is the Jeep running? The pump works.
Now we have filter or injectors. Its possible the injectors are dirty. That dirt had to come through the filter to get to the injectors. The filter is an inexpensive maintenance item thats easy to change. Give it a try before tearing into the vehicle.

EDIT: There is a difference btween "injector cleaner and fuel system cleaner". Injector cleaner takes carbon off the injectors. Carbon buildup wont cause a miss although it may cause surging and lose of power but not intermitantly. Fuel system cleaner is supposed to clean the internals of the fuel system of debry.
Its possible that the "surging" and missing are unrelated. If thats the case, go back to the beginning and handle the problems one at a time.

[JDusen4211]

thanks for taking the time to help... i really appreciate it! we are going to figure this out one day! haha!!

to clear up any confusion: symptoms are that it idles rough at around 600rpm and sounds like it misses. the rpms surge a little at idle (+/-100). somedays it runs better than others. if you hold it at 2000rpm you can here it miss ever so slightly every 2-3 seconds. it has hesitated a few times in the last 3months, but it doesn't die and it catch back up to normal immediately, like nothing ever happened.

checklist
-new air filter, plugs, wires, rotor, cap, iac motor, tps sensor, map sensor, 02 sensor, injector cleaner (two times and i now know is worthless...)

-i sprayed water on the distributor coil and wires to see if there was any arcing (done both in daylight and at night). yielded no results.

-i have pulled the plugs a dozen times since i initially replaced them about 5000 miles ago. they still look like new and don't seem to have any wear or deposits.

-i cleaned out the throttle body where the iac inserts, but there really wasn't any carbon build up.

-to check for vacuum leaks, i sprayed throttle bottle cleaner and carb cleaner on every hose/line and around the intake and listened for the motor to pick up or simply change. yielded no result.

-checked fuel pressure with a mechanical gauge from autozone. when just turning the key to the run position (motor off) the fuel pressure was 45 or 48 psi, i forget which. with the motor running it was rapidly fluxuating between 45 and 52 psi. i think the fluxuation was just from motor vibration and a cheap gauge. not sure. (since the pressure was good and even, didn't replace fuel pump and assembly)

-checked fuel injectors by unhooking them one by one while the motor was running. as i unhooked each one, it ran worse (duh!) there was no difference in how bad it ran between each of the injectors meaning that each one made it run about as badly as the next.

-noticed a dent in the pipe just before the cat. but i don't think it is an issue. someone suggested the cat being clogged, but it doesn't lack any power so i don't think that is an issue either.

- i have noticed that when i crank it, there is water coming from the tail pipe... i crank it ever couple of days and i don't think it is an abnormal amount considering the humidity here, combustion rxn, etc.

things to do still
-check compression. (will be next week before i get my compression gauge when i head back home. but yall don't think it is that, so that is a good thing!)
-check wiring and grounds.

question about the fuel filter, it only comes with the purchase of a new fuel pump since it is inside the tank. should i go ahead and replace that?

since we pretty much think it is injectors, what do i need to do to clean them?

once again thank a ton for all the help!

[Ray H]

I forgot, you have a 97. The filter is in the tank with the pump. Thats a PITA. Its supposed to be a "life time" filter, for whatever thats worth. It would require dropping the tank and dropping a couple hundred$ to replace. Are you also having hard start (long cranking) problems? Thats another symptom of a clogged filter. If you experience hard starting. Try cycling the key a couple times, holding the key for a couple seconds while the fuel system primes, before actually starting it. The pump will run for a couple seconds each time you cycle it to prime. If you prime the fuel system a couple times and then you start it and it starts immediately, theres a good chance youve found your problem.

[JDusen4211]

nope, no hard starting problems... everything is just dandy except for the bad idle and missing problems as well as the occational hesitation. sorry i think i have forgotten to post the year for a while... but it is a 97 cherokee 4.0L. thanks a bunch though!

Originally Posted by Ray H

Are you also having hard start (long cranking) problems?

[Dale Aeppli]

Originally Posted by JDusen4211

nope, no hard starting problems... everything is just dandy except for the bad idle and missing problems as well as the occational hesitation. sorry i think i have forgotten to post the year for a while... but it is a 97 cherokee 4.0L. thanks a bunch though!

Get a vaccum gauge and hook it up ,they can tell you a lot if you learn to read them You can get at parts store they have sheet that explains the function of the gauge. I use mine all the time. Have one mounted in my 97 -4.0 Dale

[AlohaBra]

On the dent before the cat on the Left side exhaust pipe, it is supposed to be there for clearance on bumps from the front axle. I had the dealer look at it and they didn't know.... so I found an exhaust systems shop and they informed me about it. Mine is a two door 97 Sport...the exhuast is a little different from the 4 door.

[JDusen4211]

Interesting.... seems kinda odd though cause there is pleanty of room... i have a pic of it if you would be willing to look at it to confirm. im not sure how to insert a pic on here, but i can email it to you or anyone else for that matter. thanks john