Aussie Mike

Hi, I have just purchased a 97 Cherokee with 155,000 k'S on it, has been sitting for 12 months unused. Overall it is in perfect condition and appears to have been well looked after and maintained. Drove it approx 1,000 k's on highway cycle, did about 6 klm's per litre to begin with then climbed to a very acceptable 8 + per litre. All of a sudden it developed a bad miss when at cruise speed with my foot just on the accelerater, when I accerated it would change down, not miss but not have a load of power either. Eventually the CEL came on, showed running lean, reset CEL ran fine for another 500k's but klm per litre dropped to about 6 again.
HAs now develped the mis again, no CEL, running rich and lumpy.
Spark plugs are grey and clean, tailpipe black/sooty. o2 senser black and sooty?

Can anyone tell me what the problem could be, love this Jeep, great ride, but this is driving me crazy. Appreciate your knowledge.

Apologies for the long post, first time on site so trust have not breached any protcols!!

chill

had to have my Ausie friend at work here translate. I'm use to miles per gallon. I'd start with full tune up. fuel filter, O2 sensor. check fuel rail pressure. check for vacuum leaks. normal fuel milage for 97 with manual is around 18mpg highway, 14 for auto. check battery cables make sure there tight, both ends. OBD2 is very voltage sensitive.

Aussie Mike

Thanks for taking the time to respond and apologies for delay getting back.

I have pulled the throttle body off, cleaned the IAC unit, checked battery terminals, seem tight and clean.

Got a replacement front 02 senser and installed it, like magic the mis is 95 -97 gone. Refilled it with petrol so that I can check k's per litre now.

Certainly running and idling nicely, just have to find the cause of the slight mis at cruise speed. It is when you are driving along with your foot just on the accelerator at almost any speed.

Thinking maybe bad plug leads or rotor cap - distributer cap?? Not a lot of $ to replace so think I will try that.

The other thing I thought may be contributing to the problem is the rear senser??

Thanks again and also for the aussie translater

kjc

Yes, as chill suggested above.. especially a quality dist. cap, rotor and wires. I wouldn't worry about replacing the downstream O2 sensor, all it really does is report how well your catalytic converter is working. The one you already replaced helps to control fuel mixture. Also, those plugs can look ok and still cause a mis.. get some champion coppers.

Aussie Mike

Thanks, will try Plugs and cap, just priced one here in Australia, Cap, plug wires and rotor comes to just over $100.00 AUD, can get same delivered from thre USA (Rockauto) for about one quater to a third of the price.

have been told it can also be the IAC unit as well, so may get one of those and replace anyway as a precaution.

Aussie Mike

Have just replaced the TPS, IAC and MAP sensers, a little sharper ppower wise but rough idle at the lights amd miss's still at cruise speed, a little different but still a problem.

Could it be as simple as a bad gasket under the throttle body? Looks ok but I know they can be touchy and cause a lot of problems.

Appreciate any feedback.

Still waiting on plugs, leads, rotor and distributer cap.

kjc

You might check for stored engine codes. Rough idle could be a vacuum leak anywhere, not just under the throttle. Have you checked the vacuum reservoir and all the vacuum lines. They're often ignored, and a cheap fix. You said you had the throttle body off, ya? Did you re-use the old gasket? Maybe put some gasket sealer on it. A little shot of starter fluid (ether? vapour.. not lighter fluid) around possible leaks will show you a change in idle.

Aussie Mike

Thanks KJC, I have just reused the old gasket, looked ok but understand they can be tricky. I will try some gasket sealer.

Have generally checked hoses and replaced one small one that was perished, the resk look good.

I will check the items you suggest and put nes rotor, plugs and leads + distributer cap on today of they arrive as well and let you know the outcome. The power is certainly crisper withthe new items fitted.
Comes the worst I may just go to the wreckers and get a secondhand throttle body with IAC, TPC and MAP on it and try to see if any difference, will cost $100 to $150 but worth a try for my sanity I think, just in case one of the new parts are faulty as I have read ocurs at times.

Aussie Mike

Could I also use throttle body cleaner to check for leaks?

Re stored codes, local parts shops here don't do free checks, if I buy a cheap scanner/code reader will that give me the stored info?

The other thing I will do, as Chilli suggested is check the fuel pressure, so will have to get a gauge for that as well, although I suspect this is not the cause as it starts up easily and without any hesitation every time.

Aussie Mike

Fitting new copper plugs, leads, distributer cap and roter this morning, miss still present, and rough idle. Pulls really well when I accelerate, although still miss's if I drop down to 3rd (auto) and hold at about 2000 rev's.
Will continue looking for a vacumm leak, suspect I can hear a slight leak in manifold but hard to tell with moror running/noise.
Will find a smoker and try the suggested path of blowing smoke into the vacuum hose from the brake booster.

Will also put some gasket sealer on the gasket at the throttle body just to be sure there is nothing leaking there.

captainwoot

Just a thought, now that you have it tuned and have verified fuel pressure etc...does it idle smooth? just wondering about a compression check..a low performing cyl would be evident at idle and low rpm,,
Good luck

Aussie Mike

Idles ok to begin with and sounds ok when you load it up, missis when driving ata steady rate at any speed/revs and when sitting at lights starts to run/idle rough and a little rich as I can see some balck smoke at tailpipe most times.

Strange as after I put the new 02 senser in it was running better and idling better even though it had the miss still at cruise speed. Plugs were nice and grey when I pulled them at that time, when I changed them this morning they were black and a bit sooty again.

I am wondering if I have a dud o2 senser. Or maybe just a dud jeep.

Starting to think it is time to just cut my loss's and sell it to the wreckers! Shame as I think it is just one simple thing that I just can't find.

If it had a bad cylinder would it still go well under acceleration and sound ok/good when loaded up with rev's on a slope?
Also it has run well in the recent past, and the miss did go away for a short time after I fitted the new 02 senser.

Aussie Mike

Fitted CPS today and put gasket sealer under the throttle body yesterday.
Miss is down to about 10% of what it was but still lumpy.
Sprayed carby cleaner whereever I could see that there may be a vacuum leak, none found.
Also did a smoke test, cigarette smoke blown through a hose connected to the intake manifold.
Where to from here??

captainwoot

If you can make it miss under load, or in park, can you isolate the cyl? If you can narrow it down to a specific cyl thengo from there.

If it sat for a year...anychance its just poor fuel ??

Aussie Mike

Thanks, compression check has been suggested but have not got there yet, need to get hold of a gauge.
It does not seem to mis under initial load, eg my driveway is steepish and if pulls up it without any hesitation and feels really strong. the mis really shows itself when at cruise speed, any cruise speed. but less then what it was before I out the new cps in.
also it did run well initially after sitting, and at one stage was pulling just over 8 k's per litre. Everything it has been doing seems to vary. eg when the computer was reset the first few times it cleared right up and went like a train. Now that the mis has settled in, although now less with the new cps as mentioned above.
feels lumpy also, surgy.
maybe a faulty MAP?
or maybe its the main computer playing up.