My 2.8 Cherokee is grumpy

15

Asked by Nov 19, 2016 at 03:45 PM about the 1986 Jeep Cherokee 2 Dr Pioneer

Question type: Maintenance & Repair

The time light shows an erratic crazy timing and the car pops and idles rough

21 Answers

52,015

The timing chain may be stretched out.

1 out of 1 people think this is helpful.
52,015

If the distributor bushings are worn the timing may be erratic.

1 out of 1 people think this is helpful.
15

You mean the rotor? Replaced, still same, could be the map sensor? I have replaced alot of parts but not successful, replaced chain, rebuild carb, redone throttle shaft, alot alot, what does the fire timing regulations, the map or something else?, I bought a maintenance book also.

52,015

Not the rotor but the internal parts to the distributor. Depending on what type of ignition system you have, the bushings being worn can cause the timing to jump all over the place. You may want to get a new distrubutor.

1 out of 1 people think this is helpful.
52,015

If you replaced the timing chain did you replace the gears?

1 out of 1 people think this is helpful.
Best Answer
15

If I disconnect the 4pin connection to the distributor tha engine idles ok

15

I will try to do that with the distributor thanks, let you know

52,015

Try to wiggle the rotor around. If there is any play side to side then the bushings are worn.

1 out of 1 people think this is helpful.
15

I 've checked the voltage of the O2 sensor and comes out 0,2 it should fluctuate, id does but a little, the timing is way too advanced, if I unplug the air mix solenoid in my carburettor the voltage goes to 0.5 where should be, if I unplug the map sensor hose the timing goes closer to the 6' btdc os so, I will check the right voltages of the throttle position sensor and the MAP, check other sensors, but it could be the PCM? I need to take it out and check the connections, it became a Nightmare, or the most challenging yet. I will figure it out, but at what cost!!!

3,425

Hello, You mentioned that by unplugging the connector the jeep idles fine. That is what you do to set the timing, so that you have base. SO, it sure would sound as though the timing is either off baseline, (too advanced), or if not, when plugged back in, timing is being manipulated too much by the electronic controls. Remove the connector again, and get a known factor for base timing...and let us know what that is... AND, what it appears to be CONNECTED as you increase rpms to about 1500 from idle. Report that also. Good Luck ATM

2 out of 2 people think this is helpful.
15

The timing is set to factory spec with the 4 pin wire off 6 bdtc, but when I accelerate seems okay, with or without wires I think also the o2 sensor value fluctuates, unless I keep steady RPM then it shakes a bit, drops to .2 volts , I connect and disconnect things to try timing and O2 voltage, I read that .5 volt is the right value range for a correct carb emission value, I was wondering if the MAP sensor if at fault for everything.

3,425

Hello, Might be, could be, maybe... You see I really need to know about that timing curve @ those rpms. You know, it is very difficult to get one these jewels so-so as in just right...That carb was not very great...and you seem to know it well...and the metering rod problems, cross leaks and such. Refresh for me the briefly history of engine...work done (mechanical), miles, etc. in your own words. ATM

1 out of 1 people think this is helpful.
15

I've replaced the engine with a used one, did compression tests, the old one was mixing water with oil, kind of low compression on a cylinder and had a little knock, junk. The new one starts easier but still similar misbehaving good cold or warm but as soon it gets to temp. op. condition it idles porly, I bought a special sensor tester, and noticed that the idle misfiring is due to a lean/timing condition, the timing goes way over the max gauge, and 1 inch over to the left of the pulley mark. The electric air/gas mix gets activated and lean condition occurs, I think. After all the work that I've done to it, it is so frustrating, my wife sais that if does not go we can junk it. I can start buying pmc, map, cat, etc etc, basically it is not gonna happen, not funds to waste on it, the car over all is in good condition, everything works well, does not leak anything, because I fixed everything. The timing is always advanced, I'm sure that someone that had the same problem knows what is the part that is failing to report the right info to the PMC. or the PMC is fried or so, I was thinking about the MAP sensor to be at fault and sending erratic info about timing, but what about the air/gas solenoid, before it did not do that I think, because the carburetor throttle shaft was super loose, and I bought a throttle shaft rebuilding kit and fix it, nothing, should do better but no, that solenoid has to be activated all the time, before I think it used to be on an off as needed.

3,425

Well, I kinda see what's going on...Just your description of that idle missing/popping like sound shows high timing, and with that you need richer mixture... Map sensor has little to do with timing, only fuel enrichment is this scheme, @ idle.. ...other sensors tell ecm more about timing curve,...at idle. Listen, I just don't know...question...Do you live in a smog state? with inspections? One of best ways/Cheapest ways we were able to give a little life, with decent service was an entire upgrade...in those days. Carb and Intake replacement...Edlebrock. Cheap, normal HEI distributor... And those little engines became very stable, with a nice torque curve, and reasonable mileage. And pretty much trouble free... Don't know if this is an option or not. I can feel your frustration, as well as anyone who every worked on 2.8 w/carbs will tell you... And yet, I still don't know the upper extremes of that timing, ..total advance? ATM

15

I live in California, the worst of the "smog States", I understand that is important to keep cars smog safe, but in this State you cannot do too many modifications, not different carbs, would not pass the visual, I'm going true the manual and check the all sensors system and start to rule out one thing at the time. unplug the pmc and check for faults, I believe that there is a reason for it to behave like this. And then, after I found the problem I'll let you know, also I will get 1/2 gal of gas and burn it. Easier and cheaper to get a new one, this time fuel injected. My grandfather sold mopeds, and one day a guy came to his store to buy a new moped because he got fed up of his old one, he got stranded for too many times and too many time he had to call the mechanic to fix it, so a way he did not have to deal with it, he got a ride to the gas station to buy a qt of gas and burn it.

15

Sometimes you get and sometimes you loose. Probably the moped needed some gas, but in the tank.

3,425

Okee Dokee,...I hear you...all this time I been using 5 gallons of diesel to rid my soul of gremlins...I can switch to half a gallon of gas, and save myself a couple of bucks...:_) Back on Cherokee Cher,....ok...you sound ept up on that system...just mentioning...you know those metering rods, (yes, even controlled by ecm) were horrible about sticking when the body of that carb got hot...just something that I remembered turned out to fix a few. I meant to ask the other night,...have you ever driven with the 4 plug controller for the HEI disconnected? How does it run...any power loss>? Any power gain, with the smooth idling? Good Luck ATM

15

the other day I was a little frustrated, When I unplug the hose from the MAP the timing goes to specs

3,425

Hello,...well, that is totally normal, and within specs. It should go to base timing, (before rpm advance) when at WOT, (Wide open throttle)...like when you floor it, and engine vacuum drops to near 0, in theory. I think you may be ok on that timing advance, the ecm will advance up to 30° at idle, I think the problem relies in not rich enough, miss-fire under idle, lean condition. And any vacuum leak will only exacerbate the problem...and erratic idle will affect signals from sensors to ecm...I am thinking, get the idle steady, smooth...maybe timing will stay static more... Any How, Good Luck, ATM

15

I've checked the voltage fluctuation of the o2 sensor, at idle is very low voltage, about 0.2 if I rev the engine the voltage goes up, and I was able to use the gas idle adjusting screw, not the air, on the carburetor, the voltage reading goes up, but not enough, should be around 0.45 or so, so I'm thinking, or there is air that goes in somewhere,or the EGR does not open at idle as it should, oxygen going in from a pump on the exhaust, but why the mixture solenoid gets activated, The PMC? Mhhhh!! more investigation is needed, I do not want to continue buying things without results, I was checking on those internet forums and I did found some, but not answer.

15

I was reading that at idle the mixture solenoid is activated, I've accessed the idle mixture screw, and backed up a little and the overall thing gets better, the car does not have too much power now, like I remember, I'm not sure, because, I've been driving a Saab 220hp so I cannot compare it, Today I will play a little with it and see, feels like something in the carb got plugged, I've disassembled the carb too many time now.

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