I have a 1994 Jeep Cherokee with inline 6 that has quit firing on one of the bores. Because it has the MPI injector thing and the plugs look okay, I suspect the fuel injector is the problem.

I know what the fuel injector does, but otherwise I know nothing about such systems. I am wondering, is there some way to check the system out? Do they have common problems? Any advice in this area would be useful. I draw a blank myself.

Than again I suppose I could change the spark plugs or the wires, or something. After getting a couple of shocks I temporary gave up on finding the non-firing bore by pulling spark plug wires.

John

 

Do you know which cylinder is dead? Do you know if you're missing fuel or spark in that cylinder? Many possible causes.

 

What leads you to believe that there's a dead cylinder?
Is there a Check Engine Light on?
What codes are being thrown?

 

Okay, how do I get the engine codes from a '94 Cherokee?

 

https://www.google.com/search?q=How+...ient=firefox-a

 

The short term problem is that I would just as soon not go to a mechanic, so I am sorting out what I can do myself. I may have an issue with the motor getting overheated. The radiator juice was low. When I started the motor up later, it was a steady miss, the sort that is expected with a non firing bore. The problem developed suddenly with no side issues that I am aware of. The motor does not run as much differently with a spark plug wire pulled off as one would hope for discovering which bore is the problem. If nothing else develops I will do a compression test.

 

Once you've pulled the codes we can offer better advice.

Please, don't do anything until you know what the codes are.

 

You sure the cylinder is not packed full of cheese?

 

I hate it when that happens, so how low? Did the engine overheat to the point that it would no longer run? Do you hear a knocking sound?

 

We've started using Swiss and noticed better airflow.

You can pull the connectors off of the injectors one by one instead of pulling the plug wires, looking for the cylinder that makes no change in the idle.
If this started immediately after an overheat, I'd do the compression check sooner rather than later. No sign of antifreeze in the oil or steam from the exhaust I hope?

 

I would be working with the Jeep in a more timely way, but I am swamped with things that are more pressing.

To recap, I have a ’94 Cherokee with the inline 6. The motor is less than the best. I run heavy oil because it uses oil, some of it going out the crank case vent. Also the oil pressure light goes on quickly once the motor warms up.

Driving home I may have caused the motor to get hotter than usual because I ran low on radiator juice. The next day when I started it up, it was missing on one bore, apparently, and ran rough generally. Initially I had backfiring, but that has gone away.

Anyway, no antifreeze in the oil or oil in the antifreeze. Pulling the plugs indicated that the number 2 bore was not doing anything. The others were more variable and I was not always sure.

I did a compression test and got results generally better than expected. Maybe it was the heavy oil. Going from the front, the readings were 135, 155, 145, 130, 135, and 132.

The plugs were another matter. The first was black with soot. The second was black with soot and damp with gas. The remaining four were similar and not troubling. A little soot at the base, perhaps from running cold.

So, what would cause a plug to be covered with soot when there is, apparently, no issue with compression?

 

Check codes ......http://jeep-xj.info/HowtoECUcodes.htm

 

Weak spark or excess fuel. Stored codes might point you in the right direction.
What did the plugs look like mechanically, were they noticeably worn with large gaps?

 

Just as a point of information, the numbers above are from my third compression test. The first was with an old gauge that I could not get to work. The second was with a Harbor Freight item that was defective, and not all that good even if it had worked properly. I finally ordered a moderately priced Actron that is shy on features, but hey it works.

By my standards the plugs are about half wore out. They all had big gaps when I first removed them. Long ago I took to using small gaps on older motors based on the general observation that they were more likely to start, and would fire on all bores more quickly during start up, should that be an issue.

Given that plugs could be the issue, at the least I will buy two more, and maybe six.

Thanks for the advice.

John

 

Well, I finally got around to checking the codes. I get a 36, an air switch solenoid circuit issue apparently. Meanwhile I do not know what the air switch does, where it is, and I have been unable to get any useful information from the internet or this board.