Now, before anyone says anything, I’ve done my testing and replaced what came out faulty.

Essentially, I’ve been having a very inconsistent and random misfires in any given gear. Doesn’t matter if I floor it, accelerate like a grandma, or anything in between, it’ll miss and then never miss again for a time.

Now, I had thought that the MAP sensor was going out, and I tested it. Found some dead spots in the voltage as I drew more vacuum, so I replaced that.

No change in that.

Tested the TPS, found that it was reading the wrong voltage at idle, and would also give false readings after I moved the throttle blade, so I replaced that.

Still no change.

Ignition coil checks out at 1.2 ohms, and I just did wires, cap, rotor and plugs.

I also tested the crank sensor, it reads in 5 volt increments, even when hot, with no dead spots. (I hand turned the crank while back probing the sensor wire), so that checks out.

Only thing I haven’t checked is the distributor sync, but if the distributor was out of sync then it would misfire all the time, right?

Anyway, i’m trying to narrow this problem down. Since I don’t have OBD2, I can only really guess. After I changed the MAP sensor and the TPS, my Jeep felt way different. I’m netting better MPG, i’m able to hold my speed up a hill in 5th gear, and it accelerates a little easier.

Well, that really only leaves a few things:

Vacuum leak? Eh. The only one I have as of right now is at the intake port on the 3rd cylinder, and i’m changing the gasket this weekend.

O2 sensor? Maybe. I doubt it’s ever been replaced since 95, and it would make sense if it acts up and reports the wrong AFR, causing a misfire

Jumping timing? Doubt it. If it jumped timing then id be down on compression, and I doubt this thing would run

Stuck lifters? Again, doubt it. If I had a stuck lifter, it would miss a lot more than randomly.

Leaky injector? Eh. Most of the times i’ve seen a leaky injector, it just runs rich and you have trouble starting after you warmed it up.

I would love some suggestions on what to do next. I’ve already ordered a timing chain, water pump with gasket, o2 sensor, motor mounts and transmission mounts, output shaft seal and some redline MT90, and I plan on doing that very soon when it gets here.

 

Secondary ignition is what comes to mind when I read this. A secondary ignition misfire feels like fishbites. Like a little (or hard) nibble, but not rhythmic.

Secondary ignition is anything from the coil to the spark plug. Coil, cap, rotor, wires, or plugs.

I had one very recently. I went ahead and changed the cap, rotor, plugs, and wires, but it stayed. I found a massive crack in my ignition coil, but only after I hosed it down with degreaser and wiped it down. I'm 99% sure it's the original 352k mile coil.

 

Another possibility is the connection to the coil from the PCM. If it's loose, it will bounce around and produce random misfires.

 

cam position sensor is another possibilty

 

Youd be right.

The connector for the coil lost its clip, and was halfway plugging in. I taped it down in place and so far so good. Not a single stumble ever since Friday.

 

Can you get a sample of gas from the injection manifold? Let it sit for a while in a glass jar and see what happens?