No CEL, very frustrating. I will try taking it down the road with the upstream O2 unplugged.

 

Well fellas, I think I’ve answered all my questions.

Found milk on the oil dipstick this afternoon. Looks like I blew my head gasket.

The jeep was at operating temp when I ran the oil out, so I’m sure that’s what happened. Looks like I’ll be tearing into the top half of the engine and refreshing everything. Thanks for all the guidance and assistance, hard lesson to learn.

 

When my upstream O2 sensor started crapping out, I'd get all sorts of bucking at part throttle when accelerating. When I unplugged it, the problem went away immediately. At full throttle it ran fine since it went to open loop and ignored the sensor.

 

Welp, I guess I need to schedule a visit with my eye doctor, because there was no water in the oil. I drained the oil into a glass jar and inspected all of it, it was clean as a pin. I’m. It sure what I saw, but I didn’t find any froth of any kind.

What I did find was sand in one of my spark plug wires, and another wire that wasn’t even connected. I also found brown dust in my coil pack wire. It’s possible that I was only firing on 5 cylinders, maybe even 4.

New plugs, new wires, runs like a dream.

 

Pull one plug wire at a time while its idling. You can track down wich cylinders its missing on this way

When a Plug wire us pulled it will emmediatly start running rough if it wasn't running on the cylinder it wont change.

Good luck. Dont throw in the towtowel yet. Youtube is your friend.

 

I think pulling the plug off the injector might be a better idea unless you want this guy to see what getting zapped by the coil feels like haha.

 

HA, yeah, that makes sense, but didn't go that route. Just doing a visual on what came out of the plug wires was enough to convince me that it probably wasn't firing on all cylinders. I also found a dirt dobber's nest below the distributor, which is maybe where some of the dirt came from. It definitely benefited from a good ignition system refreshing.

 

True, there is a certain skill to handling plug wires on a running engine. If the injectors can be reached, that way is preferred.

But then there are cars like my 300 where neither plug wires nor injectors can be reached without 30 minutes of parts removal what will 100% prevent the engine from running. Thanks Ma.

 

You can gauge how well spark output is by how much it hurt

Sometimes watching it run in the dark makes plug wires stand out because you see it arc to ground through the cable or cap

 

So I thought that new plugs and wires had my problem fixed, but I noticed the phenomenon again the other day, 3 days later. More bucking/jerking under load, and poor fuel economy as well. I have never experienced misfire in an engine, but I believe that is what I'm experiencing.

Very frustrating. I am going try a new distributor cap and rotor this weekend and see if that fixes the misfire issue.

Given that all of this started when I drained the oil out of the crankcase while running it, what are the chances that this misfire issue is coming from engine damage from running it without oil? My next question is am I getting proper compression in all cylinders? I am going to have my mechanic check on that for me. Also, I'm wondering if the ignition coil and ignition distributor (the disc shaped thing under the distributor cap) might be going out? I suppose Crank sensor is possibly at fault too?

Still no CEL, getting more and more stumped...

 

Getting zapped by a plug wire is at the very bottom of MY list of things I dont want to get zapped by..... But if you want to save a few ounces of fuel, then sure, pull the injector plug.

 

Just for the sake of updating the story for any who might find this useful in the future, here is where I'm at.

Problem: misfire under load, which came about after I had the oil leak problem stated above.

This weekend I added a new distributor cap, rotor, and ignition coil (my 98 has the single coil connecting the battery to the distributor). Only thing I DIDN'T change was the little stator disk under the distributor cap. Two days later and so far so good. However, I went through this last week and it misfired again 3 days after adding plugs and wires (when I hit the 1/4 mark on my fuel tank, interestingly). I'm holding my breath, but if it does misfire again, my next area to address is fuel, since I can now check off any ignition related issue. I know my fuel pump isn't 100% since I have to give it the poor man's prime on cold start. Though not likely, I figure it's possible that a weakness somewhere in my fuel pump assembly could cause a lean condition under load? Not sure, but that's my next suspect area.

I'm pretty confident I've got compression in all cylinders, so I don't think thats it. But I also might do a compression test if it misfires again.

Also had a mechanic friend scan over all the major sensors to make sure the numbers look good, so I can check that off too.

If I've learned one thing, it's that misfires are NO FUN.