Misfire / rough idle

[KingCarGuyZ]

Yeah anything helps honestly. I am going get a compression tester, and test the compression. It seems to rev okay... but if the engine is trying to rev under load the entire vehicle violently shakes. I had just put gas in it 9/20/20 so it has fresh gas. I might try getting new cam and crank sensors see if that helps. I have seen on some other post that it could be part of the valve-train, so I am also going to try to take the head cover off and check all of my valves because maybe one of them is being held open or something, not really sure.

I don't know if i mentioned this earlier, but there is a puffing noise coming out from the exhaust that doesn't sound normal. It might just be a symptom of a misfire, or maybe not. Figured id throw that in.

Edit: Do you think there is any chance there is a ground problem between the spark plug and the block?

Sticky/ poorly sat valve? Puffing sound makes that seem likely. If you could get a sniffer on it to tell if it’s running rich or lean that might be useful.

you could certainly check your ground impedance and or clean your grounds. Couldn’t hurt might help.

did it used to run fine? Just start doing this one day, slowly, new to you?

 

[Huskey411]

Sticky/ poorly sat valve? Puffing sound makes that seem likely. If you could get a sniffer on it to tell if it’s running rich or lean that might be useful.

you could certainly check your ground impedance and or clean your grounds. Couldn’t hurt might help.

did it used to run fine? Just start doing this one day, slowly, new to you?

Yes, it ran perfectly fine for before. It just randomly starting running absolutely terrible and doing the vibration under load. But after testing spark and fuel it tells me it is probably compression. I plan on checking that today.

 

[KingCarGuyZ]

Yes, it ran perfectly fine for before. It just randomly starting running absolutely terrible and doing the vibration under load. But after testing spark and fuel it tells me it is probably compression. I plan on checking that today.

It would be incredibly unusual to just loose compression like a light without some sort of massive failure that you would notice.

I’m guessing timing. Either mechanically out of time or more likely the crank/cam sensor thinks it’s out of time.

I’d go ahead and check the compression though, can’t hurt. Might tell you something. If nothing else it’s good info to have. And it lets you get another look at the spark plugs to see if they look interesting.

 

[Steel City 06]

Yes, it ran perfectly fine for before. It just randomly starting running absolutely terrible and doing the vibration under load. But after testing spark and fuel it tells me it is probably compression. I plan on checking that today.

See if you can do a leakdown test as well. Leakdown tests will actually tell you what the problem is as opposed to just having a problem. (However, a leakdown test only verifies valve operation at TDC.)

 

[Huskey411]

[Solved]
So it ended up being a bad spark plug. I had rented a compression tester from a local auto parts store, and went to the engine and took all of the spark plugs out to test the cylinders. Each of the cylinders had good compression 160,150,170,165,170,180psi in order. So I figured those were all fine, and so I went to put the spark plugs back in. One I noticed was really squished in, like maybe it had fallen or something and gotten the end squished in, so I re-gapped that one and all of the other ones to .35 and started to reinstall them. I put them all in different just to double check to see if the problem was isolated to one cylinder. Then as I was starting one of the plugs, the top of it broke off.

so I though that couldn't be good. And so I installed it anyway and started the jeep. There was still a misfire. I went back to the tailpipe and you could still hear the puffing sound from earlier startups with the misfire and it smelled very rich and it looked like gas was actually coming out of the tail pipe. So I went back to the engine bay, and took the broken spark plug in, and replaced it with one of the old spark plugs that still worked, and the jeep started right up and sounded normal again and did not have a weird vibration. So I took it around the block to see if it still had that vibration when under load and it was gone, and it was perfectly normal again.

So I am thinking what happened was, that positive node on the spark plug was not making good contact with the actual plug to make a spark when it was installed in the engine block. But when I tested it, the spark plug was upside down with the sparking part up in the air, which put pressure on the node in the coil rail to actually make it spark so it looked like it was working.

Thank you for all the help and good insight you provided me it was very helpful and gave me some comfort as to what could have possibly been wrong with my jeep.

now it appears I have developed a coolant leak from what looks like a drain pipe from the interior so now its time to chase that.

P.S. The spark plugs were Autolite APP985s.

 

[Steel City 06]

For the leak, the most common leak location is rainwater coming in through the cowl. Remove the cowl cover and unblock the drain. If the cowl drain is plugged, the cowl can flood and either roll into the cabin overnight or slosh in while you are driving around.

It could also be a plugged A/C condensate drain. Check and clear that.

If it is coolant, it would be coming from the heater core. Since the coolant is almost boiling, it will typically create a lot of steam or fogging inside the cabin if the car us warmed up.

 

[Huskey411]

For the leak, the most common leak location is rainwater coming in through the cowl. Remove the cowl cover and unblock the drain. If the cowl drain is plugged, the cowl can flood and either roll into the cabin overnight or slosh in while you are driving around.

It could also be a plugged A/C condensate drain. Check and clear that.

If it is coolant, it would be coming from the heater core. Since the coolant is almost boiling, it will typically create a lot of steam or fogging inside the cabin if the car us warmed up.

Yeah It's coolant, and that's what I figured was the heater core. I have heard it is a terrible job and really don't want to do it haha.

 

[Steel City 06]

Yeah, it's definitely not a fun job.

You can bypass the heater core temporarily by connecting the two hoses inside the engine compartment with a connector. I believe one hose is 3/4" and the other 5/8". That will stop the flow to the core. It will mean no heat and no defroster until it is fixed.

You do not want to simply plug the hoses. The heater core circuit is also the bypass circuit for the thermostat and water pump, and you could boil the coolant in the block or cavitate the coolant in the water pump if there is no flow.

Edit: 3/4" not 1/2"

 

[Daryl]

Yeah, it's definitely not a fun job.

You can bypass the heater core temporarily by connecting the two hoses inside the engine compartment with a connector. I believe one hose is 1/2" and the other 5/8". That will stop the flow to the core. It will mean no heat and no defroster until it is fixed.

You do not want to simply plug the hoses. The heater core circuit is also the bypass circuit for the thermostat and water pump, and you could boil the coolant in the block or cavitate the coolant in the water pump if there is no flow.

Exactly. @Huskey411 if you decide to replace the heater core at a later date, use something like this:
https://rover.ebay.com/rover/1/711-...0001&campid=5337789113&icep_item=252807513172

 

[Wayne Mathson]

What mod is this? K suspension, I'm not seeing that.

TJ/LJ Viper Coil Mod
https://www.ksuspensionfab.com/store/p149/TJ/LJ_Viper_Coil_Mod_.html#/