Check engine light and cylinder misfire codes

[Boludo]

1996 Grand Cherokee 6 cyl 4.0, check engine light is on and throwing multiple 43 codes, which is for cylinder misfire. The engine runs smoothly. I did a compression test and all cylinders are between 100 and 115 psi. I know that 120 to 150 is the range it should be, but how low is low enough to throw the error codes?

It seems to lack a bit of power and is getting poor gas mileage...around 12 or 13 MPG. It is stock, no lift, stock tire size.

Plugs, plug wires, cap, rotor were recently replaced and look good.

It is not burning oil...no smokey exhaust.

Any thoughts/solutions for this?

Thanks.

 

[bryson]

Improperly gapped plugs? Bad/faulty plug wires? I know you said they're new, but you never know.

 

[thenag]

I am sure this isn't it but if we are stabbing in the dark...

On my 07 f350 the evap canister clogged up and after running for a while the fuel tank would have negative pressure, i would get multiple random miss-fires, the v10 would start to run poorly, as we were troubleshooting it I un-screwed the gas cap and everything went back to normal. (installed a new evap can and it works fine. That era of Fords has a known issue with the evap system)

I am sure this doesn't help but I figured I would throw it out there

Nathan

 

[gijohn40]

My 06 LJ does the same thing. and it doesn't have plug wires. I guess I need to pull the plugs and replace them they have been in for about 50,000 miles...

 

[RogueJeepr]

Could it be the cat(s) ?
Had a friends car do the same thing and replacing the cataletic converters got it to pass smog.

 

[gijohn40]

I just replaced all the cats on my jeep... The misfire is only happening when I start the jeep. so its a timing issue I believe. My LJ has 146k on it and probably still has the original timing chain.

 

[Cascadia]

My 04 Lj used to do the same thing. It was a bad vacuum line on top of the motor that had a crack in it. Caused it to run poorly sand shoot misfire codes. Not sure if it's it but that's what mine was.

 

[Boludo]

I disconnected the battery to reset everything. The check engine light turned off. Took it to get inspected and it passed, then the light came back on and stayed on. So...as long as the light was off it passed.

 

[Boludo]

Good point. They look pretty new. The previous owner put them on, not sure when, but I guess I'll replace them to rule that out.

 

[Toad]

One thing about mopar products is you need to use Champion plugs in them. I have seen a lot of silly issues caused by different plugs.

 

[thenag]

One thing about mopar products is you need to use Champion plugs in them. I have seen a lot of silly issues caused by different plugs.

That is true my father in law put some stupid "E" plugs in his ZJ and the XJ (my wife had the xj before we met... it was stock..) after about a year they both had mis-fire issues, he was in CA and had to pay a shop to diagnosis and fix. (I have run Bosch without issues, but Champion is usually recommended)

Nathan

 

[Boludo]

That is true my father in law put some stupid "E" plugs in his ZJ and the XJ (my wife had the xj before we met... it was stock..) after about a year they both had mis-fire issues, he was in CA and had to pay a shop to diagnosis and fix. (I have run Bosch without issues, but Champion is usually recommended)

Nathan

I have always run Champion too but these were not. I think I'll change them out and see if that helps.

 

[74highboy]

i would check the running compression test it should be about half of normal pressure if its lower suspect valve spring problems

 

[Kiel]

Pull the wires as you go to see if the cylinders drop as its running, 100 psi isn't good