weebur
NAXJA Forum User
- Location
- Northern Illinois
I thought I’d throw this out here for the guys that are getting persistent codes for #3 cylinder misfires on the 4.0L engine.
After getting tired of resetting the codes and rough idle I checked around and learned that the problem was most likely “Heat Soak” whereas after running the 4.0L in a hot environment and then shutting down would cause the fuel in #3 fuel injector to vaporize and cause a lean mixture/misfire. The factory came up with a hokey fix that involved wrapping the injector with insulating tape. I tried wrapping mine with aluminum foil and blocking off the spaces in the intake manifold that may have allowed heat from the exhaust manifold to heat up the injector(s)…no help. I should add that my engine would throw a code while idling, not after shutting down, which should have provided enough airflow to prevent heat soak.
I checked with my local part stores and saw that AutoZone offered original replacement injectors and a “redesigned” one for several bucks more. I had them pull the redesigned version and saw that it’s felt heavier and appears to be made of stainless steel. I was low on cash and decided to just go with the original injector and replace the “O” rings on the other injectors.
After pulling the fuel rail/injectors and replacing the O-rings I noticed that the new #3 injector with a new O-ring slid into the recess easily, a LOT easier than the other injectors. All of the recesses in the intake manifold where cleaned and lubed so I have to think that the hole for #3 injector was bored too big at the factory. What I’m thinking is that when my intake manifold got hot it created a vacuum leak past the O-ring on #3 injector causing a misfire/code.
For what it’s worth, I suggest that anyone with a rough idle/#3 cylinder misfire issue consider just replacing the fuel injector O-rings before spending several hundred bucks on new injectors. It’s an easy job and hell, the O-rings are only a $1.50 or so for two O-rings. Ten bucks in O-rings and an hour labor might just be the ticket. My engine is running smoother and so far no codes/misfires.
'97 XJ Country
4.0L/AW-4
118,000 miles
After getting tired of resetting the codes and rough idle I checked around and learned that the problem was most likely “Heat Soak” whereas after running the 4.0L in a hot environment and then shutting down would cause the fuel in #3 fuel injector to vaporize and cause a lean mixture/misfire. The factory came up with a hokey fix that involved wrapping the injector with insulating tape. I tried wrapping mine with aluminum foil and blocking off the spaces in the intake manifold that may have allowed heat from the exhaust manifold to heat up the injector(s)…no help. I should add that my engine would throw a code while idling, not after shutting down, which should have provided enough airflow to prevent heat soak.
I checked with my local part stores and saw that AutoZone offered original replacement injectors and a “redesigned” one for several bucks more. I had them pull the redesigned version and saw that it’s felt heavier and appears to be made of stainless steel. I was low on cash and decided to just go with the original injector and replace the “O” rings on the other injectors.
After pulling the fuel rail/injectors and replacing the O-rings I noticed that the new #3 injector with a new O-ring slid into the recess easily, a LOT easier than the other injectors. All of the recesses in the intake manifold where cleaned and lubed so I have to think that the hole for #3 injector was bored too big at the factory. What I’m thinking is that when my intake manifold got hot it created a vacuum leak past the O-ring on #3 injector causing a misfire/code.
For what it’s worth, I suggest that anyone with a rough idle/#3 cylinder misfire issue consider just replacing the fuel injector O-rings before spending several hundred bucks on new injectors. It’s an easy job and hell, the O-rings are only a $1.50 or so for two O-rings. Ten bucks in O-rings and an hour labor might just be the ticket. My engine is running smoother and so far no codes/misfires.
'97 XJ Country
4.0L/AW-4
118,000 miles