Search the Community
Showing results for tags 'tuning 4.2l jeep mopar efi'.
Found 1 result
Vehicle background: 1983 Jeep CJ7 Laredo 4.2 with Hesco MPI kit Westside Performance Valve Cover (thick cast aluminum replica of the stock cover) T-18 four speed Dana 300 Dana 44 axles front and rear (4.27 to 1) 36" Swamper TSLs I bought this Jeep in 2003 odometer had 145,000 miles, now has 170,000, it does not get driven all that often. Plaque on the motor reads "MOPAR Performance", it is a mopar 4.2 crate motor with a remanufacture date of 1998. My estimate is that the motor has ~80,000 miles on it. Issue: Recently failed low speed NOX during my last CA smog test, measured 1,322 and max is 1,066 (fail). High speed NOX readings were measured at 948 and max is 968 (pass). For the last 3 or 4 tests high NOX have been an issue. Before I went to test my jeep I changed the oil, it was a quart low. I removed and cleaned the plugs. The fourth plug from the front had quite a bit of carbon buildup. After the test i decided to do a compression test. Got the Jeep up to operating temp and did my first test dry. Readings from front of motor (water pump) to back were 121, 128, 123, 137, 124, 122. The fourth cylinder had a compression reading about 10% greater than the others. This was the same cylinder that the spark plug with the carbon buildup came from. Next I performed the same test but this time adding two squirts of oil to each cylinder before the compression test. My readings were within 1-2 psi of my dry test. My diagnosis is that the cylinder head needs to be rebuilt. The cylinder head is worn letting excessive blow by enter the combustion chamber through the CCV valve which vents to the number 4 cylinder where the oil is burned. This is why i was a quart low when I changed the oil and why cylinder 4's spark plug was all coked up. Does this sound reasonable? Can i rule out rings in this case? What do you think? Thanks for the help!!