The engine on my 89 XJ (renix 4.0) would run better with 92 XJ (Mopar 4.0 HO) injectors.
Did an injector swap today and had a bit of difficulty with O-Rings wanting to slice on the fuel rail end but he darn thing starts easier, runs a lot better and hopefully won't get worse MPG.
Could have been lazy/leaking/stuck injectors too. Last time I had the intake off I took the injectors over to a local diesel repair shop. They cleaned and tested them. Think I paid about 5$ an injector.
Those o-rings are a problem on my ZJ. Coated them in motor oil but still cut one of them. Then again "bad things happen" if they ain't tight.
Although, you might get worse milage since better performance tends to increased the lead content of the right foot.
I used the Wally World equivalent to WD-40 to lube the O-Rings after RV silicone lube didn't work well which is why I cut the O-Rings, I think.
So far the mileage, by fuel gauge observation only, seems to be going toward the "E" a bit slower because I don't need to press the gas pedal as much for the speed I'm traveling.
But the real test will be when I take the 12 foot yacht out to my local fish hangout and try to pull the trailer back up the launch ramp.
I use a front mount reciever (1 1/4") to launch with so I have tio use reverse to get back up the ramp.
Before it took considerable throttle to do it.
Filled up on the 3rd after a tune-up with Champion plugs and new airflilter and 139.2 mles later (including a trip from Canon City to Colorado Springs and return) 28.06 mpg.
But I'm going to double check it because only about 20 miles was city driving.
Bud, I made the mistake of having my daughter pick up a set of plugs for me. She took what the book at AutoZone said - some Champion platinum or the other. At least she got the Champion part of the equation right. Being a bit lazy and forgetting past experience, I put them in - then satrted to recall WHY I specified the old copper based truck parts. It ate those fancy long life plugs in under 2000 miles.
I'll have to look up the exact number, but someone - likely Mike Romain on this forum - got on this several years ago and pointed me to a specific Champion plug that turned out to last longer and ran noticeably better than the ones the book calls for. I think the Champion part number was 3310 but I'll double check when the company leaves Friday. Made a world of difference for me. The summer I spent running back and forth between the Springs and Abilene, TX I was getting 27+ on the highway with the a/c running full bore all summer.
I usually buy the cheapies, the copper core (RN9YC, iirc, for the 4.0) plugs.
Single side electrode, full size center electrode (platinum plugs have an undersized center electrode and I was taught that to get more current (flow) thru a small conductor you needed more voltage (pressure) and a 0.036" gap.
In all honesty, with resistor plug wires I'd rather have the old non-resistor plugs (Champion N9YC for the 4.0) or the old wire type plug wires with resistor plugs ... less overall resistance equals fatter sparks equals easier starts in the cold better performance and economy.
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