Renix-Era Fuel Injector Cleaning w/Seafoam
My rig is a '90 xj 4.0 auto, which came with 152k on it. I've had it a couple months and have cycled through various minor maintenance issues. New plugs, cap, rotor, wires, and even a new dizzy. I live in smog-test-free Mississippi, so ran a straight pipe with NO cat and NO muffler, and added a cheap Ebay cone air intake. These yielded a massive mpg and power improvement, but I was still having some fuel delivery problems that occasionally caused sputtering, especially when idling in traffic.
At first, I tried both Techron and Seafoam in the tank. Both times, this proved disastrous, as it dislodged gunk from the bottom of my ancient fuel tank and clogged the pump temporarily. Until I get around to swapping in a new poly tank, detergents in the tank are officially off the table.
I had the typical problems of a VERY low idle (250 rpm!), and lengthy cranking times in the morning. After researching, I found that the injectors, once fouled, won't close off fully when you shut down the motor, and will drip fuel into the cylinders. You can confirm this as i did...by doing an oil change and smelling LOTS of gasoline in the oil drain pan!
I removed the air tube at the throttle body (this is done with a "star" screwdriver, just 3 screws.) and used throttle body cleaner and a toothbrush to remove all the accumulated gunk on the butterfly. After replacing the intake tube, I purchased a can of Seafoam, and unhooking the vacuum hose at the FRONT of the valve cover, used an eyedropper to slowly drip the Seafoam into the hose while the engine idled.
This process will take about 20 minutes, and to be effective, you don't wanna just dump all the Seafoam in too quickly. That will not only stall the engine, but also, won't clean as effectively.
Usually when doing an injector cleaning at my old lube shop job, we would run the car for a good 30 minutes as a dripper bottle slowly dripped injector solution into the booster line, periodically revving the throttle. This would always yield large quantities of white smoke out the tailpipe, and brackish watery goop would splatter out as well. However, while cleaning my XJ today, there was NO smoke at all....just an initial splatter of a small quantity of black sooty gunk.
WOW what a difference! My idle is now around 1k rpm, and the motor runs smoother than a baby's keister.