5r55s Engagement issues | Ford Explorer Forums - Serious Explorations

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5r55s Engagement issues


Active Member
March 30, 2014
Reaction score
City, State
Manville, NJ
Year, Model & Trim Level
1999 Ford explorer xlt
2007 4.0 xlt with the 5r55s with 134k miles

I inherited this truck from my father in law, no idea on prior maintenance. When I got it they said it drove with no problems, I had to wait a month to register it so I never drove it before I started a tune up. I have changed so far the spark plugs, wires, the fuel rail pressure sensor/fuel tank pressure sensor(it was under the intake a saw both names used for it), Throttle body gasket and intake gasket,PCv valve,evap purge valve and the hose from it to the intake. Everything was motorcraft except the fuel pressure sensor And the gaskets were fel pro. I turned it over and it misfired so I shut it off immediately, double checked my wires and plugs and one plug ended up being bad. Replaced it with another motorcraft spark plug and The misfire was gone. Drove it and experienced bad engagement at 20-25 mph and 35-40 miles an hour especially up hill. It would take a couple seconds to upshift while making a slight grinding noise from the transmission.parked it and changed the trans Fluid and filter, diff fluids and transfer case. Used mercon 5 for trans and transfer case. I pulled the negative terminal on the battery and left it off overnight to Hail Mary pass hope the shift tables reset. Didn’t work. There was no metal at all on the magnet, no debris in the pan. The old Fluid was a bit black and not sure how much i drained cuz a decent amount ended up on me, ended up putting in just over 6 1/4 quarts subtracting what came out from what I put in after letting it drain til it was just a drip. so now Im not sure if I need to change the solenoid pack, or the servos with the aj1e replacement. Or if I messed something up when I did my tune up.
some additional details, while I had the throttle body off And cleaning it I noticed it wasn’t fully closed and to close it I had to push on it and it went back to slighty open after I removed pressure. I’ve never seen this throttle body without an IAC valve so not sure if that’s normal or if the throttle body needs to be changed, after removing the intake for the fuel pressure sensor, my rpms were all over the place and I had multiple codes for the throttle position sensor. Checked it out and the insulation was gone on a section of all 4 wires. Thoroughly taped it up and the code went away and the car drove but still was having trans issues. That day the “ghosts in my machine” thread popped back up in the 4th generation forum and I found more exposed wiring on the MAF and coolant temp sensor. Taped them up didn’t see any difference in the MAF reading on my scan tool(4.5-4.9 mgs at idle). Decided to buy a cheap MAF off rock auto compared to the old one and looked the same with slightly different Looking Wire. Turned the car over and the revs were going crazy and the MAF was up around 38mgs which was the highest reading I’d previously seen and Slowly faded to 22mgs but the car was still randomly revving. Put the old one back in and the engine ran fine. Not sure if new one was **** or if that’s a clue to my transmission problem.
Sorry for the novel wanted to provide as much detail as I can thanks for any help


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