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RPM drops to 1000 at highway speed ??

Can anyone shed light on my issue? 96 Ranger 4L 4x4 auto 93,000 kms

Trans rebuilt 6,000 kms ago... i am noticing that when cruising at about 100 km/h (about 60 mph), RPMs are at about 2100, if you let off the gas they drop to like 1600, seems normal, but then if you just coast for a couple seconds more, the RPMs dip to like 1000 and back to about 1500 and back and forth a couple times...you can hear the engine speed changing...as deceleration continues eventually it levels out again. Hitting the accelerator brings it back to 2000+ with no stumbles, slipping or other issues. What could be causing this? Torque converter issues? I thought the TC unlocking was the initial RPM drop from 2100 to 1600. I dont know how it can go as low as 1000 at such high speeds. Sensor issues? Anyone know where to focus my attention? No check engine lights, very stable idle at about 800, no OD lights...i do have a 3-1 downshift deceleration 'clank' when coming to a stop, i think comes from the tranny ... please help

thanks

Reply to
tyson.morrow
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Reply to
Big Shoe

The TC locking and unlocking rarely causes the rpm's to change more then a few hundred. What you are describing sounds like the transmission is not working right when you are coasting. Some of the internal parts there to prevent other parts from rotating at the wrong time, like when you are coasting. I'm not familiar with any of the detailed internals but I suspect the problem could be as simple as a bad solenoid all the way up to the transmission being about ready to go out.

Reply to
Ashton Crusher

Sounds like a "possible" coast clutch concern... IIRC, this will be solenoid controlled.... a code scan may be in order or diagnostics performed by someone hat can actually do some hands on testing.

What warranty was offered by the rebuilder?

Reply to
Jim Warman

Thanks for the replies, Went for a drive with the trans tech guy and scan tool, there were no stored codes (no surprise since the engine light has not come on). Everything checked out normal except some fluctuations from the MAF sensor in time with the RPM changes. But the torque converter unlocking was the initial 2000-1600 RPM drop. After that the engine just..stumbles and hunts for a bit while you are coasting. I am going to try cleaning the MAF I think, and see if that helps. I do know my air filter was pretty much black when I changed it last. As for the downshift clunk, again the scan readings were normal, but it was confirmed the clunk/bump is felt and heard right at the 3-2 shift. They have suggested dropping the rear driveshaft to eliminate the chance its because of driveline slop (but i recently had it checked out and was ok...) and driving it in 4wd to see if the clunk is still there on the downshift. they agreed to try this next week. There is a 12,000 km (or maybe, hopefully, miles) 1 yr warranty on the rebuild (done in March, 6000 kms ago). They seemed stumped with this and claim 4r55e's do not generally have this particular issue. They are clearly reluctant to drop the trans again to look for internal issues. Tomorrow, hopefuly I am going to put the truck on a hoist and lift the rear wheels up and get my buddy to hit the throttle until 3rd gear, and then let off the gas and allow it to downshift on its own and look/listen for the exact location of the clunk, assuming it will still happen (it does when coasting to a stop).

Jim Warman wrote:

Reply to
tyson.morrow

Reply to
Ashton Crusher

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