Unexpected downshift and/or Electrical problem
Thread Starter
|
Junior Member
Joined: Mar 2007
Posts: 6
Likes: 0
Unexpected downshift and/or Electrical problem
Hi all,.. After searching the forums for over 2 hours I've not found anything even close to my problem, so I'm hoping some super smart experienced tech is out there reading this.
1999 150 Lariat 200,000km with 5.4 and (sorry) unknown to me trans probably 4r70. Been working fine for years. Developed a bad COP one day driving home from work and with some old fashioned shade tree mechanic thinkin' (and hints from here) I found which coil was bad. (yes, it was the passenger rear cyl). Of course after pulling low voltage wires off each coil one by one and the computer trying to compensate, the SES light stayed on. So I disconnected the battery over night to try to reset the codes/light. This worked fine.
Once running on all 8 again, the first few hours of driving I could feel the trans learning, the downshifts a little abrupt etc. All perfectly normal and it fell back into a normal pattern and that was 4 weeks ago.
So, driving to work yesterday morning at 60-65 mph in o/d at cruising throttle (no CC on, just that light pedal pressure) Suddenly it feels like the trans downshifts or converter unlocks,... and my eyes catch the tachometer dancing at 3000-3500 instead of 2000! It only happened for a second or less. I instinctively backed out of the throttle and it returned to normal. Then when I pulled off at my exit,... it happened again, this time i heard the engine rev and let off throttle but noticed tachometer AND SPEEDOMETER were bouncing off 0 and then all was normal again. This happened once more on my 25 minute commute. There is no duplicating the load/speed aspect of it. I've been around long enough to know that its electrical in nature. I had no problems diagnosing the bad coil, But this ones got me stumped. Took a 5 hr round trip last weekend without issue, problem started on Monday. The only variable I can see recently is the rising temps and the damp roads. It was a terribly cold winter, and I went along without issue until the bad coil. Now its getting warmer and the roads are wet but I don't see anything like huge puddles to run through that might get a wiring harness wet. I was kinda hoping i'd see a common, easy to fix problem on this forum but like I said, I looked for hours and saw nothing where both gages dip to zero for an instant at 60mph or so while experiencing a loss of power or what seems to be a loss of power because of an unexpected downshift/rise in revs. It could be a total loss of power, but nothing besides engine/trans is affected. What is common to both tachometer and speedometer input and could affect transmission shifting? the CPU?
Help? any Ideas?
1999 150 Lariat 200,000km with 5.4 and (sorry) unknown to me trans probably 4r70. Been working fine for years. Developed a bad COP one day driving home from work and with some old fashioned shade tree mechanic thinkin' (and hints from here) I found which coil was bad. (yes, it was the passenger rear cyl). Of course after pulling low voltage wires off each coil one by one and the computer trying to compensate, the SES light stayed on. So I disconnected the battery over night to try to reset the codes/light. This worked fine.
Once running on all 8 again, the first few hours of driving I could feel the trans learning, the downshifts a little abrupt etc. All perfectly normal and it fell back into a normal pattern and that was 4 weeks ago.
So, driving to work yesterday morning at 60-65 mph in o/d at cruising throttle (no CC on, just that light pedal pressure) Suddenly it feels like the trans downshifts or converter unlocks,... and my eyes catch the tachometer dancing at 3000-3500 instead of 2000! It only happened for a second or less. I instinctively backed out of the throttle and it returned to normal. Then when I pulled off at my exit,... it happened again, this time i heard the engine rev and let off throttle but noticed tachometer AND SPEEDOMETER were bouncing off 0 and then all was normal again. This happened once more on my 25 minute commute. There is no duplicating the load/speed aspect of it. I've been around long enough to know that its electrical in nature. I had no problems diagnosing the bad coil, But this ones got me stumped. Took a 5 hr round trip last weekend without issue, problem started on Monday. The only variable I can see recently is the rising temps and the damp roads. It was a terribly cold winter, and I went along without issue until the bad coil. Now its getting warmer and the roads are wet but I don't see anything like huge puddles to run through that might get a wiring harness wet. I was kinda hoping i'd see a common, easy to fix problem on this forum but like I said, I looked for hours and saw nothing where both gages dip to zero for an instant at 60mph or so while experiencing a loss of power or what seems to be a loss of power because of an unexpected downshift/rise in revs. It could be a total loss of power, but nothing besides engine/trans is affected. What is common to both tachometer and speedometer input and could affect transmission shifting? the CPU?
Help? any Ideas?