Bad Down Shift
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Elder User
Joined: Jan 2008
Posts: 698
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From: Guymon
Bad Down Shift
I was getting on the highway the other day almost floored and I hit a bump and lost all my power for a few seconds!!! (Dash, radio, and tcm for sure) Well I was just doing almost 75-80 (possibly faster but not sure) when it downshifted into 3rd and put my rpms around 3700-3900 (not sure on exact speed or rpms). First question is, how bad is 4,000 rpm on these engines. since 3300 is the begenning of the redline or yellow line. Dave, can you figure my speed at 3700rpm with 215/85, 4:10 and e40d?? I know for a fact my tach show around that.
Second, Does anyone have a starting point the electrical connection that would cause loss of power. (tach still worked though). After the power came back on, it went back in 4th at about 60-65 and continued on my way. I noticed when I hit bumps, the dash would flicker before but this time was a few seconds. Checked my electrical connections at the solonide and battery and they are good as well as the ones on the starter and ground to the frame. Any starting points from here. Any of you have this problem before. thanks
Second, Does anyone have a starting point the electrical connection that would cause loss of power. (tach still worked though). After the power came back on, it went back in 4th at about 60-65 and continued on my way. I noticed when I hit bumps, the dash would flicker before but this time was a few seconds. Checked my electrical connections at the solonide and battery and they are good as well as the ones on the starter and ground to the frame. Any starting points from here. Any of you have this problem before. thanks
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
3600 RPM would put you at 78 MPH in direct drive.
3700 RPM would have you at 80 MPH in direct drive.
Actually the red line should be at 3600 on the tach.
Sounds like a connection loose on the passenger side inner fender.
Not sure if the wire stayed yellow on the newer trucks, if it did there is a connector near the voltage regulator.
Check that connector for signs of overheating.
If it breaks connection, all cab power goes out.
At the very bottom of the picture is the yellow wire I am talking about.
I cut the wire on both sides of the grey connector under the tape wad where it was originally.
The small green/red stripe wire is also in the connector, which is where it still is.
Only the yellow wire melted the connector.
Actually I used a copper split bolt to join the wires, the tape around the split bolt just looks bad.
3700 RPM would have you at 80 MPH in direct drive.
Actually the red line should be at 3600 on the tach.
Sounds like a connection loose on the passenger side inner fender.
Not sure if the wire stayed yellow on the newer trucks, if it did there is a connector near the voltage regulator.
Check that connector for signs of overheating.
If it breaks connection, all cab power goes out.
At the very bottom of the picture is the yellow wire I am talking about.
I cut the wire on both sides of the grey connector under the tape wad where it was originally.
The small green/red stripe wire is also in the connector, which is where it still is.
Only the yellow wire melted the connector.
Actually I used a copper split bolt to join the wires, the tape around the split bolt just looks bad.
Elder User
Joined: Aug 2007
Posts: 728
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first of all . loosing power to the pcm will not cause any downshift
with nopower to the pcm or transmission 4th gear is always default
secondly if the trans did downshift to third it would have to be commanded by the o/d cancel button in order for the processor to also command the coast clucth on in order for the trans to have engine braking
and this isnt instatanious on these vehicles
if the tcm just downshifted from 4th to 3rd the transmission would free wheel due to the input onw way clutch allowing it to overun the input shaft speed
with nopower to the pcm or transmission 4th gear is always default
secondly if the trans did downshift to third it would have to be commanded by the o/d cancel button in order for the processor to also command the coast clucth on in order for the trans to have engine braking
and this isnt instatanious on these vehicles
if the tcm just downshifted from 4th to 3rd the transmission would free wheel due to the input onw way clutch allowing it to overun the input shaft speed
Thread Starter
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Elder User
Joined: Jan 2008
Posts: 698
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From: Guymon
well, thanks and I get what your saying. May have just been a freak accident. I just know it threw my rpms up real high and stayed there. My OD cancel button does work and the yellow light on it works as well. I did not pay attention to see if the light came on while this happend though. As long as it don't happen when Im going any faster. Thanks for Input guys. I Just drove it over 1000 miles and no problems yet.
