Intermittent transmission problems
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Intermittent transmission problems
First thing let me say any help is much appreciated. I own a 1993 F-150, it has a 302 V8 and a EOD4 Auto transmission. The problem I am having is intermittent which makes it very tough to diagnose. You can start the truck up and drive it for roughly one hour with no problems, then with no warning the transmission will freewheel or go into a false neutral, the speedometer will freeze at 70 or 80 MPH, and the odometer numbers bleed together like a bad horror movie. This all happens very quickly,then I let off the throttle and the transmission will clunk back into gear and then will shift harshly and at the wrong rpm. At this point I have two options pull off the road and shut off the motor and wait five or ten minutes then the speedometer will reset itself and the transmission will shift properly again. The other option is to put the tranny into second gear and finish my trip. Option two is not good on the interstate.
Post Fiend
Joined: Mar 2002
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From: Bonita Springs FL
The electronic tranny needs to know the speed of the truck in order to shift properly. There's a sensor in the rear axle called the VSS (vehicle speed sensor) that feeds that info to the computer. Since the speedo is fed by the signal from that sensor and is also affected, my guess is that the VSS is hosed.
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Thanks AndyM, I have installed a speed sensor on the truck and it has helped. I can now drive for about 90 minutes or so and then the speedo and odometer loose it.
It will still reset its self after a five or ten minute shut down. one thing I notiiced with the new speed sensor is that the needle on the speedometer is more shakey it fluctuates a good bit after 60 miles per hour. I am thinking about buying some sort of code reader to help me figure this thing out. any suggestions?
It will still reset its self after a five or ten minute shut down. one thing I notiiced with the new speed sensor is that the needle on the speedometer is more shakey it fluctuates a good bit after 60 miles per hour. I am thinking about buying some sort of code reader to help me figure this thing out. any suggestions?
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Joined: Apr 2005
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I have been experience the same troubles with my trucks transmission. The overdrive light starts blinking from what i notice when its very hot outside or the truck has been sitting in the sun for a while. I brought the truck to Aamco transmission they pulled they found a faulty code i believe it was a 400 number code. Which is the Vehicle speed sensor. I dont know whether to buy a new one or not. Any suggestions?
Post Fiend
Joined: Nov 2001
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From: Topsfield, MA
The vehicle speed sensor is nothing more then a magnet, just make sure it's clean and the electrical connections are good. There shouldn't be any reason to replace it unless it got damaged somehow. They don't typically fail because they're such a simplistic device.
The transmission you have is computer controled, the computer uses different signals, like throttle position, speed, load, etc to shift the trans. It sounds like you're having some problems with the PSOM (programable speedometer/odometer module). It doesn't sound like there is a problem with the transmission itself, it sounds like there is a problem in the way the computer is handling the operation of the transmission. Computers don't typically go bad either, so that leads to something wrong with the information the computer is getting to control the transmission. You're computer is getting improper feedback and doesn't know the proper way to handle the transmission. Does the way I came to that conclusion make sense?
You can look up "bad psom" in a search more info...but it sounds like you should replace the speedometer unit in the dash. You should get one from a junkyard and see if it works/fixes the problem.
The transmission you have is computer controled, the computer uses different signals, like throttle position, speed, load, etc to shift the trans. It sounds like you're having some problems with the PSOM (programable speedometer/odometer module). It doesn't sound like there is a problem with the transmission itself, it sounds like there is a problem in the way the computer is handling the operation of the transmission. Computers don't typically go bad either, so that leads to something wrong with the information the computer is getting to control the transmission. You're computer is getting improper feedback and doesn't know the proper way to handle the transmission. Does the way I came to that conclusion make sense?
You can look up "bad psom" in a search more info...but it sounds like you should replace the speedometer unit in the dash. You should get one from a junkyard and see if it works/fixes the problem.
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Joined: Apr 2005
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Thats interesting that you mention that there is something possibly wrong with the trucks computers. The people over at Aamco transmission mentioned that they had a hard time getting my trucks codes. The computer in the truck was not responding to anything until they found a faulty code (code 452) insufficienct input from vehicle speed sensor. I also understand that there are two speed sensors. So there is now a possibility my computer in the truck is messed up or the sensors are acting up.
