Speed Sensor through 1987
Recently speaking with another turbo-mopar member I complained that after I thrash on the Charger and come to a stop the idle is running at 2000 rpm. He told me that the speed sensor is the usual cause of this problem.
I could only find scant info on this mysterious part and decided to know more. I had an allegedly bad one in my parts, so I disassembled it. No easy task. Here are the results. As you probably know there is a gear on one end that is driven by a shaft in the transmission. At the top is a connection for the speedo drive cable. The port that you plug the wires into has two pins which are connected to a magnetic reed switch. My multimeter showed me that the switch is normally open. On the main shaft of the sensor is a disk with 8 small magnets embedded in it. A signal from 2-14 of the LM provides a potential on one side of the switch. The disk is in close proximity to the switch and when the magnet passes by the switch the magnetic field closes the switch momentarily sending the signal to a ground. The computer counts each of these pulses and the computer processes them. Beyond that I do not know how much effect this has on the operation of the car. Hopefully someone on the site can elaborate further. At this point my only choice is to buy a new sensor unless some can give me a another cause for the high rpm idle. Usually I can turn off the engine and restart and the idle is back to normal Attachment 62058
Attachment 62058
Re: Speed Sensor through 1987
Quote:
Originally Posted by
jeff1234
Recently speaking with another turbo-mopar member I complained that after I thrash on the Charger and come to a stop the idle is running at 2000 rpm. He told me that the speed sensor is the usual cause of this problem.
I could only find scant info on this mysterious part and decided to know more. I had an allegedly bad one in my parts, so I disassembled it. No easy task. Here are the results. As you probably know there is a gear on one end that is driven by a shaft in the transmission. At the top is a connection for the speedo drive cable. The port that you plug the wires into has two pins which are connected to a magnetic reed switch. My multimeter showed me that the switch is normally open. On the main shaft of the sensor is a disk with 8 small magnets embedded in it. A signal from 2-14 of the LM provides a potential on one side of the switch. The disk is in close proximity to the switch and when the magnet passes by the switch the magnetic field closes the switch momentarily sending the signal to a ground. The computer counts each of these pulses and the computer processes them. Beyond that I do not know how much effect this has on the operation of the car. Hopefully someone on the site can elaborate further. At this point my only choice is to buy a new sensor unless some can give me a another cause for the high rpm idle. Usually I can turn off the engine and restart and the idle is back to normal
Attachment 62058
Attachment 62058
Here is a good resource on the speed/distance sensor: http://www.minimopar.net/speedsensor.html http://www.minimopar.net/ecu/speed_dist_se.html
I know a malfunctioning sensor can cause weird idle issues as the car comes to a stop. Typically I've read it causes a drop in idle, and the engine may stall. But I wouldn't rule out your situation.
Re: Speed Sensor through 1987
I've almost always found that cleaning the AIS area in the TB with carb cleaner was the solution for a high idle. That's given that there's no vac leak of course.
Re: Speed Sensor through 1987
Re: Speed Sensor through 1987
Quote:
Originally Posted by
cordes
I've almost always found that cleaning the AIS area in the TB with carb cleaner was the solution for a high idle. That's given that there's no vac leak of course.
I need to clean the AIS 2X per year. Also remember to clean the carbon around the throttle plate as well while you are there.
http://www.turbo-mopar.com/forums/sh...7-and-older-T1
Re: Speed Sensor through 1987
I did look at the info on minimopar.net. I work with this stuff at work to some extent and I can tell you I wouldnt try that mod to hall effect sensor without a good schematic.
Re: Speed Sensor through 1987
Quote:
Originally Posted by
jeff1234
I did look at the info on minimopar.net. I work with this stuff at work to some extent and I can tell you I wouldn't try that mod to hall effect sensor without a good schematic.
I checked the hall effect datasheet and it is not as simple as one would hope. In fact, the datasheet for the HES listed on minimopar from Digikey states "Not suitable for automotive application" . Sounds like a research project to me.
Re: Speed Sensor through 1987
Aren't the later sensors hall effect? You just need to tap into the 8v feed from the HEP if my memory serves me correctly. I want to say you could use one from a 94 Shadow. I've never had enough problems with the SDS to actually look into it.
Re: Speed Sensor through 1987
Cordes, my speedo is mechanical, the hall effect speed sensors have no mechanical tower to plug the speedo cable into.
- - - Updated - - -
chromguy, thanks for that tip as well.
Re: Speed Sensor through 1987
83scamp, thanks for the link, very informative. My buddy Lohnnie has a awesome 84 Rampage we have been working on for three years. Hope to have it on the road this year. If you are on the Rampage facebook site he might have posted pic's. It's blue. jeff
Re: Speed Sensor through 1987
Quote:
Originally Posted by
jeff1234
Cordes, my speedo is mechanical, the hall effect speed sensors have no mechanical tower to plug the speedo cable into.
- - - Updated - - -
chromguy, thanks for that tip as well.
Shoot. I didn't even think of that.
Re: Speed Sensor through 1987
Quote:
Originally Posted by
jeff1234
Recently speaking with another turbo-mopar member I complained that after I thrash on the Charger and come to a stop the idle is running at 2000 rpm. He told me that the speed sensor is the usual cause of this problem.
I could only find scant info on this mysterious part and decided to know more. I had an allegedly bad one in my parts, so I disassembled it. No easy task. Here are the results. As you probably know there is a gear on one end that is driven by a shaft in the transmission. At the top is a connection for the speedo drive cable. The port that you plug the wires into has two pins which are connected to a magnetic reed switch. My multimeter showed me that the switch is normally open. On the main shaft of the sensor is a disk with 8 small magnets embedded in it. A signal from 2-14 of the LM provides a potential on one side of the switch. The disk is in close proximity to the switch and when the magnet passes by the switch the magnetic field closes the switch momentarily sending the signal to a ground. The computer counts each of these pulses and the computer processes them. Beyond that I do not know how much effect this has on the operation of the car. Hopefully someone on the site can elaborate further. At this point my only choice is to buy a new sensor unless some can give me a another cause for the high rpm idle. Usually I can turn off the engine and restart and the idle is back to normal
Attachment 62058
Attachment 62058
You can replace the reed switch pretty easily if you can solder. They are cheap online. I got one out of a $7 door alarm from home depot. Just seal the housing back up with silicone and crimp it back shut.
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