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Discussion Starter · #1 ·
What would cause the tach to work and then not work. Also have transmission problems. I know there related but don't know where to start since its intermittent. Haven't been on here in quite some time. I have a 1990 with 408,000 miles IDI. Automatic Trans.
 

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What would cause the tach to work and then not work. Also have transmission problems. I know there related but don't know where to start since its intermittent. Haven't been on here in quite some time. I have a 1990 with 408,000 miles IDI. Automatic Trans.
frayed wires at the connector on top of the oil fill/injection pump gear cover. Or that sensor going bad.
 

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What would cause the tach to work and then not work. Also have transmission problems. I know there related but don't know where to start since its intermittent. Haven't been on here in quite some time. I have a 1990 with 408,000 miles IDI. Automatic Trans.
Sounds like a bad tach sensor. The sensor feeds the tach, cruise control and the transmission. I have replaced mine twice on my 1990 with 305k.

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Discussion Starter · #5 ·
Thanks for the replies. Is ford the only place to get the part?
 

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Discussion Starter · #8 ·
I found it on amazon. $66.XX. Free shipping with my prime account.
 

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That's not a bad price, mine went out when my '91 was only about 5 years old and back then it was $50 from Ford.
 

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Discussion Starter · #11 ·
I replaced the tach sensor and still have the issue. Just got back from a fifty mile trip and it stopped working 3 times. I popped it in nuetral and turned on and off and tach started working. Where to look now?
 

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Put your truck info in your signature, don't have to go back and look what it is. Check mark "Show your Signature" then it's always there.

There is also a relay hanging on the drivers side close to the firewall, it may be intermittent. If the truck came with a tow package, there will be two of them.
 

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I have been dealing with the same issue on my 90 IDI. Tach would kick on and off randomly and when hitting larger bumps in the road.

Replaced the sensor (had bare wires on the sensor end plus had low Ohm readings on the sensor) and still had the same problem. I ended up pulling all connections along the harness apart, cleaning them, and putting them back together making sure everything was tight. This including the ones on the transmission and the TCM relay on the drivers side firewall (sits next to the EEC plug). I also removed ALL ground connections, cleaned them, and re-attached. I found 2 that were pretty corroded.

2 days so far and no issues.



I replaced the tach sensor and still have the issue. Just got back from a fifty mile trip and it stopped working 3 times. I popped it in nuetral and turned on and off and tach started working. Where to look now?
 
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