no tach/tranny no shift
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no tach/tranny no shift
hello
i need some help with my 1991 f250 7.3 idi. the problem is my tach quit working and tranny auto tranny quit shifting unless you manually put it in the gear. seems as if i only have 2nd and 3rd gear. i am thinking it is a vss sensor. wanting to know if i'm on the right track or sould i go to the tach sender?
i need some help with my 1991 f250 7.3 idi. the problem is my tach quit working and tranny auto tranny quit shifting unless you manually put it in the gear. seems as if i only have 2nd and 3rd gear. i am thinking it is a vss sensor. wanting to know if i'm on the right track or sould i go to the tach sender?
Post Fiend
Joined: Nov 2004
Posts: 5,638
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From: Manitoba
Yes it is the tach that is causing the problem. You need both speedo and tach working flawlessly.......
A dead tach sender should/would send the automatic trans into a "failure management mode" (limp mode) with harsh engagements and firm shift feel and an abnormal shift schedule. It has no effect on a manual trans only the Tach readings.
Check the wires where they exit the big nut on the oil filler housing , known to short out due to bare wire.....
Replace the tach sender on the oil fill housing a big 1" nut with 2 wires. Ford only part Engine RPM sensor E5TZ-17B384-A about $50. You can remove and clean it but usually changed later too.
You can test it too, hold it in the air away from ferrous metal, using an ohm meter lead on each wire you need DC resistance between 2000-3000 ohms.
A dead tach sender should/would send the automatic trans into a "failure management mode" (limp mode) with harsh engagements and firm shift feel and an abnormal shift schedule. It has no effect on a manual trans only the Tach readings.
Check the wires where they exit the big nut on the oil filler housing , known to short out due to bare wire.....
Replace the tach sender on the oil fill housing a big 1" nut with 2 wires. Ford only part Engine RPM sensor E5TZ-17B384-A about $50. You can remove and clean it but usually changed later too.
You can test it too, hold it in the air away from ferrous metal, using an ohm meter lead on each wire you need DC resistance between 2000-3000 ohms.
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i've chaged the tach sender and the vss and the problem is still there. i've checked the wires to the coupler behind the passenger side battery. traced it to the driver side firewall and lost it in all the wires! i'm looking for a electrical trouble shooting manual online. not having any luck. can anyone help?
Posting Guru
Joined: Oct 2005
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From: Powell River B.C.
Is your tach still not working? I would check the connections on the instrument cluster, I seem to recall someone here having a problem caused by dirty connections, may be corrected by simply unplgging and replugging in the connector for the instrument cluster. Same can apply to the PCM connector, the Shift lever postion, etc. If your tach is now working, and transmission is not, you should get a code reader and check for codes before it drives you crazy looking for loose wires who know where. A OB1 code reader for a Ford is about 30 bucks at Wally world or other parts stores.
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this problem is becoming my demon. i want the thank everyone for there help. i've changed the vss, tach sender and checked the connections behind the inst. cluster and checked all the wires and couples that i can find. is there any reset buttons or disconnects i have to check or reset?
Laughing Gas
Joined: Mar 2007
Posts: 754
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From: southwest Wisconsin
I just had the opposite problem with a truck I just bought, this circut was draining my battery when truck was off. My band-aid fix was to power it from a source that is hot only when the switch is on. Any hoo, getting back to your problem, on my 91 F250 7.3 there is a fuse link where this wire is hooked to the junction near the pass side battery. Have you checked to see if this fuse link is OK?
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Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
What you are describing sounds more like a PCM power failure. With no electrical power to the computer or the transmission, all you get is reverse with selector in "R", second gear in "1" or "2", and fourth gear in "(D)". I this what you are getting?
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Lead Driver
Joined: Nov 2003
Posts: 6,900
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From: Campbell River, B.C.
I would start checking wires, a PCM is pricy, wires and relays are not. I don't have the OEM wiring diagram for the E4OD since I run an aftermarket system. You can get a haynes manual for $20 that should include the wiring for the transmission. I dealer might even help you and print off a copy of the wiring diagram.
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