Tach Troubles
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Senior User
Joined: Aug 2001
Posts: 275
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From: Lexington Park, MD
Tach Troubles
Hey there everyone,
I have a 91 F150 XLT Lariat with a 302. Its got the gauge cluster with the tach. Well, the tach jumps straight to 3500 rpm when I put the ignition in run. The only time it moves is if the engine rpm goes higher when accelerating. It'll go to about 4000 and fall back to 3500. It stays there until you shut the truck off. I used to be able to slap the dash and it would start working again, but one day I found myself wanting to punch the dash, but it would not go down, so I left it alone.
My truck has a stock everything electrical. Does it sound like Im gonna have a shorted wire in the dash or something? Any help would be greatly appreciated. Thanks in advance.
I have a 91 F150 XLT Lariat with a 302. Its got the gauge cluster with the tach. Well, the tach jumps straight to 3500 rpm when I put the ignition in run. The only time it moves is if the engine rpm goes higher when accelerating. It'll go to about 4000 and fall back to 3500. It stays there until you shut the truck off. I used to be able to slap the dash and it would start working again, but one day I found myself wanting to punch the dash, but it would not go down, so I left it alone.
My truck has a stock everything electrical. Does it sound like Im gonna have a shorted wire in the dash or something? Any help would be greatly appreciated. Thanks in advance.
Thread Starter
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Senior User
Joined: Aug 2001
Posts: 275
Likes: 1
From: Lexington Park, MD
Tach Troubles
Tonight Im planning on tracing the wires to/from the tach and take some voltage and resistance readings. I should just be lookin for straight up 12 v dc right? I want to be sure so I dont mess up my multimeter. Im curious because it gets a signal off of the ignition coil. One more question, does anyone know around how many ohms I should expect to see if I shoot the wires from the under dash area? Thanks in advance.
Chris
Chris
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Senior User
Joined: Aug 2001
Posts: 275
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From: Lexington Park, MD
Tach Troubles
No, Ive never messed with it. One day it just started doing it. Ive let it be weird for a good while now. Im fixin to put some after market gauges in, and I really want to get all my gauges working good. I decided not to get an aftermarket tach. Its not a dummy gauge and it works good when it does work, so I need to fix it.
Chris
Chris
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Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Tach Troubles
1) It's mechanically able to go below 3500, as evidenced by it being down with the key off.
2) From what you said, it DOES report the correct RPM above 3500, so it works and the needle is installed correctly.
Those two facts tell me that it's an internal electronic fault, within the tach head itself. I don't think it's anywhere in the coil circuit or the tach wire. I'd start looking for a replacment tach or cluster.
2) From what you said, it DOES report the correct RPM above 3500, so it works and the needle is installed correctly.
Those two facts tell me that it's an internal electronic fault, within the tach head itself. I don't think it's anywhere in the coil circuit or the tach wire. I'd start looking for a replacment tach or cluster.
Thread Starter
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Senior User
Joined: Aug 2001
Posts: 275
Likes: 1
From: Lexington Park, MD
Tach Troubles
Hmmm. Thats an interesting point. Yeah, I cant even see where the cluster would connect, let alone get to it, without it disconnected like the book says. Id rather do it all together and just end up with good gauges say, after a weekend of work. I could take the time to shoot wires then I guess. Can you get a tachometer head from the parts store? Or would I be better off to just pull a cluster out of a truck in a junkyard and hope it works? (Thats assuming that I find one with a tach cofiguration,ha!) I have one last question and then Ill shut up: Where can I get this "hook tool" that is needed to take off the wiper and headlight *****? Ive already had to replace one wiper ****, and that little thing aint cheap. Id gladly put the money toward that tool as long as I aint gotta buy more of those *****. I appreciate all the help and information. Thanks in advance.
Chris
Chris
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Joined: Nov 2002
Posts: 9,987
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From: Memphis, TN
Tach Troubles
You can bend a piece of stiff wire, or buy a set of picks at Wal-Mart or a parts store for ~$4 for 4 tools. You can see one from the WM set in this picture.
You can see how to remove the cluster here.
Parts stores don't sell the tach, and I don't think Ford does, either, but you could check. They're all over the junkyards near me, and every one I've pulled has worked (even the burnt one).
You can see how to remove the cluster here.
Parts stores don't sell the tach, and I don't think Ford does, either, but you could check. They're all over the junkyards near me, and every one I've pulled has worked (even the burnt one).
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Thread Starter
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Senior User
Joined: Aug 2001
Posts: 275
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From: Lexington Park, MD
Tach Troubles
Man, I sure appreciate the help. Stuffs a lot clearer to me now. Im gonna go see about gettin those picks and look for a cluster at a junk yard. Unfortunately, there is only two junkyards around here in this town, and one doesnt have 87-91 body styles. I havent been to other yet. Well I guess I better leave all yall alone and get started. Hopefully I can help yall someday. Thanks again!
Chris
Chris
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