7.3 tach failure HELP PLEASE

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Jan 21, 2015 | 01:03 PM

shane86

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7.3 tach failure HELP PLEASE

Ok been battling all week an put almost 600 bucks into it. Tach will not work until i drive for about 15 min. I have replaced the following parts. alternator, eec relay, trailer tow relay, selinoid, neutral safety switch , throttle positon sensor, tach sensor, cluster for all guages. batteries . Trans is in safe mode until tach starts working please help

Jan 22, 2015 | 10:54 AM

Phy

Fleet Mechanic

Joined: Jan 2011

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From: 8600 ft in Colo

I'd check all the wiring between the tach sensor and the pcm. (I've had a connector that was sensitive to engine compartment temperature before.)

Jan 22, 2015 | 05:25 PM

FORDF250HDXLT

Fleet Owner

Joined: Jul 2006

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From: Mi'kma'ki

what year is your truck too shane?

Jan 22, 2015 | 08:01 PM

shane86

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Its a 1990.

Jan 23, 2015 | 11:20 AM

shane86

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Still nothing is helping have spent 900 bucks on all kind of relays an sensors. Have looked all over for broken wires an found nothing wrong with them. Still in limp mode

Jan 23, 2015 | 01:36 PM

madpogue

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Joined: Oct 2003

Posts: 8,476

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From: Madison, WI

Stop throwing money/parts at it and TEST. See post #2; have you checked continuity of the wires from the tach sensor connector to the TCM, under both conditions (tach working / not working)? Have you measure the resistance of the tach sensor when cold, and again after warming up? Something is happening in that 15-minute period, as suggested above, probably temperature-related. It's most likely something you can measure, but swapping parts won't provide that information.