[V8] Tach drop out

[Tony and Lillie]

The tach signal comes in on Plug T14a/1. It is a Yellow wire that comes from 
the ECU to the IC.

Tony Hoffman

----- Original Message ----- 
From: <dsaad at icehouse.net>
To: <v8 at audifans.com>
Sent: Friday, August 25, 2006 7:25 AM
Subject: Re: [V8] Tach drop out


> This smells like a connection problem in the IC to me.
> I don't have the schematics in front of me, but if you have the schematics 
> and
> can follow them, and can use a volt meter, you should be able to locate 
> the
> problem.
>
> First, locate the signal source. This is almost certainly the ECU, and it 
> is
> probably a pulsing signal - so it will be hard to measure with an ordinary 
> meter
> but if yours can read frequency then you are good. The tach is responsible 
> for
> turning this pulse into a voltage for display - the tach is really just a 
> volt
> meter, as is the speedo. They both work the same way, only the frequency 
> of the
> signal is different.
>
> (btw, I went through this same procedure to identify my bad speedo sensor)
>
> You will need to attach your meter to the signal at the ECU and monitor it 
> while
> driving, or do whatever needs to be done to make it fail. If the signal 
> drops
> out then you have an ECU problem. (I really doubt this - it is just the 
> first
> step)
> If everything is OK, it is time to pull apart the IC and attach the meter 
> right
> at the tach terminal - you may need to solder here. If the signal drops 
> out, you
> have a connection problem. If not you still have to verify the 12V and 
> ground
> supply to the tach but most likely there is a broken wire or intermittant
> connection. I found the interconnect wires between the IC sections were 
> cracked
> on mine. There is a design weekness (IMHO) where the interconnect ribbon 
> cables
> can vibrate and crack over time.
>
>
> Dave
>
>
> Quoting Mike Del Tergo <mdeltergo at hotmail.com>:
>
>> That will keep you busy. On the tach I don't know if it is the IC as I 
>> have
>> "fixed" that.  Suddenly, it will go to zero (or not come on) and stay 
>> there
>> only coming on intermittantly.  Others have said these can go bad, but 
>> no
>> one seems to have a way to check if it is the tach or wiring.
>> Mike
>> PS had to go to a wrench to get the O2 off but all seems good now.
>>
>> >  Mike sorry I haven't gotten back but I was doing my
>> >T-belt on my Green 93 v8 & the Euros, & the 2benn coil
>> >overs & stuff ready for //sfest. I'm just doing a few
>> >more things beforhand but I will check to see if I
>> >have a tach. Whats wrong with the tach?? I all so have
>> >to search around for the armrest strut.
>> >I'll get back to you tomorrow
>> >Thanx
>> >Ron
>> >
>>
>>
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>
>
>
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