FACTORY V-8 TACH +GUAGE TROUBLE SHOOTING

[MIKESMONZA]

FELLOW H- BODY'S ;,,, OK. THE DEAL IS WHEN I START THE CAR THE TACH RED LINES.,,, IS THE( CONDENSOR WITH WIRE ASSEMBLY )THAT WAS ON THE 75- MONZA 262 V-8 INTAKE THROTTLE BRACKET GONE BAD IT HAS A PLUG THAT LET'S YOU HOOK UP TO THE TACH SIDE OF THE DISTRIBUTOR AND PLUGS INTO THE FEED TO THE TACHWIRE OR AM I MISSING A GROUND WIRE A PART# FOR THE CONDENSOR WOULD BE NICE AS I BROKE MY SPARE ONE OFF THE TOWNCOUPE AND HAVE NOT TRIED THE ONE OFF THE 77 MIRAGE , ALSO IF THIS MAKE'S A DIFERANCE I AM LOOKING FOR A WIRE THAT THAT CONTROL'S THE AMP GAUGE,,,, (MISTERY'S OF THE WIRING SCEMEMATIC ) I HAVE BUT CAN NOT SEEM TO LOCATE.,,,, HELP MIKE

[MIKESMONZA]

BUMP/; HELP READ ABOVE POST NO REPLY'S MIKE

[NixVegaGT]

Sorry I don't know anything about this yet. I would like to though just in case... Thanks for the question...

[cjbiagi]

Mike, the condenser can make the tach act crazy. I don't know for sure if it's your problem, but I did have a similiar problem years ago with my tach that was just acting wildly and it was a problem with the condenser.

[MIKESMONZA]

THAT'S WHAT I REMEMBER BEFORE THE ENGINE INSTALL,I HAD PULLED THE ONE OFF THE "MIRAGE " (SAME SET UP) TO FIND OUT IF IT WAS RELATED.,,,, OR THE SAME PROBLEM AND WAS LOOKING AT THE 75'S UNIT (BROKEN WIRE AT SOLDER JOINT) AND ATTEMPTED TO SOLDER THE WIRE BACK ON THE CLIP WHEN I LOST IT ( I MEANT MISPLACED IT ) AND HAVE FORGOTTEN WHERE I PUT THE PIECES.,,,, PART NUMBER #,,,,,,,,ANYBODY THE MIRAGE'S UNIT DID NOT WORK IN EITHER CAR SO I NEED TO HAVE TWO EVENTUALY THANK'S CLYDE AND NIXVEGAGT I THINK MAYBE A 75 CORVETTE HAD THE SAME PIECE , CAN ANY ONE CONFIRM THIS ?,,,,,,ATTACHED IN LINE TO THE TACH WIRE AT THE HEI DISTRIBUTOR ALSO CAN ANY BODY TELL ME IF THEIR FACTORY V6 WITH TACH OPTION HAD A SIMLAR SET UP AND THIS MIGHT BE THE "SMOKING GUN" THAT SET'S THE FACTORY 4 TACH TO WORK WITH THE V-6 V-8 AFTER A CERTAIN YEAR.!!!! I STARTED THINKING ABOUT THIS AFTER REREADING THE TACH ARTICLE'S LAST POSTED LAST WEEK OR SO MIKE

[olds70supreme]

Sorry for the old post bump, but did you ever solve the problem? I have a similiar problem with my tach. I have a v-6 w/ HEI and the tach pegs to the extreme clockwise position whenever the engine is running. I unplugged the tach wire from the distributor cap and started the car, the tach needle sl..o...w..l..y rose. I don't know what this tells me about the tach. Anybody know how to diagnose this problem without playing the "I'll replace parts until the problem goes away" game?

Thanks.

[MIKESMONZA]

I answered in a pm ealier,, But thought I would give a little in sight,on what to check# 1 braided loose ground at firewall, bad thread, needs retaping with self taping screw,and coroision control,,,,,#2 other end of braided ground conection at block manifold need's some of the same attention in tightness and coroison,,,, # 3 the main "body" ground at battery needs to be cleaned underneath,,,,,# 4 remove tach filter and ckeck for bad solder job or deteriating or weak wire's from the wires exposed to the elements coroision,,plastic slip lock conections can have internal coroison,,,try a flat tiny jeweler's flat bade slip under the plastic unlock the brass terminal's tang and slip the cover off and check, # 5 Then if tach still will not respond check the brown wire going to the tach, It has a similar end that can become copromised and needs checking,and cleaning,and #6 take off the distributor top cover on HEI unit and verify the Tach Tang is grounded,,screw can be loose,,,Mike try these before going any- where else,

[spyder_xlch]

Glad to see Mike got the caplocks unstuck.

[Len]

Perhaps this will help.

Len

[Len]

Ops !!! this might be easer
Len

[MIKESMONZA]

What GM book/ manual is that, The color jump's out at you,,,Thank's Len, Now if some body could find out how the tach's filter modify's the signal,,, we can put this in the Got r'done file,,,,MIke

[Len]

It's 1980 pontiac supplment manual. (canadian)
The zig-zag lines in the filter are resistors and the flat line over the curved line are fixed capacitors. I think that the filter is desined to eleminate voltage spikes from the the distributor thats just what I think, perhaps someone withmore knolage of this would be willing to enlighten us ???????

Len

[spyder_xlch]

Len, you pretty much sumed it up.

[Len]

It would be intresting to know the values of the the resistors and capacitors for future reference.
Len

[zeke]

The resistors and capacitors form what is known as a "low pass filter". The purpose is to keep high frequency noise from entering the electrical system and causing radio interference. (RFI)