Motor Swap - Gauges Problem
Thread Starter
Pro
Joined: May 2007
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From: Warrenville IL
Motor Swap - Gauges Problem
As a fun project his winter I accumulated all the parts to build a correct 1970 LT1 motor. Once completed I took it down to my local shop to have them drop it into my 1975. Nice upgrade for the old dog 165 HP motor, etc.
The ony variations from stock on this motor are a couple of items to ensure I didn't lose any gauges or have to change any gauges. So I've got an HEI distributor, and new Oil pressure and temperature units for a '75, not a '70.
I went down last week to check the progress and the guys got everything running and broken in. They still need to adjust the timing a little more. The one problem seems to be that several gauges are not reading properly. The tach is maxed out, the oil pressure and temperature gauges aren't reading properly, etc.
Any ideas what could cause this? I believe they tried both my new sending units and the originals. So I'm assuming it's something like a ground?
The ony variations from stock on this motor are a couple of items to ensure I didn't lose any gauges or have to change any gauges. So I've got an HEI distributor, and new Oil pressure and temperature units for a '75, not a '70.
I went down last week to check the progress and the guys got everything running and broken in. They still need to adjust the timing a little more. The one problem seems to be that several gauges are not reading properly. The tach is maxed out, the oil pressure and temperature gauges aren't reading properly, etc.
Any ideas what could cause this? I believe they tried both my new sending units and the originals. So I'm assuming it's something like a ground?
Race Director
Joined: May 2006
Posts: 16,528
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From: Dayton, Ohio
One of the things that often happens in an engine swap is the black 14 gauge ground wire gets put on the pos post of the starter solenoid BECAUSE the wire end is large and will fit the pos post.
It should go under one of the starter mounting bolts or one of the bellhousing bolts.
It should go under one of the starter mounting bolts or one of the bellhousing bolts.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Your sending units need to match the gauges. They work as a set and are calibrated to read [approximately] correctly. The sending units and gauge calibration changed over the years, so you need to get the correct senders. [lectriclimited.com has correct units]
Thread Starter
Pro
Joined: May 2007
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From: Warrenville IL
...Roger... - Would that wire short all gauges, or just a couple?
7T1vette - That's what I did, I bought new '75 sending units to match my '75 gauges. The threads and adapters all mounted to the heads and block as expected but they read wrong.
7T1vette - That's what I did, I bought new '75 sending units to match my '75 gauges. The threads and adapters all mounted to the heads and block as expected but they read wrong.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Pre 74 the wire attached to the pos post would cause the wiper motor to get hot and run your battery down.
Since GM changed the wiring I have seen that wire reek havoc on the harness. It can cause wires to melt through their insulation ,crossing circuits and so on.
This wire when connected wrong can do some really unpredictable things.
I would have your mechanics do the old standard test for gauges to get a basis for whats going on.
With the ign key in the ON position.
Pull wire off temp sender in the drivers side head-- the gauge needle should go to max cold.
Now ground that same wire to the "engine"-- the needle should go to max hot.
Key ON
Pull the wire off oil pressure sender-- needle should go to max high pressure
Ground the sender wire to the "engine"-- needle should go to max zero oil pressure
Let us know what happens.
