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Oil pressure switch/Electric choke.


psychostang
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Ok, so my new Edelbrock Thunder series AVS 2 carb should be here today.  It has an electric choke.  In my search, i see that Ed recommended a PS 64 switch from Standard Motor Products.  Is this the right switch?  Has anyone used this switch with success?  Also, did you have to use an adapter for the Wildcat block.  This is a 401 block.

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I’m in the same boat as you regarding oil pressure switch. There are plenty of oil pressure sending units available new. I’m using my original switch that is 1/8” x27 thread pitch for my 401 block. I’m putting in a supplemental oil pressure gauge tucked away nicely in the ash tray. I’ll still have the idiot light. I added a brass adapter T that has two female 1/8” x27 inlets and one male 1/8” x27 thread pitch. The male of the T goes in the block, the middle inlet is for the copper tube pipe that connects to the gauge. The top inlet is where you mount your oil pressure sending switch.

i have my engine out for rebuild, but I can find a pic of the hook up. It’ll be in another message.

Turbinator

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The oil pressure switch I recommended has two functions. One is to supply a signal to the oil pressure light.  As long as the engine is producing oil pressure, there is a connection which keeps the light off. A second terminal on the oil pressure switch provides 12V to the electric choke. The ONLY reason I suggested using this oil pressure switch is that there is no voltage going to the choke unless the engine is running.  If you wire the choke directly to a 12V source, the choke starts opening the moment the ignition key is switched on.  If your engine dies and you don't turn off the key, the choke is still opening.  

 

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You'll see three terminals on the oil pressure switch. One goes to the light on the dash.  12V goes into the second and when there's pressure, 12V comes out of the third and goes to the choke.  I think you need to use an adapter to thread the switch into the block.  This setup was OE on some 80's era Buick Skylarks.  

Edited by RivNut (see edit history)
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Same thing could be used in Turb's setup.  You'd use the three prong sender in place of the single prong sender and wire it as I described.  Turb's setup is for the idiot light and an additional oil pressure gauge - no provision for an electric choke.

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5 hours ago, RivNut said:

Same thing could be used in Turb's setup.  You'd use the three prong sender in place of the single prong sender and wire it as I described.  Turb's setup is for the idiot light and an additional oil pressure gauge - no provision for an electric choke.

Ed, 100 % true. Now, I’ve got an electronic choke but my choke is not connected to the oil sending unit. Help me out here.. Why would I need the oil pressure switch and the electronic choke “ talking” to one another. If it’s obvious I don’t mind being dumb for a minute.

Turbinator

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An electric choke should be powered only when the engine is actually running (not just key-on). Otherwise it can get out of sync with the engine temperature while the key is on, and cause the engine not to start. There are many ways to accomplish this, but few as simple as screwing a different switch into a preexisting oil port.

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51 minutes ago, Turbinator said:

Ed, 100 % true. Now, I’ve got an electronic choke but my choke is not connected to the oil sending unit. Help me out here.. Why would I need the oil pressure switch and the electronic choke “ talking” to one another. If it’s obvious I don’t mind being dumb for a minute.

Turbinator

They're  not "talking" to each other.  Oil pressure in this particular sending unit does two things. One - it makes the idiot light go off.  That's one wire, just like the original.  Two - it closes a switch between the two other terminals. One of those terminals goes through a wire to a 12V source, the other terminal has a wire going to the electric choke.  When the sending unit closes the switch, 12V goes to the electric choke.

 

If you were to disconnect the single wire going to the idiot light, the other two wires would continue to operate the choke.  If one of the two choke wires were pulled, you would disconnect 12V from the choke. Two separate and independent functions controlled by oil pressure and its sending unit.

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5 hours ago, RivNut said:

They're  not "talking" to each other.  Oil pressure in this particular sending unit does two things. One - it makes the idiot light go off.  That's one wire, just like the original.  Two - it closes a switch between the two other terminals. One of those terminals goes through a wire to a 12V source, the other terminal has a wire going to the electric choke.  When the sending unit closes the switch, 12V goes to the electric choke.

 

If you were to disconnect the single wire going to the idiot light, the other two wires would continue to operate the choke.  If one of the two choke wires were pulled, you would disconnect 12V from the choke. Two separate and independent functions controlled by oil pressure and its sending unit.

Ed, thank you for the explanation. I believe understand. Thank you for taking the time to explain. Much appreciated.

Turbinator

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5 hours ago, KongaMan said:

The oil pressure unit is a convenient way to intelligently wire an electric choke.  IMHO, it's better than hooking it up to an ignition circuit or tapping an alternator wire.

Mr. Konga Man, thank you for your insights. I’m not certain how my electric choke is wired. Since the choke works fine right now I believe I’ll leave it alone.

Thank you

 Turbinator 

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Hooking it up to the coil would ONLY allow about 9 volts when running & the choke would most likely take too long to open. This then cuts into fuel mileage.  There USED TO BE an electronic choke assembly that had a heat sensing unit I bolted to the rear of the head. Two wires went to the choke housing. One wire went to 12 volts constant & the other was a switched 12 volts.  The problem with hooking the one wire to 12 volts with the key on, engine running is that you go into the store for 10-20 minutes & since the choke had no voltage going to it the choke would start to close which makes for hard starting. The electronic unit sensed the heat & kept 12 volts on it until the head temp came down far enough to interrupt the circuit & turned off the 12 volts. Unfortunately they have been out of production for years.  Occasionally would find some on E-Bay, But that has turned dry for a number of years now.

 

Tom T.

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17 minutes ago, telriv said:

Good idea Bob.

Tom, some place I heard, “ keep fixing it until it is broke.” If it is working and safety is not in jeopardy leave it be.

it took awhile to figure out the adapter that went to the M10x1 threadpitch oil pressure gauge male connection on the back of the gauge. Fortunately, I got it figured out. Got black hose fitted on the copper tubing.

Thank you

 Turbinator 

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Ok, so it looks like the PS64 switch is the same 1/8th X 27 thread pitch as the block, so I shouldn't need an adapter.  I'm also going to order a PT139 Original GM  3 way oil pressure switch connector pigtail.  Should make installation easier.  Thanks all for your advices.

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For my Riviera, I have an Edelbrock electric choke cap on the original AFB wired with a DPST 12V Relay to the "Cold" Idiot Light switch. I did this to save wear and tear on the heating element. This is before I realized an Edelbrock product is better than those sketchy brands.

So, when the Cold light goes out, so does that heating element, The underhood temps should be enough especially since I have vacuum to the choke from a copper tube coil with the heater hose running through it.

Yet to test it out. There's no seats in my ride!

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9 hours ago, psychostang said:

Ok, so it looks like the PS64 switch is the same 1/8th X 27 thread pitch as the block, so I shouldn't need an adapter.  I'm also going to order a PT139 Original GM  3 way oil pressure switch connector pigtail.  Should make installation easier.  Thanks all for your advices.

Hi Andrew,

  I had years of experience with this sender in the field on GM trucks, last version of the old straight 6 292`s. I recall the initial discussion a couple of decades ago when this sender was suggested as a remedy for the original choke/hot air system and may have initially suggested it then. In the above application this sender was used for electric choke operation. I believe GM also used this as a switch for electric fuel pumps in automotive applications. The GM senders performed well but occasionally their failure would lead to breakdown whether it was the sender itself or the associated wiring. If/when the sender fails, the choke will close, even on an engine which is up to operating temp, and eventually choke the engine into a non-op condition. I wouldnt be afraid to use it because the failure rate was low, especially if one pays attention to the wiring installation, but keep in mind we were using GM senders. I would suggest not using today`s bottom of the basement bargain brands we often see as an option. Buy the best quality parts available.

  The best alternative for someone who has an original style hot air system carb is to restore that system to original operation. It`s not hard, its a simple system.

  Another point which occurs to me and I havnt seen mentioned is no one should have the key in an "on" position without the engine running anyway due to point burning, etc...

  Good luck!

Tom Mooney

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21 hours ago, telriv said:

Hooking it up to the coil would ONLY allow about 9 volts when running & the choke would most likely take too long to open. This then cuts into fuel mileage.  There USED TO BE an electronic choke assembly that had a heat sensing unit I bolted to the rear of the head. Two wires went to the choke housing. One wire went to 12 volts constant & the other was a switched 12 volts.  The problem with hooking the one wire to 12 volts with the key on, engine running is that you go into the store for 10-20 minutes & since the choke had no voltage going to it the choke would start to close which makes for hard starting. The electronic unit sensed the heat & kept 12 volts on it until the head temp came down far enough to interrupt the circuit & turned off the 12 volts. Unfortunately they have been out of production for years.  Occasionally would find some on E-Bay, But that has turned dry for a number of years now.

 

Tom T.

My car has one of these that was installed decades ago....works great!

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It would be nice to have a Choke position sensor with indication on the instrument panel rather than frequent stops to pop off the Air Cleaner top to check.

Since my previous rides were too precious for our treacherous winter roads and only summer driven, I'd experiment with a Lean Choke finding a balance with the spring and vacuum. Once set underhood temps prevented the choke from ever closing completely. Seemed to work fine for me and I live in northern Canada. If it was a little cooler than normal on start-up, I'd give a couple more pumps on the accelerator. At worst, if it sputtered-out, I'd start it again and be on my way. Usually I'd start driving gently before that would happen. This was with a copper tube looped on a header tube.

Switching to a ceramic cap with the electric element I found the electric Edelbrock cap with the 2 perpendicular contacts and a packard 56 connector interfered with a low profile aircleaner. So I switched it with a no name cap with the new carb install. I burned-out 2  and put the Edelbrock cap back on and simply bent the 2 contacts flush with the cap. Good since. Quality shows.

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23 hours ago, 1965rivgs said:

Hi Andrew,

    The best alternative for someone who has an original style hot air system carb is to restore that system to original operation. It`s not hard, its a simple system.

  Another point which occurs to me and I havnt seen mentioned is no one should have the key in an "on" position without the engine running anyway due to point burning, etc...

  Good luck!

Tom Mooney

 

Tom - totally agree!

 

The electric choke is NOT a good option for anyone running a vehicle with an automatic transmission made before maybe 1975. The electric choke is timed to a pre-set actual time, rather than the engine temperature. I personally learned how bad this option is by "fixing" the defective hot air choke on my wife's car about 1975. She would start the car with the intention of going shopping, drive to the first stop sign (about 3 blocks), the engine would stall, and would NOT restart. Let us just say she was less than happy with this arrangement! ;) 

 

The original hot air chokes are keyed to the temperature of the engine. When I correctly repaired the hot air choke and placed the electric choke in the round file, the issue completely disappeared, and my wife was again happy with the car.

 

Generally, the cause of failure of a hot air choke is burnout of the heat stove (a tube pressed into the exhaust cross-over, a chamber in an exhaust manifold, etc.). Obviously, the better fix is to repair/replace the damaged part.

 

However, it is quite easy to still make the hot air choke function correctly without doing the proper repair using this "workaround":

 

Hot air choke heat stove

 

Here is a bit of history of the automatic choke, and adjustment, for any who might have an interest:

 

Automatic chokes

 

Jon.

Edited by carbking (see edit history)
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1 hour ago, carbking said:

 

Tom - totally agree!

 

The electric choke is NOT a good option for anyone running a vehicle with an automatic transmission made before maybe 1975. The electric choke is timed to a pre-set actual time, rather than the engine temperature. I personally learned how bad this option is by "fixing" the defective hot air choke on my wife's car about 1975. She would start the car with the intention of going shopping, drive to the first stop sign (about 3 blocks), the engine would stall, and would NOT restart. Let us just say she was less than happy with this arrangement! ;) 

 

The original hot air chokes are keyed to the temperature of the engine. When I correctly repaired the hot air choke and placed the electric choke in the round file, the issue completely disappeared, and my wife was again happy with the car.

 

Generally, the cause of failure of a hot air choke is burnout of the heat stove (a tube pressed into the exhaust cross-over, a chamber in an exhaust manifold, etc.). Obviously, the better fix is to repair/replace the damaged part.

 

However, it is quite easy to still make the hot air choke function correctly without doing the proper repair using this "workaround":

 

Hot air choke heat stove

 

Here is a bit of history of the automatic choke, and adjustment, for any who might have an interest:

 

Automatic chokes

 

Jon.

John,

  Many years ago I used an auxillary choke stove on one of my cars as a temporary fix. I dont know if they are still available but they were found in the "HELP" display which was a turnstyle type presentation in many auto parts stores. They may still be available. I remember the unit working but not nearly as well as the original thru manifold heating process....but it worked well enough to be serviceable.

  I probably have one laying around here somewhere as I`ve dismantled quite a few cars that had this temporary fix.

Tom

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Tom - as I stated earlier, the better fix is to fix the cause. The heat stove is a workaround, how well it works depends on how well it was made, and where it is placed. But even a poorly made/placed heat stove with the original hot air choke is much better (opinion) than an electric if one has an older automatic transmission.

 

Carter used to include a heat stove with new aftermarket carbs that were equipped with hot air chokes. This is where I got the idea some 50 years ago. But putting the electric choke on my wife's car convinced me. ;)

 

Jon.

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