Choke works,oil pressure gauge works ,choke light always on

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Beenz

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98407
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Keno
Truck Year
1982
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C1500
Engine Size
305
Hello all ,I have an 82 GMC C1500 with a 305 ,recently swapped the intake and carb to edelbrock electric choke , everything was fine for a couple days then boom choke light went on and stays on .I have since replaced battery and alternator(needed it anyway) ,looking into it I learned it acts as low oil pressure light as well ,but the gauge seems to be working, at idel it's right in the middle when accelerating is raises accordingly,but yet the light continues. A : should I be worried? B : if choke works can it still be a faulty oil pressure switch ?? .any insight would greatly be appreciated.
 

chengny

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1986
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K3500
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350/5.7
Hello all ,I have an 82 GMC C1500 with a 305 ,recently swapped the intake and carb to edelbrock electric choke , everything was fine for a couple days then boom choke light went on and stays on .I have since replaced battery and alternator(needed it anyway) ,looking into it I learned it acts as low oil pressure light as well ,but the gauge seems to be working, at idel it's right in the middle when accelerating is raises accordingly,but yet the light continues. A : should I be worried? B : if choke works can it still be a faulty oil pressure switch ?? .any insight would greatly be appreciated.

A: I wouldn't get too stressed about it. I would be far more inclined to believe that what the gauge indicates is your actual oil pressure.

B: Yes, a faulty oil pressure switch will cause the CHOKE warning light on the dash to illuminate. Also, remember to keep in mind that the power supplied to the electric choke -via the switch - only serves to open the choke plates. It has nothing to do with closing them. They will close on their own, regardless of whether power is supplied to the coil or not.

Originally, the purpose of the electric choke heater was simply to cause the choke plates to begin opening as quickly as possible - and without any assistance from the operator. This was GM's response to the new (at the time) mandated EPA regulations regarding tighter hydrocarbon/carbon monoxide limits in the exhaust gas stream.

Since this all happened before the widespread use of Engine Control Systems (read the ECM/ECU). The engineers came up with the idea of powering up the choke heater using the oil pressure switch. Since the switch contacts close at 10 psi, the choke heater coil was energized almost immediately - upon establishment of engine oil pressure.

This set-up was short lived - it was abandoned with the advent of electronic engine management control.


Having provided you with way TMI, be aware that while a Rochester Q-jet's heater coil is grounded through the carburetor body, the Edelbrock coil requires an independent ground lead. There should be two terminals on the coil housing of your new carb. Be sure one is connected to a ground lead that goes to a clean spot on the intake manifold (or where ever is convenient). And the other runs over to the oil pressure switch.

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I don't know how interested you are but, here is how both circuits (choke heater and choke warning light) operate:

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Yeller

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Cloverdale, CA
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Blayne
Truck Year
1983
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K10
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383
Hello chengny, I found this site trying to understand the OPS schematic. Your explanation and drawings helped me understand the dark blue wire serves as a ground with the switch open. Appreciate your help.
About 12 years ago I installed a jumper wire in the OPS connector after an engine swap because I thought my switch was bad or I had possible wiring issue. Last weekend while correcting a windshield wiper pump issue, I decided to fix the decade old OPS issue. I verified 12V from the pink/white wire side of connector and decided I should go ahead and replace the switch. Dang! Same issue with replacement switch, choke light on with engine running normally. Drove the truck for dump run with choke light on and on next engine start the light was out. Thought about not worrying and decided to try couple more checks. With everything cooled down I removed connector from OPS and tested for voltage using test light instead of mm and noticed voltage at both sides of unplugged connector. Hooked connector back up, started engine and choke light is on. Shut engine off and restarted, choke light on and that confused me a little. I then checked voltage at choke and by gosh 12V, let engine run and choke coil did not heat up and open choke. I then jumpered the OPS connector and noted correct choke operation. My next step was to install a couple jumper leads to the OPS to avoid further burns and checked to see if new switch was closed with engine running, no joy, switch open.
Because my original switch worked before engine swap and new switch seemed to work after driving truck and doing second start, I am stumped. OPS is installed above oil filter, sender behind manifold. Tempted just to continue with jumper wire but wondering what I’m missing besides a little skin from left arm.
Thanks
 
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