what is this? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CT-Truckster · 09-08-2003, 08:46 PM

on my 84, right above the oil filter in the side of the block, some wires going to a fitting there.

87 STEPPER · 09-08-2003, 09:07 PM

Might be a block heater for winter time.

Can ya post a pic of it?

CT-Truckster · 09-08-2003, 09:28 PM

well you may not be able to tell much with all the oily scum but here it is

**crossy** · 09-08-2003, 09:34 PM

that is the second oil pressure switch , I THINK that is the one that makes your choke light come on . never understood that but I always liked having an idiot light and gauge. WHY CHOKE GM ? WHY?

you could pull it off and jumper between the two female spades and see for sure. DAVE

CT-Truckster · 09-08-2003, 09:45 PM

you just may be right crossy. my choke light goes on and off randomly and i didn't know why. the choke isn't even hooked up. and would it have anything to do with the oil gauge not working? it aint worked in a long time, i just keep a constant check on the oil level considering how much it leaks. i replced the sending unit behind the distr. but it still didn't work. maybe a short in ther wiring or something.

*racedvl* · 09-08-2003, 09:49 PM

It actually turns the electric choke on. When pressure is senced, power then is applied to the electric choke.

apstguy · 09-08-2003, 11:40 PM

Are you sure? I have an original 85 and has no such thing. My oil pressure and oil switch is on a tee in the back next to the distributor. Maybe that is why?

*racedvl* · 09-09-2003, 07:51 PM

In my 86, when I installed the engine, I had no power to the electric choke until I used a jumper wire on that connector. BTW, orginally on my 86, wich was a 4.3L mind you, the pressure swich was at the back of the intake, not by the oil filter. GM did that both ways as far as I could tell.

Prerunner1982 · 09-09-2003, 08:19 PM

my 82 has this as well....

**crossy** · 09-09-2003, 09:54 PM

both of ythe 86 blazers & the 84 I tore apart had it at the oil filter. another GM mystery .:-) DAVE

CT-Truckster · 09-09-2003, 11:13 PM

i bet that is why I couldn't get any power to my choke last winter, so i just left it unhooked instead of trying to figure out why. but know i know, and as GI Joe says, knowing is half the battle.

**crossy** · 09-09-2003, 11:31 PM

There is no reason to go through a Winter chokeless for something that simple. A choke only needs 12volts of the ignition. If you look at your fuse box there are extra spades in there and you can even run a wire right from the one that says 'IGN' right to the choke. put a small inline fuse in the wire and your set. BTW. the choke thermostatic coil also commonly goes bad if you have the stock QJ and even if the w ire is hooke up you will not get the choke to open. The stinkin little choke coils cost upwards of $35 too!.I think on most of the 80's trucks there was a seperate fuse for the choke itself and whatever the rating is on that fuse is what you should install inline. prolly a 10 amp?. DAVE

**swervin ervin** · 09-09-2003, 11:31 PM

If it has two prongs, it's the oil pressure switch. One, it's the oil pressure sending unit. The other is up top, beside the distributor. It seems the placement of these things were different, in different years. My 85 has both up top in a brass tee. The 87 van has the switch up top and the sender down there above the oil filter. Only GM knows why they had so many variations about the placement.

**swervin ervin** · 09-09-2003, 11:42 PM

Dave,

the reason behind a oil pressure switch, for the choke is very simple. When you press on the pedal, the choke closes. When you start the vehicle, the choke starts heating up, if the switch sees oil pressure. As long as the engine has oil pressure, it receives power. No pressure, as per the switch, no power. The reason is so the choke won't open unless the engine is running. If this switch wasn't used, all you would have to do to make the choke open is turn on the ignition. If this happened, the engine would still be cold, and the choke wouldn't work when you started it up.

Now, after TBI came into the picture, this switch is used to supply power to the fuel pump. Same sequence. After it starts, if oil pressure isn't sensed, it shuts off power to the fuel pump. This is a safety feature. Say you wreck and the engine dies, but the switch is still on. Without the switch, fuel would still be pumping and if a leak were to occur, well you see how this wouldn't be a good thing.

There was a guy a long time ago, running around town with a built up Vega. He has a big V8 in this thing, along with just about all you could do to one. Talking about a lot of money here. The one thing he didn't have was a oil pressure switch. Well, you guessed it. A gas hose ruptured on it one day, and started a fire at the header. In his haste to get the fire out, after the engine died, he jumps out, leaving the switch on. Put it this way, it burned slam to the ground, because the fuel was pumping like a fire hose.

Mike

**crossy** · 09-09-2003, 11:57 PM

[QUOTE]Originally posted by swervin ervin
[B]Dave,

the reason behind a oil pressure switch, for the choke is very simple. When you press on the pedal, the choke closes. When you start the vehicle, the choke starts heating up, if the switch sees oil pressure. As long as the engine has oil pressure, it receives power. No pressure, as per the switch, no power. The reason is so the choke won't open unless the engine is running. If this switch wasn't used, all you would have to do to make the choke open is turn on the ignition. If this happened, the engine would still be cold, and the choke wouldn't work when you started it up.

The bimetal strip in the choke takes several minutes to get to the point where it opens it up. The switch would only delay that by a few seconds until it sees oil pressure. All the aftermarket carbs are set up the same way ,but they never mention about running it through a pressure switch. It was decent idea by GM.
All I am saying to these guys is that if you have the switch bypassed for one reason or another you don't have to be without a funtioning choke. Holleys are not too bad wiithout one but QJ's are downright miserable without one. DAVE

09-08-2003, 08:46 PM	#1
CT-Truckster ? Join Date: Jul 2002 Location: Dyersburg, TN Posts: 471	what is this? on my 84, right above the oil filter in the side of the block, some wires going to a fitting there.

09-08-2003, 09:07 PM	#2
87 STEPPER STILL PLAYS WITH TRUX Join Date: Nov 2002 Location: Melbourne, Fla. Posts: 2,764	Might be a block heater for winter time. Can ya post a pic of it? __________________ ~~Bruce~~ MY 87 STEPPER MY 99 2D/WD TAHOE

09-08-2003, 09:34 PM	#4
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	that is the second oil pressure switch , I THINK that is the one that makes your choke light come on . never understood that but I always liked having an idiot light and gauge. WHY CHOKE GM ? WHY? you could pull it off and jumper between the two female spades and see for sure. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

09-08-2003, 11:40 PM	#7
apstguy LED King Join Date: Jan 2003 Location: Sacramento, CA Posts: 2,088	Are you sure? I have an original 85 and has no such thing. My oil pressure and oil switch is on a tee in the back next to the distributor. Maybe that is why? __________________ Tyler 1985 C10 305 w/ Bowtie OD TH700R4 3.42 LSD 202,000 miles 2006 Ford Focus ZX3 5-speed Stick 2016 Chevy Spark EV Gone: 2002.5 VW GTI 24v VR6 Gone: 2008 VW R32

09-09-2003, 08:19 PM	#9
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	my 82 has this as well.... __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

09-08-2003, 09:28 PM	#3
CT-Truckster ? Join Date: Jul 2002 Location: Dyersburg, TN Posts: 471	well you may not be able to tell much with all the oily scum but here it is

09-08-2003, 09:45 PM	#5
CT-Truckster ? Join Date: Jul 2002 Location: Dyersburg, TN Posts: 471	you just may be right crossy. my choke light goes on and off randomly and i didn't know why. the choke isn't even hooked up. and would it have anything to do with the oil gauge not working? it aint worked in a long time, i just keep a constant check on the oil level considering how much it leaks. i replced the sending unit behind the distr. but it still didn't work. maybe a short in ther wiring or something.

09-08-2003, 09:49 PM	#6
racedvl Account Suspended Join Date: Jan 2000 Location: Woodstock, IL Posts: 7,020	It actually turns the electric choke on. When pressure is senced, power then is applied to the electric choke.

09-09-2003, 07:51 PM	#8
racedvl Account Suspended Join Date: Jan 2000 Location: Woodstock, IL Posts: 7,020	In my 86, when I installed the engine, I had no power to the electric choke until I used a jumper wire on that connector. BTW, orginally on my 86, wich was a 4.3L mind you, the pressure swich was at the back of the intake, not by the oil filter. GM did that both ways as far as I could tell.

09-09-2003, 09:54 PM	#10
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	both of ythe 86 blazers & the 84 I tore apart had it at the oil filter. another GM mystery .:-) DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

09-09-2003, 11:13 PM	#11
CT-Truckster ? Join Date: Jul 2002 Location: Dyersburg, TN Posts: 471	i bet that is why I couldn't get any power to my choke last winter, so i just left it unhooked instead of trying to figure out why. but know i know, and as GI Joe says, knowing is half the battle.

09-09-2003, 11:31 PM	#12
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	There is no reason to go through a Winter chokeless for something that simple. A choke only needs 12volts of the ignition. If you look at your fuse box there are extra spades in there and you can even run a wire right from the one that says 'IGN' right to the choke. put a small inline fuse in the wire and your set. BTW. the choke thermostatic coil also commonly goes bad if you have the stock QJ and even if the w ire is hooke up you will not get the choke to open. The stinkin little choke coils cost upwards of $35 too!.I think on most of the 80's trucks there was a seperate fuse for the choke itself and whatever the rating is on that fuse is what you should install inline. prolly a 10 amp?. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

09-09-2003, 11:31 PM	#13
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	If it has two prongs, it's the oil pressure switch. One, it's the oil pressure sending unit. The other is up top, beside the distributor. It seems the placement of these things were different, in different years. My 85 has both up top in a brass tee. The 87 van has the switch up top and the sender down there above the oil filter. Only GM knows why they had so many variations about the placement. __________________ Mike 1985 Chevy C-10

09-09-2003, 11:42 PM	#14
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Dave, the reason behind a oil pressure switch, for the choke is very simple. When you press on the pedal, the choke closes. When you start the vehicle, the choke starts heating up, if the switch sees oil pressure. As long as the engine has oil pressure, it receives power. No pressure, as per the switch, no power. The reason is so the choke won't open unless the engine is running. If this switch wasn't used, all you would have to do to make the choke open is turn on the ignition. If this happened, the engine would still be cold, and the choke wouldn't work when you started it up. Now, after TBI came into the picture, this switch is used to supply power to the fuel pump. Same sequence. After it starts, if oil pressure isn't sensed, it shuts off power to the fuel pump. This is a safety feature. Say you wreck and the engine dies, but the switch is still on. Without the switch, fuel would still be pumping and if a leak were to occur, well you see how this wouldn't be a good thing. There was a guy a long time ago, running around town with a built up Vega. He has a big V8 in this thing, along with just about all you could do to one. Talking about a lot of money here. The one thing he didn't have was a oil pressure switch. Well, you guessed it. A gas hose ruptured on it one day, and started a fire at the header. In his haste to get the fire out, after the engine died, he jumps out, leaving the switch on. Put it this way, it burned slam to the ground, because the fuel was pumping like a fire hose. Mike __________________ Mike 1985 Chevy C-10

09-09-2003, 11:57 PM	#15
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	[QUOTE]Originally posted by swervin ervin [B]Dave, the reason behind a oil pressure switch, for the choke is very simple. When you press on the pedal, the choke closes. When you start the vehicle, the choke starts heating up, if the switch sees oil pressure. As long as the engine has oil pressure, it receives power. No pressure, as per the switch, no power. The reason is so the choke won't open unless the engine is running. If this switch wasn't used, all you would have to do to make the choke open is turn on the ignition. If this happened, the engine would still be cold, and the choke wouldn't work when you started it up. The bimetal strip in the choke takes several minutes to get to the point where it opens it up. The switch would only delay that by a few seconds until it sees oil pressure. All the aftermarket carbs are set up the same way ,but they never mention about running it through a pressure switch. It was decent idea by GM. All I am saying to these guys is that if you have the switch bypassed for one reason or another you don't have to be without a funtioning choke. Holleys are not too bad wiithout one but QJ's are downright miserable without one. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.



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