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Manifold Heater and Heater switch location

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Loopytheloop View Drop Down
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    Posted: May/31/2018 at 5:25am
Hi All, you may be help me on this topic. 
 
 I am exchanging the Holley Carburator with a EFI Holley 2300 2 BBL. 
 I need to connect the heater sensor on the intake manifold but I do not know if the right location is in the  front or the back of the motor AMC 258 6cyl 4.2L. 
 I do not find this information on any books for AMC 258. 
 Thanks in avance for any help. 
 Cheers

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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2018 at 6:45am
There should be approximately equal vacuum in the intake along the length-- doesn't matter where you attach the sensor. Heat should distribute pretty evenly along the intake as well. Shouldn't matter where you attach the sensor. I think I'd put it toward the front, as the rear cylinders heat up a little faster than the front.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Loopytheloop Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2018 at 8:51am
Thank you very mush Farna, this is helpful
Cheers
Loopytheloop
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2018 at 12:36pm
What year? If 82 or later, there is a sensor in the FRONT end where the coolant went in. That's where the factory measured for the electric manifold heater.
IS that Holley system sensing coolant temp? If so - front is best as that's true engine temp - by the time it gets to the rear it's losing a bit of heat to the intake and through the intake, to the air.
Not a lot, but it will be warmer at the front since that's where the water comes in and that's where the factory sensed for the electric heater relay system.
If it's not for 82 or later, they must just be checking the temperature of the cast iron intake.
In that case it would be hotter in the middle due to the exhaust heating the center of the intake and the bottom of the carb.

Vacuum will be the same pretty much through the whole intake......... but heat, depending on the year... will indeed vary. 
until the engine reaches 165 degrees (f) there is an ELECTRIC heater in the center, so the middle will be hotter or warmer until the engine reaches operating temperature when that heater shuts OFF.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Loopytheloop Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2018 at 12:54pm
Thanks very mush Billd, this is helpful.
According the serial number identification my Jeep CJ7 was made in 1985. 
I will follow your recommendation.
Cheers
Loopytheloop in France 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2018 at 6:35pm
OK 1985 will definitely be the aluminum intake and exhaust that is NOT bolted to the intake.
When the engine is cool, as in when it is first started, an electric heater in the middle of the bottom of the intake heats the center of the intake below the carburetor. This takes the place of the exhaust heating the intake and carburetor in older engines (the 258 before 1981 for example)
It helps avoid cold driveability issues, cold stumble and helps atomize the fuel in cold air.
This heater is run through a relay that is usually on the right side of the engine bay. It may be different on Jeep but that is where it is on the cars.
The intake heater relay operates the heater in the intake. The relay has power when the engine is running and has oil pressure because the power for the relay coil runs through terminals on the oil pressure switch. 
And when the engine is cool, the relay is grounded through a sensor on the intake manifold, USUALLY in the front part, left side, of the manifold. It may have one or three terminals on it.
Coolant circulates through the intake and when the coolant reaches about 165 degrees (f), the sensor breaks the ground for the intake heater relay, the relay points open and the electric heater is shut off - the intake is now heated by the coolant circulating through the intake. 
So it's electric when it's cold, until it reaches 165 degrees then the temp sensor in the intake shuts down the relay because the coolant is now warm enough to warm the intake.

In the first picture below, the temperature sensor that runs the heater relay is in the lower left part of the picture, and it's broken LOL but you can still see the shell of the switch, below the hose fitting on the left end - or front - of the intake.


Here is the same intake, the bottom, and you can see the round area where I removed the electric heater just to see how it was made (I have two or three of these on the shelf and got curious - and promptly broke the heater in the process.
The switch I speak of is sticking up in this picture, 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2018 at 6:36pm
PS - I am very interested in how you come out with this, how everything works. And when you get to that point, pictures would be nice. I love Jeep vehicles, too...........
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