258 Intake Manifold / Heater

jay79cj7 · #1 (**permalink**) 02-16-2007, 01:21 AM

I am in the middle of a 4.0 head swap on my 79. It turns out that my 79 intake doesn't bolt up like all the write ups say it will. I got an 83 intake off ebay and its quite a bit different than the 79. I am hoping you guys can help me understand what some of these differences are.

For one, this one has an electric heat element in the intake rather than being heated by the exhaust gas like the 79. (The 79 intake and exhaust bolt together in the center under the carb.) How do I wire this new heater up? I have read that it is powered off a relay activated by an oil pressure switch and a temperature switch. I found the temp switch in the intake, but where is this oil pressure switch? And where can I get one? I would like to have this heater working without using a switch in the cab.

And what is this red thing on the top of the intake, just forward of the carb by cylinder #3? I found this picture that shows what I am talking about. Its the red thing almost dead center in the pic.
http://www.bustedjeep.com/projects/tbi/DCP_0711.JPG

Thanks guys.

jay79cj7 · #2 (**permalink**) 02-17-2007, 01:25 AM

C'mon guys, a little help?

Thanks.

RLBJeep · #3 (**permalink**) 02-17-2007, 12:25 PM

The manifold heater http://i163.photobucket.com/albums/t...00180WinCE.jpg is controlled by the manifold heater relay http://i163.photobucket.com/albums/t...01421Small.jpg. The relay is powered by the OP switch http://i163.photobucket.com/albums/t...itchMedium.jpg which on a 258 is located just north of the starter. The OP switch also controls the echoke. There is an orange wire running from the relay http://i163.photobucket.com/albums/t...01422Small.jpg that connects to the red wire that powers the manifold heater. Hope this helps.

jay79cj7 · #4 (**permalink**) 02-17-2007, 06:55 PM

Thanks!

RLBJeep · #5 (**permalink**) 02-18-2007, 07:01 AM

Here is a better explanation and pictures of the manifold heater http://home.sprynet.com/~dale02/manifold.htm. If you find out what that red thing is please post http://i163.photobucket.com/albums/t...0221Medium.jpg as it is on my list of parts disconnected by the PO that need to be identified and reconnected.

jay79cj7 · #6 (**permalink**) 02-18-2007, 02:04 PM

Thanks again! I had found that same page before I posted, but I can't find any that makes mention to the red fitting. I took it out of the manifold yesterday and it looks like a temp switch. Its not in the coolant or air passages; the hole it is screwed into is a dead end. I am wondering if it is to be used for the electric choke? (Which I don't have yet anyway.) I'll post if I figure it out.

That oil pressure switch you posted earlier was exactly what I was looking for. My pressure sender (for the gauge) threads directly into the block. I guess I just need to find myself that T fitting and the other switch.

RLBJeep · #7 (**permalink**) 02-18-2007, 10:30 PM

The other switch has 2 prongs http://www.partsamerica.com/ProductD...pe=417&ptset=A and actually powers the electric choke and manifold heater relay. I jusr got mine up and running today.

jay79cj7 · #8 (**permalink**) 02-19-2007, 12:18 AM

So... How is the electric choke wired up? Is it on the same relay, or a separate one?
Thanks!

RLBJeep · #9 (**permalink**) 02-19-2007, 09:30 AM

Quote:

Originally Posted by jay79cj7

So... How is the electric choke wired up? Is it on the same relay, or a separate one?
Thanks!

You will need to find the OP switch connector in your harness (if not cut off by PO) http://i163.photobucket.com/albums/t...p/DSC01417.jpg. There are 2 red wires, 1 red and 1 red w/white tracer leading into the connector. 1 has power with the key in the on position. The other wire should lead to a 6 pin connector http://i163.photobucket.com/albums/t...00179WinCE.jpg. The wire coming out of the opposite side of the 6 pin leads to the echoke. When you start your jeep the OP switch senses the oil pressure and then provides power to the echoke.

RLBJeep · #10 (**permalink**) 02-19-2007, 02:17 PM

Quote:

Originally Posted by jay79cj7

I am in the middle of a 4.0 head swap on my 79. It turns out that my 79 intake doesn't bolt up like all the write ups say it will. I got an 83 intake off ebay and its quite a bit different than the 79. I am hoping you guys can help me understand what some of these differences are.

For one, this one has an electric heat element in the intake rather than being heated by the exhaust gas like the 79. (The 79 intake and exhaust bolt together in the center under the carb.) How do I wire this new heater up? I have read that it is powered off a relay activated by an oil pressure switch and a temperature switch. I found the temp switch in the intake, but where is this oil pressure switch? And where can I get one? I would like to have this heater working without using a switch in the cab.

And what is this red thing on the top of the intake, just forward of the carb by cylinder #3? I found this picture that shows what I am talking about. Its the red thing almost dead center in the pic.
http://www.bustedjeep.com/projects/tbi/DCP_0711.JPG

Thanks guys.

The red thing on top of the intake, just forward of the carb is a knock sensor http://home.sprynet.com/~dale02/knock.htm since your jeep is a '79 you have no computer (MCU) and the knock sensor will not be used.

jay79cj7 · #11 (**permalink**) 02-19-2007, 11:47 PM

Thanks man. Excellent detective work.