[Hogdaddy1993]

I have recently acquired a 304 Jeep engine and I would like upgrade my CJ from the underpowered 151 Iron Duke to the 304. The question that comes to mind is will the existing wiring harness work with the 304? Or will it need to be modified.
Any comments as Im sure this swap has been done before.
Thanks in advance,

 

[Lew360]

I don't have your answers but I'm going to follow this thread because I would love to do this as well!

 

[keith460]

The 304 engine will have simpler wiring than the 4 cylinder iron duke engine. 304 engine only needs basic ignition system to make it work and very little emissions components since the last ones used in the Jeep CJ was in 80-81. You'll be removing extra wires that aren't necessary for the 304 as the iron duke for 83 has many emissions components and wiring that won't be needed. Nutter Bypass comes to mind.

Find a wiring diagram for your model year 304 engine, say 1979, and use that as a reference.

 

[Krkman13]

I have recently acquired a 304 Jeep engine and I would like upgrade my CJ from the underpowered 151 Iron Duke to the 304. The question that comes to mind is will the existing wiring harness work with the 304? Or will it need to be modified.
Any comments as Im sure this swap has been done before.
Thanks in advance,

So I recently bought a 86 cj7 with an unknown 304. Turns out original was the 4 cylinder. Motor needed a carb and had a bunch of parts from PO. Anyways i now have 3 engine wires only. 1 for distributor, 1 for the temperature guage, and 1 for the alternator. Thats it. There is also one plug to the tranny.

Take a look...

My 1986 cj7 has a 304....

Still working on these backup light wires. Here is a close up of the water tight connector that goes to the top of the transmission t5... Got me baffled because its not on the t5 schematic. Its the same orange and red thats not plugged into anything nearthe battery, last picture below...

www.jeepforum.com

 

[jeepdaddy2000]

The first question is are you going to have issues with emissions in your state?
If not, then you will need to decide what ignition you want to run. Simplest is points/petronix or an HEI. You can adapt the stock autolite but you will need to get the components for it.
After that, basic choke, oil and temp sensors, and charging system will round out the needed wiring.

 

[Hogdaddy1993]

So I recently bought a 86 cj7 with an unknown 304. Turns out original was the 4 cylinder. Motor needed a carb and had a bunch of parts from PO. Anyways i now have 3 engine wires only. 1 for distributor, 1 for the temperature guage, and 1 for the alternator. Thats it. There is also one plug to the tranny.

Take a look...

My 1986 cj7 has a 304....

Still working on these backup light wires. Here is a close up of the water tight connector that goes to the top of the transmission t5... Got me baffled because its not on the t5 schematic. Its the same orange and red thats not plugged into anything nearthe battery, last picture below...

www.jeepforum.com

That sounds like a pretty easy connection, three wires. So the 304 doesn’t have any sort of engine control module . I certainly don’t have one on my 151 harness.
Thanks again for your input, you got me going in the correct direction.

 

[Hogdaddy1993]

The first question is are you going to have issues with emissions in your state?
If not, then you will need to decide what ignition you want to run. Simplest is points/petronix or an HEI. You can adapt the stock autolite but you will need to get the components for it.
After that, basic choke, oil and temp sensors, and charging system will round out the needed wiring.

I like points, I grew up with those.
Emissions is not an issue.
Keeping the ignition system basic is a plus for me.
I will have to study up on the HEI as well.
Thanks for your comment.

 

[Krkman13]

I will have to study up on the HEI as well.

Not much to study up on, just one ignition switched hot wire. Its also in my thread. The coil and ignition module, and old distributor get thrown away.

Summit Racing™ HEI Distributors SUM-850048
$179.99

 

[Matt1981CJ7]

If you go with an HEI, it's recommended to wire it thru a relay to give it higher amperage directly from the battery.

Matt

 

[Krkman13]

If you go with an HEI, it's recommended to wire it thru a relay to give it higher amperage directly from the battery.

Matt

I didn't know that, does it really draw that many amps?

 

[Matt1981CJ7]

I didn't know that, does it really draw that many amps?

The HEI needs full unrestricted battery voltage. 10 -12 gauge wire is recommended.

A lot of guys make the mistake of using the old exterior coil wire to power the HEI, which has a resistive wire in the circuit, so their HEI is only getting somewhere around 8-9V instead of 12V.

Similar to the headlights on a CJ, relays improve performance a bunch.

Matt

 

[Lew360]

If he actually has an Iron Duke then it should be HEI ready, since it came form the factory with one.

 

[Mister4x4]

That sounds like a pretty easy connection, three wires. So the 304 doesn’t have any sort of engine control module . I certainly don’t have one on my 151 harness.
Thanks again for your input, you got me going in the correct direction.

Later model 304s came with a Duraspark ignition system from the factory. If your 304 comes with a factory distributor, and you don't have the rest of the system on your harness, it would be better to just pull the dizzy and go HEI, as others have recommended.

If you do have them, there will be male counterparts for these guys (that's the Duraspark module you would need, if so).

 

[jeep_boy02]

Later model 304s came with a Duraspark ignition system from the factory. If your 304 comes with a factory distributor, and you don't have the rest of the system on your harness, it would be better to just pull the dizzy and go HEI, as others have recommended.

If you do have them, there will be male counterparts for these guys (that's the Duraspark module you would need, if so).

And if you do have the factory dizzy and wiring, I'd still recommend going DUI HEI and messing around with OEM stuff.

The factory Motorcraft 2100 carb is also the best carb to have. It out performs any edlebrock or truck avenger, so keep that rebuild in mind too. Or go FI

buying too many parts for too many Jeeps

 

[Hogdaddy1993]

Great information
Thanks again