SOHC to DOHC

99_fly_by · Post by **99_fly_by** » Mon Sep 28, 2009 11:05 am

alright guys. my 2.0 SOHC has offically shit the bed. im orderin a new engine today an i wanna switch to the 2.0 DOHC. now my question is, its a 99 SOHC ATX but i want the DOHC. do i need a DOHC ecu? in Mass we need matching VIN #'s cause of inspection. they scan the VIN off the ecu an if it doesnt match your car, your screwed. does the AFX ecu from howell or the mopar performance come with the software to program it?

sabu · Post by **sabu** » Mon Sep 28, 2009 11:16 am

You don't need to change it but it is recommended. The SOHC PCM has less advanced timing. If you are keeping your ATX then it should work just fine.

Also if you are doing a complete DOHC Long block swap, you need a DOHC harness as well.

99_fly_by · Post by **99_fly_by** » Mon Sep 28, 2009 11:43 am

it is a DOHC longblock. i supply manifolds, oil pan, and valve cover. anything else i will need? already planned on gettin the hood with the "power bulge". where can i get a new wiring harness? im not doing this myself either. no time at all or the patience to do so. do shops usually take care of the harnesses and what not or is that all on me?

sabu · Post by **sabu** » Mon Sep 28, 2009 2:08 pm

I would assume, unless the shop has a supplier for harnesses, you are doing the leg work yourself. A DOHC ATX harnes won't be the easiest thing to find. Most ATX are SOHC. I think finding a running DOHC car is a better bet. Easier and less hassle than getting all these parts for a swap. But an auto wrecker is going to be your best bet to find a harness.

DOHCRT · Post by **DOHCRT** » Mon Sep 28, 2009 8:22 pm

You should really consider staying with the SOHC engine unless you plan to swap to an MTX. DOHC ATX cars are the slowest.

The shop you are going to bring the car to probably has no idea what you need to do the swap. A dealership can program the PCM to match the VIN and mileage of your car. Some of the DOHC power steering stuff is different, so keep that in mind.

roysneon · Post by **roysneon** » Mon Sep 28, 2009 11:05 pm

Yep. The DOHC makes power higher in the rev range than the SOHC does, making the DOHC less useful with the auto transmission because it won't always let you rev high enough to make more power than a SOHC engine.

I would grab a harness from a DOHC anyway if you're not doing the swap yourself. There are a few wires that need to be extended from everything I've heard, and honestly I don't trust anyone else wiring on my cars.

99_fly_by · Post by **99_fly_by** » Tue Sep 29, 2009 8:42 am

after reading those and doing some research ima say ill keep the SOHC

roysneon · Post by **roysneon** » Tue Sep 29, 2009 10:29 am

I would do the same. With an auto transmission it's your best bet, and although there are no real major issues per se with the DOHC, the SOHC valvetrain is simpler, therefore inherently less prone to failure.

Ghost Neon · Post by **Ghost Neon** » Tue Sep 29, 2009 1:13 pm

sabu wrote:I would assume, unless the shop has a supplier for harnesses, you are doing the leg work yourself. A DOHC ATX harnes won't be the easiest thing to find. Most ATX are SOHC. I think finding a running DOHC car is a better bet. Easier and less hassle than getting all these parts for a swap. But an auto wrecker is going to be your best bet to find a harness.

Just for informational purposes, the engine harness is not connected to the transmission. The engine harness from a dohc does not differentiate between atx and mtx neons.

roysneon · Post by **roysneon** » Tue Sep 29, 2009 2:15 pm

Transmission is not electronically controlled at all, except for torque converter lockup, which harness comes pre-wired for.

fuzzyneon · Post by **fuzzyneon** » Wed Sep 30, 2009 11:57 pm

99_fly_by wrote:it is a DOHC longblock. i supply manifolds, oil pan, and valve cover. anything else i will need? already planned on gettin the hood with the "power bulge". where can i get a new wiring harness? im not doing this myself either. no time at all or the patience to do so. do shops usually take care of the harnesses and what not or is that all on me?

you can cut hood bracing to fit dohc thats how mine is

infil · Post by **infil** » Sat Oct 03, 2009 1:05 am

for a shop to supply a harness youll be looking in the thousands. a replacement harness for a dohc fire rebuild i did was quoted at 1300 wholesale. extend the ect wiring and call it good, IIRC thats the only difference in the dohc/sohc harnesses.

Ghost Neon · Post by **Ghost Neon** » Sat Oct 03, 2009 11:22 am

infil wrote:for a shop to supply a harness youll be looking in the thousands. a replacement harness for a dohc fire rebuild i did was quoted at 1300 wholesale. extend the ect wiring and call it good, IIRC thats the only difference in the dohc/sohc harnesses.

Wanna say the cam sensor could use another few inches, but this is quite correct. All sensor are the same as long as you stay within the model year of the neon.