GM LS2 (D585) COIL PACK SWAP

by Scott Taylor March 25, 2017

GM LS2 (D585) COIL PACK SWAP

Many of you have been asking how I did my GM Ls2 coil pack swap, so here is my write up on how to do it step by step. Before we get started I thought I would give a little explanation on why this is beneficial to us.

In the quest to achieve higher and higher horsepower levels, there comes a time where we need to upgrade the ignition system. As we increase boost and hp levels, we always need to increase fuel injectors, intercoolers, piping, exhaust Etc. well the same is true for the ignition system! Now before anyone gets all upset with me here, yes Nissan did a great job with the ignition system on the z32. But as we all know, this was way back in the 1990's. As with everything, times have changed and technology has made great improvements!

As we start increasing the boost levels to north of 20 Psi, we start to experience what is known as "spark blowout". This occurs when the cylinder pressures and fuel mixtures become too great for the spark plugs to jump the spark across the gap. to battle this issue, we would simply close the spark plug gap down from the oem .044" to anywhere from .025"-.032". While this helps to prevent the dreaded blow out, it often comes with a price of poor idle. Anytime we close the gap way down, it can lead to a rougher idle.

So I know some of you will be thinking, this is why HKS makes the twin power ignition amplifier right? Yes this was the old school way of combating the above mentioned problems. HKS did a good job with developing the twin power, and it does work pretty well. However, it is still limited by the output voltage of the oem coils!

Fast forward to today. As we have started to see more and more VG's making north of 700whp, the need for a better, stronger ignition system has never been more important. The answer was simple to find. All I had to do is look to other platforms that have been making higher HP than us for a lot longer than we have! So I turned to our brothers in the RB world along with the 2JZ and LS platforms. While researching this topic it became very clear to me that the GM LS2 coil packs where the way to go! It has been said by many, that there is simply nothing stronger without spending huge amounts of $$$!

Simply put, our coils produce roughly 21k volts. The LS2 coils can produce upwards of 42k volts! That is an impressive improvement from a coil, roughly the same size as our OEM coils. (Isn't technology great?)

Now for the best part. We know all too well the problems we have with our PTU's (Power Transistor Unit). They are always going out and the connections are always wreaking havoc. Well the good news is the PTU, also called the Igniter, is built in to each coil. This means we get to delete the problematic PTU forever! Yay!

The performance gains are pretty self explanatory, but the best part about this swap is the cost. While the price of the Twin Power is in the $400.00 range, these coils can be had for much less. Better, stronger spark for less money? Now that is right up my alley! I bought 8 coils from the local Pick N Pull for $125 and all the plugs for $5. Not bad.

Another non-performance benefit to this MOD is that the coil packs are mounted under the plenum, which allows for the plenum to be shaved and the wiring placed under the plenum. This goes well with the shaved and tucked trend we see a lot of these days.

I have ran these coil packs on my Z since March 2014 with no issues. I have made 900whp with them running NGK Iridium 7 (NGK part#2667) (BKR7EIX) gapped to .032" on E85. They can be removed to access the spark plugs without pulling the plenum as long as the cover you see in the pics below is not used. I have been to the 1/4 mile track numerous times and to a road course at MSR Houston and have never had any issue with them coming disconnected.

Here is what you will need:

6 AC Delco brand ignition coils from the 2000-2003 Chevy and GM trucks, Tahoe's and Suburbans. Known as the D585 coil pack.

You want this one with the white epoxy Do not use these that have

the black epoxy

The cheap ebay coil packs caused me a nightmare of issues with misfiring as they would run perfect till 12psi of boost and then they would randomly drop different cylinders. This kept me from boosting any higher. Kind of like a rev limiter! Use only GM A/C Delco brand coils with the white epoxy! I have found that you can buy these used for less than $100 from the Facebook LSX sales pages.

6 Coil pack connectors

You can buy them either individually, or in a harness like this.

If you buy from the pick n pull, you can score something like

this. all the coils with the plugs on the metal mount.

You will also need some wire cutters, soldering iron, solder, heat shrink and a dremel tool or an air die grinder with a carbide burr and a upper plenum gasket.

Start by removing the metal mounting bracket from the coil packs

Remove the spark plug boot from the end of your VG coil packs.

Measure and cut of the last 1/2" of the boot. This allows the spark plug to sit all the way into the coil pack and make contact with the coil.

Then just push the boot on to the GM coil packs. A little glue can be used here if you feel that you need it. I did not use any and they have never come off yet.

Now go ahead and pull your plenum and remove your spark plug tubes.

Here you can see that the coil packs will not fit

Past the valve cover overhang.

Here I used my air grinder and a carbide burr to make short work of the overhang. It doesn't needmuch removed, just enough to make it clear

Here I used my spark plug tube into a way to hold down

the coils, but this prohibited me from removing the coils

and plugs without pulling the plenum. So I no longer

use these! This is up to you but I haven't had any come loose.

I cut my OEM harness all the way back to the firewall as far as I could and separated the wire to redirect them better for under the plenum use. Always solder the wires and use heat shrink tubing to cover the joints so you have no shorts or tape to come unravelled due to heat etc.

Here is the wiring diagram for the LS2 coils.

(A) needs to be grounded to the engine block. You can use individual grounds or one single ground. I wired them all together and found a Ground bolt on the back of the plenum where some other grounds are attached.

B,C,&D all get connected to the OEM coil wires

(B) gets connected to the OEM harness ground, This should be the thinner of the 2 black wires.

(C) gets connected to the +5V signal from the ECU/PTU. This is the red/pink wire.

(D) gets connected to 12v+ which is the larger thicker black wire that is in the middle in between the other two wires.

Please note that the #1 cylinder uses a black signal wire from the ECU/PTU instead of a red wire.

DO NOT MIX THESE UP!

If you ground the ECU wire it will fry your ECU and will need replaced.

Delete the PTU:

Here you simply cut the wires and solder & heat shrink them together.

Do them one at a time so you don't mix them up.

this step is much easier if you have the PTU relocated to the front under the nose panel.

The black ground wire is the PTU ground and is left disconnected.

If you want to, you can get rid of the plugs all together by soldering the other colored wires together in the same way as this pic shows. I do not have any pics of this but I chose to go a step further and remove all plugs for the PTU and solder the Blue and red wires together as per the Wiring diagram above. This eliminates another possible failure point.

The D585 coils use a little higher Dwell setting then our OEM coils. They operate best at 5ms and our VG coils are around 2-2.5ms. The D585 coils will run fine on a factory ECU and will still produce much more spark at that setting, but to take full advantage of them, you will want to adjust the dwell using Nistune etc. I can do this for you (or anyone that tunes with Nistune) if needed and send a new chip for your socketed ecu.

If you have Nistune, You can increase the Dwell to 5ms like this

Here is the finished product. A very clean look and makes my Plenum pull a 5 minute affair!

If you have any questions I can be reached on Facebook or by Email.

Facebook name : Scott ZShack Taylor

Email: thezshack@yahoo.com

Twinturbo.net name: Scott zshack taylor

Written by:

Scott Taylor

ZShack

16321 Loch Katrine LN

Houston, TX 77084