September 20, 2021

Using a 97-99 ECU In a 95-96 DSM

If you have a 95-96 DSM, you may end up using a 97-99 ECU in your 2G at some point whether it be from using a 2Gb EPROM ECU or an H8 Blackbox ECU. Maybe your 95-96 ECU took a shit and all you had was a 97-99 ECU to replace it with. Maybe you want to try out the H8 Blackbox 2G ECU found in the 98-99 DSM’s and you want to give ECUflash and Ceddy Mods a shot. Or maybe you found a really good deal on a 97-99 EPROM ECU with DSMlink and you want to start tuning with that. Whatever the case may be, there MAY be some changes you need to make to your spark plug firing order and/or your fuel injector firing order.

Words By AJ Hunsinger // Images By AJ Hunsinger

So you swapped your ECU out of your 95-99 DSM with one of the ECU’s mentioned above. You go to turn the key and fire up the engine, but it won’t start. Instead, it’s making a popping/backfiring noise. This is normal, your spark plug firing order needs to be changed. Or, reversed essentially.

Originally, off of the coil pack, from left to right as it is mounted in the factory location, your firing order should be 4-1-2-3. You need to reverse it to 3-2-1-4 with the 97-99 ECU.

So now, you have reverse the spark plug firing order and now she fires up and runs just as it did on the 95-96 ECU, or close to it. You MAY be done. Or, you will find that you experience weird issues while cruising. It is very common to have a slight hesitation while cruising when you are in/out of boost and/or under light throttle. The remedy is to swap the injector plugs around, similar to what you did with the spark plug wires.

Again, you may not need to swap your fuel injector plugs at all. In fact, up until a week or so ago, I have never had to do it with ANY of my 12+ DSM’s in the 10+ years I have been involved with these cars. I recently put an H8 Blackbox ECU in my 2G Spyder GST and experienced the weird cruising hesitation problem. I also noticed that the engine/exhaust sounds different while decelerating. Almost like a very minor misfire that produces a very faint, but noticeable “rumble”.

It is hard to say what exactly causes it or why it happens with some cars, some ECU’s, etc., but I believe a lot of it has to do with the type of cam and/or crank sensors that you are using. On my Spyder, I am still using the 2Ga cam and crank sensors whereas in the past, I have ALWAYS used a 1G CAS in all of my DSM’s. And from what I have seen over the years, the only people that have had the weird cruise hesitation when swapping the ECU was the people using the 2Ga cam and crank sensors. Usually, if you use a 1G CAS, you will not have to swap the injector plugs. This is because the 2Ga uses an “inverted CAS”.

Anyway, if you get the cruise hesitation, you will need to swap your injector plugs.

Injector plug 4 needs to be swapped to cylinder 2.

Injector plug 3 needs to be swapped to cylinder 4.

Injector plug 2 needs to be swapped to cylinder 1.

Injector plug 1 needs to be swapped to cylinder 3.

If you are using DSMlink, there is an option to invert the CAS by checking the “Use non-95/96 style cam angle sensor” checkbox in the “Misc” tab of the “ECU Config” tab (called “Invert CAS” option in the ECU→Miscellaneous dialog in the older V2 application). Checking this box in DSMlink still requires you to reverse the spark plug firing order.

If you are using an Evo or 3G Eclipse ECU, while still running the 2Ga CAS, you will most likely be a victim to the cruise hesitation problem as well.

I would also like to add that if you are using your 95-96 ECU and swap in a 1G CAS, you may also need to reverse your firing order. Usually, you won’t have the cruise hesitation, but you will have an entirely different problem while cruising if you are on a stock ECU without DSMlink. You will most likely experience an intermittent random misfire, usually while cruising, in any gear. It will feel and sound like you are all of a sudden running on 3 cylinders.

The only way to get rid of of when it happens is to shut the car off (while in neutral and coasting, or pulling over and stopping). Once you fire it back up, the misfire will be gone but could come back once you get back up to speed just a few seconds later, or it won’t come back for the rest of the day. The problem is intermittent.

There are two permanent fixes. You can do the “10K Pot Mod” which consists of wiring up a potentiometer into the barometric pressure sensor wire at the ECU harness, or get DSMlink and check the “invert CAS” option as discussed above.