Dwell reduction circuit to run Toyota COPs on stock ECU

timk · Postby **timk** » Thu Feb 02, 2012 3:21 pm

Is anyone here interested in a circuit to run Toyota COPs on the stock ECU?

I am looking at doing a run of these dwell reduction boards, unpopulated the cost would be approx $25 each:

Details of the circuit here:
http://www.miataturbo.net/showthread.php?t=19780

The circuit has been tested on an NA8 and NB8A. My OEM coils are suspect so I am looking at replacing them with the Toyota units I have sitting in the shed. Also no more ignition lead replacements!

Cheers

sailaholic · Postby **sailaholic** » Thu Feb 02, 2012 3:30 pm

You know you'll end up with a non standard ecu anyway!

On a serious note, great idea, would be in if I was running a stock ecu.

Non genuine coils (cop) are only about 100 bucks with pig tails on Ebay now.

Sent from my GT-I9100 using Tapatalk

hks_kansei · Postby **hks_kansei** » Thu Feb 02, 2012 3:37 pm

Would maybe be interested, assuming it would be 100% compatible with stock ECU.
(Would prefer some form of replacement coils rather than go on-plug)

How well does the dwell reduced work? I always thought it wasn't great and that's why most people go to a standalone ECU with Coil on plug?

zossy1 · Postby **zossy1** » Thu Feb 02, 2012 4:14 pm

Lots of people have run the COPS with no dwell reduction on the OEM ECU. Only a few reported problems, generally in dedicated track cars that spend most of their time at high RPM.

rascal · Postby **rascal** » Thu Feb 02, 2012 5:06 pm

I'd be interested in one. (mines an NB8A)
I currently run a piggyback to control dwell for my COPs so don't need it as such, but for $25 it would be nice to have the ability to plug the std ecu back in and still keep the COPs, without the worry of frying them.

p.s. What does unpopulated refer to?

timk · Postby **timk** » Thu Feb 02, 2012 6:58 pm

rascal wrote:p.s. What does unpopulated refer to?

It means I supply the PCB and a BOM, then you source the components and build it.

I might see if I can get a mob to quote on building them.

Cheers

rascal · Postby **rascal** » Fri Feb 03, 2012 10:19 am

Hmm, thats me out then, unless a populated version is available.

My soldering skills leave a lot to be desired...

manga_blue · Postby **manga_blue** » Fri Feb 03, 2012 10:33 am

Sab, if I'm reading the miataturbo thread correctly it seems to be for the later NA8 with OBD sold here in 96/97. Is that right?

Rascal, there's about 30 minutes worth of soldering on that board. Buy a soldering iron and solder from Jaycar, dismantle an old board from a dead radio or something, google 'how to solder', practice soldering a few components and then you're fully trained for this job.

Scoota · Postby **Scoota** » Fri Feb 03, 2012 12:48 pm

Hi Sab.

I'm very interested in the dwell adjuster circuit, DIY-style. I've just finished my first electronics project (Jaycar Digital Fuel Adjuster) and I'm ready for another project. I'm definitely in for $25 if it will be suitable for my NA6. Will it?

I don't have the COPs yet, but it's definitely on the agenda for me. Weren't you making these a little while back? Can I possibly get one from you?

Cheers,
Trav.

manga_blue · Postby **manga_blue** » Fri Feb 03, 2012 2:06 pm

BTW, the miataturbo article also refers to running a 10,000uF/16V/105deg capacitor across each COP power supply 12v/GND pair to counteract voltage drop inherent in the original Mazda wiring loom. Here's where to get them locally for less than $2:
http://australia.rs-online.com/web/p/aluminium/4909894/

manga_blue · Postby **manga_blue** » Fri Feb 03, 2012 2:49 pm

manga_blue wrote:BTW, the miataturbo article also refers to running a 10,000uF/16V/105deg capacitor across each COP power supply 12v/GND pair to counteract voltage drop inherent in the original Mazda wiring loom. Here's where to get them locally for less than $2:
http://australia.rs-online.com/web/p/aluminium/4909894/

Correction: one 10,000uF cap across the whole 12V supply or two 4,700uF caps, one for each pair.

zossy1 · Postby **zossy1** » Sat Feb 04, 2012 12:17 am

manga_blue wrote:
manga_blue wrote:BTW, the miataturbo article also refers to running a 10,000uF/16V/105deg capacitor across each COP power supply 12v/GND pair to counteract voltage drop inherent in the original Mazda wiring loom. Here's where to get them locally for less than $2:
http://australia.rs-online.com/web/p/aluminium/4909894/

Correction: one 10,000uF cap across the whole 12V supply or two 4,700uF caps, one for each pair.

This has nothing to do with dwell - this is the tach mod. According to Reverent, it is not necessary but most people running COPS and standard tach circuit (ie. not direct from the MS) do run this (there have been plenty of reports of tach malfunction without it when running COP ignition). I have the caps ready to install in my COP loom.

Note that your caps should be 105 degree models. Most of the cheap nasty caps will not last long under the bonnet, especially if your car is turbo'd and/or does track work. Many people recommend Rubycon caps as the best for the job so that's what I bought.

timk · Postby **timk** » Sat Feb 04, 2012 7:58 am

The cap is for voltage drop, but I have read that the loom already has a cap built in. I'm going to try and source a spare to pull it apart and confirm.

Does anyone know the dwell times on the earlier NAs?

zossy1 · Postby **zossy1** » Sat Feb 04, 2012 8:15 am

saboteur wrote:The cap is for voltage drop, but I have read that the loom already has a cap built in. I'm going to try and source a spare to pull it apart and confirm.

Does anyone know the dwell times on the earlier NAs?

My understanding is that the OEM ECU does the job of the caps in the OEM loom...? Either way, if running the OEM ECU with your COPS you should be fine...

manga_blue · Postby **manga_blue** » Sat Feb 04, 2012 9:53 pm

No, these caps were all about voltage drop. What they were saying is that the wiring from the ecu to the coils is a bit weak so there's a 3.5V voltage drop at the coils. This put the coils near the bottom limit of their operating range. Basically they presented 3 options:
1. Install the dwell adjusting circuitry and the caps, giving you full voltage at the coils and the right dwell.
2. Install the dwell adjusting circuitry and beef up the wiring, probably by direct wiring from the MAIN relay and down to a strong engine earth.
3. Do nothing, so that the weak voltage at the coils compensates for the overlong dwell.

Options 1 and 2 look like the better solutions. No one was sure whether or not option 3 was good enough (i.e. how long it might be before you fried the coils)