Injector Resistor Box Questions...

I replaced the stock injectors in my '88 MX-6 GT (~310cc) with a set from a 7m Supra (440). I was running a high duty cycle on 10-12psi on my DIYPnP and since changing the injectors it falls on its face at anything over 3,000rpm and any boost it goes completely lean. I've upped my fuel map and no change to the condition... Anyone know what size resistors I need to put inline, or is there a setting to change that will correct this? Ran fine before swapping out injectors...

Check your texts, son!

www,jgsturbo.com/d21main.html

Or a Honda resistor box.

Or if you have the flyback board on your Megasquirt (if an MS as new as yours even needs it) you can just change the PWM values to compensate for Low Z injectors.

Or you can go super cheap and head to radioshack and get one appropriate ohm 50-75w resistor for each injector driver on MS. Wire them inline from MS before it even gets in the bay so they aren't just hanging out. These things get HOT though, so springing for heatsinked ones is not a bad idea.

Can't you do pwm instead of the resistors?

Maybe, i not very MS knowledgable

Lol I posted pwm stuff on your thread on mx6.com.

He's running a DIYPNP - these do not have the PWM current limiting circuit.

So inline resistors it is then? 10 ohm/50 watt work for this?

I would use a lower ohm rating, like 5 ohms.

What's the target "ideal" range in terms of injector ohms for that type of Megasquirt?

That's the question I was trying to ask Ben, just fidnt know how to word it. Can you give me a precise part i can get to get these to work?

The only reason i asked it is because the factory injectors are something like 14ohms.

The Supras are 2.9ohms. 5ohm resistor only gets us to 7.9ohms. If that's cool with Megasquirt then that works just fine, and i'm sure you can get those already heatsinked (and you WILL want the heatsink) off of Ebay for cheap.

Or call JGS and see if they have the 5ohm variants under a different application.

This turned out to be a real PITA on my MS in the 924s as they use low R injectors. I tried resistors and what not and I ended up using the current limiting option in MS instead of resistors. With the resistors the injectors would stop working at about 3K rpm. With current limiting it works perfect.

I would get the "big list" of injectors and see if you can find some that are high R with the proper CC rate and then look up the cars that they are in and start JunkYard hunting.

Dan if you don't have a copy of the list I can email it to you if your email is still the same. I think I still have your email. Ohya and I think I still have a set of injectors from the 3000 TT motor I had I think those are 34 lb but I don't know the R at the moment.

3-6 ohms per injector is a good value. The DIYPNP drivers overheat if they hit 5 amps, and these keep things under that limit.

Matt,

Is it best to put a resistor in line with each injector or do the math and put a suitable sized resistor in line with each injector circuit that is sized for the number of injectors that each circuit is controlling. I think this was my issue and ultimately I did the math wrong when calculating the proper size resistor for each circuit that had 2 injectors on it. With the help of the great people over at the MSEXTRA forum (and maybe from you directly) I ventured in to the world of current limiting and never resolved why the resistors did not work.

I had 1 25W 10R resistor for each pair of 2.4R injectors and it would stop working over about 3K rpm on the stim.

Mazda Carnage said: There might not be much difference in peek flow cc but if you look at the Ohms they operate differently when swapped from year to year. example: the 88-89 injector flow a max of 324cc @ 12.6 Ohms, the 90+ flow a max of 326cc @ 13.7 Ohms. Question 1, how much gas do the 90+ injectors flow @ 12.6 Ohms? Question 2, Does the 88-89 ecu put out 13.7 Ohms to the injectors or is it's max 12.6 Ohms? Question 3, what happens to the 88-89 injectors if they are given 13.7 Ohms? Obviously there are no flow gains after 324cc and 12.6 ohms or witch hunter would have label them differently. do the overheat or fry? Question 4, how often do you unplug the wire harness from the injectors, for it to be worth the swap to save the extra minute removing the impractical 88-89 injectors takes? --------------- I run the 90+ injectors in my 89 but I have messed with every aspect of air flow and everything else, somehow during daily/normal driving the 90+ injectors go through more gas then the 88-89 that should deliver more gas at lower Ohms, cant tell you about top end because of added injectors, also the fuel rail is ported and I run 38lbs base pressure on a 255lph. Here is a list of injectors that should fit our rail and use the 90+ clip and are Saturated/high impedance like ours (not peak and hold/low impedance): 87-88 Toyota MR2 4AGE NA 213cc – Beige Top #23250-16080 89-91 B2220 Truck 224cc - Yellow Top? #23250-74040? 99-00 Mazda Miata 240cc - Thin Red Body #195500-4430 Toyota 4AGE 250cc – Green Top Toyota 4AGE 250cc – Violet Top 94-97 Mazda Miata 254cc - Tan Top #195500-2180 01-05 Mazda Miata NA & TURBO 265cc - Thin Lt. Prple #195500-4060 Toyota 3SGE 295cc – Green Top 89-92 Toyota Supra 7MGE NA 305cc – Light Green Top #23250-70080 93-95 Toyota Supra 3.0L 312cc - Maroon Top #23250-46030 Toyota 3SGE 315cc – Pink Top 90-92 MX6/626/Probe Turbo 326cc - Gray Top #195500-2150 89-91 B2600 Truck 326cc - Gray Top #195500-2150 Mazda 323 GTX TURBO 360cc - Black Top #195500-2130 Celica/MR2 3SGE NA 370cc - Green Top #23250-74160 Mazda RX8 420cc - Yellow Body #195500-4450 89-92 Toyota Supra 7MGE TURBO 430cc – Black Top 89-92 Mazda RX-7 NA 440cc - Blue Top #195500-5740 89-91 RX-7 NA 460cc - Red Top #195500-2010 89-91 RX-7 TURBO 550cc - purple top #195500-2020

Not responsible for accuracy of listing, etc etc etc...

You could probably get a set of RX7 460s that would PNP and be high Z on MiataTurbo, but you'll be into those for more than you paid me for those 440s + a set of resistors.

Alternatively, i think there's a set of RC Engineering 550s on MiataTurbo right now for under $200 i think. I was going to pick those up for myself, but i'm a little short on cash at the moment.

dean1484 wrote: Matt, Is it best to put a resistor in line with each injector or do the math and put a suitable sized resistor in line with each injector circuit that is sized for the number of injectors that each circuit is controlling. I think this way issue and ultimately I did the math wrong when calculating the proper size resistor for each circuit that had 2 injectors on it. With the help of the great people over at the MSEXTRA forum (and maybe from you directly) I ventured in to the world of current limiting and never resolved why the resistors did not work. I had 1 25W 10R resistor for each pair of 2.4R injectors and it would stop working over about 3K rpm on the stim.

If you're controlling 2 injectors per circuit/MS output, 25w isn't enough. Someone on Miataturbo was wondering about the same thing a couple years ago and Matt was suggesting a 75w resistor. (And 3ohm i believe)

dean1484 wrote: Matt, Is it best to put a resistor in line with each injector or do the math and put a suitable sized resistor in line with each injector circuit that is sized for the number of injectors that each circuit is controlling. I think this way issue and ultimately I did the math wrong when calculating the proper size resistor for each circuit that had 2 injectors on it. With the help of the great people over at the MSEXTRA forum (and maybe from you directly) I ventured in to the world of current limiting and never resolved why the resistors did not work. I had 1 25W 10R resistor for each pair of 2.4R injectors and it would stop working over about 3K rpm on the stim.

The trouble with resistor power ratings is that they aren't exactly conservative; your setup probably was overheating the resistor.

If you are running batch fire injection, one resistor per bank is acceptable, BUT it needs to be a big one. NEVER put injectors from different banks on the same resistor.

If you are running sequential, you MUST have one resistor per injector.

And note that a lot of OEM resistor packs are multiple resistors in one package.

Yep the dam things were getting really hot. The only thing that I think saved me was that I had them mounted to a big piece of alu (part of the original DME case) and that acted as a heat sync and the fact that I was bench testing them and could feel them getting hot before I cooked anything.

Here is a photo of the set up before I changed it to current limiting (Just bypassed the resistors).

And just to prove that I am a bit nuts Here is me bench testing the setup with the complete engine harness and all the stock sensors with the stim and a throttle body from a 951 using the TPS as it is a linear unit instead of the 944 on off switch, and the WBO2.

Spaghetti piled on my dinner plate looks more organised than this mess LOL.

You can see that the resistors are not not connected. I was testing it with current limiting at the time.

Why not just use a resistor pack from a 4 cyl Toyota?

Just called the local radioshack. the closest resistor they have in stock is an 8 Ohm, 20watt. would that be sufficient? Will heat be a big issue with these?

My 25's were not enough. Matt can probably give some guidance here. I have seen people take 3-4 sand resistors and wire them in parallel in each injector bank and it has worked. I assume that you could do something like that.

WIthout checking things (it has been a while so verify this before you wire it in to your system) I believe if you put them in parallel you increase the total wattage by the sum of the wattage of each resistor while maintaining the resistance. If you put them in line you maintain the maximum wattage of the lowest rated resistor that is in line and increase the resistance by the sum of the resistors in line with each other.

I have a formula for this some place I can post but it would be much better for some one like Matt to chime in and give some guidance.

I have some of the S5 rx7 NA injectors listed above. (89-91 RX-7 NA 460cc - Red Top #195500-2010)

They were just cleaned when I bought them 5 years ago. I didn't need them (bought a fuel rail and the seller threw them in).

You can have them for the price of shipping.

I would consider sending them out to get checked.

Let me know,

Rob R.

wvumtnbkr at hot mail dot com

So 'Im making an assumption that the difference in resistance was letting the injectors work below 3k rpm and any boost pressure, and are shutting down at anything at over that threshold. wired my stock injectors back up and all is good in the world.... Til my new Injectors come!!!

Yep. That is exactly the same thing that was happening with my set up until I got rid of the resistors and went to current limiting.