FxF

My quest began like this. I had my original fuel injectors removed and sent to a shop for cleaning. At the end of the day the shop replied that my injectors were to damaged to use even in a stock TurboII.
Info on my injector problem: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/bad-fuel-injector-problem-313589/

I decided to install new injectors (2x550cc primaries and 2x720cc secondaries). I got the Denso 720cc secondary injectors from www.rx7.com with 2 connectors and 2 resistors. The wiring harness injectors plug on an S5 is oval shaped, so you need the connectors to hook the injectors on.
Almost all the injectors that are 550cc and above are low impedance injectors and my old ones were high impedance, so you need the 10 Ohm resistors to get them to work properly.
Info on injector impedance: http://www.rotaryresurrection.com/ro.../injector.html

Here is the info on the installing procedure: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/how-will-i-install-denso-720cc-secondaries-329066/ and here are the pictures.

All the needed items. The photo is missing 2 more resistors


Denso 720cc injectors


These are the wiring harness injector plugs from an S4. You can also use them, if you don't want to buy new connectors. I didn't use them after all.


These are the resistors RX7.com sells. We need 2 10 ohm resistors. One for each injector. They have 3 ohm written on them. Don't worry they work just fine.


These are the connectors RX7.com sells. We need 2 of them. One for each injector.

FxF

Remove the intercooler


Slice the connector wire and install the resistor. One resistor per injector. Keep it consistant. I sliced the red and white wire of the connector in both connectors as you can see.



Remove the upper intake manifold. Remember the procedure cause it is a difficult part and you will need to reinstall it when you are done....

Here are my stock wiring harness secondary injector plugs. They are longer than the primary ones. This is were you are going to cut and install the new connectors.


Sorry but I don't have any photos of the procedure, cause my mobile phone run out of battery at that point. More photos when my 550cc primaries are done.

I also put some heat resistant material around the resistors for extra causion and wrapped the new connectors(after the installation) with electrical tape.
I would have done the primaries too, but I didn't know that resistors were needed also for them, and I didn't have the extra 2.

Do this on a cool engine or allow the engine to cool off before you do any work.


-Fanis

91mazdarx7

looks good so far keep taking pics when i get money for a walbro and 720 injectors if i do it myself i may need to look at soome of these posts like yours so far so good man

torean

thank you!!

NZConvertible

The ECU will be seeing only half the impedance required, so I doubt it will work fine at all. I wonder how long it'll be before you fry the ECU's injector drivers...

hondahater

iTrader: (2)

ok this makes me worry. the guy that owned the car before me had some 720's put in the secondaries however there are no resisters. I have an 88tII would I need resisters??? Thanks. What happens if you need resisters but don't have any???? Thanks.

hondahater

iTrader: (2)

common all these people viewing and no one to answer my post fine I'll just blow up my engine

NZConvertible

I don't believe there are any high-impedance 720cc/min injectors, so there must be resistors in there or it would've quickly fried the ECU.

hondahater

iTrader: (2)

huh???? My car works just fine and I have no resisters at all. I know this because I just took off the uim and had my injectors cleaned and everything and didn't see any resister anywhere. Very very very strange. So everyone that has an fc and wants to put 720cc injectors in has to have resisters???

ok just got this off of rotary resurrection website:

"86-87 13B T low square center 550cc tan 195500-1370"

The low in that statement means low impedance and if you say all 720's are low then I should have no problems, right?

hondahater

iTrader: (2)

hey FxF where did you get those connectors? Mine are falling apart so instead of getting a hole new wiring harness that sure would be nice! thanks.

NZConvertible

The resistors will be at the ECU, which is a better location anyway.

hondahater

iTrader: (2)

well I just sent my ecu off to rtek and installed a safc and redid some grounds at the ecu and didn't find a single resister.

Ocelot

Yeah if you have an S4 with 720cc injectors you are fine, the S5 ones with 720's need the resistors.

hondahater

iTrader: (2)

ahh thats what I was thinking thanks for confirming ocelot!

NZConvertible

You're half right. Only pre-87.5 S4's have low-impedance injectors. Post-87.5 S4's and all S5's have high-impedance injectors and hence need resistors installed if you swap low-impedance ones. Hondahater has an 88...

hondahater

iTrader: (2)

so how come it didn't fry my ecu???

jacobcartmill

iTrader: (6)

then you obviously have high impedence aftermarket injectors if your ECU still works and you have no resistors.

Rex4Life

I have an 88 T2 setup and the stock system has high impedence injectors. Put in 720s last nite and today I put in the resistors.

Best way to find out is just take a resistance measurement of the injector. I believe RC engineering sells some high 720's but not sure if they fit our rail.

jacobcartmill

iTrader: (6)

i believe they do also. aftermarket high imp injectors may be rare, but i'm sure they make them.

FxF

I was worried myself when they first arrived from the U.S. and I called Rocky (from RX7.com) on the phone to talk to him about the resistors. He said that these are the resistors they use on their customers TurboII's with no problem what so ever. I trusted him, because their shop is one of the best in the U.S. and my car is running with no problems for 2 1/2 months now.

-Fanis

FxF

I got the connectors from RX7.com

-Fanis

hondahater

iTrader: (2)

I looked there but couldn't find them I'll do another look on that site. Thanks.

FxF

Clik here http://www.rx7.com/store/rx7/fcfuel.html

-Fanis

hondahater

iTrader: (2)

thanks for the link I didn't see that before. Anyways its kinda strange because they have one set from 84 to 87 and the other set is from 89-92 but there is nothing about the 88's??? I'm assuming because some 88's use low and some 88's use high impedance injectors.

torean

yeah...why dont they have plus for the later s4s?....i was thinkin maybe that the plugs fit and wouldnt need the adapter...u'd just have to wire in the resistor into the stock harness...someone please clearify