https://www.rx7club.com/3rd-generation-specific-1993-2002-16/hesitation-after-1600cc-injector-install-591282/

Car is 1988 Turbo II, built 10/87 (high impedence injectors stock), now with low impedence 720 secondarys.

So I had been having a 3800 hesitation that I just couldn't get rid of. I cleaned all the grounds, added ECU ground, etc. The previous owner had installed 720 secondary injectors with the standard Radio Shack 10 watt/10 ohm resistors. Well after poking around the forums for a while I found that thread ^ , regarding hesitations on FDs installing low impedence secondary injectors with a Power FC.

Somebody had also mentioned in a different thread (2nd gen thread) that they measured the resistance on the stock 87 resistor pack to be around 6 ohms or so. I cannot verify this though. So I cut out the Radio Shack 10 ohm resistors and installed 6 ohm resistors from Mouser Electronics (link in that thread).

The car no longer stumbles at 3800 rpm now. I will say though that it still has a slight lean spot according to my wideband (whereas before it went a lot leaner). I probably should have gotten 4 or 5 ohm resistors but I wanted to be conservative . 3 ohms seem a bit much, but apparently FD's do run them.

Anyway that's just something for everyone here to consider. I know that people have this problem with Rtek ECUs as well. I'm not sure why some cars are fine with 10 watt 10 ohm and some aren't.

 

Stock resistor shown in the attachment

 

Those new 6-ohm resistors...
How much wattage are they rated for?


-Ted

 

This is what I bought:

http://www.mouser.com/search/Product...key71-RH10-6.0

10 watt, 6 ohm, solder lug terminals on the end. You just thread the wire through the little hole in the terminal and solder it.

 

I'll have to try this out and do a couple of logs on the palm to compare.




I'm running 4 x 10ohm resistors now for the secondaries and primaries.

 

do you^^ have a hessitation problem running four low impd injectors with resisters? im gonna be running that with 10 ohm resistors, but i am still at the point where i can change things around, so is it worth it?

 

Thanks for the update!! Ill be ordering some 6 ohm resistors too. but I think you may need more than 10W resistors though

Power = V*V/R = 12*12/(6+2.5) = 17 watts

 

Maybe your injectors are getting "lazy" (stiff). The 10 ohm limits current a lot more then 6 ohm...Some random math:

Low impedance injector resistance: 2.8 ohms
Ohm's law for current: I=V/R

So with 10 ohm, your injector current is limited to:
I=12/12.8
I= 0.93A

With 6 ohm:
I=12/8.8
I=1.36A

So a 6 ohm resistor will allow the injector to snap open faster.

Only at 100% duty cycle.

 

I have an rtek 1.7 ECU that I will try this with as well. The Rtek guy actually recommended this first...

I don't even know what brand injectors are in my car (previous owner put them in), but I think they have 10k miles on them or less. It could be possible that some brands are less "stiff" than others and thus they work fine with 10 ohm resistors.

 

you're welcome for the suggestion and apparent fix.

try RX7 store and find out where they get their resistors for their performance FD secondary fuel rail kit. apparently they have been using their 3ohm resistors with those kits for a few years now.

i had originally stumbled across it when doing a large single on an FD and found they supplied me with 3ohm resistors so to be sure i asked around the third gen forum and GoodfellaFD3S posted the helpful link and i figured it related to the FC transition points as well.

https://www.rx7club.com/showthread.p...tore+secondary

 

well i just pulled my 10 ohm resistors and installed 6.2 ohm 25 watt resistors. ..and the hesitation is still there although it is not nearly as bad and often as before, but it happened as it usually does, around 0 psi, staging rpm