Can i use a low/high-imp injector combination?

[Justen]

So after my rebuild, i put my stock injectors back in when installing the motor again. But I ordered a pair of bosch 1600cc low-imp monsters to replace my secondaries, haven't put them in yet though. I'd like to install them before i go in for a tune.

What I'm asking is for someone to confirm that i do have stock high-imp injectors in my 90' Turbo II. The stock ones are Denso 550cc reds.

...And is it possible to use high-imp primaries but low-imp secondaries in the same car?

If anyone knows where i can find a write up of how to solder in the resistors, that would be awesome. Thanks.

[Phoenix7]

1990 Turbo injectors are high impedance because the electrical system is high impedance.

Someone will correct me but as I understand, running low impedance injectors in a high impedance system will overheat and kill them.

http://www.rotaryresurrection.com/2n...ctor_info.html

Originally Posted by RotaryResurrection

If using LI injectors on a HI harness, you must splice into the harness at each injector lead (for a total of 4) 10 ohm/10watt resistors available at Radio Shack for a couple of bucks. It doesn't matter which wire of the 2 per injector you splice to, polarity isn't an issue here. This bumps the LI resistance up to acceptable load for the ECU to see.

[RETed]

Yes, all Kouki FC's run high impedence fuel injectors.

Throwing the low impedence fuel injectors into an originally high impedence set-up will fry the stock ECU.

Installing resistors is the standard thing to do.

What bothers me more is...
Are you trying to do this with the stock ECU???


-Ted

[RotaryProphet]

The problem is, even with resistors on the low impedance injectors, you'll have two high impedance injectors that open at the correct rate (about 1ms before the start of fuel flow @ 13v), and two high impedance injectors (thanks to the resistor) that open more slowly (about 1.4-1.8ms @ 13v, depending on the brand.) If both injectors acted like that, you could tune around it by increasing the injector open time in the ECU, but you'll probably have some trouble tuning the transition from your primary to secondary injectors; bringing them in earlier to compensate for the fact that a 1.5ms pulsewidth is giving you basically no fuel.

It's definitely doable in a mainly street driven car, but it wouldn't surprise me to see some hesitation in there at the boost threshold.

[RETed]

Originally Posted by RotaryProphet

The problem is, even with resistors on the low impedance injectors, you'll have two high impedance injectors that open at the correct rate (about 1ms before the start of fuel flow @ 13v), and two high impedance injectors (thanks to the resistor) that open more slowly (about 1.4-1.8ms @ 13v, depending on the brand.) If both injectors acted like that, you could tune around it by increasing the injector open time in the ECU, but you'll probably have some trouble tuning the transition from your primary to secondary injectors; bringing them in earlier to compensate for the fact that a 1.5ms pulsewidth is giving you basically no fuel.

This point is moot.
The stock fuel delivery with the stock ECU always runs on the rich side.
Running slightly lean due to the increased dead time of the fuel injectors is not going to noticably change the way the engine is running.


-Ted

[djmtsu]

Originally Posted by Justen

The stock ones are Denso 550cc reds.

I thought the stock high impedance 550's are purple?

Mine are.

[RETed]

Originally Posted by djmtsu

I thought the stock high impedance 550's are purple?

Mine are.

Something is wrong.
Purple tops are low impedence.
Purple tops should also be rectangular plug.

Red tops are high impedence.

These color combinations are for stock FC injectors only.

The only purple top, high impedence fuel injectors I know of are 850, side-feed injectors that FD's run as secondaries.


-Ted

[djmtsu]

Originally Posted by RETed

Something is wrong.
Purple tops are low impedence.
Purple tops should also be rectangular plug.

Red tops are high impedence.

These color combinations are for stock FC injectors only.

The only purple top, high impedence fuel injectors I know of are 850, side-feed injectors that FD's run as secondaries.


-Ted

O RLY?

89-91 13B Turbo, high oval center, 550cc, purple, Denso# 195500-2020

[Justen]

My mistake, they are 550 purples.

I don't think i will put the low imp injectors in untill i get a standalone anyway, because i hear 1600s will most likely dump to much fuel into the motor when they actaully kick on, especially with the higher fuel press of a Walbro.

...But this lag in the injector cycle that you mentioned, wouldnt it be compensated for when i have the standalone tuned?

If worse comes to worse i could try to find low imp primaries and solder in resistors for all four injector leads.

Suggestions?

[RotaryProphet]

Originally Posted by Justen

...But this lag in the injector cycle that you mentioned, wouldnt it be compensated for when i have the standalone tuned?

If worse comes to worse i could try to find low imp primaries and solder in resistors for all four injector leads.

Suggestions?

If you have a standalone that allows separate injector characteristics for different injector banks, then yes, that would solve the issue. Actually in that case, the ECU probably supports low impedance on one bank and high on another, so you wouldn't have any issue at all. Problem is, I'm unaware off the top of my head of any standalone ECU that does support that setup, save perhaps a Megasquirt, which has two totally separate injector driver circuits, and the software to tell it to use pulsewidth modulation and load clamping on the low impedance injectors, and full 12v on the high impedance side.

As for putting in low impedance injectors for primaries and using resistors all around, if you go standalone, just let them all be low impedance; just so long as you're not mixing, you'll be fine on almost any standalone. The only time you'd need to do that is if you're staying with the stock ECU.

[RETed]

Originally Posted by RotaryProphet

Problem is, I'm unaware off the top of my head of any standalone ECU that does support that setup, save perhaps a Megasquirt, which has two totally separate injector driver circuits, and the software to tell it to use pulsewidth modulation and load clamping on the low impedance injectors, and full 12v on the high impedance side.

Haltech's could do this from day one.
Previous models can handle up to a 1A current draw through each fuel injector channel.
If you wanted, you could mix and match high and low impedence to your hearts content, but I would not recomment doing that with each "bank" on a staged set-up.

Current Haltech models can control up to a 2A current draw, as some "high performance, motorsports" fuel injectors now ohm out down to 0.5-ohms.

Haltech's could always run low impedence fuel injectors on one bank and high impedence fuel injectors on the other without fuss.
No need for resistors...
No need for outboard impedence circuits or driver boxes...


-Ted

[RotaryProphet]

Originally Posted by RETed

Haltech's could always run low impedence fuel injectors on one bank and high impedence fuel injectors on the other without fuss.
No need for resistors...
No need for outboard impedence circuits or driver boxes...


-Ted

Well, there you go, Haltech can do it, too. I've never tuned one, but it's still nice to know.

[RETed]

Originally Posted by Justen

My mistake, they are 550 purples.

If they are 550's purple, then they are low impedence.
Do you have the fuel injectors resistor "box" located in the engine bar right behind the passenger side headlight?

...But this lag in the injector cycle that you mentioned, wouldnt it be compensated for when i have the standalone tuned?

Ignore all of that.
It really doesn't apply to you.

If worse comes to worse i could try to find low imp primaries and solder in resistors for all four injector leads.

Suggestions?

As you have already said, dropping 1600's without proper control is going to lead to a badly running engine.
Basically, once you go into boost, the engine will flood with no much fuel that the engine will conk out on you.
Don't bother worrying about such things until you get everything sorted out properly.


-Ted

[Phoenix7]

yes, like RETed brought up....if you're on the stock TII ECU then stick with 550s otherwise the car will not run or run craptastically. You can't control 1600s with the stock ECU or piggy-back.

[dudemaaan]

In the FD's the most popular ecu to run is the pfc which only supports high impedance injectors. The options we use around this are either resistors, or the FJO injector driver box, this converts the signal to use the injectors as they were designed as peak and hold. More fuel is available by using the injectors as peak and hold. The bosch 1680's are 5.1 ohm which just barely exceeds the pfc injector driver circuits, many people get away with no resistors, or as low as a 1 ohm resistor is considered within the driver's limits. I personally use 4 ohm resistors because that's what came with my injectors.

The pfc can also be used on 2nd gen rx7s by using an adapter harness. You can't run larger injectors on the stock computer without it running like crap, and you can't change the impedance of the injectors or it will run like crap and you risk burning up the injector drivers. You need a standalone computer and then you can mix and match and tune it out.