Honda CRX Forum banner
1 - 20 of 21 Posts

·
Registered
Joined
·
111 Posts
Discussion Starter · #1 ·
I'm about to order a resistor for my new injectors, but can't find specs on the OEM resistor box. Ideally, someone has opened theirs and knows exactly what's in there. At the least, I'm hoping one of you wouldn't mind getting an accurate resistance reading off your box so I can order factory spec resistor and then just go overkill on the power rating.

Right now I'm thinking one 11.5ohm, 100w will do the trick and I can bolt it right to the Skunk2 IM using the No2 bung mounting hole. The math says a 20w resistor would be sufficient, but better safe than sorry.
 

·
Registered
Joined
·
1,382 Posts
It is in the service manual test procedures. It should be pretty low if I remember correctly, like 4-7 ohms or so. Don't have a manual here so I cant look it up for you.

There is no magic in there. Since you have 4 injectors there are 4 resistors with a common ground. 10-15W per resistor should suffice. This is also described in the test procedure.
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #4 ·
jfrolang said:
What injectors are you using that require an aftermarket resistor? If you need a resistor there's nothing wrong with OEM.
I'm just using OEM spec SI/HF injectors. I don't have any desire to pay more money for a used OEM part when I can buy a single new resistor that's superior to OEM while still being cheaper and with a more attractive case. Do you have a resistor box? Anyone willing to measure the resistance of theirs?
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #5 ·
I found a procedure in the Haynes manual that says it should read 5-7 ohms.

Also, why would Honda use 4 resistors instead of just 1 in the resistor box? Has anyone verified this, or is it misinformation. I find it hard to believe Honda would use 3 extra resistors in a situation where 1 is all that's needed.
 

·
Registered
Joined
·
3,879 Posts
5-7 Ohms is the resistance range called for in the manual. There are 4 resistors in the resistor box (one for each injector) and they should be at least 10 watts each. There is a reason the OEM resistor box looks like a big heat sink.

Your not likely to build a workable resistor box for as cheap as you can buy a used one.

Mike
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #7 ·
msc said:
5-7 Ohms is the resistance range called for in the manual. There are 4 resistors in the resistor box (one for each injector) and they should be at least 10 watts each. There is a reason the OEM resistor box looks like a big heat sink.

Your not likely to build a workable resistor box for as cheap as you can buy a used one.

Mike
Where are you getting the info that there's 4 resistors? Not saying you're wrong since I can't find specs on the box anywhere, but 4 just doesn't make sense. I might understand 2 so there's redundancy in case one goes bad, but 4? Here's my logic...

ECU is designed to drive 12 ohm injectors...
Low impedance injectors are 2.5 ohms...
12-2.5=9.5 ohms needed for the resistor...
12v through 12 ohms of resistance creates 12w with a current of 1 amp!

So on paper it looks like one 9.5ohm resistor with a 12w power rating is all that's needed and that's still overkill because...

1) Its run intermittently and
2) It doesn't actually create 12w of heat because the injectors and ECU carry some of that load as well.

I can get that resistor along with heat sync brand new for $2! If I'm missing something please let me know. I wish I had a box to pop open!
 

·
Registered
Joined
·
1,382 Posts
Again, 4 because you have four injectors.

If you cannot find a diagram anywhere you haven't looked very hard. First hit in Google:



So tell me how can 1 resistor do the same?

How difficult can one make it for himself wanting to replace a perfect sealed box with the right connector, which is cheap as chips too, with some DIY resistor hack.
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #9 ·
NovaVTEC said:
Again, 4 because you have four injectors.

If you cannot find a diagram anywhere you haven't looked very hard. First hit in Google:



So tell me how can 1 resistor do the same?

How difficult can one make it for himself wanting to replace a perfect sealed box with the right connector, which is cheap as chips too, with some DIY resistor hack.
What is the source of that diagram and what makes you think it's correct? I'll I'm happy to make an illustration for you if you're actually wanting to know how one resister performs the same function and not just making a rhetorical statement.

Please help me out. Surely someone on this forum has an OEM box and 5 min to get the resistance values a cross all 4 outputs for me.
 

·
Registered
Joined
·
3,879 Posts
Your Haynes manual is saying 5-7 Ohms. The factory service manual says 5-7 Ohms. What more do you need in the way of confirmation? I can see being skeptical of Haynes but you don't seem to be willing to believe Honda on this one.

I don't know the source of the schematic posted but it's consistent with all the Honda service documentation as far as the basic circuit is concerned. There is an error in that they call the low impedance injectors "peak & hold". The distinction of "peak & hold" describes a drive circuit not an injector. The drive circuit used in the Honda ECU is not a peak & hold circuit even on the OBD0 ECUs used with low impedance injectors. It's in error to describe any injector as "peak & hold" and the drive circuit in question is not even "peak & hold".

There is a huge difference between the single resistor you propose and the 4 resistor network as used by Honda. Go ahead and draw your circuit and start considering what if scenarios. If one injector shorts out, Honda circuit car runs on 3 cylinders, your circuit car dies. If the ECU flakes out and fires more then one injector at a time, Honda circuit replace the ECU and the car is fine, your circuit the resistor and possibly injectors get cooked. There are also advantages for heat distribution inside the resistor box and the shedding of heat. Again there is a reason the resistor box is a large heat sink. On a hot day the under hood temperature can exceed 150 before you even start the car and can go well above that if stuck in traffic. The resistor box needs to be able to get rid of it's heat in that environment so it needs to be way overkill compared to working in a shirt sleeve environment.

My advise is that if you want to dabble in automotive engineering that you try to fully understand the design requirements before you declare everyone on the Internet and Honda to be wrong about how to solve a problem.

The best help anyone can give you on this would be to slap you upside the head and scream in your face "JUST USE THE DAMN FACTORY RESISTOR BOX".

Mike
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #11 ·
Lol, sorry I'm not trying to frustrate anyone, just trying to understand and I still don't. I'm not looking for advice, just that specific info. It's okay if you're not interested in the details if this system, but I am. Here's where I'm confused...

1) 5-7 ohm resistor box + 2.5 ohm low impedance resistor = 7.5-9.5 ohms, which means a 12 ohm injector without the resistor box is too much resistance, but I was under the impression that using high impedance injectors was an option.

2) Where is the info that there's 4 resistors coming from? Why not just measure the resistance and be done with it. The exact same resistance across all 4 outputs would indicate only one resistor. Variable resistance would indicate 4 individual resistors.

Again, sorry if I frustrated anyone. I just don't want to buy a resistor box just to take readings and then resell. I'll draw up a few schematics in a bit to run by you. Thanks.
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #12 ·
Here you go. The circuit you refer to as "my circuit", although I assume this it the circuit in the OEM box until I can determine otherwise, and the same circuit with 4 individual resistors. Here's the



1) The circuit path in case of an injector short is identical in both circuits.
2) The engine bay temp only dictates which resistor to use, not the circuit. 4 resistors not rated for engine bay temps will not last long either. Obviously I would get a resistor that could handle the load even after temp derating.
3) if the ECU, fires two cylinders at once, it will derate the resistor by 50%. Therefore, it's better to use a single resistor rated for twice what's needed than 4 individual resistors, because it would perform the same function while also being under half load in normal operation.

If I'm wrong, please explain why. I haven't bought a resistor yet and don't plan to until I can talk someone into testing their box or if need be, buying and OEM box to test. Either way, you can't deny that a new box to OEM specs would be better than a 20 year old box, lol. Everyone says there are 4 resistors, but no one saying this can find the info from honda, a reputable service manual or from testing an actual box. It doesn't make sense that there would be 4 injectors and I think its just been said so many times that people just think its true regardless of how illogical it is. Even if you wanted 4 resistors in case one goes bad, you still wouldn't wire it on for each injector, you would wire them parallel, so that all 3 resistors could go bad and you would still be firing all 4 cylinders! I call BS on this one resistor per injector theory.
 

·
Registered
Joined
·
1,382 Posts
I find it baffling how you make all this out of an obvious resistor box which actually has FIVE wires.
You can not use one resistor since they are current limiters for the individual injectors. PGMFI batch fires all four for enrichment. That and 1 resistor would change the current in each individual injector thereby altering the current limiting function.
Also when one is shorted out batch firing will no longer work because the short is now shorting out the other injectors too. Like msc said.

Engine bay temp is just part of the calculation of how big the heat sink should be for the application. Most heating will come from power dissipation. As long both of these factos make it stay below the design temp it is OK. No resistor is designed with ambient temperature in mind but an operating temp.

Here is your final proof. From a '89 PGMFI training manual issued by Honda Benelux:



Now go get yourself a beer and and a 20 yo OEM resistor assy and relax.
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #14 ·
NovaVTEC said:
I find it baffling how you make all this out of an obvious resistor box which actually has FIVE wires.
You can not use one resistor since they are current limiters for the individual injectors. PGMFI batch fires all four for enrichment. That and 1 resistor would change the current in each individual injector thereby altering the current limiting function.
Also when one is shorted out batch firing will no longer work because the short is now shorting out the other injectors too. Like msc said.

Engine bay temp is just part of the calculation of how big the heat sink should be for the application. Most heating will come from power dissipation. As long both of these factos make it stay below the design temp it is OK. No resistor is designed with ambient temperature in mind but an operating temp.

Here is your final proof. From a '89 PGMFI training manual issued by Honda Benelux:



Now go get yourself a beer and and a 20 yo OEM resistor assy and relax.
Awesome, thank you! The batch firing instead of sequential was the piece of the puzzle I was missing. Makes sense now. Don't be baffled. I call it attention to detail. My wife calls it anal retention. OEM it is.
 

·
Registered
Joined
·
1,382 Posts
You're welcome.

Attention to detail is not the same as questioning common knowledge.

Last piece of this circuit's puzzle would be that what msc said about not being true Peak and Hold. A true Peak and Hold circuit would, for the duration of the time it takes to lift the injector pintle valve needle, short the series resistor (peak current and fast action) using a second transistor. When the pintle needle is up, this transistor opens and the current is limited (hold) to prevent the initial high current to fry the injector. Our box and injector makes for a true saturation system.
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #16 ·
NovaVTEC said:
You're welcome.

Attention to detail is not the same as questioning common knowledge.

Last piece of this circuit's puzzle would be that what msc said about not being true Peak and Hold. A true Peak and Hold circuit would, for the duration of the time it takes to lift the injector pintle valve needle, short the series resistor (peak current and fast action) using a second transistor. When the pintle needle is up, this transistor opens and the current is limited (hold) to prevent the initial high current to fry the injector. Our box and injector makes for a true saturation system.
Gotcha. In that case, would it make more sense for me to return my injectors and get high impedance 9.5 ohm ones and not deal with resistors?
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #18 ·
NovaVTEC said:
Yes. No disadvantage here!

Check this out:

http://www.hondata.com/techlowohminjectors.html
Ahhhhh!!! That's what I read early on in research that confused me so much! Check this. Run 2.5-3 ohm resistors with a 5-7 ohm resistor box. That's a total of 7.5-10 ohms, right? Ditch the resistor box and just run 12 ohm resistors and by my simple math either the low impedance injectors are 2-4.5 ohms too low or the high impedance injectors are 2-4.5 ohms too high. What gives? No matter how I look at it, one of those options has to be wrong. Hmmm... Unless the 2-4.5ohm difference is within the computers margin of error, in which case I'm overthinking everything, which I've been known to do also.
 

·
Registered
Joined
·
1,382 Posts
That is the point. The absolute current through the injector is not so critical. it is more important that they are all the same (injector resistance + resistor) to obtain same actuation speed. The 5-7 ohm spec indicates a 16% tolerance!

I wonder why it is you want to use the 12 ohm saturated type? Can you not stay stock?
 

·
Registered
Joined
·
111 Posts
Discussion Starter · #20 ·
NovaVTEC said:
That is the point. The absolute current through the injector is not so critical. it is more important that they are all the same (injector resistance + resistor) to obtain same actuation speed. The 5-7 ohm spec indicates a 16% tolerance!

I wonder why it is you want to use the 12 ohm saturated type? Can you not stay stock?
Yeah, I'm going to use stock. Everything I've read says stock OBD-1+ injectors are 12 ohm.
 
1 - 20 of 21 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top