# fuel injectors...difference high or low impeadance??



## Brad Boardwell (Dec 12, 2004)

What is the difference between a high and a low impeadance injector?? I mean, I know the obvious reason...the current, but which is better and why???


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## TBT-Syncro (Apr 28, 2001)

*Re: fuel injectors...difference high or low impeadance?? (Brad Boardwell)*

you have two choices, using the type that work with your ecu or using the wrong type and installing a resistor.
you need high impedance.


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## Brad Boardwell (Dec 12, 2004)

Ok.... I already knew that if I used low impedance that I would have to use resisters...and I didn't want to do that. I wanted to know why there are low and high impedance injectors?? Is it just because some computers need one or the other, or is there a performance difference??


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## [email protected] (Jan 13, 2005)

*Re: (Brad Boardwell)*


_Quote, originally posted by *Brad Boardwell* »_Ok.... I already knew that if I used low impedance that I would have to use resisters...and I didn't want to do that. I wanted to know why there are low and high impedance injectors?? Is it just because some computers need one or the other, or is there a performance difference??

Brad, this is fairly easy to explain. First, understand that injectors are pulsed by the ECU to stay open for longer or shorter periods of time. This variable duration is what determines how much fuel is sprayed into the combustion chamber. You'll see injectors described, for instance, as "380cc" or "36lb". That means the injector delivers 380cc per minute or 36lb per hour (with a standard test fluid like n-heptane at a standard testing temperature with a 3bar/43.5psi fuel pressure). These tests are conducted at 100% duty cycle meaning that the injector is held wide open (coil fully energized for the entire test period).
At 100% duty cycle, a high-impedance 380cc injector will flow the same exact 380cc that a low-impedance version will in a minute's time. However... things change dramatically when you're opening and closing the injector so as to moderate fuel flow to match the engine's load. The faster the injector can be fully opened/closed, the more precise the dose of fuel can be delivered.
This is hugely important at idle and very high rpms. During idle, only a very tiny amount of fuel is needed. Duty cycle may only be 1% or possibly less. A huge injector has to be cycled on/off extremely quickly to maintain the proper air/fuel ratio. If the injector's response is too slow, there will be no way to keep things steady and balanced. Meanwhile, at high-rpms there is only the briefest amount of time to get the fuel into the chamber before the intake valve/s close.
Finally, let's discuss high versus low-impedance... A low-impedance circuit could also be described as low electrical resistance. Lowered resistance in the driver circuit means that more current is delivered to the injector's coil. That extra energy energizes the injector's coil and snaps the injector open faster/harder than it can with less current. High-impedance operation is the reverse. So, generally speaking, low-impedance = faster and high generally means slower.
Low-impedance injector drivers (the apparatus in the ECU that controls and delivers the electrical current to open/shut the injectors) are beefier, more complex, and more expensive. So, most factory ECUs are equipped only to run high-impedance injectors. ALL VW factory ECUs take high-impedance only. Throw some lows in there and you'll fry parts.
Now, here's where I get a free advertisment...









You see that (red) waveform? That's what you'd see on an oscilloscope if you tapped an injector wire and looked at a low-impedance injector pulse. There is a peak (spike) current level that slams the injector open and then a hold current (flat point) that keeps it open. The peak/hold firing arrangement is almost only seen used with low-impedance designs. A high-impedance driver only sends a pulse that resembles only the flat section of that red waveform. Since there is no initial high-voltage jolt, the injector opens more slowly than with the low-impedance/peak & hold firing scheme.
Here's something else to remember: Adding resistors to make low-impedance injectors work on a high-impedance circuit is not ideal. Why is that? The resistors reduce the amount of current available to open the injector. Low-impedance injectors typically have heavier return coil springs (which are of fixed strength and shut the injector against the fuel pressure). Reducing the current strength means that it won't have as much "electrical muscle" to open against that spring. So, you often end up with an injector that's slower than if you started off with a high-impedance injector in the first place.
I hope that this info helps you understand why high and low-impedance injectors are specified for different applications! If you have any further questions, just ask.


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## Brad Boardwell (Dec 12, 2004)

Scott, That is EXACTLY what I was looking for...WOW, what an answer!! Thank you 
I knew that they both delivered the same fuel ( as cc's or lbs per hour), but I did not know about the opening and closing, and the seat pressure in the low impedence injectors...
And your prices are very good... Thanks Scott for your post...


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## mk2vrooom (Oct 15, 2003)

*Re: (Brad Boardwell)*

well damn...thats one of the better responses ive seen here in like...a VERY long time!


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## [email protected] (Jan 13, 2005)

*Re: (Brad Boardwell)*

I'm here to help.








P.S. I used to spend summers down there in Mack Town, GA. Napier Avenue rEpRAzeNT!!!


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## elio (Nov 15, 2006)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Brad, this is fairly easy to explain. First, understand that injectors are pulsed by the ECU to stay open for longer or shorter periods of time. This variable duration is what determines how much fuel is sprayed into the combustion chamber. You'll see injectors described, for instance, as "380cc" or "36lb". That means the injector delivers 380cc per minute or 36lb per hour (with a standard test fluid like n-heptane at a standard testing temperature with a 3bar/43.5psi fuel pressure). These tests are conducted at 100% duty cycle meaning that the injector is held wide open (coil fully energized for the entire test period).
At 100% duty cycle, a high-impedance 380cc injector will flow the same exact 380cc that a low-impedance version will in a minute's time. However... things change dramatically when you're opening and closing the injector so as to moderate fuel flow to match the engine's load. The faster the injector can be fully opened/closed, the more precise the dose of fuel can be delivered.
This is hugely important at idle and very high rpms. During idle, only a very tiny amount of fuel is needed. Duty cycle may only be 1% or possibly less. A huge injector has to be cycled on/off extremely quickly to maintain the proper air/fuel ratio. If the injector's response is too slow, there will be no way to keep things steady and balanced. Meanwhile, at high-rpms there is only the briefest amount of time to get the fuel into the chamber before the intake valve/s close.
Finally, let's discuss high versus low-impedance... A low-impedance circuit could also be described as low electrical resistance. Lowered resistance in the driver circuit means that more current is delivered to the injector's coil. That extra energy energizes the injector's coil and snaps the injector open faster/harder than it can with less current. High-impedance operation is the reverse. So, generally speaking, low-impedance = faster and high generally means slower.
Low-impedance injector drivers (the apparatus in the ECU that controls and delivers the electrical current to open/shut the injectors) are beefier, more complex, and more expensive. So, most factory ECUs are equipped only to run high-impedance injectors. ALL VW factory ECUs take high-impedance only. Throw some lows in there and you'll fry parts.
Now, here's where I get a free advertisment...









You see that (red) waveform? That's what you'd see on an oscilloscope if you tapped an injector wire and looked at a low-impedance injector pulse. There is a peak (spike) current level that slams the injector open and then a hold current (flat point) that keeps it open. The peak/hold firing arrangement is almost only seen used with low-impedance designs. A high-impedance driver only sends a pulse that resembles only the flat section of that red waveform. Since there is no initial high-voltage jolt, the injector opens more slowly than with the low-impedance/peak & hold firing scheme.
Here's something else to remember: Adding resistors to make low-impedance injectors work on a high-impedance circuit is not ideal. Why is that? The resistors reduce the amount of current available to open the injector. Low-impedance injectors typically have heavier return coil springs (which are of fixed strength and shut the injector against the fuel pressure). Reducing the current strength means that it won't have as much "electrical muscle" to open against that spring. So, you often end up with an injector that's slower than if you started off with a high-impedance injector in the first place.
I hope that this info helps you understand why high and low-impedance injectors are specified for different applications! If you have any further questions, just ask.

















Scoot great info. I have a doubt can be AUQ injectors compatible with an AGU engine? 
In any case will be great to have more info about other 1.8T engines injectors for comparison purposes, let's say code, flow @ xx psi or bar, engine and car that uses it.
Thanks in advance for your help.


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## [email protected] (Jan 13, 2005)

*Re: (elio)*


_Quote, originally posted by *elio* »_Scoot great info. I have a doubt can be AUQ injectors compatible with an AGU engine?

The AUQ injectors are physically too short to fit in the AGU. However, you could use the AGU injectors in the AUQ if you added spacers to move the fuel rail up a little bit. Nobody would want the AGU injectors, though, because they're *tiny*.









_Quote »_In any case will be great to have more info about other 1.8T engines injectors for comparison purposes, let's say code, flow @ xx psi or bar, engine and car that uses it.

Okay, how about our trusty old 1.8T injector database?







Come on now... ask me a hard question!

_Quote »_Thanks in advance for your help.

¡Ése es porqué estoy aquí!


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## elio (Nov 15, 2006)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
The AUQ injectors are physically too short to fit in the AGU. However, you could use the AGU injectors in the AUQ if you added spacers to move the fuel rail up a little bit. Nobody would want the AGU injectors, though, because they're *tiny*.








Okay, how about our trusty old 1.8T injector database?







Come on now... ask me a hard question!
¡Ése es porqué estoy aquí!
















That was the info that I really needed. Excellent http://****************.com/smile/emthup.gif Thanks a lot
Muchas gracias y saludos


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## elio (Nov 15, 2006)

Mr [email protected] thanks a lot for your help. Friend I am having problems with my stock injectors. Car is hard to start when engine is warm, smells like too much gas and when starts it done very accelerated and after goes normal. Idle is quite fine no rough at all. This occur after a injector cleaning process. I think that injectors remains little opened after engine is off.
Ok the big question, do you have this injectors #06A906031 for my AGU engine? I am planning a Turbo upgrade but not know so I will need good injectors for one o two maximun before I do the trubo upgrade.
Friend, what do you suggest me? can you help me?


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## elio (Nov 15, 2006)

Hi Scoot do you have any comment?
Thanks,


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## Motohead (Aug 27, 2001)

*Re: (elio)*

What is considered high and what is low?
Thanks for the explanation by the way http://****************.com/smile/emthup.gif 
-Drew


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## [email protected] (Jan 13, 2005)

_Quote, originally posted by *elio* »_I am having problems with my stock injectors. Car is hard to start when engine is warm, smells like too much gas and when starts it done very accelerated and after goes normal. Idle is quite fine no rough at all. This occur after a injector cleaning process. I think that injectors remains little opened after engine is off.

I suspect that some dirt that was loosened during the cleaning process is now holding the injector/s open. So, you are getting a temporary rich condition because of the extra fuel in the cylinder/s. I would send the injectors back to the place that did the service and see what they say.

_Quote »_=do you have this injectors #06A906031 for my AGU engine?

Elio, we specialize injector upgrades. Unfortunately, in this case, I cannot supply you with a stock replacement.

_Quote, originally posted by *Motohead* »_What is considered high and what is low?

Drew, high-impedance injectors are always somewhere between 12ohms resistance and 16. The lion's share range between 14 and 16 ohms. As for the low-impedance, those are available between 2 and 6 ohms with most between 2 and 4 ohms.

_Quote »_Thanks for the explanation by the way http://****************.com/smile/emthup.gif

Better-informed consumers make wiser investments in quality equipment. We're happy to help.


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## elio (Nov 15, 2006)

*Re: fuel injectors...difference high or low impeadance?? ([email protected])*

Hi again Scott. As you recommend me the injectors was cleaned again and car continues with problems. 
As you remember my injectors was cleaned the first time showing that 2 injectors have been really dirty, the flow ranges was, 95%, 96%, 74%, 76%. But inclusive now after the second cleaning process, the car is still hard to start. When is cold it starts at once but with a rough idle for about 3 seconds and after get stable. And when the engine is warm, I need turn the ignition twice for few second until it starts. In both cases smells some gas, like the engine was flooded. Ok but when engine is running is really smooth and the gas milleage is good as usual and no DTCs at all.
I scanned with the VAG-COM a this is what I obtain,
Control Module Part Number: 06A 906 018 CG 
Component and/or Version: 1.8L R4/5VT MOTR HS D02
Software Coding: 04000
Work Shop Code: WSC 01317
5 Faults Found:
16502 - Engine Coolant Temp. Sensor (G62): Signal too high
P0118 - 35-10 - - - Intermittent
01249 - Fuel Injector for Cylinder 1 (N30)
26-10 - Output Open - Intermittent
01250 - Fuel Injector for Cylinder 2 (N31)
26-10 - Output Open - Intermittent
01251 - Fuel Injector for Cylinder 3 (N32)
26-10 - Output Open - Intermittent
01252 - Fuel Injector for Cylinder 4 (N33)
26-10 - Output Open – Intermittent
The coolant temp needle in the cluster is showing temps normal, and rock steady at normal operating temperature. I logged it too with VagCom and seems to be a correct measure compared with the cluster needle too.
Finally can a small Engine Coolant Temp sensor can cause too much trouble? or do I have all injectors leaking?
I appreciate your advice about this. This is making me nuts.








Thanks,


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## elio (Nov 15, 2006)

Also, sorry to ask this here.
Thanks,


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## [email protected] (Jan 13, 2005)

*Re: fuel injectors...difference high or low impeadance?? (elio)*

Elio, I'm really not a stock ECU expert. However, I'd replace that coolant temperature sensor and see what happens.


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## elio (Nov 15, 2006)

*Re: fuel injectors...difference high or low impeadance?? ([email protected])*

Hi again Scott and friends.
Well sorry to post here my problems, but the issue of my car is really weird.
Anyway I changed the coolant sensor on Monday for the green top one and clear DTCs. But the car remains with the same problem.
Last night I scanned my car again and found no codes at all. I use an electronic cleaner to clean MAF and ICU connectors and contacts. I haven't clean the MAF element yet.
After that I log blocks 2, 3 and 6 with the VagCom under this cases,
1.- from engine off, startup to idle at 90ºC normal temp engine operation. You can find this log here: http://www.dropfiles.net//file...e.xls
2.- from idle, a fast acceleration at neutral speed to almost 6000rpms and idle again. You can find this log here: http://www.dropfiles.net//file...e.XLS
3.- and finally from idle again to engine off. You can find this log here: http://www.dropfiles.net//file...f.XLS
From my point of view everything seems to be ok. Also I think that the MAF is working quite good. I will try to log a run in 2nd gear up to 6000rpms to check the logs again. But until now when the car is running is quite smooth, excellent mileage, fast acceleration, no misfires at all and rock steady idle.
All the problem could be in the injectors? what do you think?
Again, friends this is making me nuts....... comments and ideas are highly appreciated.
Thanks again for your time and support with me.
Regards,


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## [email protected] (Jan 13, 2005)

*Re: fuel injectors...difference high or low impeadance?? (elio)*

Elio, I would start a new thread about this topic. This one isn't going to bring the attention that you need because of the unrelated subject.


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## elio (Nov 15, 2006)

You are right friend. Sorry to post this question here.
Thanks,


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