Switched 12v to Injectors
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Switched 12v to Injectors
Hey all,
I'm building up my ms3 with an ms3x for my stock ka24e. I was wondering why the injectors need switched 12v when they are being controlled by the ms3x? The fets used on the ms3x have a 70v drain-source clamp which is well above 12v so it doesn't seem like an issue to me. Is there something I am missing? I would prefer to leave the injectors hooked up to constant 12v so I don't have to modify the stock wiring harness. Thanks for any input y'all have.
I'm building up my ms3 with an ms3x for my stock ka24e. I was wondering why the injectors need switched 12v when they are being controlled by the ms3x? The fets used on the ms3x have a 70v drain-source clamp which is well above 12v so it doesn't seem like an issue to me. Is there something I am missing? I would prefer to leave the injectors hooked up to constant 12v so I don't have to modify the stock wiring harness. Thanks for any input y'all have.
Re: Switched 12v to Injectors
if its powered of a constant feed you may find the 12v is back fed through the ecu preventing it from powering down when you turn the key off.
this goes for all things the ecu is controlling switched 12v is the way to go
this goes for all things the ecu is controlling switched 12v is the way to go
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
Re: Switched 12v to Injectors
Your stock harness has 12v to the injectors at all times? Never seen that. They are usually switched via the ignition switch (and maybe a relay etc), same as other engine electrics.Stingy49 wrote:Hey all,
I'm building up my ms3 with an ms3x for my stock ka24e. I was wondering why the injectors need switched 12v when they are being controlled by the ms3x? The fets used on the ms3x have a 70v drain-source clamp which is well above 12v so it doesn't seem like an issue to me. Is there something I am missing? I would prefer to leave the injectors hooked up to constant 12v so I don't have to modify the stock wiring harness. Thanks for any input y'all have.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
MS2 V3
EDIS
Tech Edge O2
London UK.
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Re: Switched 12v to Injectors
I'm with Dave on this!! I've never heard of such a thing.
What make and year? I'd like to look at the schematics.
Ken
What make and year? I'd like to look at the schematics.
Ken
1979 Corvette - 383 CID SBC w/ Holley Pro-Jection 900 CFM TBI, 4-85 lb lo-z injectors & Walbro 255 pump
MS2 v3 w/extra 3.4.2 Release
36-1, Delphi LS2/7 coils in wasted spark, driven by v2.0 logic board from JBPerformance
Spartan Lambda Sensor from 14point7
TinyIOX from JBPerformance
MS2 v3 w/extra 3.4.2 Release
36-1, Delphi LS2/7 coils in wasted spark, driven by v2.0 logic board from JBPerformance
Spartan Lambda Sensor from 14point7
TinyIOX from JBPerformance
Re: Switched 12v to Injectors
Thanks for all the replies!
The car is a 1989 Nissan 240sx with the ka24e motor. You can see how it is wired in the snip from the FSM I've included. Sorry about the low quality image, the pdf it's from isn't the best quality. http://i.imgur.com/xcbhziR.png. It's definitely an uncommon setup from what I can tell.
Also, I asked one of the EE's at work and they were explaining to me that the mosfets used to control the injectors can be turned on by the fluctuations in the 12v line while the motor is cranking. The source and drain pins are capacitively coupled which means that those fluctuations can bring the gate voltage high enough to turn on the fet.
I was hoping to avoid cutting up the stock harness but it looks like that is unavoidable . Thanks again for the advice.
The car is a 1989 Nissan 240sx with the ka24e motor. You can see how it is wired in the snip from the FSM I've included. Sorry about the low quality image, the pdf it's from isn't the best quality. http://i.imgur.com/xcbhziR.png. It's definitely an uncommon setup from what I can tell.
Also, I asked one of the EE's at work and they were explaining to me that the mosfets used to control the injectors can be turned on by the fluctuations in the 12v line while the motor is cranking. The source and drain pins are capacitively coupled which means that those fluctuations can bring the gate voltage high enough to turn on the fet.
I was hoping to avoid cutting up the stock harness but it looks like that is unavoidable . Thanks again for the advice.
Re: Switched 12v to Injectors
Interesting - never seen that arrangement before.
I'd do all the power side by the wiring diagrams given in the manuals linked to from this site. No point in guessing things might be OK. I do often start off with a stock harness as a basis - but they always needs quite a bit of modification. Perhaps get one used - if you want the ability to swap back to the original injection easily.
I'd do all the power side by the wiring diagrams given in the manuals linked to from this site. No point in guessing things might be OK. I do often start off with a stock harness as a basis - but they always needs quite a bit of modification. Perhaps get one used - if you want the ability to swap back to the original injection easily.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
MS2 V3
EDIS
Tech Edge O2
London UK.
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Re: Switched 12v to Injectors
Have you verified that schematic? All manuals have some errors in them...
Re: Switched 12v to Injectors
billr wrote:Have you verified that schematic? All manuals have some errors in them...
Checking that tonight
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Re: Switched 12v to Injectors
I've never seen a Nissan that DIDN'T have the 12V switched to the injectors.
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
Tha Otha Toy: 1923 T-bucket Hot Rod, Currently Sniper'd
Tha Daily: 2005 Chevy Blazer
Tha Summer Daily: 1987 Buick Skyhawk hatchback
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
Tha Otha Toy: 1923 T-bucket Hot Rod, Currently Sniper'd
Tha Daily: 2005 Chevy Blazer
Tha Summer Daily: 1987 Buick Skyhawk hatchback
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
Re: Switched 12v to Injectors
I checked today after work and the injectors have 12v relative to the neg terminal even while there is no key in the ignition.
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Re: Switched 12v to Injectors
That's just a bad idea overall.
Even though you don't want to change it, it'll be safer in the end to change it.
Even though you don't want to change it, it'll be safer in the end to change it.
Tha Toy: 1973 Datsun 240Z Turbocharged, and loads of fun, now MS'd
Tha Otha Toy: 1923 T-bucket Hot Rod, Currently Sniper'd
Tha Daily: 2005 Chevy Blazer
Tha Summer Daily: 1987 Buick Skyhawk hatchback
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
Tha Otha Toy: 1923 T-bucket Hot Rod, Currently Sniper'd
Tha Daily: 2005 Chevy Blazer
Tha Summer Daily: 1987 Buick Skyhawk hatchback
Tha Long Term Project: 1985 GMC S-10 Jimmy, hasn't been fun for a while
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- Super MS/Extra'er
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Re: Switched 12v to Injectors
Yep. You can get away with this with the MS3X injector drivers, but not with the main board drivers. Why Nissan ever did this is beyond me.Stingy49 wrote:I checked today after work and the injectors have 12v relative to the neg terminal even while there is no key in the ignition.
Matt Cramer -1966 Dodge Dart slant six running on MS3X