The Top Mitsubishi Galant VR-4 Resource

Join the best E39A 1991-1992 Mitsubishi Galant VR-4 community and document your GVR4 journey.

  • Software Upgraded - Reset Your Password to Login
    In order to log in after the forum software change, you need to reset your password. If you don't have access to the email address you used to register your GVR4.org account, you won't be able to reset your password. In that case, follow the instructions here to regain access to the forum.

What is Proper ISC Voltage and where to check?

moidsm1

Well-known member
Joined
Nov 30, 2009
Messages
116
Location
Tucson, AZ
Ok,

Im hunting down my idle surge problem. Im at the point where I have tested the ISC coils and all is good. I now want to test the voltage going to the ISC at the harness connector. This is what it looks like looking straight into it:

! !
1 2 3
-------
4 5 6

With the key in the on position what pins do I check and what voltage should I see? Ive read the Vfaq and Terry has a method of using LED's Since then has anyone found a good way to check the voltage here? Im assuming anything wrong here would mean either my wiring is bad or the ECU ISC driver board is bad. Thanks
 

Adorsey

Well-known member
Joined
Apr 22, 2009
Messages
355
Location
mass
If you pull the ISC motor out, and check it, you should be able to put 6volts without friing the motor. I have to check the amount of volts but im almost sure its 6
 

Isn't your coolant to the TB blocked off? Did you do the FIAV block off yet?
 

Adorsey

Well-known member
Joined
Apr 22, 2009
Messages
355
Location
mass
This is directly off VFAQ, read it and weep

Testing this thing!
This is a pretty simple process:
Remove the connector to the ISC There are six pins on the ISC. They are labeled 1 2 3 across the top and 4 5 6 across the bottom. (see left)

Measure the Resistance between pin's 1-2, 2-3, 4-5, and 5-6
Each pair of pins measured should read 28-33 Ohms
Note: The values should measured with the car off and cool!
If any of the "coils" (which is what you're testing) are bad then your ISC needs to be replaced
If all the coils were good there's one other thing to check on the ISC


Use a 6volt battery (lantern or camera battery) and apply 6 volts to the ISC motor.
Use jumper wires to connect the positive (+) terminal of the battery to terminals 2 and 5 of the ISC and the negative battery terminal to terminals 3 and 6 of the ISC.
If there is no movement or vibration from the motor, then it is bad
Note: The use of a 12volt battery will destroy the ISC motor!!
 

moidsm1

Well-known member
Joined
Nov 30, 2009
Messages
116
Location
Tucson, AZ
Yes Ihave done the FIAV Blockoff,

The reason I am trying to find the right voltage is because while testing the connector from the harness with a meter I am getting 12 Volts across pins


2-3 and 4-5

This is while looking at the connector like this.

I I

1 2 3

4 5 6
 

Adorsey

Well-known member
Joined
Apr 22, 2009
Messages
355
Location
mass
^? its a bad ISC if only "some" or none of the conections work.
 

moidsm1

Well-known member
Joined
Nov 30, 2009
Messages
116
Location
Tucson, AZ
Right, I tested the ISC by itself with good results. Back to my original question, how many volts is the ECU supposed to be supplying to the ISC? 6 Volts? Im getting 12.
 

Adorsey

Well-known member
Joined
Apr 22, 2009
Messages
355
Location
mass
Search /ubbthreads/images/graemlins/dunno.gif
 

stevep

Well-known member
Joined
Oct 23, 2004
Messages
416
Location
St. Charles, IL USA
Quoting moidsm1:
Back to my original question, how many volts is the ECU supposed to be supplying to the ISC?


Just looking that the MPI wiring diagram would make it clear that the two center pins receive power from the MPI relay. So they get whatever the car's system voltage is at the time.
 

moidsm1

Well-known member
Joined
Nov 30, 2009
Messages
116
Location
Tucson, AZ
I found my answer on DSMTuners! But you are right Stevep. The MPI circuit provides the ISC motor with 12V. So why does the VFAQ have us testing it with 6V?

Here is what I found on Tuners. I confirmed with a wire diagram I already had!

click
 

stevep

Well-known member
Joined
Oct 23, 2004
Messages
416
Location
St. Charles, IL USA
LOL, thanks for linking me back to one of my posts.
I believe the factory service manual and VFAQ that copies the FSM information has you use 6v to be safe and avoid burning out any of the coils.
 
Last edited:

moidsm1

Well-known member
Joined
Nov 30, 2009
Messages
116
Location
Tucson, AZ
I didnt make the connection. Thank you Steve for you knowledge. So now that my voltages are correct, my idle surege hunting will continue. I WILL FIND A CURE DAMNITT!
 

stevep

Well-known member
Joined
Oct 23, 2004
Messages
416
Location
St. Charles, IL USA
Have you pulled your ISC and make sure it moved like in the youtube video I keep linking on Tuners? After bootim the ECU homes the ISC by stepping it all the way out, then back to 0, before moving to the position for starting the car.

Remember that idle surge is caused generally caused by too much air bypassing the closed throttle plate. That can be from leaks (internal and external, pressure testing will only find the external ones), incorrect BISS adjustment, throttle cable too tight, bad ISC, bad FIAV, or damaged ECU.
 
Support Vendors who Support the GVR-4 Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications RixRacing RockAuto RTM Racing STM Tuned

Recent Forum Posts

Top