ECU/ISC Driver question

[992gnt]

As I work through many, many issues with 1587, I have found that I have a blown ISC driver (IC105). According to ECM Tuning, the drivers do the following functions:

IC104 controls ECU pin 14 ('90) or 6 ('91+), MAF Reset signal. The other half of the chip is unused on US DSMs.
IC105 controls ECU pins 67 and 68, Idle Speed Control (ISC) Servo (coil pair B).
IC106 controls ECU pin 57, Fuel Pressure Solenoid (FPS), and ECU pin 105, Boost Control Solenoid (BCS).
IC107 controls ECU pins 58 and 59, ISC Servo (coil pair A).
IC108 controls ECU pin 53, EGR Solenoid, and ECU pin 62, Evap Purge Solenoid.
IC109 controls ECU pin 56, Fuel Pump Relay, and ECU pin 65 Air Conditioner Compressor Clutch Relay.

So my question is this. If IC105 is toast and causing my idle surge, and IC108 controls emissions solenoids - and I have no emissions equipment except the o2 sensor, could I conceivably swap IC108 and IC105 to fix my idle surge problem?

The ecu is out to install DSMLink tomorrow when it arrives, so I'm trying to get the ecu squared away prior to starting that project. And before anyone asks, I just put in a brand new ISC yesterday so there shouldn't be any lingering issues there that would blow a good driver. I think the driver has been cooked for some time.

 

[AllanL]

possible?

but have you tried checking the continuity between the isc pins on the ecu and the isc drivers?

this link is for an early evo (I~III), but the checking way is the same; just take note of the functions of each isc driver.
click

hth...

 

[992gnt]

Thanks for the link. I think I'm gonna give it a try, and I'll check continuity when I have it apart. 105 blew on the top, so there looks to be very little damage to the board. I'll take some pics and report back later today if anyone is interested.

 

[992gnt]

Well I swapped drivers and still have idle surge, so either I screwed up the swap somehow, or I have other problems. No CEL from the swap either.

 

[AllanL]

CEL won't be lit up by this. /ubbthreads/images/graemlins/ooo.gif

How about the continuity from the ecu socket pins to the corresponding pins of IC105 and IC107? /ubbthreads/images/graemlins/confused.gif

To test the tracks of the ecu, please measure continuity between ic driver pins and the ecu pins for the loom.
Ic105 pin1- ecu pin 68- reads continuity
Ic105 pin7- ecu pin 67- reads continuity
Ic107 pin1- ecu pin58- reads continuity
Ic107 pin7- ecu pin59- reads continuity
*looking from the bottom-side of the ecu [the side with many solders], ic pin 1 is right-most ic driver pin...

Also check harness wiring continuity:
Isc pin1- ecu loom pin58
Isc pin4- ecu loom pin68
Isc pin3- ecu loom pin59
Isc pin6- ecu loom pin67

/ubbthreads/images/graemlins/jawdrop.gif

 

[992gnt]

The ECU comment was in regards to placing an obviously burnt chip into IC108, which controls EVAP and EGR solenoids. The board checks ok for continuity, so I'm going to rig something up to test the harness next.

EDIT:

Harness is good. Next step is to swap in a known good ecu, while I send mine away for repair. Really makes no sense though.

Used brown top ISC - No high idle cold (very hard to start), steps maxed at 120 all the time, no surge
New black ISC - High idle cold works correctly, steps drop to zero and stay there (occassionally I'll see steps around 9-10), idle stays high and surges - unless the ac is on, then it's just high (1700 or so rpm).
Harness - continuity check ok
Drivers to ecu pins - continuity check ok
Driver ohm check - differs slightly on two pins from link above, but all drivers match, so I'd say ok

Not much left to troubleshoot unfortunately. /ubbthreads/images/graemlins/banghead.gif