The real title is "Duty Cycle setting". (the ECU controls idle speeds at all times, if the ISC works at all.)
is no idle speed adjust at all on G16's, you
can only center the range
of ISC control, with the DUTY CYCLE adjustments.
(vacuum leaks, ISC stuck, Idle switch stuck open (5v)engine not really hot at 180F or more. IAC stuck open or is not really hot, and more...)
If regulation fails, or the RPM is not 800, or near (50rpm is spec variance) then the ISC has failed, this is an ECU servo loop action. (dogmatic servo loop)
The ECU watches RPM at all times, hot, and if not at 800 due to loading factors on the engine (alternator loads) or driver moves the A/T shifter from park to drive, the ECU sees the RPM drop, then opens the ISC to correct this error, this is a software loop in the ECU, it is a dogmatic loop, endless..... and the net result is idle regulation to 800 at all times HOT (A/C off, and P/S not in overload)
There are only 2 sources of air,hot engine, the ISC and the bleed screw, so if you have air (vacuum) leaks, you may never get this servo to work at all.
The ISC can only open 100% and close 100% , if this action can not reach 800 RPM the ISC servo CONTROLS FAIL . (means idle speeds are out of CONTROL of the ECU)
I just found a Duty meter that works, see the sparts list. $25 tool + RPM and Dwell.
Failure causes (vast): I can't set the duty cycle. (or idle is out of control HOT)
Common failures: ( idle speed
out of control or can't set duty cycle) HOT ENGINE ONLY 180F+.
Any leak in the plenum not from ISC and the bleed, is WRONG.
Below is 16v MPI engine the Yellow words are don't touch me.
The bracket has cut angle tab blocking the adjustment screw, on purpose, leave it alone.
It's blocked for a reason. The screw is found on all engines 1991 to 1999 on the throttle body TBI or MPI engines.
The TBI 8V screw is HERE ! for all 1991 to 1995 engines
The 8v screw is painted white and the screw has a plastic cap , warning you, DON'T TOUCH ME.
Materials/tools : needed: ( depends on your tool crib! )
BEGIN: DUTY CYCLE calibration. (the most easy way is here.)
Some later cars are more easy to set, try this.... 1996+
The early cars used a custom Suzuki current duty meter, impossible to find, or buy.
A cold engine can races at 1500 RPM there is no stopping that. (the IAC is physical) unless hacking that is fun.... some do.. (it may race faster in Alaska) COLD.We have no spec on the IAC except closed at 150F. I have no idea who far it can fully open say at -40F (or C)?
However I did this. at -10F
ISC Tests: Same basic method on all 1991 and newer. The 89/90 idles up for Head lights and Rear Defrost too.
And theory is all in the above link.
Best other postings on this subject:
Figure 4: (scope signal of actual IAC valve.) It's off a bit, all you need to do is make the wave equal, for 50% Duty. 2.5mS up, and 2.5 mS down. 5mS period. (200 Hz)
Below the ISC is closed too long, so cut down the bleed, less air on bleed is CW turned. The bleed valve is just a simple cone-screw air valve. (CCW is more air)
If your idle is at 800, and the duty is in the ball park, all is well do not over do this.. This setting will not cause AFR to be wrong.
The above is live ISC signal with my scope, 200 Hertz. Connected directly across the IAC solenoid coil. (not it is set wrong,,,, but engine is cold , so is normal.)
The scope is ground busted (floating) so it can't upset the ECU driver.
25% closed because I made an intake leak, on purpose.
Under the duty cycle test above, the signal would be set to 50/50. 2.5 high and 2.5 mS low.
Turn the bleed screw CW, to lower bleed air and see the Duty rise, to 50% and stop.
Factory way , Pins for DUTY, are here. (pin 6 , or pin A as the case my be) (left to right, early 16v, then 8v DLC, and the right side is 1996-98 (USA) th
The Duty pin (6/A) is dead until the Diagnostic Request pin is grounded!
I've never got these duty pins to work, on 89-95 cars, I use a scope or voltmeter at the ISC pins. directly connected to ISC pins. OR THIS METER.
The FSM on early cars shows a current mode, duty mete,r to measure duty cycle, we have no such meter..... so skip all the below for duty checks pre 1996
I'm told the 1996 and newer cars in USA the FSM method that uses the 6 pin DLC pin 6.
8 valve TBP only, idle switch. Is pin C, per this Factor FSM drawing. The harness wire is blue-white. in all cases.
The switch can be tested for less than 500 ohm, key on, not running, unplugged.
or checking the voltage on the pin key on running and connected (be sure dash pot retracts or this test fails) If this switch fails, ISC regulation will be DEAD.
PIN C must be at 0v (never 5v) or the ISC will never ever work.
16 Valve MPI idle. Pin 2 must be 0v at idle, or the Idle controls will be dead. (ISC dead, and not regulating RPM at 800 hot) The harness wire is blue-white. in all cases.
You can see pin one is BOTTOM.
This is the new $25 meter that I tested, it works perfectly for RPM & Dwell, (4cycle only) and DUTY. Sold on Ebay, see materals above.seen on EBAY. IT WORKS
Works best for 1989 to 1995 G16 engines. Newer cars we can use OBD2 scan tools and do this. (and other ways, stated in the FSM 1996) ( a direct link)
I'm testing it here, now...... against a very accurate scope.
This is the most safe way for ECU, of all. Unlike pesky scope grounds and the ISC blue wire, issue landing on earth ground horrors.... or lacking a scope differential probe set.
ECU pins wrong list: MPI example only: 1992-95 G16B RUNNING at idle.
A2, Start Pin? in wrong state , this is the cranking signal to the ECU, tells the ECU to open the IAC and inject for slow cranking conditions and low air supply. 12vdc is cranking and 0v is not cranking, if at 12vdc running, ECU will get confused.
if A2 is 0v cranking the ECU will be confusedand inject wrongly.
A6, on DLC pin, bad at 0v, 12v is good."test switch term" I call it timing freeze. jumper, might be left in place or wire shorted to body of car.
A17, Diag. mode jumper left in the connector? 0v wrong. or shorted to car body , wrong. 12v good.
A18 , 0v is ok, , and is the idle switch is closed. 5v is WRONG.
A22 , tells the ECU that you are in drive.12v now is a lie. 0v is correct. if at 12v the ECU uses a very powerful idle up duty cycle and makes setting duty impossible.
B7 , Throttle angle sensor (TPS) near 1v (if way off may confuse any ECU)
B8, MAF at 1.7 to 2 vdc? (the ECU can only detect dead MAF, not weak, so we use a DMM meter and test it directly.
B20, (it's a fast moving 02 signal, and if way off the engine can go rich or lean, a scan tool shows it working or not... and closed loop. ( if engine goes lean, idle can surge out of control, lean can cause idle to fail easy so can gross misfiring)
B21 is IAT, I think this is not important here. what 1-2v or so, depends on air temp. 2v = 100F air temp, a warm engine heats its own air up to about 140F (run long enough) but not in Alaska..
B9 is ECT and is 0.65v = 180F. lower is hotter and ok. Above 0.83v is a hard failure here, (thermostat bad)
As seen here. MPI (see page 1 and 2 of FSM)
DSO= Digital Storage Oscilloscope. GMM = Graphing Multimeter.
OTC = Over the counter. (after market ,store bought , not Suzuki bought)
CTS means coolant temperature sensor , aka; ECT. new name is Engine Coolant Temperature (sensor) The are both the same and have 2 pins.
TV =Throttle Valve or butterfly plate.
TB = Throttle body.
Rev 16. for 1989 /90 coverages read the FSM for those years. OR HERE:
Questions, post them here: http://www.fixkick.com/bbs2/Suzuki-bbs/forumdisplay.php?fid=2