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Testing the Igniter


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#1 arbor

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Posted 19 May 2020 - 11:56 PM

Hey guys,

Can any one chime in on how to test the igniter out of a 86? I am trying to track down what is causing the the huge delay / stumble  when the ECU/MAP checks for atmospheric pressure every 2 mins as its very pronounced. I am struggling to believe this is how they designed the car to idle.

As seen in the pic I want to verify that my igniter is function correctly but the manual leaves a lot to he desired and I have no clue on what they mean by input and outputs.

I have probed the ECU whilst the car was idling and nothing seems amiss according the the FSM, so I'm at a loss.

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#2 scott87star

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Posted 20 May 2020 - 08:53 AM

The ignitor either works or it doesn't, its not the cause of your stumble.
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#3 tux

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Posted 20 May 2020 - 10:12 AM

How do your plugs look?  Are you sure vacuum lines are hooked up correctly?

#4 arbor

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Posted 20 May 2020 - 11:35 AM

View Postscott87star, on 20 May 2020 - 08:53 AM, said:

The ignitor either works or it doesn't, its not the cause of your stumble.

Even if the Igniter intercepts the high altitude adjustment and solenoid?

View Posttux, on 20 May 2020 - 10:12 AM, said:

How do your plugs look?  Are you sure vacuum lines are hooked up correctly?

Plug are new and vacuum line are routed correctly / new. The car doesn't exhibit this issue with the MAP is unplugged. So I have an electrical gremlin in the high altitude circuit which the FSM doesn't go into, I'd love to see the supplement service manual as it supposedly goes into more detail.

I have a used MAP sensor coming to try out to rule if its the MAP sensor that is lazy/faulty and I have  a spare ECU to try.

#5 mikec

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Posted 20 May 2020 - 12:09 PM

The ECU sends two signals to the ignitor: one tells the ignitor when to monitor for engine knock and the other tells the ignitor "cold engine or high altitude, either way advance the timing an additional 5 degrees."   The ignitor does not send anything back to the ECU other than ignition pulses - the same signal that drives the tachometer.  This comes from the ignition coil actually.  The ECU uses these pulses to know if the engine is actually running (if the engine stalls/stops, the ECU cuts power to the fuel pump in case the engine died from the car being in an accident - don't want the fuel pump running, pushing fuel out busted fuel lines) and, if the throttle body nose switch says the throttle is at idle, the ECU looks at the ignition pulse rate to determine engine RPMs and adjusts the Idle Speed Control (ISC) motor as appropriate to get the proper idle speed.

So, if your engine will run and the tach works, you can be pretty sure the ignitor is functioning.  It's a simple "electronic ignition" box, not a highly sophisticated computer.

Do you live at "high altitude" - above 3900 feet or 1200 meters barometric/pressure altitude?  If so, the ECU should be requesting the timing advance.  If not, you'll still have the timing advance on a stone-cold engine; it'll suddenly go away once there is some temperature in the coolant.  Look for the wiring harness bundle between the air filter canister and passenger fender... there should be a pair of connectors hanging from it (or taped to it) that are not plugged into anything but should have protective caps.  One will have a single wire, one will have multiple wires.  On the 2-wire one, jumper the two wires together.  That forces the system into "warm engine, low altitude" mode so you can verify the ignition timing is a proper 10 deg BTDC once the engine is fully warmed up.  Let the engine cool completely and restart... timing may be a little different as idle RPMs will be higher, affecting the distributor timing advancer components.  Remove the jumper.  Did the timing increase (advance) 5 degrees?  If so, the ignitor is 100% functional.

Folks have long complained that StarQuests have a weird/unsteady idle.  I've only driven 87-later models that don't have the solenoid and pressure sensor; the 87-later cars have a dedicated barometric sensor in the airflow sensor assembly and don't measure boost pressure at all.  So they don't have this 2-minute cycling thing; I've never experienced it myself to know if your car's symptoms are typical or abnormal.  Mitsu did a lot of experimenting in the 86 ECU programming too; some 86s for example run just fine with the primary airflow sensor removed - relying on the MAP sensor only - while others flat-out suck without the airflow sensor.  That tells us the software in 86 ECUs varied over the production year.  One thing about the ECU error codes: the ECU only looks for significant "out-of-bounds" errors from most of the signals; it really isn't that good at detecting most failures.  So, just because the ECU isn't throwing error codes, don't assume that means the sensors are 100% okay.

With the engine warmed up and idling, the output voltage of the pressure sensor should be between 0.2 to 1.2 volts, momentarily jumping to 1.5 to 2.6 volts every two minutes.  This is on pin 8 of the pressure sensor which is one of the two pins closest to the locking/indexing tab of the connector.  (the other pin is +12volts if the engine is running so it'll be obvious which pin to test/use)  Use a voltmeter to measure the voltages.

mike c.

#6 arbor

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Posted 20 May 2020 - 01:11 PM

View Postmikec, on 20 May 2020 - 12:09 PM, said:

The ECU sends two signals to the ignitor: one tells the ignitor when to monitor for engine knock and the other tells the ignitor "cold engine or high altitude, either way advance the timing an additional 5 degrees."   The ignitor does not send anything back to the ECU other than ignition pulses - the same signal that drives the tachometer.  This comes from the ignition coil actually.  The ECU uses these pulses to know if the engine is actually running (if the engine stalls/stops, the ECU cuts power to the fuel pump in case the engine died from the car being in an accident - don't want the fuel pump running, pushing fuel out busted fuel lines) and, if the throttle body nose switch says the throttle is at idle, the ECU looks at the ignition pulse rate to determine engine RPMs and adjusts the Idle Speed Control (ISC) motor as appropriate to get the proper idle speed.

So, if your engine will run and the tach works, you can be pretty sure the ignitor is functioning.  It's a simple "electronic ignition" box, not a highly sophisticated computer.

Do you live at "high altitude" - above 3900 feet or 1200 meters barometric/pressure altitude?  If so, the ECU should be requesting the timing advance.  If not, you'll still have the timing advance on a stone-cold engine; it'll suddenly go away once there is some temperature in the coolant.  Look for the wiring harness bundle between the air filter canister and passenger fender... there should be a pair of connectors hanging from it (or taped to it) that are not plugged into anything but should have protective caps.  One will have a single wire, one will have multiple wires.  On the 2-wire one, jumper the two wires together.  That forces the system into "warm engine, low altitude" mode so you can verify the ignition timing is a proper 10 deg BTDC once the engine is fully warmed up.  Let the engine cool completely and restart... timing may be a little different as idle RPMs will be higher, affecting the distributor timing advancer components.  Remove the jumper.  Did the timing increase (advance) 5 degrees?  If so, the ignitor is 100% functional.

Folks have long complained that StarQuests have a weird/unsteady idle.  I've only driven 87-later models that don't have the solenoid and pressure sensor; the 87-later cars have a dedicated barometric sensor in the airflow sensor assembly and don't measure boost pressure at all.  So they don't have this 2-minute cycling thing; I've never experienced it myself to know if your car's symptoms are typical or abnormal.  Mitsu did a lot of experimenting in the 86 ECU programming too; some 86s for example run just fine with the primary airflow sensor removed - relying on the MAP sensor only - while others flat-out suck without the airflow sensor.  That tells us the software in 86 ECUs varied over the production year.  One thing about the ECU error codes: the ECU only looks for significant "out-of-bounds" errors from most of the signals; it really isn't that good at detecting most failures.  So, just because the ECU isn't throwing error codes, don't assume that means the sensors are 100% okay.

With the engine warmed up and idling, the output voltage of the pressure sensor should be between 0.2 to 1.2 volts, momentarily jumping to 1.5 to 2.6 volts every two minutes.  This is on pin 8 of the pressure sensor which is one of the two pins closest to the locking/indexing tab of the connector.  (the other pin is +12volts if the engine is running so it'll be obvious which pin to test/use)  Use a voltmeter to measure the voltages.

mike c.

Mike I was hoping you would chime in, as I have learnt a lot from your replies in the past.

I thought the plugs on on the passenger side hardness were for the ECU/02 codes and fuel pump diagnosis? Every time I do a TPS/ISC reset I use my timing light to verify the timing and RPM's its right around 10 degrease when warm, I haven't checked what it is when cold though.

when I bought the car is had been hacked up, was only running on MAP and no ISC etc and I have been slowly piecing it back together and the last hurdle was the solenoid switch, I have no idea what the car was like before it was messed with.

When I said I probed the ECU I mean back pinning with a multi meter against the FSM spec's and everything seemed to be functioning as it should the Map was working correctly and you could see it momentarily jump to 1.5-2.6 volts as it checked for atmospheric pressure but when it does that the idle drops and goes lumpy then within 5-10 seconds it flips back to normal. However sometimes on a cold ish engine it will get stuck on the atmospheric switch and the only way I can get the car to come out of it is to rev it.

This behavior has me running round in circles, I have a laundry list of parts that I have replaced as maintenance and the CTS is one of them before some mentions it.

I am starting to wonder if the ECU is just on the fritz.

#7 arbor

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Posted 20 May 2020 - 04:24 PM

So for any one following along, on my lunch break today I had a chance to mess with the car, working from home during the COVID-19 has its perks I guess.

so I swapped my ECU out for the spare I have, no not sure how to tell which build dates are what? But the car acts differently for sure. The problem with the weird stumble followed so that rules the ECU out.

I did notice that when the car goes into its weird stumble that if I tap the solenoid it comes back to normal. This solenoid is brand new and a Chinese Mits part https://www.amazon.c...0?ie=UTF8&psc=1. Question remains do they run on the same voltage and or is it just a crappy part to begin with or am i looking at a failing MAP. I'll have to wait till I get my new to spare to try.

I did put a multi meter on it and could see if flick the solenoid but it happens so fast that it was kind of hard to see how many volts it was.

Edited by arbor, 20 May 2020 - 04:26 PM.


#8 mikec

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Posted 20 May 2020 - 05:50 PM

Is your car idling properly between the 2-minute pulses?  I.e. are the idle RPMs actually set by the ECU?  Some folks use the screw at the base of the throttle body (pointing towards the passenger side of the car) as an "idle screw" like the old carb days.  Nope, this is a backup absolute minimum idle screw that should only engage if the ISC motor stuff is totally whacked out.  If, when the engine is warmed up and idling, turning the screw clockwise (as you face it) half a turn affects the idle then it was not set correctly.  Under normal operations, this "fixed SAS" screw does nothing.  Instead, the idle is controlled by the ECU and the ISC motor.  At the end of the ISC assembly is a small button switch (aka "nose switch") that tells the ECU "throttle plates are at idle" which makes the ECU switch to open loop fuel control and use the ISC to get the proper idle RPMs.  If that switch is prevented from closing by a mis-set fixed SAS screw, the idle of the car will always be lumpy and touchy.  A bad idle switch won't help either.

The FAQ contains procedures to properly adjust the idle system on StarQuests, it varies depending on model year.  Basically though the procedure is to let the engine warm up, turn off the engine, turn the key back ON for a while so the ECU pre-sets the ISC to the position where it thinks it will get the right idle RPMs, then turn the key off to lock the ISC in this position, unplug the ISC electrical connector and run a ground to the harness side of the connector to mimic a closed idle switch (it should be closed), start the engine, and then use the idle screw on the cable linkage - the screw with a hex shaped head.  This calibrates the mechanical mechanism of your car and engine to the ECU and ISC/MPS system.

The 2 minute solenoid cycling... the documentation doesn't specify if that happens whenever the engine is running or only when it's not idling.  It says "every two minutes" which is not needed at idle... you are not going to be climbing or descending mountains at idle!  A snapshot of barometric pressure when the car is started, and then every couple of minutes when it's actually driving is all that is really required.  A screwed-up fixed SAS screw or idle adjustment procedure means the ECU thinks the engine is not idling so it "might be climbing mountains" and thus the barometric pressure needs to be checked.  The ECU and ISC also respond to the air conditioner turning ON/OFF... opening the throttle plates a little when the A/C turns ON.  If your A/C actually works (not a given on old cars!) turn it ON while the engine idles.  The RPMs may drop a little but should recover if the ECU, ISC, and idle switch are working.  If it drops and stays dropped, that's a clue your idle stuff is not adjusted properly and it could be screwing up the 2 minute cycle.

mike c.

#9 arbor

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Posted 20 May 2020 - 06:42 PM

View Postmikec, on 20 May 2020 - 05:50 PM, said:

Is your car idling properly between the 2-minute pulses?  I.e. are the idle RPMs actually set by the ECU?  Some folks use the screw at the base of the throttle body (pointing towards the passenger side of the car) as an "idle screw" like the old carb days.  Nope, this is a backup absolute minimum idle screw that should only engage if the ISC motor stuff is totally whacked out.  If, when the engine is warmed up and idling, turning the screw clockwise (as you face it) half a turn affects the idle then it was not set correctly.  Under normal operations, this "fixed SAS" screw does nothing.  Instead, the idle is controlled by the ECU and the ISC motor.  At the end of the ISC assembly is a small button switch (aka "nose switch") that tells the ECU "throttle plates are at idle" which makes the ECU switch to open loop fuel control and use the ISC to get the proper idle RPMs.  If that switch is prevented from closing by a mis-set fixed SAS screw, the idle of the car will always be lumpy and touchy.  A bad idle switch won't help either.

The FAQ contains procedures to properly adjust the idle system on StarQuests, it varies depending on model year.  Basically though the procedure is to let the engine warm up, turn off the engine, turn the key back ON for a while so the ECU pre-sets the ISC to the position where it thinks it will get the right idle RPMs, then turn the key off to lock the ISC in this position, unplug the ISC electrical connector and run a ground to the harness side of the connector to mimic a closed idle switch (it should be closed), start the engine, and then use the idle screw on the cable linkage - the screw with a hex shaped head.  This calibrates the mechanical mechanism of your car and engine to the ECU and ISC/MPS system.

The 2 minute solenoid cycling... the documentation doesn't specify if that happens whenever the engine is running or only when it's not idling.  It says "every two minutes" which is not needed at idle... you are not going to be climbing or descending mountains at idle!  A snapshot of barometric pressure when the car is started, and then every couple of minutes when it's actually driving is all that is really required.  A screwed-up fixed SAS screw or idle adjustment procedure means the ECU thinks the engine is not idling so it "might be climbing mountains" and thus the barometric pressure needs to be checked.  The ECU and ISC also respond to the air conditioner turning ON/OFF... opening the throttle plates a little when the A/C turns ON.  If your A/C actually works (not a given on old cars!) turn it ON while the engine idles.  The RPMs may drop a little but should recover if the ECU, ISC, and idle switch are working.  If it drops and stays dropped, that's a clue your idle stuff is not adjusted properly and it could be screwing up the 2 minute cycle.

mike c.

It starts runs and drives, it idles normally until it starts checking for the atmospheric pressure that when it gets angry. I can drive the car and it behaves normal. I have reset the ISC countless times and can do it with my eye closed. The nose switch is working and appears to be touching. The 86 cars do not have a SAS screw, just the one idle screw. regardless the car idles at 850rpm.

From my understanding that the solenoid only checked for pressure at idle not when driving? I'll have to double check the literature of that.  

Car doesn't have AC any more so that's a non issue. Also if the idle was set incorrectly, why does tapping the solenoid make the car idle normal again?

Edited by arbor, 20 May 2020 - 06:45 PM.


#10 arbor

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Posted 21 May 2020 - 06:32 PM

Here's a video of the car doing its stupid thing, ignore the noisy lifters....that's on the to do list.

Multi meter is connector the prongs on the solenoid.

https://www.youtube....<br /> <br /> I'm getting pretty close to getting scott to throw MS in my spare ECU and be done with it because this crap is getting frustrating.




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