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| Can I manually manipulate my idle speed? (Page 5/10) |
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Mike in Sydney
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APR 22, 02:36 AM
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| quote | Originally posted by Patrick:
The EGR valve only opens under certain conditions while driving. On the OEM style EGR valves, you can actually open the valve by hand by sticking a finger up through a hole on the underside of the valve housing and pushing the valve open. The engine will stumble. If your EGR valve does not have the holes in the underside of the EGR housing, a vacuum pump will open the valve... and again, the engine should stumble. I personally don't feel your elevated idle RPM speed is EGR related.
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Another way to test the EGR valve is to remove the vacuum hose and open the valve by hand by sticking a finger up through a hole on the underside of the valve housing and pushing the valve open. While open, put a finger over the port where the vacuum hose goes and release the valve. If the valve diaphragm is OK, you should feel suction at the port and the valve should remain open, Removing you finger, the valve should close.
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Kitskaboodle
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APR 22, 02:38 PM
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Paul, the instructions for the cable in your link says it won’t work on 85 V6’s and that’s what I have. Strangely, the other one that’s $114.95 does say it will work with 85 V’s. I’m confused. 🙁
Also, I really would like to bite the bullet and get the scan tool, especially because it seems these idling & driveability issues are non-stop. 🙁
Patrick, as I mentioned previously I’m going to do the iac port block off ((while running) test today.
Vintage- Nut (and others) thanks for the info on the egr valve. I will test that later with the Mighty Mite and see if I can verify operation.
Kit
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Vintage-Nut
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APR 22, 07:07 PM
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And remember to try your spare MAP sensors.....
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Romsk
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APR 22, 09:09 PM
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Kit,
The Coolant Temperature Sensor (CTS) goes to the ECM. Based on this ECM circuity and the coefficient direction of this sensor, the voltage to the Analog to Digital Converter (ADC) inside the ECM rises as temperature goes up. So it has a positive temperature coefficient overall.
My GUI displays this as raw hexadecimal, raw decimal, and in degrees F or degrees C.
The Manifold Air Temperature (MAT) Sensor called the Intake Air Temperature (IAT) Sensor on the Fiero goes to the ECM. This nomeclature difference is because GM decided to measure air temperature at the Air Cleaner rather than in the Intake Plenum (Manifold). Based on this ECM circuity and the coefficient direction of this sensor, the voltage to the ADC inside the ECM falls as temperature goes up. So it has a negative temperature coefficient overall.
My GUI displays this as raw hexadecimal, raw decimal, and in degrees F or degrees C.
The Manifold Absolute Pressure (MAP) Sensor goes to the ECM. Based on this ECM circuity and the coefficient direction of this sensor, the voltage to the ADC inside the ECM rises as pressure goes up (or so called vacuum decreases). So it has a positive pressure coefficient overall.
My GUI displays this as raw hexadecimal, raw decimal, and in inches of Mercury (inHg) or millimeters of Mercury (mmHg).
When I was coding my GUI, I found tables (similar to the CTS table shown previously). I also measured their resistances at 0 C, 25 C, and 100 C, and various pressures respectively. Then I correlated those to what the ECM reported in raw decimal. Then I performed polynomial curve fits (from all those data points) to find the polynomial coefficients so I calculate the temperature in C (or pressure in mmHg) directly from the raw decimal value. I still have the curves for the CTS, the IAT Sensor, and the MAP Sensor. Since the GUI does all the conversions for the user, I never showed these curves. But since they may help users in diagnostics and testing these sensors, I am going to add these curve graphs to the GUI so you can see each sensor in: temperature/pressure vs. resistance vs. voltage vs. ADC raw value vs. units in F or C/inHg or mmHg.
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Romsk
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APR 22, 09:22 PM
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Kit,
Sorry, but that is true. The 1985 V6 ECM uses a slightly different ALDL stream. And all the IL4 ECMs had even more different ALDL streams.
It took me years (off and on) and empirical observations and experiments to figure out what all the 1986 to 1988 V6 data streams meant.
If I had an 1985 V6 ECM, I could upgrade the GUI to "decode" it as well.
But there is no one source with ALL the information needed to fully decode each ALDL data stream - GM was never forthcoming with that. I found hints and clues as I came across them (sometimes conflicting info) which took years.
If GM would give me (not gonna happen) the ALDL data stream specs on how to decode each data word, then the GUI could do them all - but the 4 cylinder ECMs used the 8192 baud rate and that may be too fast for the GUI to handle with all the things it's does in real time.
If anyone has a 1985 V6 ECM I can borrow, I should be able to reverse the data streams and code the GUI to process them.[This message has been edited by Romsk (edited 04-22-2025).]
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Romsk
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APR 22, 09:30 PM
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Kit,
The $84.95 Fiero GT ALDL Adapter shown my web page and one of those sold by The Fiero Store, is the one I designed. I offer support and free consultations on using it.
The $114 Scan Tool also sold by The Fiero Store is not mine. Therefore, I don't support it or consult on using it.
Maybe try Red Devil River for the 1985 V6 ECM.[This message has been edited by Romsk (edited 04-22-2025).]
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Kitskaboodle
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APR 23, 09:26 PM
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No, I didn’t forget about swapping a spare map sensor. 😊
Paul, thanks for all that info. I sent 2-3 emails to that Red Devil guy a long time ago but he never responded. I finally gave up
trying to contact him.
Ok, here is what I did this afternoon:
1) Installed new AC/Delco pcv valve
2) Swapped MAP sensors (I have 3 spares- all are used- one of the 3 is a factory GM Map so I installed it.
3) Started car with throttle body boot off. (engine dead cold)
4) Engine went right to 2450 rpm and stayed there. Let it run for about 4 minutes.
5) Put finger inside throttle body and plugged IAC hole/port. Engine rpm went way down immediately (almost to stalling) but came back up
to about 500-600 rpm and would continue to run even though my finger was still plugging the hole.
6) I did this finger plugging test about 3 times and I can tell you the engine didn’t like it! I took my finger off the hole, gave it some gas by twisting the throttle valve and it would run rough, sputter and then it died twice. Then I noticed the SES light was on. 🙁
7) Started car back up and it went back up to virtually 2900 rpm and stayed there even when fully warm.
8) During the later part of this testing I also tested the egr valve. I applied about 15 hg of vacuum to the egr port itself and the rpm’s did go down but it also started to sputter & bog down too. At this point the engine was running so high in rpm I just shut it off.
I am about ready to quit on this car. It’s getting extremely frustrating. 🙁 Before I started these tests this afternoon, it would at least idle down to 1400 when warm but now its racing at 2900
rpm when fully warm. At this point the car is virtually undriveable. 🙁
Kit[This message has been edited by Kitskaboodle (edited 04-23-2025).]
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cartercarbaficionado
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APR 23, 09:44 PM
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Patrick
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APR 24, 02:14 AM
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| quote | Originally posted by Kitskaboodle:
Put finger inside throttle body and plugged IAC hole/port. Engine rpm went way down immediately (almost to stalling) but came back up to about 500-600 rpm and would continue to run even though my finger was still plugging the hole.
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The engine should've stalled, and you've already confirmed that there is no vacuum leak downstream of the TB. Whether the idle set screw on the TB still has the factory plug covering it or not, IMO the idle set screw needs to be adjusted. If it was me, I'd remove the plug, and then with the engine running, I'd slowly back off the set screw until the engine stalls while your finger is covering the IAC port.
It's possible the TPS would need to be adjusted afterwards, as it's supposed to be .5v with the throttle shaft positioned at idle. (Don't bend the tang. Rotate the TPS unit instead).
There could still be a problem with the IAC valve not performing as it should (due to the valve itself or ECU/sensors/wiring), but one step at a time.[This message has been edited by Patrick (edited 04-24-2025).]
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1985 Fiero GT
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APR 24, 06:17 AM
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| quote | Originally posted by Romsk:
If anyone has a 1985 V6 ECM I can borrow, I should be able to reverse the data streams and code the GUI to process them.
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If you pay for shipping I'll loan you mine, I can ship it from New Brunswick or Maine.
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