b16 bad idle with PR3, good with PM6
11-18-2008, 10:37 AM
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b16 bad idle with PR3, good with PM6
I have a 91 CRX HF with a B16a running OBD0. I am using a PR3 ECU and I have both oxygen sensors installed correctly.
The car idles very low when warm, like 300 rpm with occasional stalling. When cold it seems normal, like ~1500 rpm, but once it starts to warm up (and the FITV starts to close I'm guessing) the idle comes down to 300 rpm.
My first thought was the IACV, so I took it off and cleaned it, and checked to make sure it moved freely. I even tested it on the car as per the crx manual and it appears to be working (it 'clicks' like the manual says it should when you short A11 on the harness plug to ground). As far as I can tell though, the PR3 ECU never opens it so the idle just drops to ridiculously low rpm.
Just for the hell of it, I decided to swap out the ECU with the one from my 88 Si (PM6); when I started it with that ECU the idle came to a nice and solid ~800 rpm (car was already warm). With the PR3 it was stalling at idle, and by changing nothing but the ECU the car would suddenly idle beautifully.
Another issue I notice is that when I short the timing connector to set the spark timing on the PR3 nothing happens. Spark timing remains constant and idle speed doesn't change at all.
So basically:
PR3:
-very low idle speed/stalling (IACV not doing anything)
-shorting the timing connector does nothing
PM6
-everything is fine
Seems like the PR3 just never goes into its "idle loop"; if the ECU never thinks it's at idle it won't open the IACV and it probably won't respond to the timing connector.
I checked the TPS voltage; 0.5V closed and 4.5V open
Also checked the timing connector circuit; one side goes to pin B20 on the ECU and the other goes to ground, is this correct for the PR3? (I think B20 is correct but is it supposed to go to ground or 12v on the PR3?)
The car runs well otherwise; 40-50mpg on average and seems powerful enough, the idle just doesn't work. Currently I'm getting it to idle by allowing a vacuum leak, but the idle speed isn't very stable that way.
Is there something in the wiring I need to change (like does the PR3 use a different pin than A11 for idle control?) or do you think this ECU is just bad? I opened it up and didn't see any damage nor did it appear that the chip had been changed, but I don't really know.
The car idles very low when warm, like 300 rpm with occasional stalling. When cold it seems normal, like ~1500 rpm, but once it starts to warm up (and the FITV starts to close I'm guessing) the idle comes down to 300 rpm.
My first thought was the IACV, so I took it off and cleaned it, and checked to make sure it moved freely. I even tested it on the car as per the crx manual and it appears to be working (it 'clicks' like the manual says it should when you short A11 on the harness plug to ground). As far as I can tell though, the PR3 ECU never opens it so the idle just drops to ridiculously low rpm.
Just for the hell of it, I decided to swap out the ECU with the one from my 88 Si (PM6); when I started it with that ECU the idle came to a nice and solid ~800 rpm (car was already warm). With the PR3 it was stalling at idle, and by changing nothing but the ECU the car would suddenly idle beautifully.
Another issue I notice is that when I short the timing connector to set the spark timing on the PR3 nothing happens. Spark timing remains constant and idle speed doesn't change at all.
So basically:
PR3:
-very low idle speed/stalling (IACV not doing anything)
-shorting the timing connector does nothing
PM6
-everything is fine
Seems like the PR3 just never goes into its "idle loop"; if the ECU never thinks it's at idle it won't open the IACV and it probably won't respond to the timing connector.
I checked the TPS voltage; 0.5V closed and 4.5V open
Also checked the timing connector circuit; one side goes to pin B20 on the ECU and the other goes to ground, is this correct for the PR3? (I think B20 is correct but is it supposed to go to ground or 12v on the PR3?)
The car runs well otherwise; 40-50mpg on average and seems powerful enough, the idle just doesn't work. Currently I'm getting it to idle by allowing a vacuum leak, but the idle speed isn't very stable that way.
Is there something in the wiring I need to change (like does the PR3 use a different pin than A11 for idle control?) or do you think this ECU is just bad? I opened it up and didn't see any damage nor did it appear that the chip had been changed, but I don't really know.
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Honda CRX / EF Civic (1988 - 1991)
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