b16a idles with pm6 but not pr3

[craftymatt]

I have a B16a swapped into a 91 CRX HF running an OBD0 PR3 ECU.

The IACV does not work when I have my PR3 ECU installed in the car. I've cleaned it out and checked the wiring, even tested it, and it seems to work fine; it just doesn't get actuated correctly by the ECU. Unless I induce a vacuum leak the car will just stall once it warms up (since the PR3 is leaving the IACV closed).
When I install a PM6 though (CRX SI ECU), the car idles great.

....So it's something with the ECU itself. The PR3 definitely recognizes the IACV, if I unplug it while running I do get a check light, it just doesn't ever actuate it.
My understanding of the IACV is that it's simply a pulse-width modulated solenoid. Power is supplied constantly to it on one side and the ECU simply grounds the other side when it wants the IACV to open (raising the idle). Does the PR3 operate differently? Like does it ground the IACV when it wants the idle to drop? Or do I most likely just have a bad ECU?

 

[craftymatt]

also, when I short the connector for timing adjustment it doesn't appear to do anything. Idle speed does not change and neither does spark timing.

I checked the wiring on the timing connector: one side goes to pin B20 on the ECU and the other goes to ground. I assume this is correct?

Basically it seems like the ECU does not ever think the engine is at idle; idle control does not work and the timing connector does nothing.
I checked TPS voltage; 0.5V when closed and 4.5V when WOT. Are there any other sensors/etc that would prevent the ECU from going to idle?

 

[scott@8pm]

Just a thought: find wiring diagrams for each ECU cars. I can set you up with all the HF/Si (PM8/PM6) diagrams, but not the JDM PR3. Get the PR3 diagrams somehow and then go thru both, draw out the ECU connectors, and look to see what matches and what doesn't. You'll have to manually wire what doesn't.

You'll have the A,B, and C connectors (or C451, C452, C453 in the diagrams) and you have to draw a picture of the connectors and label each one twice... once for the PM6 and once for the PR3.

rrrr- did that make any sense after I wrote it?

edit: the A/B/C diagnostic charts don't match the wiring diagrams for the ECU pin #s on the wiring diagrams. Honda wiring diagrams of C451 C452 C453 list pins horizontally 1,2,3,4,5,6 upper, and continue on the lower pins, as connector "A" is labeled. The Honda A/B/C charts go odd/ even. Upper row is 1,3,5,7 like you see on the tubes


That's probably no help either. damn. I tried to be coherent. I'm just no good at it. I eated a butter.

 

[craftymatt]

I compared pinouts when I first swapped in the engine and corrected any discrepancies that I saw. I was just going off internet info though so I don't know if it was 100% accurate.

I did notice that the wire for the ELD (electronic load detector?) is replaced by the knock sensor. I don't see a pin on any of the PR3 pinouts for the ELD though so it's just not hooked up at all. Does the PR3 need that somewhere else in order to idle?

 

[craftymatt]

kinda bringing this back from the dead, but I never figured this out.

Anyway, the IACV still doesn't appear to work; basically my only method of idle control is the low temp idle up valve (the one with coolant lines running into it, I don't remember the actual name). The car idles good and high when cold like it's supposed to, but is much too low when warm unless I induce a vacuum leak to bring it up.

Like I said, the ECU recognizes the IACV (if I unplug it I get a CEL for it), but doesn't actuate it. I pulled it out and tested it, it seems to be within specs and opens easily if I hook a 9v battery to it. I even tried a different PR3 ECU but saw no change.

I don't know if it's related but the timing connector still has no effect if it's shorted. I've traced the wires for both the timing connector and the IACV, and both seem to go to the correct pins on the ECU. What's going on? Has anyone else had problems like this?