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Discussion Starter #1
I recently had the water pump changed, which required the A/C compressor to come out. After getting the car back I have noticed that when the compressor kicks in the engine speed drops below warm idle, and sometimes threatens to stall before recovering. This only happens with the A/C switched on, and the AAC valve operates normally. It behaves like the ECU doesn't receive/respond to the A/C load signal to increase the idle speed. There has been no change to the F-Con map, so I am scratching my head as to what's going on.....
 

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Skyline Section Manager
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Sounds like you have not plugged the A/C pump in properly. There is a wire that goes to pin 46 of your ECU. It is that wire that activates the high idle.
 

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Discussion Starter #3
That sounds quite plausible. I will pop back to the garage that did it and get them to check the connection. I couldn't see anything unplugged when looking from the top of the engine, but knowing my luck I could have a wire break.
 

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Thats where i would start looking. Seems logical.
 

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Something isn't right here.
Pin 46 to the ecu comes from the aircon control unit (centre console) which Nissan calls the amplifier.
Then the ecu sends the signal to the compressor clutch via Pin 9.
This way the ecu can cut the aircon if the engine is driving in a max power situation.
The compressor doesn't have to be removed to do a water pump, just its drive belt.
So if the shop did actually remove the compressor, the aircon would have then been re-gassed at completion of the job and perhaps she got too much?
The AAC won't control idle if the compressor is pumping liquid, compressor won't like it either.
Back to the workshop.
 

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Discussion Starter #6
So if the shop did actually remove the compressor, the aircon would have then been re-gassed at completion of the job and perhaps she got too much?
The AAC won't control idle if the compressor is pumping liquid, compressor won't like it either.
Back to the workshop.
From what I remember the compressor ended up coming out when the water pump was changed due to space constraints down there (I have a bigger radiator). The aircon pump is definitely 'operating' after the inevitable re-gas, but I wasn't present when this was done. I had no idea it was even possible to overfill the system such that the refrigerant stays liquid, and also no idea that this would affect the AAC's ability to control the idle.....:eek:
 

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Sorry James, I presumed your car is a GTR, is this incorrect?
No need to remove the compressor to do the water pump on a GTR no matter how big your radiator as the radiator comes out for easy access to the cam belt region.
Are you sure the AAC is operating properly, plug connected?
Does the idle bump up when the power steer is activated, parking slowly etc?
 

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Discussion Starter #8
Nope - you are quite right it is an R33 GTR, and on checking my records it was the aircon radiator that came out when the water pump was done, not the compressor.

The basic functioning of the AAC seems to be okay (idle speed gradually falls as the engine warms, the adjustment screw does alter RPM, and if you unplug the thing when warmed up the revs noticeably drop). However, this morning I noted that when parked up the engine speed didn't change when I turned the steering wheel, so isn't responding to PAS load either. Surely the damn thing can't just fail in this aspect? :( I will try again later!
 

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You don't need to remove the consensor rad to change the water pump:(

Look at the wiring diagrams I posted in the electrical section.
 

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Discussion Starter #10
You don't need to remove the consensor rad to change the water pump:(

Look at the wiring diagrams I posted in the electrical section.
Having spent yesterday sorting out a replacement AAC valve after stuffing up the feeble plastic cap on mine (and cleaning the replacement), I intended to look at the wiring situation today. Alas it is horribly drizzly out, so I have postponed!

One thing I should have been paying attention to before is the ECUTalk display (whoops). Apparently AAC duty when warm is 2%, then leaps to 40-50% when the A/C kicks in (and revs drop) before returning to 2% when the compressor stops. Does this sound right?
 

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The % rise sounds about right. When the % rises, the revs drop though, yes?
 

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Discussion Starter #12
The % rise sounds about right. When the % rises, the revs drop though, yes?
Yep that's exactly right, whether A/C or sawing at the wheel while staionary. Looks like the ECU is at least trying to do the right thing. I feel some ECU pin continuity tests coming on.....
 

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You are doing the right thing. I'd guess either the air pipe is blocked or it's just not working. Is this the 2nd one you have tried?
 

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Discussion Starter #14
You are doing the right thing. I'd guess either the air pipe is blocked or it's just not working. Is this the 2nd one you have tried?
Yes and this one, thankfully with a brass cap instead of that ludicrously soft beige plastic thing on my original, got stripped completely for a thorough going over with a big can of carb cleaner (as per the numerous guides floating around). As on my original, the warm idle responds when the screw is adjusted; mechanically this AAC seems to be working. From the state of my first AAC I expect the cold start valve round the back of the engine is caked in sooty deposits as well, but cold starting has never been a problem. Gaaaaa!
 
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