2jz-gte (swap), idle up for a/c? [rare schematics inside]

[George]

A friend of mine have recently swapped a 2jz-gte, with a bit of help from me. A little problem we faced is there're no simple means of increasing idle RPM when air conditioning is on.

There's no native Toyota A/C ECU in the car, electrical part of air conditioning system is just a switch and a bunch of wires. As far as I know what we have is quite a rare kind of 2jz-gte, we could hardly find a replacement ECU (the one came with the engine had immo onboard). Here's the schematics that fit the engine (~1.5Mb each)
http://sites.google.com/site/yurybar...sch1_color.gif
http://sites.google.com/site/yurybar...sch2_color.gif

I've tried applying 12V and GND to C1,C4,C27,C28 terminals with no result at all (engine idles on at 650RPM). A fully translated and commented schematic is available here which fits the engine too, but it didn't help as well.

My guess is that the ECU we have is supposed to communicate with a/c controller via some digital line and thus it has no native means of increasing idle RPM by toggling some input to some DC voltage.

Have someone faced a similar problem? My best guess is to tweak the choke position sensor by artificially increasing its output when the a/c is on. Any other ideas?

Also, would be great if the schematics here appear useful.

[wilbo666]

The drawings / diagrams that you have posted indicate that you have a VVTi 2JZGTE for a JZS161, and you are right not many people that I know of have installed these into other cars, although the number is growing

For reference I own that book and have it scanned if you need any other pages from it
(Oh and I have an early JZS161 ECU that I want to sell too, but prbly too late for that! )

My guess is that the ECU we have is supposed to communicate with a/c controller via some digital line and thus it has no native means of increasing idle RPM by toggling some input to some DC voltage.

The below diagram shows your above comment to be correct.

I believe that the engine ECU receives the "AC ON/OFF" signal via the MPX2 pin form the AC ECU. The MPX2 pin is part of the 'Multiplex' serial network, which in the past I haven't been able to find much information on...

There is a little bit of background info in the below doc, but nowhere near the detail required for us to synthesise the serial waveform.. the best bet is to try and find someone that has a complete car / halfcut and get a picture of the waveform of the serial AC ON and AC OFF signals on the MPX2 line from the AC ECU...

http://prius2.grohs.de/ftp/Official%...munication.pdf


The engine ECU triggers the AC compressor clutch ON/OFF using pin 13 on Plug F59. And it also requires the pressure switches in the AC system to be healthy before it would do that I'd imagine.



Another option is to simply use a throttle bypass valve as used on carby cars and have that trigged by your AC signal (A little bit easier! )




Cheers
Wilbo

[triptek]

Another option is to simply use a throttle bypass valve as used on carby cars and have that trigged by your AC signal (A little bit easier! )

Looks like this will be the option i will take.

[wilbo666]

Another option again is to get a JZA80 VVTi ECU as they have the more conventional AC control arrangement (dedicated AC on/off demand pin)


triptek: Shame you pulled your half cut apart before getting a CRO on the MPX2 line! We might have had a change to come up with the elegant solution for this one!

Cheers
Wilbo

[triptek]

Sadly the AC ecu was missing out of the halfcut. I'v only got both of the Body ecu's

[wilbo666]

Bugger, always seems to be the the way isn't it

Cheers
Wilbo

[Z2TT]

Ahh, how is the A/C Idle up controlled then on the JZS161? not by ECU

[wilbo666]

Ahh, how is the A/C Idle up controlled then on the JZS161? not by ECU

Did you read my post?

The idle up is controlled by the engine ECU, but the engine ECU receives a signal from the AC ecu to say if the AC ecu thinks the AC needs to be ON/OFF.

Using the signal from the AC ecu, the engine ECU can determine if it wants to turn the AC on, in some cases the AC ecu will be saying to turn the AC on, and the engine ECU will not turn the AC on (I.e. if you are at 100% throttle)

I believe that the engine ECU receives the "AC ON/OFF" signal via the MPX2 pin form the AC ECU. The MPX2 pin is part of the 'Multiplex' serial network, which in the past I haven't been able to find much information on...

The engine ECU triggers the AC compressor clutch ON/OFF using pin 13 on Plug F59. And it also requires the pressure switches in the AC system to be healthy before it would do that I'd imagine

Cheers
Wilbo

[andrew_mx83]

either an idle air bypass system or grab an electric idle up solenoid off a carby and use it to bump the throttle stop up as required

[George]

andrew_mx83, wilbo - thanks for the idea, I guess its'ok that while some air bypasses throttle, its sensor still reads 0% ?

wilbo - you're right about being bit too late; a couple monthes ago we needed badly some ECU instead of the one came with the engine, and we still don't know a better use for the old one rather than hang it on a wall or something. We however managed to find one ECU in the Far East region, eliminating the need of international mail delivery.

I think I don't need any other schematics, the car is running ok now, but your offer was great for as far as I know it's impossible to find any other pages on the web.

[wilbo666]

You do raise an interesting point about the stock ECU perhaps having issues with a throttle bypass, perhaps it will notice the increase in RPM with zero throttle change and not be happy with this...

Can you let us know how it goes?



FYI: Madmont put some wiring diagrams up quite some time ago (He was actually the nice person who sold me the book )

http://www.toymods.org.au/forums/sho...0&postcount=98



Cheers
Wilbo

[George]

Sure, but not in the near future. We actually tried to put a 6mm T-pipe between intake manifold vacuum connector and something connected there (don't remember exactly what it was, seems like fuel vapor adsorber). What we got was lower RPM and less stable idling. I think the problem with poor idling originated in that we let some air bypass the MAF sensor. As for that car, its turbo is barely alive, we will now wait for a new one and then will dig into the engine once more, probably fixing the AC issue. I will post some info here if we have any success.

[andrew_mx83]

You do raise an interesting point about the stock ECU perhaps having issues with a throttle bypass, perhaps it will notice the increase in RPM with zero throttle change and not be happy with this...

im not up with 2j EFI systems so i may be wrong here, but wouldnt the factory setup simly open the idle speed valve more to increase the idle, with no change in throttle position?

dont see how it would be any different if you were to have another bypass system....

[George]

The fundamental difference here is that the EFI system is aware of its ISC and it does not know that you have installed some other bypass valve. This valve's action is therefore regarded by ECU as unwanted disturbance. So to my mind it's very likely that ECU will try to compensate sudden idle RPM raise due to our bypass valve action, for example by means of said ISC.

[andrew_mx83]

i was thinking that.... but if the goal is to bump up the idle when it drops from the AC compressor kicking in, unless it goes above "normal" idle speed from ur air bypass i cant see the ECU trying to compensate

do you want a higher idle speed than normal with the AC on, or just for it to not drop below normal from the load of the compressor?