A/C with MS
 

I was thinking about doing a complete standalone and I was wondering what exactly wouldn't work without the stock ECU. Will the A/C still work?

Thanks for your help

You don't mention what year you have, but on a 90 I can't find any reason why you would have trouble. The only thing I can see related to the stock ecu is the bump in idle speed when the compressor kicks on. I haven't seen as AC system intergrated with MS, but I'm sure it could be done.

This is really the only reason I'm running MS parallel with the stock ecu. Someday maybe, but knock control, WI, and boost control will come first.

I'd imagine with closed loop idle control it would be easy. Aussie Driver got it to work I think, but I never got it working too well on mine. No big deal since I don't have AC, but it does idle too low with the lights and wipers on.

His car is a '99.

Not sure on the '99. On the '90-93 the AC will not work unless the stock ECU tells it to (or something tells it to). The AC controls tell the ECU that you turned the AC on, and the ECU then turns the AC on. It's overly complex to be honest with you. No reason they couldn't have had the AC controls turn the AC on, and just send a signal to the ECU so it could idle up.

We've developed a rather custom solution to correctly interpret the signal from the AC controls and activate the AC system, properly accounting for this... but we don't have a standalone daughterboard available with the circuit, it's part of something else that's in the works to be revealed soon.

There are two wires to the A/C to the stock ECU on a 99. (lt grn/blk and blu/blk) I assume it's an input from the console and a trigger for the A/C clutch relay. There are extra I/Os on the MSII but I'm not sure about the MSnSE. Might take custom code to bump the idle, too, but I wouldn't be surprised if somebody's done this before.

I don't have a FSM, just some ECU schematics ripped from the net so the only thing I'm sure of is the wire colors. The rest is just a WAG.

Yeah, I looked over the diagrams too quickly. Looks like pin 1Q and 1S are involved. My mistake.

Jerry...I keep hearing hints of what is to come from diyautotune...you tease!

I didn't realize you were in Duluth. I keep saying I need to go MS. I hope what you announce soon convinces me!

I can neither confirm nor deny the very fun and interesting Miata related projects that we've been working on lately, the loaner Miata that's been in front of the shop for two months as well as my main DD, or the two Miata's I'm either still looking for or already in the process of buying for further development....

Wait a second... doh!



BTW --Shop is in Suwanee now as we outgrew my basement and spare bedroom last year-- feel free to drop by sometime...

:bigtu: Tease!

Thanks for that


I'll be wireing up (complete rewire) the MS in mid-april, I hope I will be able to use only MS to run everything.

If you do go complete stand alone please post and tell us how it went.

Some have swapped in a 97 alternator. There are after market thermostats to handle the fans. The variable intake could be disabled on a turbo. Still not sure about the A/C. Anything else?

My car doesn't have VVT-i so there is no problem with that. I have a Escort GT alternator if I will have to swap it, and I will let you all know how did the install go!

Has anyone got the AC to work? This is the last part for me to finish my fully stand alone system.

DB

I'd like some info with this too..

Actually, I'd like some A/C, Cruise, and IAC info for the 94-97 1.8...

The PNP system on diyautotune.com shows it'll work with A/C...

Yep, it works. However, I do find that the idle compensation reacts a little too slowly when the a/c kicks on at idle. My RPMs will drop for a second before the idle comes back up to normal, and sometimes the car will even stall. I'm thinking that behavior can be tuned out, perhaps with the adaptive idle control and/or dashpot settings.

It will drop down a bit before recovering, it should not stall though. If it does there's something else going on and it can be tuned out. Could be the base timing off, AFRs around idle out of line, TB idle screw adjusted too low, something.

Checked the TB idle setting - looks good. Idle AFRs are at about the leanest that doesn't cause an oscillating idle. Considerably richer than stoich, anyway. Base timing is at 10deg, verified with a timing light per the MSPnP instructions.

I goofed around with the dashpot settings tonight just for grins, but all I succeeded in doing was causing an oscillating idle so I set them back to your (DIYAutoTune) default settings which do give a very smooth idle overall. :)

I'm wondering if this a/c drooping issue has anything to do with the elevation I am driving at, and the low relative barometric. My house is at 8,600ft and I see 20Kpa at idle. My low speed idle is set to 900 RPMs. It is drooping to about 400rpms when the a/c is switched on. That has caused a stall just twice, both times in Denver (5,500ft) when the ambient temps were over 95F.

(Sorry for the thread hijack)

The elevation difference could play a role-- it was tuned at about 1100ft. Idle is about 27-30kpa with AC off. I'd expect the biggest role to be in the tables. That bottom row (19kpa) is considerably leaner than the second row at 26kpa and may need to be fattened a bit if that's closer to where you're idling. I've found these cars idle best at 13.3:1 on a batch injection system, and that's where they are from the factory on the 90-93 cars batch system as well. Richer would be fine though unneccesary, leaner will cause a weaker idle and a slight miss.

Which base map is your map based off of?

Yes, I'm definitely idling in the bottom row in the VE table. The map was the "with MAF" basemap that came with the MM9495 that I had shipped to me last week. I don't have my tuning laptop here with me to verify the file name, sorry (can check it tonight).

The car goes onto the dyno on Thursday for a baseline (prior to supercharging), so I can more accurately verify the idle AFRs then. Right now, the narrowband is just showing it pegged at max rich while idling, and I suspect it is in the 12:1 - 13:1 range.

Thanks Jerry.