Looking for advice on next investigative steps. Searched but didnt find anything promising.

Oh, the a/c works amazing well. Which in Texas is a good thing.

90 vert. NA auto converted to JDM Tii and 5-speed. Zeitronix w/b, RTek2 in a 370. Street ported. New - in the last few years - TPS and dashpot from Ray @ Malloy Mazda.

Here are a few short vids showing a cold startup, Zeitronix data logging and beautifully smooth idles (both warming and warmed up).

You'll see that when warmed up the TPS is at 1.02v plus yesterday I checked the TPS with the LEDs and only one light is on. And I swapped the negatives just to make sure both LEDs are working.

Here are the vids. Appreciate yall taking a look.











I browsed the EFI section and the deceleration system seems to be pretty sophisticated (more than just the dashpot) and I suspect there may be something missing from the conversion (USDM->JDM, NA->Tii, AT->MT).

Thanks a bunch and appreciate any leads.

 

The TPS is used in fuel cut. And what is the voltage output of your alternator w/A/C on and idling?

 

Hmmm... A line of investigation I hadnt anticipated. Good! In all cases the engine is fully warm and the e-fan is off.

With the a/c off:With the a/c on:

 

Is that with the efan running?

 

If you mean the voltage readings thenn yes, they are with the e-fan Off for consistency.

It would die at stop signs with the ac on before the OEM plastic rad split and we replaced it with the GS rad and GM e-fan.

 

I read the Decel section of the EFI chapter of the FSM and the only two other inputs the ECU uses are the Neutral and Clutch switches.

So I went to back probe them and was surprised to find the 1Q the clutch switch had no wire at all. I guess because it was an AT car.

And the Neutral lead 1R showed 12v regardless of what gear the tranny was in. We used V8Killer's swap thread and it looks like he just disables the Neutral Safety Switch so we probably did too. I'll have to go under the car to see if we even wired those up. We have reverse lights!

 

For a test to see if the lack of the neutral safety and clutch switches are the root cause of the engine dying at stop lights if the a/c is on, I was thinking of back pinning 1Q and 1R and chassis grounding them. If I'm reading the FSM correctly thats what the switches do.

Does that sound right?

 

The Neutral Switch voltage should be 12 volts in all gears, but 2 volts or lower when in neutral. Clutch Switch has 12 volts when depressed otherwise it's 2 volts.

 

do you still have the BACV ?

 

Satch, yes I know. I just want to make sure that if I ground 1Q and 1R that I wont fry the ECU.. My read of the FSM says that is all the two switches do.

Rob, yes. The BAC is installed and functioning. In my first post the last video shows the BAC increasing the rpms from the 875 range to ~1040 when the a/c is turned on.

 

The statement in post #7 confused me when you mentioned the grounding of the Neutral Switch as you said that's what it does. If you pulled up to a stop light would you not still be in gear? If so, then the voltage at that ECU pin would then read 12 volts and not a ground so you would not be reproducing what it should be by grounding. I must be missing something here unless your goal was to try the opposite of what it should be?

Also, what are your alternator voltage output readings not just at idle w/the A/C running, but w/the brake depressed. Are these the numbers you provided or are they different or is this rather not possible to tell since the car dies? You might want to try disconnecting the Brake Light Switch from the brake pedal and reproduce the problematic scenario you encounter, but do this in the driveway. You might find that the voltage drain w/the pedal depressed is a bit too much for the engine to overcome.

And lastly, does this problem occur regardless of whether the engine is warmed up or not.

 

I just got my AC working after a few years and started having the same problem as you anytime I came to a stop light with the clutch in it would die.
After some reading, I remembered disconnecting the clutch switch at some point so I could use my cruise control, so I hooked the switch back up and it solved the AC problem.
The clutch pedal is missing the small rubber stop to actuatoe the switch so now I need to find one or as I've read about people superglueing pennies to the spot

 

vrracing- i didnt watch the videos

is there no voltage compensation with that software? than again even then the idle coming up should be all it needs

you are saying it worked and has since then stopped working right?

 

When the engine dies in the last video in post #1, the parking brake is on and no pedals are being pressed except the accelerator. The only load on the engine is the a/c and the interior lights since the doors are open.

My harness has no wire for 1Q, the clutch switch. 1Q, the third hole from the left in the rightmost harness plug is empty. I believe that the neutral switch is not connected because 1R shows 12v no matter what gear it is in. We used V8Kilr's writeup (probably five years ago now) and here is what he says on what I believe is the neutral safety switch...

I bet the "bottom two" wires are the neutral safety switch equivalent from the a/t. He doesnt connect anything to the m/t's neutral safety switch. The red wires are the reverse lights.

So my thinking - as I tried to express in post 7 - is that I could trick the ECU into thinking that the clutch switch and neutral switch were working by grounding 1Q and 1R respectively. If I'm interpreting F2-77 and 78 correctly, both 1R and 1Q should be outputting 12v (we know that 1R the neutral switch is outputting 12v but we didnt backprobe the 1Q hole in the harness plug) which would mean the ECU thinks the car is always in gear and that the clutch pedal is always released; basically driving around. My theory is that when the car is being driven around the momentum is more than enough to accommodate the load of the a/c.

This theory is reinforced by the fact that if he engine brakes to a stop and releases the clutch as he's coming to a stop the engine doesnt die even if the a/c is on. As far as I can tell the FSM never explains why the ECU looks at 1Q and 1R when decelerating. But on our car the ECU is blind to both.

I can check the voltage with the brake pressed but since it is dying free revving it in the garage with just the a/c without the brake being pressed is there any value in doing that?

Thanks!

 

Thanks, Gambolt. I'd recalled seeing something along these lines but searching here and the other forum I couldn't find it. Thanks for reinforcing the fact that I didnt imagine that!

 

Oh Rob you're killing me! Those vids are pure art!

I don't know what the RTek does with the voltage. It didnt seem to update very frequently so I would discount the value and credibility of those numbers.

No, this is not a new problem. We have been fighting a poor (annoying not fatal) idle since the Tii swap five years ago so the dying at stoplights has not been a focus. We had the a/c charged with R134a three years ago and it blows fridged air. We replaced the TPS with a new one from Malloy, the TID with the Corksport aluminum one, replaced the BAC with our old NA one, and recalibrated the TB and now we have a beautiful flat idle.

So now the dying at stop lights with the a/c on and the outside temp in excess of 100 has popped up to the top of the list!

 

How do you adjust idle w/the NA BAC. Doesn't a turbo not have the idle adjust screw located on top of the engine as an NA does, but relies on the BAC idle adjust screw?

 

the Jspec engines didn't have an idle adjustment screw on the BAC, nor did they have an idle adjustment on the throttle body itself like the n/a engines did. they only really have the throttle cam adjustment screw for idle compensation outside the BAC valve. the Jspec is also missing the alternate idle solenoid that connects to the intercooler for higher engine loads like power steering, i do not recall if it was supposed to open with the air conditioning though. i have no real idea how they controlled the idle on the JDM market engines since there really is only the BAC valve and a basic idle setting.

could try getting a USDM TII BAC valve which will allow a certain amount of air to bypass and may assist with the idle dip on deceleration. on n/a engines if you adjust the throttle air bleed screw in too far it would start to dip due to lack of airflow when settling down to idle.

the stock top mount intercooler would block the idle screw on the throttle body anyways so mazda never had them put it on the TII throttle bodies, it would also be underneath on the TII engines since the throttle body is flipped upside down.

 

Yes, we use the big idle adjustment screw on the TB to adjust the idle. And actually we have a USDM BAC on there (NA actually) but the JDM UIM doesnt have the hole for the bleed screw air to pass thru. The BAC does work however and boosts the RPMs up more than 100 rpm when the A/C is turned on.

Here is the 1991 wiring diagram and it appears I can easily fake the clutch switch by grounding 1Q to the chassis.

 

We use the big screw I'm pointing to to set the idle. And as Karack notes that's why we have our PVC intercooler.

 

try grounding the clutch switch, if that doesn't help try adjusting the idle up with that screw as far as you can before the BAC cannot bring it down into idle mode below 1k. that will give it the most breathing room to bring the idle up when under a load.

 

Sounds like a plan.

When we set the idle we grounded the ISC and disconnected the BAC. I assume that the ECU records the current RPM as the target-RPM when the ISC is disconnected. Then we adjusted the idle with that big screw I'm pointing to. Seemed to work. The idle was at 750 before but we moved it up to the mid to high 800s as an attempt to fix the dying with a/c at stop signs. but it wasnt enough.

 

i know it's not the proper way but in my experience the BAC solenoid gets lazy over time. the 750RPM target is a little unrealistic for these cars now.

make adjustments with the engine fully warmed or it may be out of range after the engine does warm up. hotter engine requires less air to idle at the same level it was when cold.

 

Yes, we always adjust the idle with the engine fully hot. With all the data logging we can get from the RTek and Zeitronix it's pretty easy as I can watch the coolant temp on the RTek (thru the Sony Clio Palm) and I can watch the thermowax let off the throttle thru the TPS voltage on the Zeitronix.

 

Gambolt wins a prize! We pushed a paperclip into the back of the empty 1Q socket with a wire grounded to one of the ECU mounting studs. It took a bit of wiggling but the tone of the engine definitely changed. Hmmm... So when the car was hot we verped it with the a/c on it oh so gently and smoothly reduced the rpms to idle.

So we checked the clutch pedal to see if there were two switches but alas there was only one. I think that means our pedal set came from one of those crazy 86s?

My plan now is to tap into the line that comes from the clutch switch which I believe allows power to go to the starter. I'll put a relay on that and use that to control when the ECU sees the clutch being depressed.

I guess to completely fix it I'll need to get the neutral safety switch wired up too so that if he quickly takes it out of gear and releases the clutch pedal it doesn't die.