satch

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Foxed.ca - Mazda RX-7 Manuals

spectre6000

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Found it. I went through and checked every single wire and recorded the voltages. I'm comparing them to the manual now. Will report shortly.

spectre6000

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The following are measurements that read off spec. It should be noted that I'm using an '88 manual and checking an '86. I assume are be a few differences, but would like some clarification if and when possible.

pin....actual............................connected to................................................ ........Anticipated
1K.... 12V...............................shift indicator light............................................. ...should be below 1.5V key on, ~12V idling
1W... 12V (on, not running)......Heat hazard sensor............................................ ...should be below 1.5V/~12V idling
2F.... 0.84V............................Variable resistor.......................................... .........should be 1-4V depending on adjustment
2J.....1.34V............................Air flow meter (intake air temperature sensor).........should be 2-3V @68°
2L.....5.99V............................Intake air temperature sensor (dynamic chamber)...should be 1-2V @176°
2Q....1.39V............................Bypass air control valve ........................................should be 8-12V “Engine signal monitor green and red light flash”

I'm pretty sure I should be getting a few readings different from the '88 spec because I know my shift indicator light is functioning as it should.

I have no idea if the heat hazard sensor works because I haven't had an occasion (nor do I wish for one) to test it. It checks in spec when idling.

The variable resistor is out of spec, but maybe it's adjusted all the way in one direction. If I'm running super rich, it could explain a lot of what I'm seeing. Maybe it's adjusted all the way rich or it's been leaned out all the way to compensate for something?

Air flow meter and intake air temperature sensors are both out of spec, but the actual temperature of the air they're sensing could be different from the specified temperature. There could also be differences in spec for the year?

The bypass air control valve reading is off, but it doesn't have any monitor to play with... Could be a function of not having that specific tool, a model year change, or it's truly dead...

Could someone (Satch?) weigh in on this stuff?

spectre6000

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It should be 1 o'clock in relation to what orientation? If I'm leaning over the PS fender and looking down at it, it's at about 12:15. It's 3:15 though if I'm looking at it from the front. The measured voltage is below the low end of the 1-4V spectrum. If that means it's rich, I might be in luck. If that means it's almost all the way leaned out, I have issues.

satch

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2J measured 1.6 volts on my car w/the air temp at 60 degrees. And the FSM says it should be 2 to 3 volts when the temp is 68 degrees. Again, the lower the air temp the lower the voltage.

2F measured 2.77 on mine and I think it was set fairly rich. All the way to left is lean and to the right is rich. I'm going to guess you have yours relatively lean. Again, it should be more rich than lean thus the screw slot should be to the right of the half way mark.

2L is w/the engine warmed up. You might want to check it w/the engine warmed up to see if it follows form but your reading seems high. There is a way to ohm out the sensor as specified in the FSM in the ECU & emission section.

1W measures .86v w/key to on w/my car. Not sure why yours reads as it does.

2Q seems way off but do you even have the BAC and if so is it connected? It would read very very low if the key was put to start as the solenoid goes full open. Maybe you could retest the pin while the engine was idling. The wire is Blue/Green so make sure you tested the right pin/wire. If it reads really low then your ECU is telling the BAC to go full open and it should not do so w/just key to on although the engine should be cold as the BAC will operate even after the car has been run and the engine shut off (the solenoid would make a noise/vibrate in this instance).

j9fd3s

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Variable resistor: works exactly like an idle mixture screw. you should try adjusting it. it has about a 90 degree sweep, and if something is wrong it'll usually be maxed out. if everything is working it won't be maxed out.

re air flow meter: the spec is the same 86-88.

the Bypass air control valve, you might want to recheck the connector. its a solenoid, that the ecu grounds, so with the key on engine off voltage should be high.

spectre6000

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I just went out there and dicked with the variable resistor (idle mixture screw). It was almost all the way lean. I jumpered the thingy, and turned it all the way rich. It smoothed right the hell out and the screw on top of the intake started doing its job! Finally some freaking progress! I know altitude tends to cause you to have to lean things out, but that must have simply been too much. Maybe someone was trying to pass emissions? Regardless, I was able to dial in the idle speed/mixture to some degree. It didn't respond quite like I would have expected a carburetor to with the same type and degree of manipulation, but it was leaps and bounds better than what I was getting previously.

I turned it all the way rich, then adjusted the idle speed screw on top of the manifold to the idle speed I wanted. It stopped backfiring and smoothed right out. I then leaned it until it started to back fire a little, backed it up a bit, rechecked the idle speed (which didn't really move much), and got it to where it didn't backfire and idled smoothly. It smells a little on the rich side, but any leaner and it wants to backfire in the exhaust.

Then I turned the key off, pulled the jumper, and turned it back on and went for a quick drive. Frustratingly, with the jumper out, it idles higher and backfires a bit more. I still have no idea what the stupid jumper is technically doing, but I must be doing it wrong.

What's up here?

spectre6000

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it was probably 75°-80° or so here according to my weather app when I was doing this. In the sun, it might have been warmer.

I haven't rechecked it since I adjusted it just now, but I think this should be rectified.

[QUOTE=satch;11893964]2L is w/the engine warmed up. You might want to check it w/the engine warmed up to see if it follows form but your reading seems high. There is a way to ohm out the sensor as specified in the FSM in the ECU & emission section.[/qoute]

That had the engine warmed up, but it had certainly had some time to cool while I went through and took all my readings. It probably bears a second look immediately after a drive.

It reads correctly with the engine running, and that's arguably when it matters. I'm not sure either, but this one is maybe a bit lower on the priority list for today.

The BAC is certainly present (that's the thing that was mentioned earlier with the coolant lines and an air line off the side of the intake manifold, right?). I unplugged it earlier, and it looks like Clokker or myself must have greased it when we were doing the injectors and vacuum lines. It looks like it has some adjustment to it via a hex key. Maybe it needs some attention in that regard. If its purpose is to keep the idle speed from dropping below 750RPM, then given my issues starting between cold and hot it could be having some trouble.

satch

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The jumper slows down the BAC to a trickle. Your reading of the BAC was way wrong so you need to do some more investigation. Recheck the pin voltage once again as suggested w/key to on and while idling.

Don't mess w/the hex nut as the NA BAC is not adjustable. You'll just damage the item if you mess w/the nut.

Again, one terminal w/voltage and the other with a ground and it should click each and every time.

spectre6000

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Mine has far more than 90°. I want to say there's a little over 180°. It had a little room to go still in the lean direction, but it was certainly most of the way lean.

I actually had the MAF out of the car when I did the coolant flush. I was attempting to see if I could pull the radiator at Clokker's suggestion, and hadn't seen one of those bail type electrical connectors before... I unscrewed the plug from the MAF instead of unplugging it properly, and pulled the guts out. I grabbed Felix, and he found a schematic and tested it for spec. It checked out with flying colors.

spectre6000

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2Q (BAC) with the engine running at idle measured ~9.9V. That's more in keeping with expectations.

That said, it died when I started it up just now. I turned the key, it revved up a bit, then just died. This was starting it between hot and cold, and if I feathered the throttle for a few seconds it would hold an idle. Not the happiest idle, but it was ticking over.

satch

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Supposedly messing w/the screws of the AFM plug will damage the item.

There is an internal fuel switch to the AFM. Perhaps yours is acting up. Jumpering the fuel check connector will bypass this switch. Try it out and see if the car behaves better and doesn't just die on you.

If the fuel switch were not acting as it should the car would die immediately after starting up.

spectre6000

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I just retook some measurements. The adjustment of the variable resistor put that back in spec handily.

Current off specs

- shift indicator light with the engine off/key on (it functions like it should, and it's in spec with the engine running)
- heat hazard sensor with the engine off/key on (no idea on function, but it's in spec with the engine running)
- Air flow meter intake air temperature sensor is just off all together.
- Intake air temperature sensor in the dynamic chamber is also all together out of spec
- BAC is out of spec with the engine off/key on, but is in spec with the engine running

I managed to get the engine to idle about as good as I would expect it to (it smells a little rich for my tastes though) with the jumper in. With it out, it idled faster initially, then it started wandering and backfiring a little again... Then when I tried to start it between hot and cold, it wanted to die on me. What gives?

satch

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The temp sensor in the dynamic chamber is used for hot starts and maybe this is why you have idling problems in this instance. Again, use the FSM to check the ohm spec of the sensor.

spectre6000

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Dumb question maybe, but where is the dynamic chamber temperature sensor?

I'm looking at the manual, and I see a picture of the plug in the diagram. I have a plug that I don't recall being hooked to anything, but I don't know what it would hook to... Is the dynamic chamber air temperature sensor part of the solenoid looking setup that hangs below the manifold with the large air lines? Where is this bad boy? I can't test it directly if I can't figure out what the hell it looks like..

satch

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It's located near the oil sender (just to the left of the oil filter). It has a plug w/two wires and you know the color of one, Green, as it runs to pin 2L, and the other wire is a ground that will be Black or Brown.

spectre6000

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The bastahd was unplugged... With all those empty diagnostic plugs everywhere, I didn't think anything of it. Now I have to go reassess a bunch of things. I started it, and it fired right up and launched into it's not hot but not cold routine like it should. Going to go warm it up and re check a few things now...

spectre6000

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OK. Measuring. Driving. Yadda yadday. PITA.

It's behaving much better with the DAC temp sensor plugged in. I measured it plugged in, and it's still out of spec though. It's supposed to be between 1-2V at 176°, and it measured at 2.80V at an entirely unknown temperature. It instantly behaved better with it plugged in, so maybe it's getting an off reading from having been unplugged, and between both intake sensors being effectively dead, the temperature actually got hot enough to cause it to read out of spec. Is that something that can be replaced? It doesn't look super easy to get to, and may even be built into the manifold somehow.

I rechecked the temp sensor in the MAF at the ECU, then I checked it directly. Seems it's toastified. No connectivity at all for the temperature section. I can pull it out and see if it can be salvaged, or at the very least make dead certain it's not testing like it should, but it's not looking good.

I'll fiddle with the heat hazard sensor when I have more time. Probably this weekend.

Am I going to do any damage driving it with a dead MAF air temp sensor? An out of spec DAC air temp sensor? A potentially unhappy heat hazard sensor? They're all connected to some degree, so it seems less than a great idea, but there are still things I need to be able to do. If I need to park it until I can get those fixed, I need to know.

spectre6000

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Oh, I also tested the BAC directly. The manual states that with the jumper in, unplugging the BAC should cause the engine to slow noticeably. If it did, it was barely noticeable. After that, there's a separate test for measuring the resistance of the BAC. I did that as well. The spec is 10.7-12.3Ω, and it measured out at 14.0Ω... Thoughts? Maybe if things were hotter than they should have been from the temp sensors being AWOL, it upped the resistance beyond spec, and under more normal circumstances it would be back in spec?

clokker

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The heat hazard sensor is located in the cabin, under the passenger seat.
It's meant to monitor the heat from the cat, from inside the car.

I don't think it has any effect on tuning/running.

satch

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The voltage of the dynamic temp sensor can be a bit off and not a big deal. Mine reads 3 volts fully warmed and 2 volts w/key to on and I don't think it matters much. The number you are currently getting is much better than 6 volts when previously measured. The dynamic sensor is replaceable (never removed one and guess it takes either a small open ended wrench or possibly a deep socket wrench.

W/respect to the BAC if you have the car running w/the fan on and pull the plug to the BAC the engine should behave as it should want to die. The plug to the BAC does not come off easily as there is a wire ring which locks the plug tightly into place such that you would think the plug is glued on. If the plug just slides off easily then the lock ring must not be there. If it is not you might want to see if the plug can be pressed upward to create a better contact w/the BAC while the car is idling to see if there is a change in the sound of the engine.

The voltage you got at the ECU for the BAC w/key to on was way off and the driver in the ECU might be damaged. Do you remember what the voltage for pin 3B was w/the key to on. It should be close to 1 to 2 volts. If it was erroneously higher such as close to 10 to 12 volts then that might explain the BAC voltage reading.

spectre6000

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Good to know it's not a key payer, Clocker. '86 is before the lights had a test mode, so it wouldn't surprise me if it's just different. The reason I haven't messed with it yet is because I didn't want to tear apart the interior.

Is there a suggested part number? There are too many temp senders on these newfangled things... Mine is only 2.8V hot and running, and I didn't retest it off.

The engine did not even come close to trying to die. The plug is in tact and just as difficult as you described.

3B was 0.03V key on, engine off. This is within the expected range. The BAC read within spec if the engine was running... Is there a part number for that bad boy? It sounds like it's not happy.

spectre6000

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What sort of damage could occur driving it as is?

satch

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I don't know. The thing you would probably want to look out for is the exhaust manifold glowing. If not, just take it easy driving the car.

Mazdatrix will have a replacement part for the temp sensor.

The BAC is rather expensive I think if you could even find one new, so buying a used one might be required. I stated earlier, the engine would want to die if the plug was removed w/the fan on and engine idling. Did you actually pull the plug or what?

spectre6000

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I did pull the plug. It didn't die or come close.