Hey guys I finally decided to post in the "big boy" forums.

Lets dive in. I have a 1986 S4 N/A RX that I've been slowly getting to run since November. I've got it to the point where I can start the car but I can't drive it. The only way the car will start is if I hold open the flap on the AFM to let air in. I talked with a local guy that knows a little more about rotaries than I do, and he said the AFM is bad and I need a new one. I bought a brand new one (autopartswarehouse) and installed it and I have the same problem, won't start unless I prop open the flap, and if I take out the prop the engine dies.

Possibly unrelated, but it smokes A LOT when I start it (I've started it twice this way for a few minutes each, it never gets fully warm). There is no coolant missing and only a small amount of oil is gone so I assume that this is the infamous oil burning I've heard about since the car has been sitting around for around a year.

Here is where I need your help. What am I missing? There is only one thing I can think of, and that is in the photo attached to this post. There is one wire missing from the plug in that goes into the AFM. If that is the problem, where does it go into? Any thoughts? Sorry for the novel length post, I'm just trying to be thorough.

 

Attached is a view of the afm plug in when it is attached. I did the test on the AFM as per the service manual (Page 4A 54, S4 service manual) and here is the results.

E2 - VS (Suppose to be 50-500 ohms) I got 330 ohms
E2 - VREF (Suppose to be 200-500 ohms) I got 280 ohms
E2 - THA (Dependent on temperature, measured at 78 degrees F) I got 1721 ohms
E1 - FC (Suppose to be ∞) I got ∞

Now for the flap
E1 - FC fully closed (Suppose to be ∞) I got ∞
E1 - FC fully open (Suppose to be 0) I got 0
E2 - VS fully closed (Suppose to be 50-500 ohms) I got 310 ohms
E2 - VS fully open (suppose to be 50-500 ohms) I got 84 ohms

Suggestions? Ideas? I'm stumped. Like I said in the previous post the car will only start if the flap is propped open, and if I take the prop out the engine dies.

 

Really? Nobody has any idea? I really don't want to tow this car an hour and pay out the rear for a rotary specialist to just tell me I missed something simple.

More notes that may be important: if I rev the engine when the prop is in the flap, it sputters and if I rev high enough it dies (I assume not getting enough air since I can't prop it open all the way) also the smoke is white and I don't smell anything odd (no sweet smell or smell or anything burning)

 

The wiring diagram will show you that there are 7 wires for the AFM plug. You appear to be missing one of the ground wires but the diagram doesn't indicate which one. You can narrow down your problem as follows. Look for the fuel check connector. Has two wires where one is Black while the other is Brown. Both of these wires are found in the AFM plug. If you conduct a continuity test on these two individual wires you should then tell which wire is missing. If you can find continuity on both wires then the missing wire would be an engine ground.

 

The low Z harness is missing one AFM wire. The high Z '88 harness has all wires accounted for.

My opinion: don't worry about your missing wire. Chances are it's normal.

 

Yes, go for the easy stuff first. Someone mentioned the fuel jumper plug. Go here:

https://www.rx7club.com/2nd-generati...erence-671004/

Shows fuel pump check connector and circuit opening relay.

With ignition on, jumper fuel pump check connector. Leave the AFM alone put plugged in. Start engine. Does it run now? If yes, check the circuit opening relay (unplug, remove and test) - use the FSM wiring diagram to test it. See sig below for FSM.

 

thanks for the suggestions guys I'll check them out on my next day off. Right now I'm working 2 jobs so it might be a few days...

 

Update: its been a long two months and I quit one job. Finally time to work on that RX! if it was only not 100+ degrees around here. ANYWAY

STILL having problems. Here is my results from testing.

I checked the continuity in between the matching colors of the fuel pump check connector with the wires on the AFM. Ignition was in the "on" position with battery cables properly connected. Here is what I got.

116.5 OHMS from the black wire on the check fuel connector (top of image of fuel pump check connector photo) to the third from right (facing from passenger side tire, in the AFM connector photo as the connection next to my finger. This is listed in the FSM as "E2"). Hopefully my crudely drawn image will help explain.

The other wire from the fuel pump check connector (orange with blue or black dot) has NO continuity with ANY of the wires on the AFM connector.

I then thought the missing wire is obviously the one that would correspond with the wire on the fuel pump check connector, so I got a jumper wire from the fuel pump check connector and plugged it in the missing spot on the AFM connector (using similar gauge wire possibly 16 gauge. I don't have any wire connectors laying around so i just had exposed wire plugged in both ends). I then tried to start the car by jump starting it with another car (this car has been sitting around not starting for almost a year). No start.

Any more ideas guys? The closest rotary shop is about 120 miles away from me and I don't have any way to tow it. Or the money to have them fix it, nor do I trust any of these piston mechanics in town with it. I apologize for the long post, but my wife has been on my case about the "driveway paperweight" haha

 

There is a fuel switch inside of your AFM. The fuel switch has two wires running to it. There will be no continuity between these two wires w/key to on, start yes, on nope.

Also, one wire in the fuel check connector runs to the AFM but the other wire runs to the Circuit Opening Relay. Thus only one of these wires could have continuity to a wire in the AFM while the other would not unless the fuel check connector was jumpered.

 

Good to know. What should I be trying out next then?

 

This goes back to your original post, but the flapper should open some w/key to start. If it does not open then it is likely because of a vacuum leak which would prevent the door from opening upon startup.

 

And another thing. When conducting an ohm test you never have voltage running through the circuit you are ohm testing as that can damage the circuit being tested.

 

In other words I should be ignoring the missing AFM wire and looking for vacuum leaks?

 

The missing wire should be a secondary ground which was added to later models S4's, but it should not be the issue causing your problem. At the ECU, pin 2A (Brown/White wire) should read 5 volts w/key to on and pin 2E should read 4 volts w/key to on and Pin 2J should be reading 2 to 3 volts at 60 degrees Farenheit. Also, the AFM must always be plugged into the intake duct tube leading up to the throttlebody.

And the bottom two wires of the Circuit Opening Relay can be jumpered to each other and this accomplishes the very same thing as jumpering the fuel check connector. Sometimes this is necessary because the Black ground wire in the check connector might not actually be grounded.

 

Well today I had some decent weather and a day off so I thought I would try again. Car temperature was around 65 degrees when taking these measurements, pardon my crappy photos. I've never had to test wires like this before, so pardon my dumb questions, am I doing this right? On all 3 of the wires I am barely getting any readings. I also tried taking readings by pulling the plug out of the ecu and testing the exposed tip, getting the same readings.

Also I grabbed a spare bit of wire and grounded the bottom 2 wires of the circuit opening relay, thats what the bonus photo is. Once again, sorry for the crappy photo, I only have a crappy phone camera. I'm a very visual person, photos help me out a lot.

Also, thanks for your help.

 

if it starts and runs while holding the flapper in it most likely has a vacuum leak, stop messing with the AFM and start looking around the intake for any possible leak points.

the AFM also has to be INSTALLED into the intake path while starting the car or it will never run/drive.



if you want a little tip: you can drill out the blind cap on the AFM air bleed(there is a flat tip screw inside the blind cap, do not drill into that), count the turns to screw it completely down and write it down, leave it screwed all the way in and try to start the car, it should run if the vacuum leaks are minimal to at least allow you to do a thorough test of the intake system with the engine running. once the vacuum leaks are diagnosed and repaired you can return the air bleed screw position to default.

 

What are you using as the ground for the multimeter? A good source would be the mounting bolts for the ECU. And make sure the ECU is powered. W/key to on pin 3I (Black/White wire)should have 12 volts. And use the meter to measure the battery just to make sure the meter is working properly.

 

Thanks haha I was having a "blond moment."

3I got 11.7 volts (battery has largely been sitting since November, so it doesn't surprise me it is a little low.)
2A got 5 volts even
2E got 4.15 volts
2J got 2.14 volts
These were all take at appx temp of 75 degrees

As far as the AFM being plugged in, the AFM has always been set up along the intake, and the cables have been plugged in. As for vacuum leaks, I'm no expert on anything in the engine bay (thats why I'm here) but I know what vacuum hoses look like, and I've looked all around from the throttle body all the the way down to the end of the AFM looking for anything that looks unplugged, and there is only one thing that was unplugged (see photo) I plugged it in the only place that looked like it would fit. Keep in mind that the previous owner deleted all the a/c components, and was starting to get rid of the power steering components as well.

Due to my lack of knowledge, yes I did search for how to locate vacuum lines, The MAZDA RX-7 86-88 technical page and while it was useful, I didn't find any lines related to the intake missing or damaged. To the best of my knowledge anyway.

I also included a photo of my engine bay. Its a little old (the photo) but I haven't adjusted much. Maybe it will help point out anything missing. Once again, thanks for the help. I know its n00b overload.

Behold! My skills in Microsoft paint!

 

Nothing to do with your existing problem,BUT get a Fan shroud or you will experience hot engine temps.

 

Make sure the flapper to the AFM opens easily and does not get stuck closed while starting the car. And did you jumper the two wires at the Circuit Opening Relay?

 

I currently have 2 different AFMs (the original that came with the car and a re-manufactured one from autopartswarehouse.com), the flapper seems to open easily on both. Neither flapper sticks in place. Yes I jumpered the bottom two wires on the circuit opening relay I think there is a photo on one of my previous posts showing what I did.

Thanks for pointing that out, I took the photo back when I was having issues getting one of the oil cooler lines off of the car and I needed it out of the way to access it. It has since been replaced.

 

And how did you arrive in the first place that your AFM was the cause for your car to run rather poorly. Was it just because someone else said so? How do you know that your timing/CAS is set properly or not as this could very well be your problem? Have you checked it?

 

I came to that conclusion when the car only starts/runs when the flapper is propped open. Honestly I've never heard another FC running before so I can't tell if it sounds like it is running correctly. No I haven't checked the timing/CAS. I'll give it a look when I have a chance.

 

That'd usually indicate a vacuum leak

Rotary > Pistons

 

Time for more of my stupidity!

I found a vacuum leak! Actually, a missing hose. I spent a good half hour trying to find where it goes, but no not avail. Photo attached is where I found the missing hose connector. It is close to the firewall.

I used this website as a guide to find hoses and where they are/go to:
The MAZDA RX-7 86-88 technical page

I for the life of me can't seem to find where that hose would connect to. Where does this hose go to from here? Bonus points for a photo. Also, where do they sell vacuum hose? Would any auto parts store sell some (Advance Auto Parts, Autozone, etc)? If I remember correctly they come in different sizes, so what size would I need?

Would that keep the AFM from opening and letting the car start? Because unless the afm is propped open it will NOT start. Prop removed and engine will die.

Bonus photo: This neighborhood cat wouldn't leave me alone when I was putting my interior back together today!


This car is awfully frustrating.