mangofever23

New member, could not find in search.

I'm looking for someone knowledgeable on the topic to give a simple explanation of the engine management system during starting.

My daughter picked up this old 86 rx7 NA A/T and i got stuck fixing it for her. I rebuilt/repaired the engine and auto transmission. It had been sitting for probably 10 years. Anyways, I have a fuel injector cleaner full of gasoline at like 40psi hooked up to the fuel rail and it cranks fine but won't start. I closed the fuel supply valve and cranked again and the fuel pressure did not drop which means the injectors are not firing. I did test and clean them during installation and I know they work fine. There is no spark from either set of coils. I do get one spark when the key is turned from start back to off. So the coil is getting power but the power is not being cut to generate the spark. I checked for spark at the coils not at the plug wires or plugs. The fuel pump connector is unplugged. The CAS ohms are perfect. All fuses checked with test-light. The entire vehicle is stock. I've worked on hundreds of cars but never an old mazda. Before i set off testing and verifying all sorts of things I was wondering if there was some simple thing I should know that is specific to this vehicle which would prevent the fuel injectors and coils from being commanded to function. In my mind all you should need is a good ECU and Crank Angle Sensor but over the years i've learned that certain makes and models have odd "safety" features or whatever you'd call it. It may be that the ECU first checks to make sure some odd sensor is operational before allowing for the engine to be started. Is this the case? I've taken apart the ECU and I did find a burned resistor but it is apparently for the fog light circuit. I'll still fix it but I see no reason that this would prevent it from starting. Thank you for any insight you can provide!

DR_Knight

iTrader: (23)

Are you sure the ecu is getting power/ground? You should be able to check for 12v at engine harness sensor connectors. Also if the car is usdm the check engine light should illuminate for a few seconds then turn off which would indicate the ecu has power. If it doesn’t have power at least you have a starting point to look at the wiring diagrams. Injectors should have 12v at the connectors, the ecu grounds the injector to fire.

I believe you are correct regarding cas, I think you can just spin the cas by cranking the engine and it should generate spark, as long as the ecu is on/working.

Sure the burnt item in the ecu was for a fog light circuit? I didn’t know s4 rx7’s ever came with fog lights, we might just be defining fog lights differently.

Full service manuals with wiring diagrams are located here: http://foxed.ca/indexmobile.php?page=rx7manual

diabolical1

iTrader: (3)

welcome to the board.

for fuel - you should check and make sure the intake tract is intact from the throttle body to the MAF sensor. the ECU will be "looking" for the flapper door to move before it will let fuel go to the engine while cranking.

for spark - make sure the coils are bolted down securely and that there is nothing (rust, grease, debris, etc.) between them and car's body. as said above, i don't think the ECU will impede them from firing once it sees the CAS spinning. i've pulled a couple coils and found rusted/broken wires inside, but i highly doubt that would be the case with both coils on the same car. does the tach move while cranking? look up the connector diagrams and confirm 12V where they should be.

other ideas: maybe try a timing light or you could pull the CAS and spin it by hand (ignition ON, of course; and you should probably turn the engine to TDC before you remove it).

mangofever23

Thank you dr knight, the pinout diagram i was looking at turned out to be the wrong one. The burnt resistor is related to the 1s pin which is for "port air solenoid valve" whatever that is lol i'll figure it out no need to explain. I think i'll just bypass the resistor in the ecu and cut the wire then later install the resistor in the wire loom side so i can continue diagnosis today. Thank you for the link to the manuals, I had tried opening several of the links i found on this site and none of them worked. As the ecu is not currently in the vehicle I can't check to see if the MIL turns on with key on but I don't recall it doing so when i tried to start it. When i find out the root cause I'll update this post with the solution in case anyone is interested.

Diabolical- I read something about the air flow sensor flapper and the fuel system, but if i recall correctly, that was in regards to activating the fuel pump not the injectors. Although when i think about it, it would be odd for the computer to allow the injectors to fire while at the same time not allowing the fuel pump to run. So maybe it cuts those off as well until it sees movement. I do have the intake fully assembled minus the filter and cover though so as long as the air flow meter isn't faulty that shouldn't be the issue. I had toyed with the idea of removing the CAS so as to reduce the strain on the battery, starter, and internal engine components during diagnosis. I may end up doing that, thanks.