So I'm driving into work today, cruising at a good 120-130 MPH when all of a sudden, I lose power.

Tach is still showing, so that tells me ECU still has power and ignitors should still be good. I assume it's a fuel problem...

First, the problem is intermittent, the power will come back on in a little while and I can accelerate. Shortly thereafter, no dice.

Car will restart and run for exactly 5 seconds before dying again. But it starts right up every time I crank it. I still assume fuel problem... (Key on, fuel pump pressurizes the line, start engine, pump cuts out, fuel line PSI drops, engine stalls.)

Sho' Nuff... Circuit opening relay is clicking off after the engine starts.

I pulled it out and made a quick bypass out of a short piece of wire. Connect Black with a White stripe to the Blue wire and off I go, no more stumbling, and back up to speed.


Why did this fail?

According to the diagram here:
http://mazdarx7.iougs.com/fuel.shtml

It's fed by the MAF sensor... But if my MAF was disconnected, the ECU wouldn't run the engine.

Oh well, MAF is gonna get thrown out sooner or later anyhow.

 

if its still the original relay, it might've failed from wear and tear from age.

 

Nah, the relay didn't fail... I took it apart and can get it to actuate by hand...

Whatever sends power to the coil on it quits after a few seconds.

 

If the relay is clicking off then the the circuit that supplies the coil is opening. I'm sure the relay itself is fine as long as the contacts have good ohm readings. Relay coils are usually good, open or short.

 

The AFM is supposed to be supplying the ground on the circuit opening relay if the key isn't in the START position.

 

 

Like ARRGH says, the Circuit Opening Relay has TWO coils. One coil has a gnd all the time and only pulls in if the key is HELD to START.

The second coil of the Circuit Opening Relay has power all the time, but only gets a ground if the engine actually is running. The gnd comes from the afm on a series four and from the ECU on a series five.

So it makes common sense that the Circuit Opening Relay would relax if the key is let go from start to just ON..........AND the ECU OR AFM does not put a gnd on the other coil inside the Circuit Opening Relay.

You NEED to tell us what series car you have so we can explain things better. See wiring diagram for your series car and you'll see the two coils just explained above. If it's a series four, then the ECU is not the one that puts a gnd on the OTHER coil in the circuit opening relay to keep that relay pulled in. It's the fuel switch inside the afm that keeps that relay pulled in by putting a gnd on it's OTHER coil.

And another thing. The engine will start without the afm connected. The afm is not used for fuel during START. Once over approx 500rpms then the AFM is used for fuel.

 

Hmm. I didn't realize that the s5 ECU grounded the circuit opening relay just like the FD ECU does.

 

S5

 

It's an S4... 1986 GXL. I was unaware of this difference.

Also, here's the weird part.

I yanked the relay out of its housing so that I could see it move while I was trying to crank the car.

When cranking, the relay is closed, The engine will run for up to five seconds, then the relay will open. But the relay will stay closed for those five seconds after the key is released fro the Start position...

 

As you can see from the diagrams I attached for a series four.............if you jumper the yellow two socket fuel pump check connector, that act does the same thing as the fuel switch inside the afm *making*. Both acts put a gnd on the circuit opening relays coil and keep it pulled in.

So knowing that, then jumper the yellow two socket connector and run the engine. The circuit opening relay should stay closed any time the key is put to ON or better and whether or not the engine is running.

Part of what you say makes sense. If the engine starts, the relay stays pulled in even though you let the key go back to On from Start. It seems to me that what happens after five seconds you mentioned, is the engine is dying for unknown reasons, which in turn lets the vane in the afm relax and the fuel switch inside open up which in turn removes the gnd from the circuit opening relay so you now see it relax. Supposed to do that if the engine dies.

IF you jumper the yellow connector and the engine still dies after five seconds, then your problem is not the circuit opening relay imho, because I bet it stays pulled in and the fuel pump will still be running. Just a guess. Wellllllll I guess it could be if the contacts in the relay are corroded or not making good contact. Hard to say from here.

 

You can ring the contacts out with a multimeter and should see an ohm or less across the contacts.

 

Contacts are good. If I physically hold the relay closed, the engine continues to run.

 

With the engine off turn the key to run and jam the AFM open. With the relay out of the socket you should see a ground on Fc and 12vdc on B. Also make sure you have the appropriate ohmic value across B and Fc to determine if the second coil inside the relay failed.

 

Swap AFMs with the one from your parts car.

 

As I mentioned earlier, jumper the two socket fuel pump check connector and run the engine. Doing that does the SAME thing as the fuel switch inside the afm when it *makes*. If the engine still runs, then the problem is the switch inside the afm not Making.