84SE, 193k miles on original engine, mods in signature line, stock EFI/injectors/ignition...

Okay, driving yesterday (to an RX7 club event) and on the way the car just dies about 5 minutes into my trip. Would crank without issue, but wouldn't fire. The following troubleshooting performed in the 'field';

1) Checked for airway restriction, K&N filter clean. Pushing on AFM door causes fuel pump to come on and I can hear fuel running through the rail.

2) Checked for spark - spraying 'starter fluid' (ether) into intake causes car to stumble and run briefly, but not start up, so I am getting spark.

3) Fuel filter was changed last year, fuel pump is original, but it's getting fuel to the rail, so moved to Fusible Links and electronics.

4) Pulled Fusible Links for 'Main' and 'Injector' - both test okay and swapping positions brings no improvement. Shunted with 12ga wire and no change, so links are good.

Get it towed home and pull the plugs - bone dry. Not getting fuel.

At this point, I remembered that the EFI system uses the trailing coil lead to signal the ECU on when to fire the injectors, so I cut the lead from the Trailing Coil connector, splice on a spade connector and put this onto the same position on the Leading Coil - STARTS RIGHT UP. Must not have been firing the trailing coil, which could be either the Ignitor or the Coil, itself.

So, help me diagnose what to replace this weekend to get my trailing ignition back up and running. As an aside, I was able to make it to the RX7 Club press event for a new Mazda Dealership's Grand Opening, but missed the ribbon cutting. Pics to be posted when able.

Thanks, in advance; I figure you guys could confirm what I've diagnosed, as somebody has gone through this before, I'm sure!

 

Yep, sounds like a dead trailing ignitor. The SE ECU picks up the tach signal from that blue spade connector on the trailing coi. This is used to determine when to fire the injectors (each pulse). The only other things that could have happened based on your diagnosis is:

- connector came unplugged from the ignitor. As you know, the trailing ignitor is the black box on the dizzy closest to the alt. It could have been pulled loose when under the hood one time and then fell off when driving.

- coil. Not real likely as these don't fail often. You can check the resistance between the + and - terminals. Should be around 1.8 ohms IIRC. Then turn the key to on and check that both sides of the coil are getting battery voltage.

Good luck.

Kent

 

Thanks for the confirmation, Kent. The wire that I 'moved' to get it to run again was a black wiring leading to the Trailing Coil plug which is also factory-crimped into that plug with a white wire, red trace. The Leading Coil has a white wire with green trace, so I figured those were the leads coming from the ignitors to trigger the coil.

When I cut the black wire from the Trailing Coil plug and connected this to the Leading Coil, it started right up - the ECU then had a good, strong signal to fire the fuel injectors.

I don't remember seeing a blue connector on the Trailing Coil, is it possible that I have misunderstood something?

 

Hmm.. Those colors don't sound right. The trailing coil should have a BY (black w/ yellow stripe) to the + terminal and a YG (yellow w/ green stripe) on the - . The leading has BY on the + and YL (yellow w/ blue) on the -. On the trailing, there is usually two sets of wires with a spade connector. One is just a YG wire that goes to the trailing ignitor. There is also a blue plastic spede connector with two wires connected in it. I believe that either both are black or one black, one YG.

Could you maybe take a pic of the coils/wiring? It sounds like the black wire is the one that goes to the ECU. Not sure on the WR wire. I know the alt output wire has those colors.

Kent

 

Here are the pictures. In this shot, you can see where I crimped on the new (bright blue) spade connector and where the lead trigger wires connect to the left side of each coil. The coils are MSD Blaster 2's and have been on the car for 2 years without issue. Also, in this shot, you can see the markings on the coil mount for T (trailing) and L (leading) as my reminder for which is which:



Thanks for your assistance with this - I'll be swapping out the trailing ignitor today in hopes that it will fix the problem, and then I'll reconnect the tach signal lead to the trailing ignition as Mazda designed it.

I'm wondering if Mazda wired it this way so that if the Trailing Ignition went out, the owner would know it (lost tach readout or no start for EGI), since the engine will continue to run just fine without it. With the increased emissions and lowered fuel economy without Trailing Ignition, it would be important for the driver to know this. Just wondering out loud,

 

That looks right. The black wire that you moved over to the leading was originally wired to the blue spade on the - terminal on the trailing coil. What is interesting is that from that blue connector, the YG and black wire both run all the way to the ECU and connect at the same pin. I imagine it is for either to reduce electrical noise or to provide a backup path incase one of the wires became loose, corroded, or similar.

I am sure Mazda selected the trailing for the tach and the ECU so you will know if there is a loss of trailing igniton as you probably couldn't feel the difference in power/performance.

I believe that my SE has an additional connection on the trailing -. There is the blue connector (mine only has one wire in it as someone cut the other). There is also a YG wire on a normal spade connector that then goes to the trailing ignitor -. Not sure if it was aways wired that way or if someone had changed it.

One thing to remember is that if you ever lose tach/signal to ECU, you would normally be stuck since you won't have fuel. If this happens, unplug the blue connector from the trailing - and plug on the leading -. This will get you going until you can fix the trailing ignitor. I had to do this a couple times when my trailing was acting up.

Good luck. Let us know if that takes care of it.

Kent

 

What you described with changing the Tach Lead to the Leading Coil + is what I did to get it running the other day. Now, I'm just trying to get the Trailing Coil firing as it's supposed to for best fuel economy and emissions.

Thanks again for your help, I appreciate running this past members here to be sure I'm troubleshooting the right things,

 

NP. I was just saying that you could have just unplugged that blue connector on the trailing - and plug it on the leading - without cutting any wires. Just thought that may help other SE owners that run into this problem.

 

Would that have worked? The yellow wire with green trace is a trigger wire for the coil, so I would think that having both connected to the same coil would cause some problems with the ignitors.

I'll post a reply once I swap out the Trailing Ignitor and have some definitive fix on this.

 

It should be fine. You could always unplug the trailing ignitor if you were worried about it, though. Now I am curious as to how the wires run in stock form. I have a YG wire going to the trailing - from the trailing ignitor. The black and YG wire in that blue connector run across the engine bay, into a yellow connector on the passenger side. The wires from the yellow connector then run to the ECU. I suppose that since you only have the one connector for trailing, that the YG wire from the ignitor is supposed to tap into the YG wire on the blue connector.

 

Replaced the Trailing Ignitor and it fired right up after putting the Tach/ECU lead back to the Trailing Ignition (-) on the Coil.

That was the problem! Thanks for the diagnostic help,