I can use some help troubleshooting a tricky no spark issue with an AEM Infinity. Bottom line is I think my ECU may be acting wonky or I have a really odd intermittent wiring failure associated with the coil wiring.

Quick Background - I have an '89T2 with a 13BT that I built that is running an AEM Infinity EMS with 4x AEM IGN-1A smart coils in direct fire mode. Car was tuned well and has been running that way for about 3 years now, running trouble free in all that time.

In recent months I've been noticing that shortly after starting my FC while its warming up, it would intermittently start idling rough or hesitate a bit under light loads driving off, and at the same time my AFRs would trend lean of target AFR. Spent lots of time looking over logs thinking I might have a warmup enrichment issue or other fueling problem but no smoking guns were found; tweaking the fuel settings really didn't fix anything - the intermittent lean-outs continued. Then just recently, within a few minutes after starting the car and attempting to drive off, the AFRs went WAY lean (like 18's) and the car was wanting to stall - felt like it was running on one rotor. BTW, I was confident it's not a compression issue, because I have an RCT 5.2 compression tester that I periodically use to check the motor and it consistently tests with all faces both rotors at 105~118psi.

While it was idling like crap in the driveway, I grabbed my inductive timing light as a quick check to verify that all the plugs were firing. L1 & T1 were firing fine (consistent flashes), but L2 was dead (no flashes) and T2 was only firing sporadically. Shut her off, and inspected the spark plugs to make sure they weren't fouled - all 4x plugs looked like new (they were only 6 months old, barely used). Also gave the plug wires a close inspection and tested their end-to-end resistance and they checked out good as well. Next step was to check the wiring to the coils to verify that all 4 coils had power when the ignition was switched on - all good there. So now the next thing I tried was a substitution test - I placed the 2 good coils I had in the L1 & L2 positions, and I temporarily borrowed 2x known good IGN-1A coils from my FD and put those in the trailing T1 & T2 positions of the FC. Fired the FC back up, and she ran perfectly! Let her warm up, went for a short drive and there were zero lean outs or issues while driving it. Confident that I ruled out ECU or wiring issues, I went and ordered 2 new coils, and put the borrowed coils back in my FD. Curious as to why these coils would fail in only 3 years, I posted this up in the General Rotary sub-forum: https://www.rx7club.com/general-rota...-last-1147222/

Fast forward to yesterday, the new coils arrive from Summit and I put them in my FC. Start her up, and it was looking good - fired right up, idling smooth during warmup, and AFRs were tracking the target just as they should. While it was idling, I grabbed the timing light again to verify spark - all 4 plugs were firing as they should. So I pulled the timing light off and was about to go out for a victory drive, and before I could back out of my driveway, it starts running like crap again - super lean AFRs with the same apparent miss/running on 1 rotor crap. Grab the timing light again, and this time 3 of the 4 plugs are not firing. WTF?

If anyone has any ideas on how to troubleshoot this further I'd appreciate it. Since it appears that ALL of the coils can be effected by this problem, I don't think it's a wiring issue, though an intermittent signal ground return to the AEM Infinity for the 4x coils TTL triggers MIGHT explain this. It's just odd that it would happen like that all of a sudden when the wiring was working fine before and undisturbed for the last 3 years. I wish the AEM Infinity was like the Link G4+ in my FD - with the Link, you can actually test each coil, FI and auxiliary output without stating the car to do a full functional tests of your wiring harness - don't think the AEM provides similar capability.

 

Replying to my own thread with some info that might help another AEM Infinity user....

Turns out the Infinity DOES have a diagnostic function that you can use to test the wiring & functionality of all the output devices (injectors, coils, relays, etc) in a test mode. The only catch is that the diagnostic functions do not exist on the same firmware that you would use to run the engine. So you have to first "upgrade" the firmware on the Infinity to the appropriate Diagnostics firmware build for your model of Infinity. Do your tests, and when done/happy, you reload the firmware & calibration file that your car was running on before.

So after chatting with AEM tech support, I did that firmware drill and tested my coil outputs. All were working except for the T2 coil; so next step will be to disconnect the AEM ECU main connector, and do a point-to-point resistance/continuity test to that coil's connector to verify that my harness still is good. If the harness is good, it means the AEM Infinity is FUBAR'ed, and I'll have to send it back for service/replacement.