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Troubleshooting a sudden no spark issue, FD RX7


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So my FD has been running well with a G4+ Fury for quite some time now, and yesterday I had a sudden no-spark issue after the car was idling for a few minutes. Started pulling out of the driveway and it died before reaching the street. I have solid compression and fuel, so suspecting spark, I hooked up my inductive timing light and cranked - no flashes on any of the plug wires. Plugs & wires are new, so I should have been seeing regular flashes while cranking.

Since I had the laptop already hooked up for logging w/PCLink, I decided to put each coil into test mode to see if they fire, again using the timing light. I've done this before with the timing light, so I know it will reliably flash when the coil is in test mode and firing. No flashes on any coil was the result.

Next I unplugged all the coils (IGN-1A smart coils) from the harness, and tested for +12VDC at the each coil's power terminals with ignition switched on - all had good +12VDC power. Also tested continuity of the coil grounds, to battery, rotor housing and sensor ground and they all look good; basically 0 ohms on all ground paths.

Was getting dark, so I pushed the car back in the garage for the night and will work at it today. Have a couple of questions on my troubleshooting strategy for this:

1. I figure the next thing I should do is take a trigger scope log while cranking to verify that both crank angle sensors are sending good signals to the G4+. I've done this test after initially wiring the car, so I have a baseline of what "normal" looks like there. Obviously a wiring failure or bad CAS sensor will prevent the coils from firing.

2. I'm assuming if either of the CAS signals tested in #1 are bad, then none of the coils will fire. But I'm a bit confused as to why none of the coils were firing when I put each of them into test mode with PCLink, as I thought that test mode only functionally tests the coil outputs? Unless the Link G4+ also tests for proper continuity with the CAS trigger inputs during this test as well?

Thanks in advance!

 

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1 hour ago, Adamw said:

Just to back up what the scope is showing, you can confirm by watching rpm in the software while cranking.  If it sits at zero then that would confirm no trigger.

Yup, zero RPMs is what I'm seeing while cranking, so I'm going to test the CAS wiring. If the wiring is all good, and I have good CAS sensors, I should see a resistance of between 950~1200 ohms between each trigger pin and trigger ground pin on the "A" connector with it disconnected from the G4+.

But I'm still not understanding why when I put each coil output into test mode, they all failed to fire? Does the coil output test do more than just test the output side of the ignition circuits (i.e., just from TTL coil trigger to spark output), or does it also look for good continuity on the VR trigger circuits as well? If it's the latter, then it would explain what I'm seeing.

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34 minutes ago, Pete_89t2 said:

But I'm still not understanding why when I put each coil output into test mode, they all failed to fire? Does the coil output test do more than just test the output side of the ignition circuits (i.e., just from TTL coil trigger to spark output), or does it also look for good continuity on the VR trigger circuits as well? If it's the latter, then it would explain what I'm seeing.

No the coils should spark using the ignition test regardless.  But it could be something in common like a main ground broken - so the coils and CAS both have no ground reference.  Or it could have just been a timing light issue - so investigate the CAS first before getting worried about the spark test.

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1 hour ago, Adamw said:

No the coils should spark using the ignition test regardless.  But it could be something in common like a main ground broken - so the coils and CAS both have no ground reference.  Or it could have just been a timing light issue - so investigate the CAS first before getting worried about the spark test.

^That's highly likely, given the pin-out arrangement on the 2 Link connectors and how I organized the grounds on the harness. Both the trigger/CAS inputs and the TTL triggers for coils 1 - 4 reside on the "A" connector, so there is likely a common failure point.

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Another update - I take back what I said about seeing zero RPMs while cranking and doing the trigger scope capture. Did the test over, and it turns out the G4+ was reading a pretty normal cranking RPM (250~280 RPMs) while I was taking the trigger scope trace. Trigger scope trace looks the same as what I posted before though, so not sure if I'm using the software correctly and getting a good capture.

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Well after spending a big chunk of the weekend troubleshooting my wiring harness, and finding no failures there, I'm now thinking something must be broken in the G4+ ECU.

Here's what I've done to troubleshoot so far:

1 With ECU disconnected from the loom, I did end-to-end continuity tests of every wire/circuit in the harness, paying special attention to the CAS triggers and coil wiring since it's a no-spark issue. No opens or questionable connections were found anywhere.

2. Since the ECU had to be removed, and the harness partially extracted from where it runs from the kick panel to the fire wall to give me access, I double checked to ensure that none of the harness was being mechanically strained when installed and connected to the ECU. The G4+ ECU is mounted on a fabricated bracket, in the same location Mazda used for its OEM ECU on a US market FD - behind the right/passenger side kick panel, and harness is routed through the same firewall hole, though I used a mil-spec bulkhead connector there, which was included in the continuity testing (#1).

3. At this point failing to find any faults with my wiring, I reconnected the ECU to the harness, but just left it laying on the floor - figured I'd re-do the trigger scope trace tests and the coil tests before putting everything back together.

4. Pulled my fuel pump fuse so the car wouldn't start/flood and took a trigger scope trace while cranking - looked pretty normal, see here: https://drive.google.com/file/d/1SAGkC-o202Dg4A2ZmT0wNdPthUcpF6OQ/view?usp=sharing

 

5. Also re-ran the coil functional tests, and all 4x coils fired as they should.

6. At this point, I was feeling confident so I decided to remount the ECU to its bracket, and tuck the wiring back in its normal place behind the kick panel, pop the fuel pump fuse back in and take it for a test drive.

7. I had PCLink connected to do a trigger scope trace while cranking, and the car failed to start. Again due to no spark, though I'm seeing normal cranking RPMs displayed on PCLink, but the trigger scope trace is just showing what looks like random noise again. Here's that trace:  https://drive.google.com/file/d/1kUutrS31sGNEtz4FGdXTQO7hlVj19KS-/view?usp=sharing

 

At this point I'm stumped as to what to try next - can't think of anything else to check with the wiring that might be a factor. Any ideas?

Edited by Pete_89t2
fixed links to trigger scope traces
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So the difference between the successful test and non-successful was the fuel pump fuse and loom routing?  Did you try to reproduce the successful test by removing fuel pump fuse and moving loom again?

When running the trigger scope are you only clicking capture once the engine is rotating?  

Can you attach the tune so I can see arming thresholds etc.

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22 minutes ago, Adamw said:

So the difference between the successful test and non-successful was the fuel pump fuse and loom routing?  Did you try to reproduce the successful test by removing fuel pump fuse and moving loom again?

When running the trigger scope are you only clicking capture once the engine is rotating?  

Can you attach the tune so I can see arming thresholds etc.

Yes, that's correct - only difference was the removed fuel pump fuse and the ECU & loom laying slack on the floor rather than being mounted and tucked under the kick panel where it would normally be. Haven't had a chance to repeat the successful test, will get to that tomorrow.

I'm only clicking capture once, but perhaps I'm doing it wrong - I've been hitting the capture button just prior to turning the key and cranking the motor, so I expected the trace to show just noise for the 1st second or two before the cranking starts. Should I wait until the engine is cranking to hit capture instead?

Here's a link to the current tune: https://drive.google.com/file/d/12BwupTZMtN24X3NW4YClSEx1AApt6Y2I/view?usp=sharing

One other change I made that applies to both the successful & unsuccessful tests was that I installed the latest G4+ firmware that was recently posted.

 

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On 10/18/2020 at 7:35 PM, Adamw said:

You need to click capture when the engine is already turning.  

Ok, I repeated the tests again, this time using the trigger scope capture correctly. Results as follows:

#1 - Repeated test with G4+ secured in its bracket, fuel pump fuse removed so car won't start/flood - CAS triggers look pretty good to me, see linked log trace here: https://drive.google.com/file/d/1nGLm1EYB0MYAOXjyY8gtjrYhJA30_UWV/view?usp=sharing

Next I ran the functional test for the 4 coils again; this time around coil output #2 and 4 were firing consistently, but #1 was intermittent (started dead, then started firing), and #3 was dead the whole time. Instead of relying on the inductive timing light, I tested each with a removed spark plug that was grounded to the engine block with a jumper cable, and watched for the spark

#2 - Repeated test with G4+ laying loose on the floor, fuel pump fuse removed so car won't start/flood - CAS triggers looked good again, see linked log trace here: https://drive.google.com/file/d/1ZdyS_rkaZ0iyiTlru4gTMOkipJMev2yE/view?usp=sharing

Repeated the coil test, with similar results to #1 - only difference was coil #1 was firing consistently this time, #3 was still dead.

Given the coil test results, I unplugged the "A" & "B" connectors from the G4+, and repeated my continuity tests of all the coil wiring. Once again, all the wires had solid continuity from the appropriate "A" connector pin they originate from to the corresponding coil plug termination. I also removed my coils from the FD and plugged them into my FC (uses same IGN 1A coils with an AEM Infinity ECU), just to verify the coils were good, and the FC fired right up and ran on them.

At this point I'm 100% certain there is nothing wrong with my harness wiring, or the coils, and that I may need to ship the ECU in for service as my last course of action. Wish I knew someone local with a spare Link G4+ Fury that I could use for testing. Anything else I might be missing here before shipping it in for service?

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6 minutes ago, Ducie54 said:

Did you look at the log file before you uploaded it?

Of course, why do you ask? Below is a partial screen shot of the trigger scope trace from repeat test #1. I'd post the logs here, but they were too big to attach, so I linked them on a Google share.

 

Screenshot - repeat test #1.png

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Its hard to imagine how a ignition drive would only work intermittently, generally they completely fail, but you are welcome to return it for inspection if you wish.  The NZ headquarters can do a much more thorough test but you also could send it to one of regional offices where they could do a basic test on an engine simulator to confirm all ign drives are working.  We have support offices in UK, USA, & AU. 

 

13 hours ago, Pete_89t2 said:

Wish I knew someone local with a spare Link G4+ Fury that I could use for testing.

Note it doesnt necessarily need to be a Fury, any of our wire-in ECU's will plug-in to the same A connector and work. Certain things like the idle valve may not work but even an Atom will run a 2 rotor.  Your fury map can also be loaded into any of our ECU's.  Just mentioning this in case you know anyone with a Link ECU.   

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3 hours ago, Adamw said:

Its hard to imagine how a ignition drive would only work intermittently, generally they completely fail, but you are welcome to return it for inspection if you wish.  The NZ headquarters can do a much more thorough test but you also could send it to one of regional offices where they could do a basic test on an engine simulator to confirm all ign drives are working.  We have support offices in UK, USA, & AU.

It certainly is an odd one. My best guess is that the ignition drivers/circuitry is fine, but there may be a defect in the "A" header itself causing an intermittent connectivity failure - perhaps a cold solder joint where the header pins connect to the circuit board? This might explain why moving the ECU around and removing & reinserting the connector had some impact on the behavior.

I'd probably opt to send it to the NZ HQ for testing, unless you guys tell me you're confident that the USA support office has the capability to thoroughly inspect it for soldering or circuit board defects.

 

4 hours ago, Adamw said:

Note it doesnt necessarily need to be a Fury, any of our wire-in ECU's will plug-in to the same A connector and work. Certain things like the idle valve may not work but even an Atom will run a 2 rotor.  Your fury map can also be loaded into any of our ECU's.  Just mentioning this in case you know anyone with a Link ECU.   

That's good to know, might improve my odds of finding an ECU to substitute locally.

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