My #2 isn't working

[Pokey]

Well... maybe someone can help me interpret the results.  First of all, when at the coil the logic probe shows red (12V) and flashing green (the pulse signal from the ECU).  So #2 has red only, #4 (for example) has red and flashing green.

 

This is where it gets potentially weird.  With difficulty I've gotten wire to the back of the pins on the connector in the ECU on the #4 and #2 wires.  At the ECU on #4 the probe shows red (expected) and solid green - rather than the faint flashing green that happens at the coil end of the wire run.  I'm surmising that the solid green is actually a very fast flash that my eye can't perceive, and that wire resistance results in signal attenuation demonstrated by the faint flashing on the other end of the wire.  Does that sound plausible?

 

And... wait for it... on the #2 wire at the ECU I get red with a faint flashing green.  In other words, on the #4 wire-run the probe shows what appears to be solid green at the ECU and faint flashing green at the coil, whereas on the #2 wire-run it is faint flashing green at the ECU and nothing at the coil.

 

And for a bonus, the voltage at the ECU on #4 is 2.5V, and on #2 it is 12V.  That is the weirdest bit of all of this.

 

I've got to run but await all of your brilliant and creative ideas!  At this point I'm pretty much tapped out.

 

[sf4018]

2.5V for #4 ECU pin would seem ok if the engine was running when you measured it.

12V on #2 ECU pin if the wiring is all good would suggest a bad COP or a short between the 12V wire and ECU signal in the connector, that's the only thing that can be sending 12V back down the signal wire. If you disconnect the COP in this scenario does the 12V go away?

[MV8]

Greg,

when you say #2 and #4, I assume you mean ecu pins 15 and 35 for a 1342 firing order.

I'll assume your test was idling and same reference clip connections, cmos and pulse settings for all tests. All the coil triggers should flash green at the same rate with the same brightness. A higher resistance would be dimmer but same rate. A higher rate may be brighter or dimmer depending on the probe circuit design. Check the specs for your specific probe. I'm not sure I would conclude anything from the test results with the logic probe.

Since you probably don't have the extender I was talking about before, you could also remove a good coil and plug, ground the plug body with a jumper cable, connect the coil to #2 connector and crank to observe. Connect to a different one to compare. If it still doesn't work, I'd try an ecu swap.

[JohnCh]

27 minutes ago, MV8 said:

you could also remove a good coil and plug, ground the plug body with a jumper cable, connect the coil to #2 connector and crank to observe. Connect to a different one to compare. If it still doesn't work, I'd try an ecu swap.

Since it looks like Greg is away for a bit and I was there for some of the troubleshooting last weekend, I will address this.  We used a spark tester that plugs into a coil in place of the sparkplug and visibly sparks when the coil is triggered as the engine cranks. 

• When put on the end of the #2 coil, there was no spark
• When put on the end of the #1 coil, there was spark
• Plugging the #2 coil into the connector for #1, we again saw sparks, indicating the #2 coil itself was operating as expected.
• Plugging the #1 coil into the connector for #2 and there was no spark

From the above, we concluded that the issue was with either the ECU (ignition driver for #2) or the wiring for #2.

 

-John

[Pokey]

We tested my ECU in a known good car with the same result, so the ECU has failed.  I find it strange that it would fail in this way, but there you have it.  At least we have a definitive root cause.

 

@JohnCh, @sf4018 and @MV8, thank you for your help.  At this point Bruce Beachman is checking to see if Caterham will warranty the part and I'll go from there.  If I have to spend money then I'm probably going to spend it on the unlocked MBE for future proofing.