Hi Folks - I'm looking for some validation on my troubleshooting approach and tentative conclusion.
Symptom is no starting / no spark. The failure occurred as I was backing out of the garage (thankfully) - engine simply shut down and now doesn't start.
Car is a '72 Targa with a 3.6L conversion. Relatively new to me. We all like pictures, so here we go.
So, following some of the other threads here plus the diagnostic approach in the factory workshop manual I've confirmed the following without the use of Bosch Hammer tool or oscilloscope.
1. Fuel is flowing - plenty of gas smell with cranking
2. DME relay is engaging and clicking as I crank. Replaced the DME relay with a new spare I have, and same condition.
3. No spark verified
4. Measured resistance of the speed sensor (can't see the actual signal without a scope). Resistance
5. Verified 12v across both coils.
So, I'm now looking at the DME to ICU connection to see if the DME is putting out the spark signals and if the ICU is translating those signals to the coils.
This is my DME
And this is the DME to ICU connection. ICU is Bosch 0 227 200 100 (apparently NLA)
The workshop manual shows that the DME to ICU signal is a very low level - about 0.25 volts peak.
And the output of the ICU to the coils is a full 12v+ swing as the coil is energized then clamped to create the spark.
At the DME out to ICU in pins (pins 2 and 7 on the ICU) I measure:
Steady state 0.13 VDC no cranking
When cranking 0.1 VAC
Based on the workshop manual showing 0.25V peak, I would expect to see about 0.1VAC on my DMM, right?
Now to the ICU out (pins 1 and 6), I measure:
Steady state 7.1VDC no cranking (I expected to see 12V here) and
When cranking 0.6VAC (I expected to see at least 7-8VAC)
My conclusion is that the (very rare) ICU has failed.
I would greatly appreciate the wisdom and experience of anyone who can validate or provide any guidance on other places to look for the failure>
Thanks!