What would cause a coil to fire out of sync?
07-23-08, 03:05 PM
#1
What would cause a coil to fire out of sync?
The car was running great and then yesterday after changing the plugs and plug wires it wouldnt idle (it would die).
I put the timing strobe (car powered) on each of the plug wires. Except for T2, they all show the timing is correct (a bit advanced as expected because we have to keep the RPMs up to keep it running.)
Except for T2.
Note that I have swapped plugs and wires using the old stuff that worked. No difference.
What would cause only one coil to fire at the wrong time? T1 on the same unit is firing at the right time. I know T2 is firing because if I point the strobe at my hand I can see the flashing. I read 05 Engine Electrical System of the S5 FSM but they dont explain what controls when the spark is fired except on page G-3 it refers to a mysterious "Control Unit" as controlling the Spark Advance and Distribution. But I can find no other reference in Chapter 05 Engine Electrical System to the inscrutable "Control Unit." I'm assuming it is the ECU.
While I can randomly replace parts (I have a CAS from the NA and a JDM Trailing coil as well as an N370 and associated sensors on hand) I'd rather be purposeful and deliberate.
Also, how do you test the coils/ignitors; without killing yourself would be a bonus
? The FSM refers to a special tester called a Igniter Tester.
Chapter 04B tells you the voltage readings one should see on the ECU. For the Trailing Coil that would be 1G and 1J. When I test those, if the voltages are wrong does that mean the ECU is bad or that the coil is bad?
I'd noted in my post from last night that the ISC didnt do anything. Could it be that the big yellow ECU plug isnt all the way tight? I noticed that the pins for the ISC and the trailing coil (1G and 1J) are physically grouped. Of course, that would probably lead to the coil not firing at all as opposed to late (or early).
Thanks
Jim
I put the timing strobe (car powered) on each of the plug wires. Except for T2, they all show the timing is correct (a bit advanced as expected because we have to keep the RPMs up to keep it running.)
Except for T2.
Note that I have swapped plugs and wires using the old stuff that worked. No difference.
What would cause only one coil to fire at the wrong time? T1 on the same unit is firing at the right time. I know T2 is firing because if I point the strobe at my hand I can see the flashing. I read 05 Engine Electrical System of the S5 FSM but they dont explain what controls when the spark is fired except on page G-3 it refers to a mysterious "Control Unit" as controlling the Spark Advance and Distribution. But I can find no other reference in Chapter 05 Engine Electrical System to the inscrutable "Control Unit." I'm assuming it is the ECU.
While I can randomly replace parts (I have a CAS from the NA and a JDM Trailing coil as well as an N370 and associated sensors on hand) I'd rather be purposeful and deliberate.
Also, how do you test the coils/ignitors; without killing yourself would be a bonus
? The FSM refers to a special tester called a Igniter Tester.Chapter 04B tells you the voltage readings one should see on the ECU. For the Trailing Coil that would be 1G and 1J. When I test those, if the voltages are wrong does that mean the ECU is bad or that the coil is bad?
I'd noted in my post from last night that the ISC didnt do anything. Could it be that the big yellow ECU plug isnt all the way tight? I noticed that the pins for the ISC and the trailing coil (1G and 1J) are physically grouped. Of course, that would probably lead to the coil not firing at all as opposed to late (or early).
Thanks
Jim
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