No spark and i can only get 5V at the coil.
For the ecu's case resistance reading, basically put one prong on the number 4 cavity or the actual case itself and then the other to ground?
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I'm not asking for resistance, although in effect that is what you are checking
Do the following.
Get power to coil +
Double check that you have 12V direct on the coil +
Now measure coil NEG to ground. You should have low voltage, the lower the better, perhaps 1 or 2 volts. WHAT THIS SHOWS is that current is going through the coil, and that the ECU is "pulling' it to ground......which it should be.
Change nothing except the meter. Put one probe "stab" into the ECU case, and the other probe into the firewall. You should read VERY little voltage, if any. Zero would be perfect
EXAMPLE. Let's say the coil NEG voltage is quite high, 5V--8V even higher. This shows the coil is NOT drawing current
And next you measure the case of the ECU to ground. If the voltages is very low or zero, this means the ECU is probably BAD, because the case is not "above ground" and yet the coil is not pulled low
Another problem indicated by a high coil NEG reading is the connection from coil NEG to the box. This could be a broken coil NEG wire right in the ECU connector, or a corroded / loose terminal in there
BUT if the ECU case reading is ALSO 5V or higher, this means the ECU case is not grounded
Read this through carefully. What you are doing is "testing in place" trying to disturb as little as possible so you can actually find the problem.
WHY? EG: In the book they have you pull the ECU connector off and take some measurements. This is almost meaningless, BECAUSE these measurements are NOT under any sort of load, and because just the movement of pulling the connector off may "disturb" a bad connection so that "you can't find it."
