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Yeah, I know. I had edited my very first response based on a re-read of his post. I suspect that you're replying to my now-deleted/edited portion of my post.
Okay guys I totally messed up earlier. I been working 10 hour shifts and have been trying to diagnose this after work hours. I apologize and I do appreciate the help. So Bluegrass I misunderstood your directions the last time you posted and I got the measurements all wrong. I remeasured and think I got it right this time.
Originally Posted by Bluegrass
12 volt source>>>>>>>coil winding<<<<<<<to PCM ground driving circuit to>>>>>it's ground which is outside common to the motor.
Use voltmeter to test for 12 volts on each side of the coil to ground. Verifies the coil is not open with the ignition on Run.
Okay I tested the RD/LG line and got 12 volts (after all) in vehicle run position
Then I tested the Pink/White PCM wire on the other side of the coil and I got 12 volts as well in vehicle run position
So from what you said it sounds like the coil is not open while the ignition is on Run
Originally Posted by Bluegrass
Plug up the coil, start engine. Measure for voltage on ground >(the lead going back to the PCM) > side of coil with voltmeter function. It should steady voltage pulse >downward< (if) there is no fault, each time the PCM fires that cylinder in the fire order..
If it is intermittent and your sure your test connections are solid, there is a fault in the harness, connector or the PCM driver.
The downward meter movement shows the ground is being applied and all the voltage has been dropped across the coil winding except a small amount across the coil driver circuit. How far the needle drops is a function of the meter speed of movement ability.
So when I tested like this, I started about 12 volts and that slowly went down over time. I didn't know how long to test for but I ran it about maybe 10 minutes. It slowly went down. It would go 11.99 then up to 12.00, then down to 11.98 and then up to 11.99, then down to 11.97, then 11.98 ect. After 10 minutes I think I was down about 11.80 or something like that.
.
Originally Posted by Bluegrass
To test the line back to the PCM with motor off and coil plug off, use meter Ohms function to look back into the PCM for the resistance offered to make this test. The meter's Ohm function supplies voltage from it's own internal meter battery to detect current flow in a loop through the resistance back to the meter.
You have to get this down or we don't yet know what's going on.
When I ran this one, I got a 1. I think that's overload on my multimeter.
Originally Posted by Bluegrass
The PCM coil driver has a resistance to ground that can be measured with an Ohm meter. If you remove the coil plug and measure to ground on the lead back toward the PCM you should see about 10,000 ohms +/-. If very much higher, open, or lower the coil driver is suspect after eliminating the harness and PCM plug assembly
Since I totally screwed up the first time and I AM getting power to the coil but the PCM cable OHMs reads OL, does this mean my coil driver is the culprit after all?
I would say yes the coil is not open and likely good..
If you are reading an open circuit with an ohm meter function looking at the coil driver, remember, there is a connector on the rear of the PCM that could be the open for that cylinder.
Test a known good cylinder and compare, then you see/know what your supposed to measure for resistance..
After this point, if you see the driver is open after testing at the PCM, then it's PCM replacement time.
There is no further testing you can do.
.
Just to help you understand how a spark is developed at the spark plug;
When the program sends a signal the coil driver an SCR type device that handles large currents in the order of about 7 amperes, grounds the coil lead.
This happens ahead of the time for spark. It's called Dwell time. The coil's core develops a magnetic field during this time.
When the program opens the circuit to the coil, the mag field colipases around the coil windings. This induces a voltage back to the winding from the stored energy in the magnetic field. With the windings being 'step-up' in ratio, 12 volts is raised to well over 40,0000 volts.
The spark from this high voltage jumps the plug gap that starts a 'Kernal' that spreads across the combustion chamber consuming the fuel and air that expand on the piston head..
Good luck.
I'm not sure if I messed up that last ohm test. Is this (picture) how should I be testing? Because I took off the plug connector and was testing for ohms through the connector back to the PCM. Is this correct? The reason I think I did something wrong is because I am getting an OL on all the PCM lines. I tested 4 cylinders: 1, 2, 3, and 7 because they are the easiest to get to. Picture below outlining how I measured this. The other terminal is on battery negative. Please let me know if/how I am messing up.
Your doing something wrong.
The lead to test is the one going back to the PCM, NOT the 12 volt side.
They all can't be open unless the whole harness is pulled apart.
For this test, the ignition switch does not need to be On because all your trying to test for is a resistance reading.
Be sure the meter is set to Ohms function, NOT voltage or any other function. Look at the meter function symbols the switch points to..
Some times a digital meter is worse than an Analogue meter for some test functions.
Maybe it's possible you already blew the meter fuse.
Better consider having some on help you.
So I verified that the 12 volt side is the other lead (RD/LG) with the engine on. I turned off the engine and tested this side again with the ohm meter ...low setting all the way up to the highest and I get an open. I opened the multimeter and checked the fuses and they were good. I changed the battery in the meter just in case. I tested again and I get the same. I have a cheaper multimeter and tried it as well and I get the same. I have an old speaker that is 4 ohms and I tested it to make sure both meters were working and they both registered 4 ohms.
So knowing that the meter is working, I'm wondering if the wire harness connections on the way to the PCM is a problem? Could these keep me from reading the ohms of the PCM?
