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Dan, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2270
Experience:  20 Year Factory Trained Current GM Technician
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Blazer: insufficient volts comming out of coil, 12 volts..ICM

Customer Question

My Blazer has the EDI Ignition system. I'm getting volts going into the coil but insufficient volts comming out of coil, 12 volts in 12 out. I've tested the ICM and that tested good. Replaced so far is the Ignition coil, Plugs wires, Cap and Rotor, Throttle positioning sensor, and Crankshaft sensor, Still only 12 volts read on the coil while engine is turned over.. I Don't Get It ECM or PCM is the only thing I can come up with.... HELP needed
Submitted: 8 years ago.
Category: Chevy
Expert:  Dan replied 8 years ago.
What year is your blazer?
How and where are you checking the coil?
Customer: replied 8 years ago.
<p>It be a 2000 Blazer 4.3 with the spider injection. I checked the coil at the main post, the one that goes out to distributer. so I replaed the coil and it still test the same.</p><p>   Thanks, Chris</p>
Expert:  Dan replied 8 years ago.
If you hook the coil wire to the coil and take the other end off of the distributor and lay it against by a ground and crank the engine over, Will it arc?
Customer: replied 8 years ago.
Nope, it don't even give me a little snap, used a nail to secure it in the wire and checked on a ground nut and nothin.
Expert:  Dan replied 8 years ago.
Did you hold it about 1/2 inch from ground and not touching the ground?

Do You have power on the pink wire on the connector to the coil and the ignition module?

Do you have a test light?
Customer: replied 8 years ago.
Yep, on all. I checked the pink on the coil and it is getting 12 volts with ignition on same with the ignition module. I also ran the pulse check on the IM's black wire and it pulsed just like she should and that's why I'm stumped, I've been building chevy muscle cars for around ten years and a GM has never stumped me like this one, quite honestly I hate this thing more than any vehicle I've ever worked on and am considering buying all foreign from here on out unless its older than an 85'.
Expert:  Dan replied 8 years ago.
The wire going to the coil, The white wire with the black stripe. With the test light connected to the battery postive post, does the light blink when cranked the engine over with the light testing the white wire with the black stripe.
Also check that pink wire at the coil connector.I seen them broke inside the wire insolation. Sometimes the wire breaks inside and you can get power out of it when you check it but you can move it a certain way and it will loose power
Customer: replied 8 years ago.
So I hook up my positive aligator to the positive on the batt. and probe the white with black stripe leading to the coil and I should get the blinking also like on the ICM?
Expert:  Dan replied 8 years ago.
Yes but the coil connector unpluged.

Here is the chart for the ignition system test

let me know if you have any questions

Customer: replied 8 years ago.
I checked the Igni. Control terminal A (pink wire) with igni. on and I am receiving 0 volts?????
Customer: replied 8 years ago.
<p>Sorry to bug, but I was running through the test sheets u provide, thanks by the way very helpful than most diagrams I received, So now I'm stuck on this step #27 Repair the shortto ground in the tachometer signal circuit between the ignition coil and the ICM. The only connection I see between the two is the backing plate on the ICM where there is white grease visable, is that the grounding or what purpose does tht serve????</p><p>   THANKS AGAIN</p>
Expert:  Dan replied 8 years ago.
Sorry for the delay, I was trying to finish mowing my yard.

If your not reciving ignition voltage on the pink wire, we need to fix that first.

Do you have voltage on the pink wire at the IGnition Module?
Customer: replied 8 years ago.
yeper, but when engine is turned over there is no pulsing light from the white with black striped wire like I should. Check list says I need to repair the ground between the ICM and the coil, Dont know what that means
Expert:  Dan replied 8 years ago.
Ok lets get this straight, You took a test light and connectedit to the battery postive post. You checked it to a good ground and the test light lit up. You unpluged the coil connector and the Ignition module hooked up. You cranked the engine over while the test light was on the terminal C ( the white wire with the black stripe). the test light dod not blink. Right?

Then you turned the key off and touched the test light(still connected to the battery postive post) to the white wire with the black stripe. Did the test light light then.
Customer: replied 8 years ago.
Yep exactly, No blinky when cranked over, no light when igni. off on white wire, no light but test light shows one red and one green when igni. is is off on pink??? I don't know??? would a high buck scanner with real time read out solve all this???
Expert:  Dan replied 8 years ago.
You got one of those logic test light. Do you have an old fashion test light with just a bulb? You cant do this test with that kind of light.
Customer: replied 8 years ago.
<p>Shouldn't matter what test light I use, I have about ten different ones and they all draw the same conclusion?</p>
Expert:  Dan replied 8 years ago.
If the white wire lit a test light connected to the battery postive post with the key off, that wire is shorted to groundbetween the module and the coil
Customer: replied 8 years ago.
Nope no light with Ignition off, I'm saying there is no light ever on the White black stripe wire, Ignition on off or anything inbetween
Expert:  Dan replied 8 years ago.
So on step 5 you answered no and went to step 6 and then answered no to that step also.
Then you are led to step 8. Step 8 you ohm the white wire with the black stripe from the coil to the ignition module. You should have less than 1 ohm.
Then you check the voltage on the pink wire on the ignition module with the key on.

Let me know the reading on these 2 tests
Customer: replied 8 years ago.
The pink wire gives me 11.9 or 12 Volts with ignition on, same with the pink at coil. In the test's on the sheet says the white one should pulse the test light indicating that the ICM is sending the appropiate sighnal too the Coil to fire, and I get no pulsing test light. then it tells me to go to step 27 fault in ground or something... I bought a code reader scanner today and it tells me the service engine light is not on but it is, and that the system is not ready. Wondering why my SES light does not go out after the ignition is on, I thought that after ten seconds or so it was supposed to go out indicating the system is ready??
Expert:  Dan replied 8 years ago.
The white wire should pulse. on step 6 it has you to see if that wire is grounded. If it was the test light that is still connected to the battery postive cable would be lit when touched the white wire. You said the light did NOT light so you answer no and go to step 8 and ohm the white wire from the coil to the module. If that ohms ok then go to step 9 and check the voltage which is ok then go to step 10 which checks the ground for the ignition module.
Then if that is good go to step11 which checks the signal from the computer.

The SES (service engine soon) will be on untill it starts.
Customer: replied 8 years ago.
<p>so I went back and started all over and got to step 11 and it read 6 volts it says its supposed to be between 1 and 4 which leads me to step 14. also the white wire gave 2 ohms</p>
Expert:  Dan replied 8 years ago.
Did you have the volt meter set to AC instead of DC?

Did you take the reading during cranking?

Any codes setting in the computer?
Customer: replied 8 years ago.
Yep had it on ac and wife cranking engine. No codes, and can't get any cause it never starts.
Expert:  Dan replied 8 years ago.
From there it tells you to ohm the wire from the computer to the ignition module and make sure it is not shorted to power or ground. If all ok replace the engine computer and program it.
Customer: replied 8 years ago.
yah! 400$ later it was the ignition module.