Question about 2007 GMC Envoy Denali
Cylinder 4 misfire. Vehicle exhibits misfire after normal operating temperature is reached and vehicle is driving a short distance. Spark plug, spark plug wire, ignition coil and fuel injector have been exchanged all check good. Injector signal has been verified and is good. Ignition coil wiring including: power, ground, reference ground, signal have been verified and are good. Stethoscope placed around #4 cylinder shows a faint knock in that cylinder which is not heard on any other cylinders. What is the probability of the AFM lifters in cylinder 4 unlocking prematurely after the vehicle reaches operating temperature ? Is there a way to check the VLOM solenoid for that cylinder or are they all activated at the same time ? Please Help with this issue. I do not have a scanner capable of actuating the solenoids or performing any of the associated testing of the DOD system.
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Posted on Jan 02, 2017
Remove right side front tire, pull up flap by shock and you will see the two ignition coils bolted on right side of engine. Each coil fires 2 plugs, 1&3 and 2&4. Had a similar problem and it was the coil. FYI my fuel pump went out and your dead when you stand.
Posted on Sep 18, 2009
You are jumping to conclusions. Slow down.
No spark AND no injector pulse indicates none of the desired outputs were triggered. The ignition module makes spark when it receives a crankshaft position sensor signal, and then transfers control of that spark to the computer after it starts. The module takes its crank sensor signal and generates an RPM count that it forwards to the PCM(main computer) which is used for triggering the injectors and controlling timing. SO, if you had a bad crank sensor OR a bad ignition module, you could lose both spark AND fuel. a coil would not disable injector pulse. modules RARELY fail in a manner that disables RPM reference to the computer causing it to not fire the injectors...At this point, I would TEST the crank sensor as the next step. If its easier, 1 of the wires on the module goes directly there so you can test the crank sensor at the module.
Posted on Sep 18, 2009
Testimonial: "great info, thanks!"
I would check the valves for number 6. If one or both are burned, stuck or out of adjustment it would cause your problem. If a cam lobe for that cylinder is burned or badly worn it could be the culprit.
Posted on Jan 10, 2010
SOURCE: my truck has a #4
Try to check that the fuel injector, using a fuel injector tester, is getting an electrical pulse as indicated by the tester lighting up and blinking periodically.
Also, one can check the injector by putting a stethoscope on the injector and listening for a loud click.
Also, check that antifreeze is not leaking into the cylinder causing the plugs not to fire. How did the plug look that was replaced? It should have had a light brown dry appearance if normal.
Posted on Oct 07, 2010
Testimonial: "answer was very timely, and definately gave a good NEW direction to look. Thanks."
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