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Ron Z.
Ron Z., - GMC Tech -
Category: GM
Satisfied Customers: 18959
Experience:  18+yrs experience. State Inspector & GM Diagnostics/Repair
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2002 GMC Envoy: Autozone..guys..coils one says vacuum leak

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2002 GMC Envoy P0300 code thrown. Autozone guys differ on diagnosis. One said plugs one said coils one says vacuum leak. HELP! Running rough.


So the P0305 was FIRST, then AFTER you swapped coils, P0300 came up?


Customer: replied 7 years ago.


Ok. Let's concentrate on the 305. I believe that is going to be the source, and when you swapped coils, the computer was a little confused as to why the misfire on 5 was no longer there, and suddenly jumped to another cylinder, which produced the 300.


Remove the coil that was ORIGINALLY on cylinder #5 before you swapped it. Remove the spark plug (check the plug for visible cracks/diode wear) and insert it into the bottom of the coil. Hold the coil with the plug in it near a solid ground (ie. the block) and while cranking, see if spark jumps (careful not to get your hands to close to the spark, they bite pretty hard). If no soild, even spark, suspect faulty coil. If there is spark, we'll move onto another test.



Customer: replied 7 years ago.
I've got to run to get a plug socket and extension for my ratchet. Be back in a while and will perform this check.


No prob. Take your time. I'll be here and the thread remains open for another 23+ hrs.


Customer: replied 7 years ago.
I had to use a Crescent wrench to reach the engine block. Cranked the engine and received no spark. I was having a hard time keeping the plug in the rubber collar.


Looks like you've got a faulty ignition coil. It's actually pretty common, and fairly inexpensive to repair.


Customer: replied 7 years ago.
I'll run and get one... I priced at Autozone at $77 and NAPA for $64 any advice?


Stay away from Auto Zone electrical parts! You'll be doing this job again in 6mo with an Auto Zone coil!! Go with NAPA!!


Customer: replied 7 years ago.
They will get it in at 8:00 tomorrow morning. I will keep you informed as to the results tomorrow.


Sounds good.


Customer: replied 7 years ago.
I haven't forgot you... I've got the part and will install when everyone else in the house wakes up. :)


Hahhahaha! No worries! It's all good. Take your time!


Customer: replied 7 years ago.
You the man. Installed in about 5 minutes. Running smooth as stawberry wine. Now how do I clear the code? The SES light is still on..


Excellent! Glad I could help!


To clear the code, you will need to remove the "NEG" cable from the battery for 15min.


Ron Z. and 6 other GM Specialists are ready to help you
Customer: replied 7 years ago.
Thanks for your help!


Anytime! Glad I could help! Have a great day!