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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29515
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Chevrolet Avalanche 1500 2003 avalanche with 5.3 vortec engine.

Customer Question

2003 avalanche with 5.3 vortec engine. Rough idle and rattle on acceleration but wide open throttle and power are good. Changed plugs and wires, cleaned TB, sea foamed intake thru brak booster, running tank of gas with fuel treatment. No noticable vacuum leak . Running out of ideas
Submitted: 5 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 5 years ago.
Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.
Does the check engine light come on?
Customer: replied 5 years ago.

It had a no. 7 cyl misfire code and also random misfire codes. I replaced the coil pack on 7 and new plugs and wires. No more codes but engine seems to be missing. Almost seems like a faulty coil pack still but the rattle concerns me

Expert:  GM Tech (Cam) replied 5 years ago.
When did you last change the fuel filter?
Customer: replied 5 years ago.
never but wot is great. full power never feels short on fuel
Expert:  GM Tech (Cam) replied 5 years ago.
Change it and check the vacuum line for the pressure regulator to make sure there is no fuel in there. If there is the you will need to replace the regulator.
Customer: replied 5 years ago.
Already pulled vacuum line on regulator, no fuel. Can you explain why a fuel filter would effect idle but not wide open throttle and power. A dirty filter effects flow volume not pressure
Expert:  GM Tech (Cam) replied 5 years ago.
Incorrect. Dirty filter drops both pressure and flow. At higher throttle it boosts the pressure from the regulator and that may make up for some restriction.
The filter is long ovrdue so please change it and let's go from there.
Customer: replied 5 years ago.
I can check pressure at idle to verify pressure. What should it be ?. Also, what about the rattle on acceleration? Bad knock sensor, intake manifold leak, cylinder imbalance?
Expert:  GM Tech (Cam) replied 5 years ago.
55-62 is the spec and it could be misfire causing imbalance.
Customer: replied 5 years ago.

Misfire is no longer detected by computer so when you say misfire are you thinking misfire from poor fuel delivery (filter) or misfire from another possible cause.

Expert:  GM Tech (Cam) replied 5 years ago.
Both. These are bad for the back of the injectors getting plugged. Let's see what the filter is like and the pressure.
Customer: replied 5 years ago.
when you say "these are bad for the back of the injectors getting plugged" I'm not following you. Do you mean the injectors in the 5.3 vortec are commonly prone to becoming plugged ? If that is a possibility how can I check one? Pull it out and disasemble or try a new one?
Expert:  GM Tech (Cam) replied 5 years ago.
The engines prior to 2004 with old fuel filters.
Customer: replied 5 years ago.
The only recommendation you have provided is to replace the fuel filter but the problem I have described could be many other things as well. If by process of elimination, I change the filter and the pressure is good, please list the next 4- 5 possible causes of what I initially described. I know it is guess work but frankly what I am looking for is from your knowledge and experience other commonly repaired items addressing this concern.
Expert:  GM Tech (Cam) replied 5 years ago.
I prefer to work through it and follow up rather than spew a novel worth of what Ifs. Leave this open and do the parts I recommended then we simply work through then as we go saving lots of time.
Customer: replied 5 years ago.
Ok. When you say leave this open I assume you mean I should not accept your answer until I try changing the filter because that is as far as you can take this using a parts changer approach. I asked for the top 4 or 5 items to check based on the described symptoms not a novel. I would expect a top chevy tech to easily describe off hand. I unfortunatley will not accept your answer. Have a good evening.
Expert:  GM Tech (Cam) replied 5 years ago.
Thanks anyway. I am sure could have figured it out and if you notice, I only suggested replacing the part that is currently many thousands of miles overdue.