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Ok I have a 4.8 vortec left bank is not fireing I changed wirers plugs pulled injectors and cleaned them I checked volts on injector plug 7.8 I have good spark and compression now what. This is a 2003 chevy 1500. I did not check fuel pressure but when I pushed in where gauge hooks up it blew out off there heavy.


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contributions: 1947
Images: 37
Location: Oregon
how did you find out that the left bank is not firing? is it all the time or only after the engines warms up?

there is a TSB 06-06-04-046 issue date 09-12-2006 for 99-07 gmc engines, 4.8, 5.3, 5.7, 6.0, 6.2
it has to do with the ground wire G103 attached to the right side head.

bad O2 sensor could be causing lean or rich condition for one bank. Look at fuel trims and O2 waveform.

Plugged cat is also a common problem. verify back pressure on both sides.

try to verify with fuel trims, O2 sensor readings, what is the engine vacuum, and look at the misfire counter to see what is happening.


   
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03 chevy vortec thanks it miss fires when I start it also it has only one cat so why would it only affect one side I'm going to try every thing you said I will be in touch


   
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contributions: 1947
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Location: Oregon
this is what most 03 chev silverado 4.8l have for cat. with 2 pre-cat O2 and 2 post-cat O2. So, yes if you only have one cat it probably won't affect just one side.


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Only one cat with two o2 sensors I cleaned the ground wire no results next o2sensors thanks tony


   
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contributions: 1947
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Location: Oregon
You haven't told me why you believe that it only misfires on one bank. Did you have codes that says that? With only one cat and one pre-cat O2 you should have only one reading for fuel trim. How do you get bank side misfires? I would look at more of a failure of injector pulse or spark then.

check you voltages through the fuses INJ1 and INJ2 in the underhood fuse box. they should both have battery voltage key on engine off. INJ1 does the odd number cylinders and INJ2 does the even cylinders. All the injectors are independently grounded through the computer. It is possible that if you have a shorted injector that it could pull the power from the other injectors from that bank.


   
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When engine running I pulled plug wire on each cylinder on left bank great spark but no cylinder is firing I can have all four wires off plugs does not change I even jumped spark did not change when you say check volts at the fuse block should it be 12volts and if there is not 12volts what's wrong let you no tomorrow I'm about to buy a engine from aims engines out of Florida


   
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contributions: 1947
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Location: Oregon
if you are buying an engine for this car and this problem I would wait until you know what the problem is. If your problem is with the power to the injectors a new engine won't make it run better. and if the problem is with the ecm not grounding the injectors still, the engine will not make it run better. You need to find the problem.

you have two fuses for the injectors. but they all have individual grounds through the computer. Can you unplug all four injectors on the bank that doesn't fire? Ohm out the four injectors. they should all be the same resistance, (11-14 ohms). If you have one or more that are a lot lower than the others that could be the problem. If they are all within spec, leave them unplugged and start the truck up. (It should run just like you said it does when all the spark plug wires are off) while the engine is running check each injector harness connector for injector pulse. You can use a regular incandescent test light and see if the light flashes when you test both sides of the connector, using the test light to complete the circuit as if it were the injector. they should all blink in a regular pattern. If they all blink ok, plug them back on as the engine is running. Make sure you can do all this safely. with the engine running, each time to plug an injector back on the engine should run a little better. If that happens then that injector is working. if you get to one that doesn't make it run better that may be a bad injector. If that injector shuts down the whole bank that should be a shorted injector.

here's a video of a shorted injector that takes out all 6 cylinders on a V6.
http://www.youtube.com/watch?v=41SZexc_ ... Y0wF2o5WUw
the low resistance takes the power away from all the other injectors. because your injectors have two different power sources that would be why only one side turns off. That's if you have battery voltage at both injector fuses. If you don't have power at both fuses check that problem FIRST.

just things to check. you should scan for codes to see what the computer sees and has recorded. Scanner would be the first thing I would use to figure out what is going on.


   
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