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P0307 Code


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#1 MrBuck69

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Posted 22 January 2006 - 12:04 AM

I have a 2000 Tahoe 5.3L and the SES light came on and went off 2 weeks ago. Yesterday it came back on and I got the P0300 and P0171. I cleared those out because that amber light is annoying. The light came back on after a couple of hours of driving around the city and I got a P0307 code. I don't really know where to start. When I accelerate hard I get an occasional pop noise from the front of the truck. I'm thinking its my Oxygen sensors. I have a 96K and the sensors are original, truck doesn't idle as smooth as it use to and I have a AEM brute force intake with a very dirty filter that always falls off. Maybe its my catalytic convertor, meineke told me a couple of years ago that it didn't look to great. Any suggestions? If these trucks have 4 Oxygen sensors, how do you know which ones to change?

#2 dougmac

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Posted 22 January 2006 - 02:24 PM

Here is a breakdown of the codes:

P0171 System Too Lean (Bank 1) (left side)
P0307 Cylinder 7 Misfire Detected (rear cylinder on the left bank)
P0300 Random Misfire Detected

Because you have both a lean bank and random misfires, I would look for a vacuum leak that would only affect the left side cylinders. The additional # 7 cylinder code would cause me to look closely at the intake and vacuum connections that would affect cylinder #7.

You should also check the fuel pressure......low fuel pressure can also cause a lean condtion. Maybe a restricted fuel filter....

Good Luck,
Doug

Edited by dougmac, 22 January 2006 - 02:38 PM.


#3 97chevy350

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Posted 23 January 2006 - 06:34 PM

Definately change fuel filter and air filter first. P0300 is the code from hell, Multiple Random Misfire. Which is a pain to find, (a problem I am having now). Luckily you have the other codes too to help narrow it down. To check for vacuum leaks, spary some brake cleaner around the engine and listen for the idle to spike. And pull your #7 plug, take a good look at it, a plug can tell you a lot.

#4 brokedown

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Posted 09 April 2007 - 11:00 AM

Here is a breakdown of the codes:

P0171 System Too Lean (Bank 1) (left side)
P0307 Cylinder 7 Misfire Detected (rear cylinder on the left bank)
P0300 Random Misfire Detected

Because you have both a lean bank and random misfires, I would look for a vacuum leak that would only affect the left side cylinders. The additional # 7 cylinder code would cause me to look closely at the intake and vacuum connections that would affect cylinder #7.

You should also check the fuel pressure......low fuel pressure can also cause a lean condtion. Maybe a restricted fuel filter....

Good Luck,
Doug



#5 brokedown

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Posted 09 April 2007 - 11:05 AM

Here is a breakdown of the codes:

P0171 System Too Lean (Bank 1) (left side)
P0307 Cylinder 7 Misfire Detected (rear cylinder on the left bank)
P0300 Random Misfire Detected

Because you have both a lean bank and random misfires, I would look for a vacuum leak that would only affect the left side cylinders. The additional # 7 cylinder code would cause me to look closely at the intake and vacuum connections that would affect cylinder #7.

You should also check the fuel pressure......low fuel pressure can also cause a lean condtion. Maybe a restricted fuel filter....

Good Luck,
Doug


What if you are getting random misfire on 1,3,5, and 7? I have checked fuel pressure, replaced fpr,swapped coils/injectors to unaffected side, and removed intake manifold looking for cracks, all with no results. What would cause every cylinder on one side to misfire?

#6 Drunken Sailor

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Posted 03 May 2007 - 08:49 PM

You're looking at this the wrong way. I suspect your problem isn't a misfire caused by a lean condition.

You have to think about the way the PCM monitors (or doesn't) air/fuel ratio. Remember, O2 sensors don't directly measure air/fuel ratio, they measure oxygen content of the exhaust gases and this information is used by the PCM to estimate air/fuel ratio and tweak fuel delivery. Fuel trims are modified using the idea that more oxygen in the exhaust means a leaner mixture and less means a richer mixture. However, the other thing that increases oxygen content of the exhaust is... misfire! Think about it; air and fuel goes into the cylinder, is doesn't burn, air and fuel goes into the exhaust. The O2 sensor sees all this oxygen.

People get caught assuming that an O2 sensor directly measures air/fuel ratio, which it can't.

Where am I going with all of this mechanic talk?

Your misfire problem is causing the lean code, not the other way around. Time to check spark plugs, wires, injector balance, compression etc.