School me on 5.3 running lean

wannabe · Jan 30, 2013

Secondary o2's would pick up in the cat. And if you wanted to test them just pull the upstream o2 don't have to pull manifold pipe

yankster · Jan 30, 2013

throttlejunkie said:
I've thought about the cats, but would that come on so sudden?? Also, I see the pressure is a little low, but would that cause the injectors to fire that poorly, casue its having a hard time even idling now. Its straight up acting crappy now!

Cats don't don't get dirty that quickly. And 44 psi isn't low enough to see a problem until your pulling a decent load on the motor. The intake gaskets are hard plastic with a silicone or rubber ring around the intake port holes. This rubber gets hard over time and breaks loose creating a fresh air leak. The O2 sensors see a lean condition and start increasing injector pulse width to compensate which, creates a chain reaction of lean/rich conditions, eventually resulting in the random misfire codes.
I chased my tail for a while before I figured it out, so I hope this all helps. Fuel pump is $400 and a pain to replace. Intake gaskets are $75.

throttlejunkie · Jan 30, 2013

Preciate all the help guys! :dblthumb:

throttlejunkie · Feb 1, 2013

Well threw some intake gaskets on er, no luck. Loaded it up took it and had it scaned , again...said mass air. Got a new one...still same issue. :gay:

wannabe · Feb 1, 2013

im still saying fuel pump

heepr · Feb 2, 2013

What are your long term fuel trims? Have you blocked off all vacuum hoses one by one to rule out leaks? I have had ones that werent obvious with the starting fluid trick like a bad brake booster.

I agree 44psi sounds low too.

Lauderale · Feb 2, 2013

Saying fuel. Maybe perhaps change the fuel filter. See if that changes anything.

tunedportcj5 · Feb 3, 2013

Check ALL of your grounds. Depending on your harness - especially check your O2 grounds.

throttlejunkie · Feb 3, 2013

According to GM the fuel is good. Flex fuel 5.3 had less pressure 42-48. I started to swap the pump, already swaped filter, but with that pressure it would suck to replace it for no reason. Still several things and sugestions im goona try. Blows me away after having it hooked up to a bad ass snap on computer and even it was wrong. Guess it wasnt as bad ass I thought.

pillsbury · Feb 3, 2013

throttlejunkie said:
Well threw some intake gaskets on er, no luck. Loaded it up took it and had it scaned , again...said mass air. Got a new one...still same issue.

What state do you live in?

throttlejunkie · Feb 3, 2013

pillsbury said:
What state do you live in?

North Ga.

wannabe · Feb 3, 2013

tunedportcj5 said:
Check ALL of your grounds. Depending on your harness - especially check your O2 grounds.

If it was an o2 problem it would run fine on open loop.

grcthird · Feb 3, 2013

X2 on open loop. Did you ever get the code # ?

wannabe · Feb 3, 2013

throttlejunkie said:
According to GM the fuel is good. Flex fuel 5.3 had less pressure 42-48. I started to swap the pump, already swaped filter, but with that pressure it would suck to replace it for no reason. Still several things and sugestions im goona try. Blows me away after having it hooked up to a bad ass snap on computer and even it was wrong. Guess it wasnt as bad ass I thought.

what did this scanner say that was wrong? and your sure its a flex fuel?

wannabe · Feb 3, 2013

gm 5.3 NON flex fuel pressure 55-62

GM 5.3 FLEX FUEL fuel pressure 48-54

straight from mitchell..

wannabe · Feb 3, 2013

and have you looked at live data under misfire counter and seen what cylinders are giving you the problem

throttlejunkie · Feb 3, 2013

The code initially was P300, and P301, if i remeber correctly, took ita and had the snap on comuter/scanner thrown it and it read out MAF bad, with no other cades. Im goona try the open loop tomorrow, is it best to unplug the O2 sensors or do they need to be pulled out and remain pluged in? and should i pull all 4?

wannabe · Feb 3, 2013

you need to go back to the guy who has the scanner and watch all the live data while its acting up, look at the missfire counters for present AND history. open loop and closed loop refer to how the PCM is getting its info on fuel. in open loop (anything under 140 degrees and not WOT) using things like MAF,ECT,MAP,IAT, and so on.. Closed loop uses your upstream oxegen sensors. the down stream sensors are only in place to monitar the catyletic system is functioning properly and has no effect on performance

wannabe · Feb 3, 2013

p300 is random/multiple cylinder missfire, p0301 is cyl 1 missfire. sometimes you can only have 1 or 2 missfires and it will throw the p0300 because the motor will be unbalanced. just like alot of times paired cylinders will missfire together even though 1 is only miss firing.