P0300

GM Guy

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#1
Make
Chevy
Model
K1500
Year
1996
Miles
146k
Engine
5.7L
This truck has sat for a couple years. I put all new brake lines and brakes all the way around. New rotor/cap/wires/plugs. It had a full tank of (old) gas. I added injector cleaner and gas treatment just in case there might have been water in the fuel. When I first started it it ran roughly and set P0300. I found the EGR gasket was leaking and replaced it and it smoothed out. Now it has a quirk where as it warms up, it has a subtle miss after it's shifted up through the gears and unlocks the torque converter and sets a P0300. I can reset it and the code doesn't come back and the torque converter works normally, until the engine cools off (overnight) and then it will do the same thing over again. I have attached the freeze frame info that my Giotto software captured and I was wondering if someone here could help me understand how to interpret this data, if it is even helpful. I've done some searches on the dreaded P0300 code and the symptoms described elsewhere are different than mine. This miss is only detectable when up to speed and after the final transmission shift (lockup tc).
Also, how can I find out why the ABS light is on? I replaced the right front ABS sensor due to the wire being severed and the light is still on. The truck was in a light fender bender due to a blown brake line. I replaced the doghouse.
 

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grcauto

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#3
I would start by draining the tank of all that old fuel and fill with new fuel and run it for a while and see where you are at.
 

GM Guy

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#4
Mobile Dan- No it does not have an overdrive off switch.
GRCauto- I've ran out almost all of the fuel.
What about my freeze frame information?
Is there anything that jumps out at you guys?
 

billr

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#5
I'm just guessing, but the short-term fuel trims look substantially different on the two banks to me. Does this have the kind of injection, like the older TBI, that could have that happen with a bad injector? Look at the upstream O2 sensor action on each bank; maybe even swap the sensors side-to-side.
 

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#6
This is a Vortec 5.7L Yes, I did notice that the numbers were not the same from side to side, but I don't know just how to interpret that.
It has CFI and from what i have researched this system can be a problem, but there's a conversion to MFI that looks simple to upgrade to. I thought about doing this but I don't like throwing parts at a problem just for the sake of doing something. I've owned another Vortec 5.7L and it didn't give me the first problem for the 60k mi + that I drove it.
 

billr

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#7
Yeah, I doubt the cost and effort to install the MFI is worth it for you. (MFI can have failures, too) I have essentially the same engine in a '97 Express van with 170K miles, no problems. That CFI can work.

Do you know how to use live-data to watch the upstream O2 sensors "toggle" rich-lean-rich-lean...?

PS: Have you pulled the plugs for a peek at condition and taken compression readings? It never hurts to do those basic checks.
 

grcauto

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#8
I'm just guessing, but the short-term fuel trims look substantially different on the two banks to me. Does this have the kind of injection, like the older TBI, that could have that happen with a bad injector? Look at the upstream O2 sensor action on each bank; maybe even swap the sensors side-to-side.
Short term is of little value unless looking at it live. It will tell the state of the O2 sensor. The long term trims tells us more how it's doing with fuel delivery overall. The long term is a little lean but not bad and they are close bank to bank. I like to see them at + or - 5 or so, but 8 is not to worry about.
 

grcauto

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#9
This is a Vortec 5.7L Yes, I did notice that the numbers were not the same from side to side, but I don't know just how to interpret that.
It has CFI and from what i have researched this system can be a problem, but there's a conversion to MFI that looks simple to upgrade to. I thought about doing this but I don't like throwing parts at a problem just for the sake of doing something. I've owned another Vortec 5.7L and it didn't give me the first problem for the 60k mi + that I drove it.
The biggest problems these Vortek CPI systems had is the plastic breaks when you need to work on them and there's only one solution from GM to fix these.....REPLACE THE ASSEMBLY....You couldn't even replace the regulator by itself. There was a friend I had in Indy who we called the injector guru. Jim Linder of Linder Technologies in Indy Indiana. He's gone a few years now but he had developed a simple way to replace the regulators on these. I don't know how many of these kits I bought from him over the years but he sold 10's of thousands if not more. Google 'injector guru' and you'll find plenty on this old master of fuel injection.
 

grcauto

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#10
BTW you'll want to rethink that switch over to MFI. Study it close before jumping into that hornets nest.
 

GM Guy

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#11
Yeah, I doubt the cost and effort to install the MFI is worth it for you. (MFI can have failures, too) I have essentially the same engine in a '97 Express van with 170K miles, no problems. That CFI can work.

Do you know how to use live-data to watch the upstream O2 sensors "toggle" rich-lean-rich-lean...?

PS: Have you pulled the plugs for a peek at condition and taken compression readings? It never hurts to do those basic checks.
no, I haven't.
 

nickb2

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#13
I am certain you can read the readiness monitors with your giotto thing.

In mode 6, you will be able to see which cylinders are actually misfiring. Do you know how to access the mode 6 in you auto enginuity gitto?
 

nickb2

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#14
Read this artyicle, then play with your live data scan tool from enginuity. There is a wealth of info in mode 6 if you know how to read it. Just access it and post back just like you did with the freeze frames. Here is a link to that article, it talks about gm"s misfiring capabilities in mode 6 to help you understand what is going on. We want to see which cylinders are actually missing, or if all of them are missing at different times. Etc.

https://www.motor.com/magazine-summary/obd-ii-mode-6-diagnosis-driveability-corner-june-2002/