Need some po300 assistance

[taylorb71]

I bought a 2000 suburban 4x4 5.3l mainly for parts to ls swap my square body but I want to get it running decent in the vehicle so I’m not trying to diagnose it in my square body.

problem I’m having is a po300 code. At idle the check engine light will blink and it runs rough and almost sounds like lifter clatter but I’m thinking it’s spark knock because some times it will run fine and the engine sounds normal!
I’ve crudely checked each coil for spark and each spark looks nice and strong, spark plugs are good as well.

I have a feeling it’s a fuel issue as I bought it with a full tank of gas and the kid said it ran like crap. I poured a thing of Techron (or whatever it is) fuel treat and ran a half a bottle of sea foam through the pcv hose. I’m not sure if it’s made a difference or not. When I throttle it, it sounds super throaty through the intake (factory and not restricted) but taps out at about 4K rpm and takes a while to get there.
fuel pressure is good with 49psi at idle and 58 psi when I give it throttle.

when I hook my scanner up to it my o2 sensors are switching like they should when it gets to closed loop although the downstream sensors seem a little goofy. My fuel trims also seem weird. Stft1 is at -11% and stft2 is around 0%.
Map sensor is reading 11hg
Maf is reading 1.04lb
Iat and coolant temp seem to be accurate.

I’m just kind of lost. I’m thinking the fuel trims is telling me something but I don’t have much experience with values on a scan tool. Also having the downstream o2’s acting goofy by switching more than they should kind of leads me to a plugged cat or 2 as well.

I’m sorry for the huge post just lost lol

 

[Fless]

After it's in closed loop can you post both the short- and long-term fuel trims? Maybe at idle and at 1500 or so RPM? Kind of odd that your B1 STFT is so different from B2, but the LTFTs will tell a more complete story.

 

[taylorb71]

Ok I will run back out here after a bit and get it all. I took a video of it but apparently I didn’t save it on Snapchat.

 

[taylorb71]

After it's in closed loop can you post both the short- and long-term fuel trims? Maybe at idle and at 1500 or so RPM? Kind of odd that your B1 STFT is so different from B2, but the LTFTs will tell a more complete story.

Ok so I have a video of what it’s doing. BUT! when I went back out to read it again I had issues with keeping it running and even connecting to the scanner. Well I pulled the ground cable off and found it had a nice layer of green corrosion. Cleaned that off and reconnected it, mind you a battery does not stay in this vehicle, I’ve been swapping batteries around between my Tahoe and this. I don’t think it’s a ground issue beings I’ve fixed the passenger side head ground and cleaned up the ground under the drivers door. Other grounds look okay.

anyway I got it fired back up and it didn’t dip or die. I’ll include a picture of my trims.
Also both my upstream o2’a are switching properly but my b1s2 o2 is switching high to low as well.

edit** I should add that I did not get a code to pop up again but it was still very very sluggish when revving up

 

[Rocket Man]

Probably don’t want to keep pulling the battery in and out of it. These vehicles don’t like that.

 

[taylorb71]

Probably don’t want to keep pulling the battery in and out of it. These vehicles don’t like that.

I will probably end up buying a battery for it. But I will keep this in mind. Especially since I’m swapping from my 2000 Tahoe daily to this piece of junk lol

 

[Fless]

Bank 1 (driver's side) is running considerably richer than Bank 2. Your combined fuel trims (LT & ST) should add up to near zero or 5% or so on each bank.

I don't know if a MAF sensor would affect one side more than the other, but you might clean it or swap it out to eliminate it. You could have a fuel injector on that side that is staying on too long and dumping more fuel than it should. Have you looked at the spark plugs to see their condition?

I'm sure that others will have more recommendations.

EDIT: I meant to add that a flaky O2 sensor on that side could affect it. Swap them side to side to see if the rich bank moves with them.

 

[taylorb71]

Bank 1 (driver's side) is running considerably richer than Bank 2. Your combined fuel trims (LT & ST) should add up to near zero or 5% or so on each bank.



I don't know if a MAF sensor would affect one side more than the other, but you might clean it or swap it out to eliminate it. You could have a fuel injector on that side that is staying on too long and dumping more fuel than it should. Have you looked at the spark plugs to see their condition?

I'm sure that others will have more recommendations.

EDIT: I meant to add that a flaky O2 sensor on that side could affect it. Swap them side to side to see if the rich bank moves with them.

I will try the 02 sensor idea. May end up just getting new ones beings I will want new ones when I do the swap. Am I ok in assuming that the Downstreams wouldn’t be causing the issue I’m having? Everywhere I read it says they won’t cause driveability issues. They will be tuned out anyways

I do also have a whole other intake, rail and injectors from a known running motor. Last resort I’ll try that. I could also try cleaning the maf, if anything I can swap in the one from my Tahoe and test it that way.

the main reason I’m so adamant with getting it running in the burb is so I can verify the trans shifts smooth as I plan on putting that trans in my Tahoe which has a burned 3-4 clutch pack

edit** Would a plugged cat on that bank make it dump more fuel? I’m thinking not but the vehicle has 237k on it so a plugged cat is possible