Persistent P0420 and P0430

[Cj6706]

Hello All,

I’ve been searching forever it feels with no luck. I bought a used 07 Tahoe with a flex fuel 5.3. 165k miles. Decent shape but as I look into it more, maintenance was sub par. It had P0430 and a bunch of EVAP codes when I got it. Replaced the cats since it was rattling. 4 new GM O2 sensors. Cleaned the throttle body, new MAP and MAF sensors, new thermostat (was sticking), fluids etc. Runs fine until P0420 and P0430 codes pop then it runs like crap. Clear the codes and back running fine. When the codes pop it’s the same type of driving; slow speed coming to a stop in a parking lot. Feels like the converter is staying locked up and wants to die. Transmission doesn’t seem to be an issue; I think. Freeze data shows negative long term fuel trims between -6 and -10 usually at between 515 and 530 RPM at 0 MPH. Tried the spacer fix and no difference. Plugs have shown no evidence of coolant or other issues that I can see. Decided to pull the injectors and clean them. A couple of them were pretty crappy but in the end all had good spray patterns. When watching live data the long term fuel trims at cruise speeds are in the high negatives. Ranging from -12 to -18 on both sides. Post cat O2 readings are in the .09 to .1 range, which show lean (correct?). You can now feel a really significant surge. Acceleration is just fine though. Checked fuel pressure at idle and it’s 55. I read one post that leads me to look closer at the fuel pump assembly but not looking to throw more parts at it if I don’t have to. Any other ideas for things to check? Thanks.

 

[Fless]

Welcome to TYF from Colorful Colorado.


Negative fuel trims indicate rich; the computer is taking away fuel to make up for too much fuel or not enough air. How's the air filter?

What are the STFTs at 2K rpm (warm)? Fuel pressure at 2K rpm?

55 psi at idle seems pretty high; I think these rigs run in the mid 40s: 43-45psi. I'm fairly certain that the fuel pressure regulator is built into the fuel module (pump) on the NNBS so you may need to take a closer look at the fuel pressures and fuel module.

Hopefully others will chime in.

EDIT: Can you tell if the O2 heaters are working; does the system go into closed loop?

 

[Cj6706]

New K&N panel with the excess oil wiped off. Goes into closed loop just fine. I’ll check fuel and such at 2000 later and post. Thanks.

 

[89Suburban]

New K&N panel with the excess oil wiped off. Goes into closed loop just fine. I’ll check fuel and such at 2000 later and post. Thanks.

Good luck man!

 

[Cj6706]

Ok so I got back out and checked it. Key on engine off 55 psi. At idle jumped to between 60 and 62. Long term fuel trims were -8 and -10. At 2000 RPM pressure was still 60 - 62 but fuel trims were -18 and -20. I didn't check O2 readings. I’ve read that spec is anywhere from 43 to 62. Anybody know for sure? It’s obviously running way rich and defueling a ton. Weak spark? I’ve seen a couple misfires on the scan tool but not consistent. New plugs and wires but still original coils. I don’t see any indication of an air issue unless the throttle body isn’t opening as much as it thinks it is. I did remove it to clean and the bolts were barely snug. I’m starting to wonder if the throttle body isn’t opening as much as it thinks it is and it’s like driving with it choked. At idle the MAF readings are usually .01 or .02 lbs/sec.

 

[Cj6706]

Also, new MAF since I cleaned the old one with brake clean. Don’t do that. It turns the potting on the circuitry to sticky goo.

 

[CaptainAmerica1]

How are you logging your fuel pressure?

 

[Cj6706]

Gauge plugged onto the fuel rail. I’m gonna pull a plug or two out today and see what they look like as well.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Cj6706]

Well this isn’t good. Powdery white ground strap. I know these are supposed to be frugal with fuel but not this much. But explains a lot. Gonna go in and reset the fuel trims and alcohol percentage to see if it relearns.