2008 tahoe K1500. Throwing P0300(random misfire) and P0174 (lean bank 2).

5.3L 187,000 miles, it's throwing P0300 and P0174. Bank 2 would be passenger side? My thought was to check the spark plugs/coils, am I on the right path? Or is this code normally the fuel pressure regulator? Thanks for any help in advamce.

I would check for PCV, vacuum, or intake leaks near the passenger side. That code suggests that there is too much air getting into the passenger side combustion chambers.

I think if it was fuel pressure regulator related the entire engine would suffer, not just the passenger side. Unless there is a fuel pressure regulator for each side of the motor but I do not believe that is the case.

Dustin Jackson said:

I would check for PCV, vacuum, or intake leaks near the passenger side. That code suggests that there is too much air getting into the passenger side combustion chambers.

I think if it was fuel pressure regulator related the entire engine would suffer, not just the passenger side. Unless there is a fuel pressure regulator for each side of the motor but I do not believe that is the case.

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+1. I suspect intake manifold gasket leak but the first step I would take is to retorque the intake manifold bolts.

Also, there is only one fuel pressure regulator in the system for both sides of the engine, and it's in the tank with the pump.

I got the lean code once, confused the heck out of me..

I did an engine swap and i have a wideband 02 sensor installed for monitoring and tuning.

I went right to tuning since it had recently become really cold, figuring i just needed to toss some more fuel at it.
More fueling = not much change.

So i popped the hood and i heard a strange new noise.

Then it hit me, vacuum leak!

I found the pcv hose under the engine cover had come off/split and was throwing everything off.

This could also cause a misfire condition...


Moral of the story, don't overthink it.
Start with the basics, make sure you don't have a vacuum leak, and the intake tube is in good condition and attached.

Ok so I had a smoke test done, and saw that the throttle body was leaky, so I replaced it, but it was still feeling the same at idle.

Then i took it to a shop to look at the data and they said 2 and 8 were missing pretty bad. I replaced the coil and wire for both of those, cranked it and it was noticeably worse. As I was driving it felt decent, but I could still feel it missing.

I took it back to the shop, they suggested a throttle reset. When he reset the throttle, all of the guages started moving. He then shut the engine off, looked at a bunch of codes that were thrown, erased them. Cranked it back up and the guages still moved, just once every 10 seconds or more this time, instead of constant up and down.

Now it shows my engine is misfiring on 5 and a couple others, along with 8 and 2.

. So he deleted the codes again, said he "put the throttle back to where it was" and that I should do a "hard reset" on my battery by taking the terminals off and touching them together.

Driving it home was bad, it didn't stall, but it wanted to. It was surging badly going down the road too, I didn't take it over 40 mph, it was really sluggish. It was shifting hard, I assume because of the engine not firing right and being jerky.

It has no loud knocks or taps apparent, just runs horrible and I can smell all the unspent fuel.

I checked codes, I still got p0174 and p0300. But now, I have 3 new ones.

P2544- torque management request input signal "A"
U0073- control module communication Bus Off
U100- lost communication with ECM/power train control module "A"


Is there anything I can do? I'm thinking about putting the old coil wires and coil back on just to see what happens at this point. I did not change any spark plugs. Thanks for reading, all replies welcome.

With the misfires before all of this, that originally threw p174 and p0300, the truck still ran good, just had some hiccups every few redlights..
Figured any information helps.

@User_Name Whenever parts are swapped and new problems come up I recommend going back to square 1

Dustin Jackson said:

@User_Name Whenever parts are swapped and new problems come up I recommend going back to square 1

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Tomorrow I'm going to pull the spark plug on the 2 and 8, the original culprits throwing codes, see what it looks like.... I've never seen those last 3 codes, those were caused when the shop plugged up the high-tech computer and reset the throttle. Maybe they'll go away? Thanks for the reply

@User_Name I am wondering if the new throttle body is contributing to these problems as well. I might swap the old TB and coil and wire on and go from there.

These things tend to idle pretty poorly naturally

Dustin Jackson said:

@User_Name I am wondering if the new throttle body is contributing to these problems as well. I might swap the old TB and coil and wire on and go from there.

These things tend to idle pretty poorly naturally

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Thanks, I will swap it all back out tomorrow. I'm still just boggled by how the shop resets the throttle in the gizmo gadget, and everything goes haywire. I watched as he pressed the button, "throttle reset" and it all went berserk. If this truck had a tuner (which I suspect) could what he did have interfered with its settings, because of it having headers with no cat, only a single magnaflow. It only has two 02 sensors plugged into the drivers side exhaust. (Hasn't had idle issues for the last 4 months I've owned it)