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

[User_Name]

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.

 

[Dustin Jackson]

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.

 

[Geotrash]

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.

+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.

 

[Just Fishing]

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.

 

[User_Name]

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.

 

[User_Name]

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.

 

[Dustin Jackson]

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

 

[User_Name]

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

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

 

[Dustin Jackson]

@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

 

[User_Name]

@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

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)

 

[j91z28d1]

I wouldn't think a tune should be effected by doing a reset thats built in.

thats complete crap that he reset your truck, it started running horribly and then just sent you on your way like good luck.

what kinda shop treats people like that? man what they away with these days.

as said, I think I'd put the Tb back on and change plugs. that you have 2 o2's in the same side only is really weird, and definitely could be messing up the codes, like it thinks it's lean on the right side but the right side o2 is on the left side of the engine right next to the left side o2. do you have any kinda scanner at all? to look at fuel trims and do some basic diagnostics?

since it's modded, and seems oddly modded. you might just have to find a good tuner shop that can tune these trucks and have them diagnose whats been done in with it.

 

[User_Name]

I wouldn't think a tune should be effected by doing a reset thats built in.

thats complete crap that he reset your truck, it started running horribly and then just sent you on your way like good luck.

what kinda shop treats people like that? man what they away with these days.

as said, I think I'd put the Tb back on and change plugs. that you have 2 o2's in the same side only is really weird, and definitely could be messing up the codes, like it thinks it's lean on the right side but the right side o2 is on the left side of the engine right next to the left side o2. do you have any kinda scanner at all? to look at fuel trims and do some basic diagnostics?

since it's modded, and seems oddly modded. you might just have to find a good tuner shop that can tune these trucks and have them diagnose whats been done in with it.

Yeah I can look at the data, I have a cheap scanner that can read live. What would I be looking for as far as fuel trims?

 

[j91z28d1]

normally I'd look at long term trims left and right % and short term left and right %. + should be adding fuel, - is removing fuel. get an idea if the computer thinks it's rich or lean. doesn't really mean that's what it's physical doing. just what the computer thinks. like a vac leak it will need to add fuel, but a miss fire can show up in a few different ways, as rich so it's removing fuel, but also the o2 sensor only reads the amount of air in the exhaust. if unburnt fuel of a miss fire is happening, since the sensor doesn't see the fuel, it only sees the extra o2 from it not burning with the fuel. so it's a bit of a process and sometimes hard to tell not being in person where you can check plugs and other physical signs of what's going on.

also I'd look at both o2 sensor voltage, see if they are swinging back and forth pretty evenly. but with the sensors being wired differently from stock, like 2 on one bank. it kinda makes it. even harder to figure out what's going on.
I'd be seeing if you can't figure out what o2 sensor they have where. should be 4. bank 1. front and rear. bank 2, front and rear. you only needs the fronts, but for it all to work right you kinda need both front sensors to be reading the exhaust of the correct side.

 

[User_Name]

normally I'd look at long term trims left and right % and short term left and right %. + should be adding fuel, - is removing fuel. get an idea if the computer thinks it's rich or lean. doesn't really mean that's what it's physical doing. just what the computer thinks. like a vac leak it will need to add fuel, but a miss fire can show up in a few different ways, as rich so it's removing fuel, but also the o2 sensor only reads the amount of air in the exhaust. if unburnt fuel of a miss fire is happening, since the sensor doesn't see the fuel, it only sees the extra o2 from it not burning with the fuel. so it's a bit of a process and sometimes hard to tell not being in person where you can check plugs and other physical signs of what's going on.

also I'd look at both o2 sensor voltage, see if they are swinging back and forth pretty evenly. but with the sensors being wired differently from stock, like 2 on one bank. it kinda makes it. even harder to figure out what's going on.
I'd be seeing if you can't figure out what o2 sensor they have where. should be 4. bank 1. front and rear. bank 2, front and rear. you only needs the fronts, but for it all to work right you kinda need both front sensors to be reading the exhaust of the correct side.

Ok.. so I threw the old coil and wires back on 2 and 8. I unplugged the battery for 10 mins, and touched the terminals together for a few seconds. Cranked it and it still runs bad. Very intense gas smell. I can hear the air not combusting and exiting the exhaust. It doesn't stall though. Idle stays somewhat steady in park, still misses. In drive it vibrates.


I did check the codes a few seperate times, and those 3 mysterious ones were no longer present, phew. Back to 0300 and 174. But it still runs way worse than it did before the shop reset the throttle with the computer, with only those same two codes present.

Should I bother putting the old throttle body back on? It was leaking during the smoke test. Or perhaps the intake manifold fooled me and the shop into thinking it was coming from the TB? Come to think of it, there was no visible crack/hole that the smoke was coming from, just kind of under the TB. Shop sounded confident it was comin from TB.

Here's a video of the fuel trim, the camera focuses better in a few seconds.

 

[Dustin Jackson]

@User_Name Where exactly was it leaking during your smoke test? Keep in mind that if the motor is running the throttle body will be sucking in air by design..

 

[User_Name]

@User_Name Where exactly was it leaking during your smoke test? Keep in mind that if the motor is running the throttle body will be sucking in air by design..

It was coming from under/around the throttle body. No pinpoint. I should have inspected more

 

[Dustin Jackson]

@User_Name I would try the old throttle body just to be sure.

As for how to proceed, I would get another opinion on possible leaks near the intake. Avoid the original shop you used so you can get a fresh opinion

 

[User_Name]

@User_Name I would try the old throttle body just to be sure.

As for how to proceed, I would get another opinion on possible leaks near the intake. Avoid the original shop you used so you can get a fresh opinion

I have one scheduled at the chevy dealership around the corner next Tuesday. I'll swap out the TB in the meantime and report back. Thanks for the replies

 

[j91z28d1]

wow.. it's adding 29% fuel with the long term and 29% fuel on the short term on bank 2. which is the passenger side I'm pretty sure.

I've honestly not seen they much. I'm pretty sure that's maxed out, ecm throwing all the fuel at that side because it thinks it's lean. someone else here might have a better idea why it's doing that. I bet if you pull a plug in that side they are very black. if they aren't very black. it's gotta be a massive vacuum leak. something they should have seen.

how long was the run time there, I'm guessing it was long enough to get into closed loop. can you look at bank 2 o2 sensor voltage while it's maxing out the trims. I believe that's scanner will graph it out if you select it and hit one of the buttons. there's a blue one laying around here that looks the same as that one we grab for quick looks since everything laptop based is always a hassle lol. if the o2 voltage is saying Max lean it would cause the ecm to add fuel. then you need to pull the plugs to hopefully find out what it's actually doing.

o2 placement is still a wild card. but that's my guess. if o2 says it's lean but plugs are fouled out from ecm adding fuel based off bad o2. I'd throw an o2 sensor at it. or maybe just unhook the o2 sensor, usually when an ecm seen a sensor unhooked it has a stored middle of the road value to use to try and keep itself running. sometimes if an engine runs better with a sensor unhooked it's helpful in diagnosing things


the baro seems low to me. but I'm at sea level. maybe someone else can confirm that's normal where you are. but since bank 1 looks correct. it's probably not an issue.

 

[Just Fishing]

If the smoke test showed smoke under the throttle body/intake and everything was connected i would start by really looking over that area, maybe try tightening the intake down, and if that didn't work, pull the intake, tape off the ends, and smoke test the intake itself.

If that passed, then I would reinstall with fresh gaskets then re test.

With the intake off, i might be inclined to look for signs of a leak.

Other ideas would be a bad map sensor on top of the intake, and of course the O2 could be bad.