2004 Denali 6.0L throwing Codes P0174, P0171, P0101, P0446

[Marinevet]

I hooked my code reader up last night, and those are the codes I got. After some research, I found the two biggest contenders here are intake gasket leak or fuel system problem. I plan on checking fuel pressure tonight, cleaning my MAF sensor (common to make P0101 show up), and have even been told intake bolts will work loose. From what I understand, my truck has the returnless fuel system (started in 04?), so if pressure is low, it will about have to be clogged filter or pump.

The reason I checked the codes is because I'm starting to get a lull in moderate acceleration, almost like driving a diesel that has bad turbo lag. When I'm accelerating, holding my foot in the same spot, it will accelerate for a bit, kind of plateau, and then surge forward like I mashed on it. It has had what felt like a miss at idle for awhile, but ran fine at other RPM range. Also, the new found dead spots seem to only happen when the truck is at WOT, although it warms up pretty quick so it's hard to get a lot of time to check. The truck has plugs and wires with about 20000 miles on them.

Do any of you have other things I should check as well? The bad part is I don't have a spare vehicle right now, so it can't be down for too long, and I don't have a ton of money to just throw parts at it. I also don't want to drive it too long with both banks running lean, because I don't want to ruin the motor. Thanks guys.

Jeremy

 

[swathdiver]

I think the MAS is setting off the lean conditions. Where do you live? Maybe there is another member nearby that would could help or swap parts to see what you need to get it running right.

 

[DenaliJJ]

Question... was your cel on or did you just decide to hook the reader up to it? Reason I ask is everyone in awhile mine will feel like I have to almost mash te pedal to get it to kick down

 

[DenaliJJ]

Question... was your cel on or did you just decide to hook the reader up to it? Reason I ask is everyone in awhile mine will feel like I have to almost mash te pedal to get it to kick down

 

[Marinevet]

My CEL was already on. It had been for awhile, but initially it was just the EVAP code, so I didn't worry about it. But then it started to get the stumble to go with it, so I re-checked it.

Update: I checked my fuel pressure last night with a Harbor Freight $20 gauge. Turned key on, read 48 psi, but noticed after about 10 seconds it was down around 35 PSI. I also noticed that I had about a 1 drop every 3 second leak where the hose screwed onto the fuel rail (thanks HF ). I don't think that slow of a leak would have made my pressure read that low, but I am going to hook a different gauge to it tonight to verify. As of now, I am suspecting fuel filter or pump, leaning more towards pump because I don't think the filter plugging up would make the pressure drop?

Also, I did blow off the MAF sensor with some MAF sensor cleaner, I didn't really notice a difference in how it drove. At what point should I clear the codes? I wrote them all down and everything. Thanks again for all the help, I will keep updating and post final results in case others have the same issue down the road.

Jeremy

 

[swathdiver]

I think it's ok to clear them and see what comes back. Don't know how much different my truck is from yours with regards to fuel pressure, my 5.3 LC9 runs at 43-43.5 psi.

 

[DenaliJJ]

I believe fuel pressure should be around 58 and no drop in pressure.(maybe 5lbs) we don't have a fpr on the fuel rail as it's in the tank with the pump. Sooner or later the pump will completely give out so might as well change it now and fix that evap while your down there

 

[06Escalade]

I recently replaced the IMG and TB gasket during knock sensor replacement. I suggest you replace them and the harness while you have the intake off. The harness gets loose, the grommets pop out of the oil galley allowing water to pond up in the knock sensor holes. Made a difference to get that fixed. Better idle, quieter. The TSB repair to prevent future water issues is online. Also a good time to take TB off to clean thoroughly

 

[M1Gunner]

Regarding your lean codes along with the evap leak I would also check your purge solenoid. If it's starting to stick open, you will begin to have those exact symptoms which progressively worsen.

 

[Marinevet]

Update: Used buddies non-leaking pressure gauge, 48 psi with key on but holds steady, and when started it jumps up to 58 and stays right there, whether at idle or revving the engine up. I am going to replace the air filter and fuel filter both, but I don't think that is going to fix my lean condition. I think it's time to check the intake bolts and look for an intake leak. I will also check the other things you all just talked about, I appreciate it. More updates to follow as I will have some time to work on it this weekend. Thanks.

Jeremy

 

[M1Gunner]

The only issue I have with thinking it is a vacuum leak due to your intake manifold gaskets is that both gaskets would have to fail at the same time in order to throw a lean code for both banks. Not saying it's impossible, just more so unlikely. Typically one side may fail which would lead to a bank specific lean condition.

Things that could effect both banks to run lean involving air for example could be a crack in the intake air duct, a vacuum line to the intake manifold etc but those typically come with a idle surge.

Things that could effect air/fuel ratio that won't cause a surge symptom (or at least not as severe) would be a component like the evap purge solenoid (which will illuminate the money light) or the MAF sensor sending an incorrect voltage signal due to foreign debris/residue on the sensor (which would also illuminate the money light)

 

[HiHoeSilver]

Update: Used buddies non-leaking pressure gauge, 48 psi with key on but holds steady, and when started it jumps up to 58 and stays right there, whether at idle or revving the engine up. I am going to replace the air filter and fuel filter both, but I don't think that is going to fix my lean condition. I think it's time to check the intake bolts and look for an intake leak. I will also check the other things you all just talked about, I appreciate it. More updates to follow as I will have some time to work on it this weekend. Thanks.

Jeremy

Did you clear the codes?

 

[afpj]

Did you check fuel trims at idle, and at around 2000 rpm? Oxygen sensor voltage graph/pattern?

 

[BlueCollarTahoe]

i had a similar issue but running rich...turned out to be the Oxy sensors.

 

[Marinevet]

That makes sense to me. Where is the evap purge solenoid located on the truck, and is there any way to test it, or should I just replace it? I already blew off the MAF sensor, so I will check the evap purge solenoid next. I didn't get to the Yukon this weekend, I hope to either tonight or tomorrow night. Thanks again for the help.

 

[Marinevet]

Did you clear the codes?

I didn't clear them yet, I want to get the new air filter and fuel filter in first, but I didn't get to it this weekend quite yet.

Did you check fuel trims at idle, and at around 2000 rpm? Oxygen sensor voltage graph/pattern?

I am not able to check that stuff, I just have a code reader, not an actual scan tool. I don't mind paying someone to hook one up, but first I want to rule out all the things I can check myself without the scan tool.

Thanks again for all the input everyone.

Jeremy

 

[MidwestMike]

To be honest I haven't played with my newer Tahoe, but I bought a cheap bluetooth scanner that you use with your phone and Torque or some similar app.
On my last one it surprised me how much data was available. I originally bought it to try to work on towing mileage.

https://www.amazon.com/s/ref=nb_sb_...fix=OBD2+bl,automotive,227&crid=2L70ZZGVK6S0U

 

[Rocket Man]

I believe fuel pressure should be around 58 and no drop in pressure.(maybe 5lbs) we don't have a fpr on the fuel rail as it's in the tank with the pump. Sooner or later the pump will completely give out so might as well change it now and fix that evap while your down there

Actually the fpr is on the intake manifold. Don't remember exactly where but I remember removing it to reinstall on the fuel rail of my Whipple. It looks like this.

 

[Marinevet]

Actually the fpr is on the intake manifold. Don't remember exactly where but I remember removing it to reinstall on the fuel rail of my Whipple. It looks like this.

From everything I have read, this was prior to 2004. In 2004 they went to a returnless fuel system, where the regulator is actually in the gas tank.

 

[Marinevet]

To be honest I haven't played with my newer Tahoe, but I bought a cheap bluetooth scanner that you use with your phone and Torque or some similar app.
On my last one it surprised me how much data was available. I originally bought it to try to work on towing mileage.

https://www.amazon.com/s/ref=nb_sb_ss_i_3_7?url=search-alias=automotive&field-keywords=obd2+bluetooth+scanner&sprefix=OBD2+bl,automotive,227&crid=2L70ZZGVK6S0U

Do you remember which one you actually ended up buying? Those are cheaper than I thought they might be.

 

[Rocket Man]

From everything I have read, this was prior to 2004. In 2004 they went to a returnless fuel system, where the regulator is actually in the gas tank.

According to Rock Auto that one in the picture is for a 2004 but they could be wrong.