Engine vacuum, P0171 and P0174 codes.

[foxtrot moon]

2001 Chevrolet Tahoe 5.3L

Yesterday when I left work, the Service Engine Soon light came on, I checked the codes and they yielded a P0171 and a P0174. Both banks were too lean, so I figured there's a vacuum leak somewhere letting too much air in, especially if both banks popped up at the same time.

This morning when I got to work, I borrowed a scan tool from the shop next door and the codes had erased themselves by this point.

While I was in there, I took a look at the MAP sensor and it's listing 11.22inHg at vacuum. Even though the codes had taken care of themselves, I'm leaning towards the manifold gasket has sprung an air leak/leaks.

Does this sound about right and is there anything else I should look into before tearing into it?

 

[tsuintx]

With those codes present, it is more than likely that the intake manifold gasket is to blame.

 

[SLCHOE]

Agreed. The manifold gaskets are pretty common too.

 

[OR VietVet]

X3. Do the intake gaskets and new bolts/nuts. Use Felpro gaskets, ONLY. Replace the knock sensors and harnesses under the intake while in there. Use AC Delco sensors and Dorman harnesses. While apart replace the thermostst with a new AC Delco stat. Make sure all is very very clean when reassemble. New oil change with good oil and quality filter, meaning don't use a Fram filter, JUNK! IMO

 

[SLCHOE]

X3. Do the intake gaskets and new bolts/nuts. Use Felpro gaskets, ONLY. Replace the knock sensors and harnesses under the intake while in there. Use AC Delco sensors and Dorman harnesses. While apart replace the thermostst with a new AC Delco stat. Make sure all is very very clean when reassemble. New oil change with good oil and quality filter, meaning don't use a Fram filter, JUNK! IMO

I concur. If you are already there, those knock sensors and its harness are a must do as they are very common to fail and cause other codes along with their own. That can cause misinformed diagnostics by techs not familiar with these engines in the future. Also, swap out the infamous failing oil pressure switch. It's much easier to change out the oil pressure switch if you are doing the manifold rather than after.

As far as the oil filter goes, my preferences are a good WIC or Purolator filter. Fram is indeed crap.

 

[OR VietVet]

Agree with SLCHOE. Do the oil sender while there and easy access. It is no fun at all to get to it when all together. PITA.

 

[foxtrot moon]

Well, just to close this out, it ended up being the fuel pump. The day after I posted last in this thread, the check engine light went off. Drove for a few days and it was still stumbling a little bit, finally yetserday morning the check engine light popped on codes P0171B and P0174B (fuel trim system to lean bank 1 and bank 2). Checked the fuel pressure and it was holding 20-25lbs at idle. I would rev the engine and it'd cut off (actually cut off while driving...). Installed a new fuel pump, fuel filter, cleaned the MAF and TB while I was doing it all and it runs like a champ.

Just updating in case anyone else has the same problem later. I'm hoping to cam this motor in 2015, so when I do I'll be doing the sensors you guys mentioned earlier in this thread.

Thanks!

 

[OR VietVet]

Well, just to close this out, it ended up being the fuel pump. The day after I posted last in this thread, the check engine light went off. Drove for a few days and it was still stumbling a little bit, finally yetserday morning the check engine light popped on codes P0171B and P0174B (fuel trim system to lean bank 1 and bank 2). Checked the fuel pressure and it was holding 20-25lbs at idle. I would rev the engine and it'd cut off (actually cut off while driving...). Installed a new fuel pump, fuel filter, cleaned the MAF and TB while I was doing it all and it runs like a champ.

Just updating in case anyone else has the same problem later. I'm hoping to cam this motor in 2015, so when I do I'll be doing the sensors you guys mentioned earlier in this thread.

Thanks!

Don't get me wrong here. Glad it is all fixed and runs good. In your OP you never said it ran bad or stumbled, just was throwing codes. Also never said it would cut off when rev the engine. Now in the last post you make it sound like you had those problems as well but we were never told that. Is this new and when you say "was still stumbling a bit" you mean something else? Sorry to be a nit picker here but it helps all of us to get "complete" info in the posts asking for help. Anyways, glad it is fixed.

 

[SLCHOE]

Don't get me wrong here. Glad it is all fixed and runs good. In your OP you never said it ran bad or stumbled, just was throwing codes. Also never said it would cut off when rev the engine. Now in the last post you make it sound like you had those problems as well but we were never told that. Is this new and when you say "was still stumbling a bit" you mean something else? Sorry to be a nit picker here but it helps all of us to get "complete" info in the posts asking for help. Anyways, glad it is fixed.

Happens all of the time. Used to the omissions of details by customers once the dreaded CEL comes on. It's one of the reasons why shops get bad reviews.
If customers would do a better job at describing the symptoms, it would make it a lot easier to troubleshoot. Sadly, a majority of customers belive that CEL codes tell you "exactly" what the issues are with their cars. When, in reality, they tell you what monitored system is being affected either directly or indirectly by another less monitored system.

:shrugs:

 

[OR VietVet]

Under General Information and Site Comments and Feedback I have a thread posted called Sharing Information. I wish every new member who asks for help had to read that first before being allowed to do so. I also wish I could find the turd that got everyone convinced that just knowing the code tells you exactly what is wrong instead of just telling you where to start diagnostics and different systems effected. I would punch him/her right in the mouth.

It slows down the whole process when you carefully read the problem, think it through and advise and then you get more or different info and the original thought process is completely wrong or needs to be adjusted. Is very frustrating. Like a doctor dealing with a patient that will not tell you anything other than I don't feel good.

At some point I will just drop off the thread because I feel I am wasting my time.