2000 GMC 5.3 stalling?

[RonnieT]

I have a 2000 GMC 3 door Sierra  Automatic  loaded with 170,000 miles, well maintained with records kept.

  Its been stalling lately and surging  enough to be scary in traffic.

Also when I start it cold of the morning , I stand beside it and reach in to start and it has been idling low to the point of dying at least once, starts ups are good though and I always allow it to come to temp before driving. Past few days I got in the seat and turned on ignition and stepped on the accelerator before starting to give sensors a voltage value, it didn’t help.

  Today I changed the fuel Filter and it needed it but I have seen worse,

I placed my old scan tool on it and took some screen sots of it while idling, the only code was PO171 that said it was Too lean.

I looked for air leaks on the vacuum hoses and purge vale and all along the air intake boots for the MAF sensor to the valve plate , I see no cracks or breaks , nothing.

 Is there anyone that can look at these screen shots of my scanner and give me a  good guess or where to look and how to find my problem?

     Only major repair on engine was done by me about 6 years ago and I changed the Knock sensors because of detonation  and I used OEM sensors and Felpro gaskets,  I was a  Mechanic for about 25 years in the 80s-90s.

  Any help would be appreciated

[RonnieT]

a few more screen shots

[It's Tim]

What's the fuel pressure?

[Black02Silverado]

Agree, what is your fuel pressure.  The fuel pumps on the GMT800's was a main failure item.  If the fuel filter was in bad shape it could have put more stress on the fuel pump. 

 

I pulled my bed off to change the pump.  It is easy to do with two people.  Way better than trying to tackle it any other way.

[RonnieT]

Wonder what the Pump pressure should be when running? check it on the fuel rail?

 

[CamGTP]

With the vacuum regulator it's probably around 50psi at idle and it should change if you pull the vacuum line off. Under load it should always be above 50psi and closer to 55-58psi.

[RonnieT]

Ok, didn't think about pulling the vacuum off the regulator but I have  exactly 45lbs on the gauge I trust  at the fuel rail with key on and engine dead, I have exactly 45lbs with engine running and  regulator working.   so this isn't good,  causes for stalling and  surging?

[Black02Silverado]

37 minutes ago, RonnieT said:

Ok, didn't think about pulling the vacuum off the regulator but I have  exactly 45lbs on the gauge I trust  at the fuel rail with key on and engine dead, I have exactly 45lbs with engine running and  regulator working.   so this isn't good,  causes for stalling and  surging?

Yes, the fuel pump is going out.  Time to change it.  Like I posted, it is easy, worst part is getting to it and I opted to take the bed off.

[CamGTP]

If you can tape the gauge to the windshield, see what it does with a load on it.

[RonnieT]

Ok, what brand is good for new pump? My fuel gauge is always been a POS and I thought if I ever changed the pump I would change the hole unit. I don't have a lift or transmission jack anymore  so I may just tilt the bed.? 

 I see that make about 3 different ones is the code on the build sheet?  Tfc or TFU or? Ron

   

[RonnieT]

I see the code in the glove box is for a EVA  fuel pump.

 

[Black02Silverado]

Best thing is to contact the dealer with your vin.    They can tell you what you need.  That is what I did.  MS3dale who isn't on here much works at a dealership and helped me out.  Then once I got the correct part number I got it off Amazon for a good price. 

[RonnieT]

service sticker says  EVA but I can get the  Vin ,OK if someone can look it up? its better than having the wrong pump in hand with the bed up.

    Ron

Edited May 12, 2021 by RonnieT

[RonnieT]

Ok I placed the Pressure gauge on the windshield and drove around town, 30-50 miles an hour, the lowest on the gauge was @45PSI and the highest was about 48PSI fluctuated while moving and steady around 45 while idling. 

When I got home I took the vacuum hose off and plugged it and the gage grew up near 50PSI  never anymore.

 VIN is 2GTEK19TSY1222104  if someone could help with a pump part number, I am thinking to change to whole unit out.

[Black02Silverado]

56 minutes ago, RonnieT said:

Ok I placed the Pressure gauge on the windshield and drove around town, 30-50 miles an hour, the lowest on the gauge was @45PSI and the highest was about 48PSI fluctuated while moving and steady around 45 while idling. 

When I got home I took the vacuum hose off and plugged it and the gage grew up near 50PSI  never anymore.

 VIN is 2GTEK19TSY1222104  if someone could help with a pump part number, I am thinking to change to whole unit out.

I contacted MS3dale.  awaiting to hear back.