Yukon xl misfire

[duner03]

2005 gmc yukon xl Vin z, was driving up a hill in the mountains here in az started bucking and poping through the exhaust, pulled over shut the truck off waited 5 min ran fine. 4 days later same thing.

Went home pulled the plugs they were orange, new plugs wires and mass air flow sensor, new pcv hose (small crack) drove around fine, truck warmed up missing again, checked fuel pressure was at 55psi. Shut truck off held pressure. Sprayed intake and vacuum lines no leak, also a hydroboost truck so no vacuum booster. Fuel trims are .08-1.0 short and long term, check engine will flash p0174 p0171 and p0300.

Most research I've done if there is a vacuum leak the fuel trims would be high. Help

 

[nonickatall]

If you have a Vakuum leak the fuel trims are to low, because the mass air sensor measure less air, than available, so the ecu injects to less fuel than necessary..

 

[B-train]

What did you use to check for leaks? In my younger dealership days, I found that using a hose with a small amount of water around the intake plenum would work well. If it sucks in a little water, you'll see white exhaust. It can help narrow down the area, but based on the age, I would assume intake gaskets are due for replacement.

 

[duner03]

What did you use to check for leaks? In my younger dealership days, I found that using a hose with a small amount of water around the intake plenum would work well. If it sucks in a little water, you'll see white exhaust. It can help narrow down the area, but based on the age, I would assume intake gaskets are due for replacement.

Used water and carburetor cleaner

 

[Fless]

Would you confirm that the fuel pressure at the fuel rail is 55psi when the engine is running? Is that what I'm reading?

 

[duner03]

Would you confirm that the fuel pressure at the fuel rail is 55psi when the engine is running? Is that what I'm reading?

Yes

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Fless]

Without seeing any more data, I'd suspect the MAF if it's not GM OE (whether or not it's new), or the fuel pressure regulator. Doubt it would be a vacuum leak if your fuel trims (long- and short-term on both banks) are consistently that close to zero. What do you mean "the plugs were orange?" Got pics?

Is there a pressure regulator on the fuel rail? 55psi running seems pretty high; these tend to run in the low-mid 40s, say 43 or 45 psi. The initial test with KOEO (key on, engine off) does have the higher spec, but the psi should come down when the engine is running.

 

[rockola1971]

Typical culprits here are Mass Air Flow Sensor, Leaking intake manifold gasket or a vacuum line. Id pull the vac line off FPR and check fuel fuel presence(Leaking Diaphragm) and if that checks good and you are sure that manifold is good then Im laying my chips down on the MASS faulty.

 

[tomloans]

Did you check those fuel trims during the "bucking and popping sessions"? It sounds like it is intermittent so I would do that first. Are you losing any coolant? Also spraying water or carb cleaner doesn't always find the leak unless it is a large enough leak that you can tell immediately that the engine slowed down. Subtle leaks may not show up. It is really hard to tell sometimes especially when intermittent as you described. Also does it buck and pop during acceleration or during steady high speed driving. Will it do it when you are at idle? More details please.