2004 Yukon XL (Non Flex) cranks but doesn't start.

[2004YukonXL_SLT]

Hello!
I have been working a 2004 GMC Yukon XL today and have seem to run into a bit of a snag. It had been sitting for a bit and when I initially fired it up and ran ok, it would bog down under acceleration but would "drive" fine at idle. As I continued to run the vehicle it would run worse and worse. It would fire up, idle for a bit, bog down then die. I have scanned for codes and there is nothing that I can find.

I checked the battery charge, fuel pressure, all of the ground points, some of the relays and fuses. I cleaned the MAF and throttle body but with no luck. I haven't checked the spark plugs for spark. But a visual inspection of the spark plug shows that it's not new, but it doesn't look like it should have failed yet. I also sprayed the crank position sensor with compressed air (upside down, so it works as a cooler) which was something I found online.

I'm pretty lost at this point with only a few options left. Any suggestions?

 

[Fless]

Welcome to the forum from The Centennial State!

With the key turned on, engine off (KOEO), what is the fuel pressure you read on the schrader valve on the passenger fuel rail? I assume you can hear the fuel pump run.

Again, KOEO, if you open that schrader valve momentarily with a screwdriver or pick (and cover it with a rag) do you get a good spray of fuel? Or just a dribble?

Verify spark, and are the plugs wet with fuel? Condition of business end of plugs?

 

[S33k3r]

Having seen something similar, I suggest you check the alternator output, at load if possible. Your alternator may be dying. I'd get the battery tested as well. Finally, might want to check if tensioners and pulleys are working correctly. But this totally feels like a dying alternator to me.

Good luck -- stuff like this is the unfun part of any automotive work.

 

[OR VietVet]

First: Welcome to the forum.

Second: I am leaning like what @Fless said about the fuel pump but I am all about basics and believe @S33k3r also has a point as to what to check. Gotta have spark, fuel, air and compression to run. Check for these basics first.

 

[rockola1971]

How long has it been sitting? Could just be bad gas or someone helped make the gas bad by adding water, cheerios, Cheetos, Pepsi, Sugar or a host of other things that aint suppose to be in the tank.

 

[MassHoe04]

Make sure the path for the air to flow is clean and free of debris.
Look for signs of acorns, bird seed, hood insulation.

Check the air intake tube and the path to the throttle body. Maybe mice or Chipmunks made a home in the air box or intake manifold.

Also, give everything a good visual inspection. Look for any other areas where animals might have tried to nest, pee/poop on (very corrosive to wire connectors, blade connectors on fuses and relays), or wires that might have looked like something good to eat.
Inside and under the fuse box is a good place to look for that kind of stuff.

Rodents can make a real mess and can eat the insulation off wires needed for engine control modules, ignition and fuel delivery systems.
Look at wires and harnesses in the engine bay for damage.

As mentioned... Could be something on the mainline electrical. Battery terminals clean, battery cables not corroded, connections to battery/alternator/ground all clean and tight?

 

[2004YukonXL_SLT]

Welcome to the forum from The Centennial State!

With the key turned on, engine off (KOEO), what is the fuel pressure you read on the schrader valve on the passenger fuel rail? I assume you can hear the fuel pump run.

Again, KOEO, if you open that schrader valve momentarily with a screwdriver or pick (and cover it with a rag) do you get a good spray of fuel? Or just a dribble?

Verify spark, and are the plugs wet with fuel? Condition of business end of plugs?

Yeah the fuel pump runs, did a pressure test and got 49 pounds of pressure. I get a nice spray of fuel when I press on the Schrader valve.

The plugs aren't wet with fuel, but when I try to get the engine to start with an engine starter. I don't get results either. I'm about to swap spark plug cables and spark plugs (I have some lying around for another LS swap project) to see if that changes anything. Is there a good way to verify spark besides getting zapped over and over? The spark plugs that are currently in the vehicle look fine, old, but not like it's going to cause any issues.

Thank you!

 

[2004YukonXL_SLT]

Having seen something similar, I suggest you check the alternator output, at load if possible. Your alternator may be dying. I'd get the battery tested as well. Finally, might want to check if tensioners and pulleys are working correctly. But this totally feels like a dying alternator to me.

Good luck -- stuff like this is the unfun part of any automotive work.

I'll give the alternator a shot, the battery is brand new and fully charged (got it replaced under oreilly auto warranty). I have a spare alternator lying around that was tested good.

Thank you for the help!

 

[2004YukonXL_SLT]

First: Welcome to the forum.

Second: I am leaning like what @Fless said about the fuel pump but I am all about basics and believe @S33k3r also has a point as to what to check. Gotta have spark, fuel, air and compression to run. Check for these basics first.

Sounds good, as I test things I'll update this thread since I have yet to see a thread with a complete ending!

Thank you for the help!

 

[2004YukonXL_SLT]

Make sure the path for the air to flow is clean and free of debris.
Look for signs of acorns, bird seed, hood insulation.

Check the air intake tube and the path to the throttle body. Maybe mice or Chipmunks made a home in the air box or intake manifold.

Also, give everything a good visual inspection. Look for any other areas where animals might have tried to nest, pee/poop on (very corrosive to wire connectors, blade connectors on fuses and relays), or wires that might have looked like something good to eat.
Inside and under the fuse box is a good place to look for that kind of stuff.

Rodents can make a real mess and can eat the insulation off wires needed for engine control modules, ignition and fuel delivery systems.
Look at wires and harnesses in the engine bay for damage.

As mentioned... Could be something on the mainline electrical. Battery terminals clean, battery cables not corroded, connections to battery/alternator/ground all clean and tight?

I checked to make sure that everything was clean, contacts are clean, all connections look pretty good. I know engine grounding can cause issues, but I can't find a comprehensive list of where all of those points would be on this truck. I did give the wiring harness a good look over and I couldn't find anything that was glaringly disconnected.