Hard Start Poor Running

[00YukonSLE]

When dad died mom inherited his 2000 Yukon 5.3L. It has been a reliable vehicle for her for several years. But now she has a drive-ability issue. It starts hard and stumbles when you give it gas. I checked for codes and found none. I plan on taking more of a look at it in the morning. Any ideas where I should start?

[Austin83]

It could be many things. Not knowing how well the vehicle was maintained, I would look at the possibility of bad fuel, clogged fuel filter, spark plugs and wires, air filter, basic tune up, etc. The problem may not have anything to do with any of those, but they are fairly easy to check before you get crazy with it. I'd start with something simple like fresh fuel with a good quality fuel injector cleaner like Chevron Techron Fuel System Cleaner. Good luck.

[00YukonSLE]

I know the plugs are new. I plan on checking the fuel pressure in the morning. But with no codes to be honest I'm not sure what else to check.

[Ape0r]

You have a fuel, air, or exhaust problem:

 

Start with air:

Air filter clogged? (unlikely)

Throttle blades opening correctly? Could be the servo in the TB took a crap, but unlikely as I have NEVER heard of this happening.

MAF sensor frequency reading correctly? (you will need a scan tool - also check throttle position sensor if it has one)

 

Fuel:

Replace fuel filter

Fuel pressure

Injector balance test (unplug injectors one at a time, if nothing happens the injector is clogged or dead)

 

Exhaust:

Could be clogged cat. You will usually hear valves knocking if that is the case though.

 

Beyond that stuff, it is a sensor, and you will either need to hook it up to a laptop scan tool or take it in. People talk about bad gas a lot, but I've never experienced that.

[Austin83]

I'd start with the easy stuff first and work your way to the more difficult checks.

[00YukonSLE]

Well, hooked up the fuel pressure gauge thismorning. Key on engine off 20 lbs. Huh! That ain't good. Cranked the engine and she started, barely. The gauge fluctuated while cranking. but held at 20 once it started. I pulled the vacuum line off the regulator and the engine started trying to stall. Figures, add a vacuum leak to the low pressure lean condition and it isn't gonna help. Then it stalled. I looked over at the gauge. No pressure. Cycled the key and still no pressure. I'll have to make a few checks but I suspect that the pump is the culpret. I don't think I have ever had a pump go in stages like this. it is usually either it works or it doesn't. Oh well, time to finnish this cup of coffee and then get my but to work on it.

[00YukonSLE]

Well on to the next challenge. Getting the dang tank out! I have to go home and get my dremmel to cut the bolts off as they just spin. Or rather cut the bolt off the one strap that is on the tank. The rear strap is MIA.

 

Once I get the strap off is there anything I should watch out for?