2003 1500HD EVAP system

[wdrinnon]

I bought a 2003 1500HD to rebuild.  Did new valvetrain, PRC Heads, TX speed cam and tuned.  I noticed its running lean and has a hard time starting sometimes.  I checked fuel pressure and it was a little low around 50psi key on engine off.  replaced the pressure regulator(delphi) fuel filter (wix) and fuel pump (delphi).  This increased the pressure to 55psi but problems still existed.  i noticed when i replaced the pump that there is a pressure sensor on the top.  the old pump had one and the new pump has one.  The original had no wire connected to it.  i assumed at some point it went out and someone just unplugged it, but i cant find the wires anywhere.  i dont know if they cut them off or what.  With this sensor being unplugged im assuming the EVAP system will never work.  Will the purge valve ever open?  and could this sensor being unplugged cause a fuel delivery problem?  

[Jsdirt]

That's  the fuel tank pressure sensor - just lets the computer know where the tank is at regarding pressure or vacuum, and then regulates the vent and purge valves accordingly so the tank doesn't collapse, or engine stops running due to excessive vacuum.

 

A leaking purge valve will most certainly cause a lean condition. Also, if the computer is commanding a purge event and is expecting fuel vapor from the charcoal canister, the lack of fumes could possibly flag a lean condition when one doesn't actually exist. I'm not 100% versed on how the system takes that into account.

 

But if there's an air leak in the valve itself or in the EVAP plumbing or charcoal canister, when that purge valve is commanded open, it will draw unmetered air causing a lean condition.

[wdrinnon]

20 hours ago, Jsdirt said:

That's  the fuel tank pressure sensor - just lets the computer know where the tank is at regarding pressure or vacuum, and then regulates the vent and purge valves accordingly so the tank doesn't collapse, or engine stops running due to excessive vacuum.

 

A leaking purge valve will most certainly cause a lean condition. Also, if the computer is commanding a purge event and is expecting fuel vapor from the charcoal canister, the lack of fumes could possibly flag a lean condition when one doesn't actually exist. I'm not 100% versed on how the system takes that into account.

 

But if there's an air leak in the valve itself or in the EVAP plumbing or charcoal canister, when that purge valve is commanded open, it will draw unmetered air causing a lean condition.

 

Thanks for the reply.  After more investigation i have found that neither the tank pressure sensor or the the canister vent solenoid have wires connected to them.  The wires are no where to be found either.  is this because its an HD, did they have different style evap than the 1500 trucks?  When would the purge valve be commanded to close if there is no pressure sensor reading or a way to close the vent valve?  

[Jsdirt]

It only closes to test the integrity of the system. If the test detects any leaks, you get EVAP codes, small, large, or gross leaks depending on how fast the decay rate is. System should be the same on all gas trucks. If the vent valve were stuck closed, the truck wouldn't run for very long. If you're not seeing a check engine light with EVAP codes, a previous owner may have tuned it out of the PCM.

[wdrinnon]

On 4/22/2022 at 10:56 AM, Jsdirt said:

That's  the fuel tank pressure sensor - just lets the computer know where the tank is at regarding pressure or vacuum, and then regulates the vent and purge valves accordingly so the tank doesn't collapse, or engine stops running due to excessive vacuum.

 

A leaking purge valve will most certainly cause a lean condition. Also, if the computer is commanding a purge event and is expecting fuel vapor from the charcoal canister, the lack of fumes could possibly flag a lean condition when one doesn't actually exist. I'm not 100% versed on how the system takes that into account.

 

But if there's an air leak in the valve itself or in the EVAP plumbing or charcoal canister, when that purge valve is commanded open, it will draw unmetered air causing a lean condition.

 

The vent valve can't close because there are no wires connected to it.  The evap codes are tuned out for sure.  i have bypassed the entire evap system.  I have the tank venting to atmosphere, just for now to test, and the purge line is capped off.  problems still exist.  starting issues and still lean under load part throttle.  

[Jsdirt]

I'd wager the pump is insufficient for the power you're producing with the tune. Might need to find something different.

 

If you watch a scan tool, go to full throttle in a safe place in 1st gear, and watch your o2 sensors - anything less than max voltage (0.9V ± ) and the engine is starving for fuel. They should go full rich and stay there.

 

Also watch the MAF - at idle, the grams per second should be close to the engine size in liters. At full throttle it should be well into triple-digit levels.

 

You could also have an air leak either through a hose, or the intake manifold gaskets.

Edited April 25, 2022 by Jsdirt

[shakenfake]

It is his injectors. The pump will produce plenty for a heads and cam truck but those injectors are not putting out enough fuel.

 

 

[Jsdirt]

Ahh, good point - didn't even think of that. Pretty important part of fueling for me to forget, lol! 

[EErock]

Well I can't really say as if I have an answer, but i do have a similar story. I don't think I've posted here before so I hope I'm not going about this the wrong way?

I am actually curious more than anything. I noticed you mention you put a texas speed cam and a tune. Is it a stage three cam, mild?  Does it require the tune to start and idle? Are you sure there are no misfires that maybe have been tuned out? If there are misfires can you be sure its because of the cam and not because there really are misfires? That has lean problems written all over it. Is it possible that someone has tuned out an actual problem and maybe messed with the mil codes? The other thing which I don't know maybe no way someone could have made a mistake, but the cam install? How sure are you that sprockets were lined up like almost perfect?  These are questions that at one point I had to try to answer. My problem was both. The cam had been installed almost 2 teeth off and then the truck was tuned to that. The monitors would never have set no matter what I did. The truck had to have a tune to run. I had the misfires tuned out because supposedly the cam. But as you see, 1 or 2 teeth of a sprocket can cause big problems. I pulled my cam out and installed a brand new stock one. Everything is fine, the truck starts up immediately, to where i would have a problem after it ran for awhile , the next start attempt would be just that an attempt. It would take another one or two key turns to start. If my advise means anything start with the tune see what is actually tuned. maybe try to run the truck on stock tune just to see what happens?  Oh my experience is basically2004 Chevy Silverado, 1997 Silverado, 2004 Tahoe,  and long time ago 1972 K10. I'm the son of a mechanic who was always at my dads shop doing something to a car or truck, Not an expert. Take care