Tshearman

Hey guys I was hoping to get some ideas from you. I have a 99 GMC with a 4.8L that is bone stock. I replaced the evap purge solenoid with a used one off a 2000 Silverado I own to turn the check engine light off so I could sell it. Of course 2 days after replacing it and turning the CEL off the light comes back on for a bank 1&2 too lean. Any ideas why this is popping up now? I have no idea what the heck is wrong with it all my vacuum lines are fine, fuel filter was replaced about 10,000 mi ago, and it doesn't hesitate or anything. I don't think its the fuel pump because it doesn't pop up under a load just normal driving.

Any ideas would be really appreciated. I have the truck up for sale right now so I'm trying to fix the code before it scares people off.

Robert91RS

iTrader: (2)

Either the new purge solenoid is not sealing properly or or your intake gaskets are leaking. Have you removed the air cleaner recently?

Tshearman

But the purge solenoid is located on the charcoal canister. I thought it had nothing to do with the engine vacuum? Yes I have removed the air cleaner recently but all the connections are on there tight. Thanks for the help Robert!

budhayes3

iTrader: (19)

Sounds like you replaced the cannister vent valve, as the purge valve is located directly on top of the intake and will cause a vacuum leak if not properly seated. I'm not 100% sure if installing that valve incorrectly will cause a problem like your having as it's purpose is to vent the canister, and if there were a leak there you should have an EVAP code also. Since it's coding for both banks being lean, I'd check for a vacuum or air leak, maybe try cleaning the MAF sensor. Best bet would be to hook up with a scan tool so you could watch the O2 sensor activity and see what's actually going on and how they react to tests that you do like pulling the hose of the fuel pressure regulator and richening the mixture...

Tshearman

Thanks Bud. I guess the technical term would be the vent valve. Its just weird that the problem didn't surface until I replaced the vent valve but there are no EVAP codes. I checked for vacuum leaks and I've found nothing. I don't have a scan tool but I could probably track one down. I just ruled out the O2 sensors because I figured it would be one side or the other that went bad not both at the same time. Whats the best way to clean the MAF sensor? Never done that before on one of these trucks.

Another thing I should mention is that I switched out a few things at the same time as the vent valve b/c I wanted to put my truck back to bone stock to sell it. Would taking my K&N filter out and replacing it with the paper one out of the old truck cause this problem?

Thanks guys I just really want this fixed. I have people coming to look at it today so I want to at least be able to say I will have the problem fixed by the end of the weekend.

budhayes3

iTrader: (19)

Glad to help Tshearman I agree that the likelyhood of two O2 sensors going bad at once is slim. Changing the filter shouldn't make a difference, but if there was some oil on the MAF sensor from the K&N, and maybe it got somehow disturbed when you swapped the filters...could be the issue. Oil on the MAF from those filters cause MAF problems all of the time. You can clean the MAF sensor with some electrical contact cleaner, and let it air dry...clear the code, give it a ride, and see what happens

Tshearman

So thanks to college I haven't really had any time to mes with her yet. I'm really starting to think its the intake gaskets though. I've noticed it only acts up when the engine is cold and its cold outside (I'm in FL so its not real cold right now). When its warm it runs beautifully with no Check Engine Light. I'm thinkin its the silicone on the gaskets shrinking when its cold and expanding when they're hot to form a seal again?

One more thing. When it first gets started up on really cold days it runs rough as hell for the first few minutes until it warms up a little.

Robert91RS

iTrader: (2)

All common symptoms of the early style gaskets leaking. I have seen people retorque the intake bolts too. Its not the best solution but if it worked you would have $0 invested in the diagnosis. Just be careful not to over tighten.

01WS6/tamu

iTrader: (36)

Clear the codes before they show up to look at it make sure it's nice and hot when they arrive, sell it and walk away.

If you feel like fixing it ,Check PCV lines from intake to valve cover, valve cover to TB, clean MAF, make sure all air intake components are tight. Next stop intake gaskets.