2002 GMC Envoy bout 135k on it. SES light came on the other day, rode by Advance and had them check it. They said my fuel mixture was too lean. They told me to go to the GMC place and that their computer could tell me exactly what it was. Well I called them and its gonna be $100 to just plug it in. This is crazy, does anyone else have a computer like they do?

What are my options? What could it be?

I'm thinking injectors, fuel pump, or filter. I put some fuel treatment/engine tuneup in a bottle stuff in. Also I noticed my milages has gone from 18+ to around 10MPG. Is the car in safe mode, or is this from the problem?

Thanks in advance

12/11/2007 6:30:16 PM

you are just pounding some miles on that bitch

mileage is bad because its in open loop mode

O2 sensor

12/11/2007 6:35:36 PM

^ so you think O2 sensor is the problem?

12/11/2007 6:36:48 PM

it could be one of many things- but with that mileage there is a good chance of it being the upstream o2 sensor

12/11/2007 6:42:04 PM

If it was an o2 sensor its more than likely going to have an o2 fault. I'd go with a vacuum leak. Take off any decorative covers that are on the engine........get a can of brake cleaner, and spray anything that has a gasket or rubber component (intake gaskets, tb gasket, intake elbow)....

12/11/2007 6:43:51 PM

^possibility, BUT- the drop in mileage suggests that the lean condition the computer is seeing (from the O2) is not actually present- thus its dumping extra fuel to correct, which is actually creating a rich condition


also... shit.. not brake cleaner- that is not good for the engine.... use carb cleaner if you're gonna do that

[Edited on December 11, 2007 at 6:54 PM. Reason : ]

12/11/2007 6:52:35 PM

I had em clear it at advance, and it took about 30 miles for it to show back up. Not sure if this helps, but is the consense i still need to take it and spend the $100 just to know. Do regular garages have these 'better' computers?

^ Yea thats what i was thinking, the brake clean is real caustic... it eats plastic and o-rings i think

[Edited on December 11, 2007 at 6:56 PM. Reason : k]

12/11/2007 6:55:17 PM

Brake cleaner isn't going to hurt a thing if you are searching for a vacuum leak.

12/11/2007 7:20:36 PM

google it with your specific year and all see what comes up

same thing happened on my MR2, i got a guy in grantham that runs them for me...too bad its up here tho, sorry with i could help

but googling it told me what it was anyways

12/11/2007 7:26:36 PM

have advance tell you the actual code, then google the code + envoy, and enjoy.

12/11/2007 7:56:45 PM