Poor fuel economy

roadrunner · Post by **roadrunner** » Thu Dec 06, 2007 3:31 pm

Being new to the forum I just thought I'd pass along a little FYI regarding gas mileage. Aside from normal tuneups and clean fuel and properly working clean injectors I've found a little different cause of poor fuel economy. I have an 01 CC 4door 4.3 automatic 4x4. Last winter my mileage gradually went down to a difficult to maintain 13 mpg on the hiway. I tried several things then stumbled onto the apparent main cause. The check valves in the air injection system were leaking air into the exhaust system. This caused the O2 sensor to go full rich or nearly so thus destroying the gas mileage. I plugged the tubes so they couldn't leak anymore and tada!!!! the mileage went right back up to a respectable 17-20mpg! I don't even like to remember how bad the mileage was in stop and go but is now back up to 14-15 mpg. Hope this might help someone else.

F9K9 · Post by **F9K9** » Thu Dec 06, 2007 4:16 pm

Interesting advice. Can you elaborate in detail for morons like myself?

green02crew · Post by **green02crew** » Thu Dec 06, 2007 6:54 pm

haha i second that motion!

roadrunner · Post by **roadrunner** » Thu Dec 06, 2007 7:01 pm

Nobody is a moron if they have the class to ask questions if they lack firsthand knowledge or experience.
The check valves are part of the air injection pump system. They are located on metal tubes which hook up to the exhaust manifolds on both sides (on my 4.3) and are fed by hoses coming from the air pump. On my 01 this an electric affair located under the radiator support along with an electric solenoid which can also leak or stick and can trigger a P0410 code and turn on the light. To simplify for testing purposes I simply plugged the hoses that feed the air to the valves and will replace or modify later. I have read a thread somewhere else in this forum about removing the system and plugging the manifold inlets but has been a while since and I was just a visitor then so don't remember who or when or where.
I haven't priced new check valves yet so can't advise on price. Hope this is helpful for you.

F9K9 · Post by **F9K9** » Thu Dec 06, 2007 7:14 pm

I believe that you are referring to the EGR systems and GM dumped them (to the best of my recollection) starting with the '02s but, I am sure Brule will kick in if, he spots the thread.

roadrunner · Post by **roadrunner** » Thu Dec 06, 2007 7:23 pm

Can't speak to the 02's but no I am referring to the air injection pump system on the 01's. This a fresh air injection system as opposed to an exhaust recirculation system you mention. Primary function of air injection is to provide extra O2 to heat up the cat quicker to get emissions under control. I have been told by GM it is only operational for 30-45 seconds on cold startup. EGR dumps varying amounts of exhaust gas back into the intake system of the engine to lower the octane requirement of the engine.

Post by **HenryJ** » Thu Dec 06, 2007 7:24 pm

P0410

roadrunner · Post by **roadrunner** » Thu Dec 06, 2007 7:32 pm

Thanks for the link HenryJ! In my case I was lucky the valves hadn't leaked moisture into the pump before I discovered the problem. Good thing as the pump and hose was already replaced.

F9K9 · Post by **F9K9** » Thu Dec 06, 2007 7:34 pm

Sitting down and shutting up