I have pretty much 156,000 trouble free mile on my truck but my MPG is in the crapper. Would a clogged EGR valve cause this ? or what symptons would it show. It idles fine.

 

In my limited knowledge of today's modern engines, I believe that a clogged EGR valve could affect the fuel economy but I would more suspect O2 sensors and filters.

 

In theory a clogged EGR shoul actually increase your milage. The EGR system introduceses unburnt Exhaust gas back into the cimbustion chamber to be burnt again. The Exhaust gas has less oxygen content so it cannot promote combustion as well as clean air. This will reduce the efficiency of the cobustion process and reduce the power. Ever notice when you first start your truck? It is in Open Loop till it reaches operating temperature. Or when you press the accelerator to the floor. Both these instances are examples of when no Exhaust gas is present in the combustion chamber. Now becasue the PCM can pick up the lack of flow it might ritchen the Air Fuel ratio to keep combustion temps down. If so that will cost you milage.

Regards

Jean Marc Chartier

Regards

Jean Marc Chartier

 

Actually the EGR system is designed for two things. One is to keep detonation down by cooling the combustion chamber by introducing burnt exhaust gasses thus reducing heat. And second is to help with MPG by reducing temps and replacing some of the combustion charge with basically inert gasses you in turn will need less fuel.

Because of new EPA standards heavy trucks are all now comming out with EGR systems.

 

Thanks for the responses. I guess my question now is how do I know if the EGR is blocked and needs to be cleaned. I ran Seafoam thru it a few months ago and everything seems to be running fine. On a recent hwy. trip I got 17.3 MPG's, but in the city im around 10-11. 98 4.6 with 156k

 

Have you changed the plugs, fuel filter, air filter, etc. All these things can add up over time. Plus, you can decarb the motor w/ seafoam. That will really improve it.

 

you ran seafoam through the egr??

do a search here there are a lot of good pics and it is very very common for the egr ports to clog on a 4.6 and for the dpfe to go bad at the same time.

 

Plugs 56k ago, gas and air filter are about 3 months old. I ran seafoam thru the brake booster vacumm line, I thought that cleaned the intake. Does it go thru the EGR also ?

 

Lou,


That will not clean the EGR ports. The best way is to remove the elbow and clean/dissolve/scrape the carbon off.

JMC

 

Thank You