05 VOLVO truck VED D12 engine lacks power and makes 4mpg.. what is wrong?

very possible epg is mechanicaly stuck happens all the time in higher milage trucks if you have vcads you can open and close it and see if you hear epg returning back. almost all d12 that i have owned needed this changed around 1 mil or so and most people cant even find the problem. you can remove line and put air in the epg listen if you get a good return back. around 800 or 900 for part but it tend to be a pain in the ### cuz the bolts never want to come out no matter how much you heat them.

 

I had the EPG off yesterday it is functioning properly. Supply it with air and it closes release air pressure and it returns quickly.

 

than disable the air line going to the valve and test drive like this

 

under starter you have epg air valve with 1/4 air line remove air line and fold catch with zip tie and you can test like this disabling air you have no 1st position engine brake but you can see what happens

 

You should have EPG code on the dashbard if that is not working. Otherwise look for a problem elsewhere

 

Thank you i will try this.

 

Just to clarify. Does stage two use the epg and jake system together or just one or the other depending on stage 1 or 2

 

Together so i would suggest do not count on engine brake if you remove the air line.

 

but you will not have a fault code because you are disabling epg mechanicaly

 

Ok test drove the truck with air line disabled and pretty sure this is not my problem. Now i am back to square one trying to figure out where my power issue and terrible fuel mileage problem is.