Hi,there. My 01 park ave wont accel onto highway,around town it is ok.When I accel hard to merge onto freeway the engine revs to approx. 4000 rpm but does not accellrate,if I continue to climb rpm it sounds like spark knock until I back off gas pedal.Only codes stored are p0404 andp0137.When first started happening there were no codes stored,found fuel pressure approx. 10 psi low,replaced fuel pump,better for a while then SES light came on with p0404,poor accel back again.Unplugged EGR,cleaned mass air flow sensor and car ran good for a few weeks.Now wont accel onto highway,ordered EGR valve but I find it hard to believe an EGR valve can cause that much of a lean condition? Help will be greatly appreciated!

You want to address the codes and make repairs. Use Ngk/Ntk o2 sensors.
P0137 https://www.gmforum.com/obd-ii-troub...7/#post1390932
P0404 https://www.gmforum.com/obd-ii-troub...0/#post1391437
After replacing the fuel pump, what was the fuel Psi reading?
Did you replace the fuel filter?
Have you performed a tune up with plugs & wires?

I'm thinking a possible cat problem.....

I checked with vacuum gauge,pulled 2000 rpm,slightdrop in vacuum then picked up to over 20 inches fo vacuum.should i check vacuum under load during incident? What kind of readings should mass air flow show on scan tool during incident?Thanks

replaced cat today;found it almost all melted,replaced cat and car runs and accells great,SES light on again.EGR insufficient flow stored,pipe going to manifold needs cleaned?Thanks for your input

Thanks for letting us know what fixed it for the most part, you may have a dirty EGR, I'd get a new EGR gasket, remove the EGR and clean it, be sure its pintle opens and closes freely, then put it back on with the new gasket.
Clear all codes then drive and see if any come back.

When you have a partially plugged cat, the EGR pintle can actually be forced off it'* seat, and you can get a lot of exhaust gas forced into the intake....I have seen cats so bad, that if people continue to drive them that way, the constant heat from the exhaust bypassing the pintle(due to this high back pressure), can actually melt a hole in the top of the upper plenum directly over stove pipe from the EGR......so check for crud on the EGR pintle, and pull the tube between the EGR and the lower intake, and check for crud in there....

I took off the egr and tube,the egr is new and the tubes were clear.Put on the old egr valve cleared the code and drove car to complete srt'*,egr srt completed and has not reset a code.I bought a Delphi egr valve from rockauto,it appears the new valve is no good and like you said the back pressure was forcing the valve off its seat causing P0404.Thanks again for your help,Im going to drive the car on errands this afternoon so if something else comes up I will post again

I just wanted to take a second to thank TechII and WilliamE. Without guys like them being willing to share their time and knowledge with us we would be lost. Although I am not having the same issues as paug01 I was able to learn something about EGR valves that may be useful in the future. Thanks to TechII and WilliamE and all the others who help get us out of a jam.