Detonation and Hesitation 3400

[sparkplug]

So I bought my Grand Am a few weeks ago. Dealer replaced something with the EVAP system and put a new cat on the car. Now I have a problem with WOT detonation and hesitation. If I put my foot to the floor she down shifts and rpms go up. But I can hear it detonate (popcorn sounds) then rpms drop, hesitates and rpms go up and keeps doing it until I take my foot out of it. Now, normal driving it's flawless. Half and 3/4 throttle it doesn't do it as much. I get the SES flashing for misfires. I replaced the plugs with ACDelco iridium plugs and Delphi wires.

I'm thinking with 86k miles it might have some carbon build up and I'm running 2oz of Marvel Mystery Oil in the gas. I've thought about seafoaming the top end. The EGR might need some cleaning. But I'm not sure. Do you guys have any idea's what the crap is the problem?

[pocket-rocket]

I would change the fuel filter and check the fuel pressure. I wouldn't doubt if it's never had the filter changed and it's starving at RPM.

Seafoaming won't hurt a bit either.

[sparkplug]

Sounds like a plan. When I change it I'll report back. Thanks.

[TGP37]

I was just about to say, if it is a bad fuel filter......put it in park and floor it so it bounces off the rev limiter a few times. If the filter is bad, the RPM's will drop after a few limit hits.

And if you confirm it is the filter, get ready to buy a new fuel pump soon. It is very common for the fuel pump to die shortly after removing a plugged up filter. You may be able to keep the pump alive longer if the tank never goes below 1/4 full and you add seafoam or some form of upper lube to the fuel.

[pocket-rocket]

You may be able to keep the pump alive longer if the tank never goes below 1/4 full

This goes for any fuel pump, regardless if the filter is clogged or not since the fuel acts as a coolant for the pump. You should always keep the tanks as reasonably full as you can.

[sparkplug]

Sorry for the long time for my response, my car is under a 2 year powertrain warranty so I took it to the dealer. They replaced the fuel filter, fuel pump, ICM, and wires, I replaced the plugs. It helped then it started doing it again. I think I may have found my problem. I had just started the car for a few minutes to move it and I popped he hood and fresh fuel was sitting on the regulator, it may have a pin hole leak. How hard is it to remove this bad boy?