Sorry about this guys, but this is the best forum I have ever been on... My wifes 2000 Mercury Grand Marquis, 4.6 V8 has a problem. I have just replaced the fuel pump and it is now running 30# of pressure at an idle. It is running 35# with the engine off and key on. It is running 40# with the regulator unplugged. The problem is that when I accelerate quickly while driving the thing stumbles and dies. After stopping and putting it in park it starts right back up. It is pulling about 20# of vacuum at an idle and it drops to 0 and shoots up to about 23# upon gunning it wide open and quickly releasing it. (It does not die or stumble sitting in park and accelerating) ?Any ideas? Thank you much!

 

OK, Forget the previous diagnosis. What could cause this 4.6 V8 to run great and smooth until it is rolling down the road and stomped on to pass a car or get on the highway only to have it stumble and die?

 

Please, anyone got any ideas?

 

OK. Believe it or not, it is now running fine. After two days of diagnosing and testing I thought about my son changing the fuel filter on the side of the road and decided I would see if he put it in backwards or something. Not that it would make any difference, I was just desperate. Took the bracket loose and spun it around enough to see that it was in right and bolted it back in. Jumped in it to take it to Firestone for diagnosis and it will spin the tires! No bucking, jumping or missing. Go figure.... I don't care it is now running well! Thanks anyway!