Thats why I said, either a CAT (meaning a bad/blocked CAT) or an O2 sensor.

 

Well I'm just saying that a blocked CAT would only cause problems on the top end. If it was clogged enough to cause problems on the low end, the issues wouldn't get better with higher RPMs, just worse. But for the bad MPGs, it might cause slighty lower fuel economy but nothing that dramatic, when my CAT was clogged I was still pulling about 16-17MPG, but the engine wouldn't rev over 2k RPMs, if it did it would just bog down and hold 2k.
For the fuel problem, I'd check out the O2 sensors first before anything else. And for the shaking problem, something is probably out of balance since it only happens in certain RPM windows and evens out smoothly in between.

 

Not true. When I had a blocked CAT it lost the ability to even hold an idle. The only way I could get any power out of it was to hit high RPMs which, granted was a great loss of power, but power was still lost at idle and lower RPM range.

 

Sounds like a blocked cat could cause a lot more problems then. I experienced exactly the opposite as you.

 

Very much so. It was a horribly clogged CAT though, and I cut it open and it looked horrible after I took it out. Needless to say, when I replaced the CAT it ran just as good as coming home from the showroom.

 

Update: well just got back from the shop. The mechanic has replaced the cap, rotor and plugs again, also he tested the plenum gasket and it is leaking he also said "while he is there" I might as well replace the timing chain also. I dunno, am I being taken for a ride? If I am being taken for a ride its gonna be time to break my foot off in someones ***! Ill post again as soon as I get it back. If it wasnt for all you guys id still be in the dark on all of this. Thanks all!

 

Eh timing chain is ify on getting it done or not because it seems this problem happened instantly almost, and not by a stretching chain. By him saying since he's already in there, I think he means since he has all the accessories removed, which is only an extra hour of work.

Your plenum is a priorty for sure. Getting the intake off gives him a chance clean and redo half of your top end.

 

Oh hell, just rebuild the top end!.......LOL......(While your there).......Ya right!


I still think he needs to look at the O2 sensor and CAT!

 

your being taken for a ride, if it was the timing chain the problem woulda come up slowly, not suddenly, and in most cases timing chains are lifetime parts (you will replace it when you rebuild the engine)

 

[quote=hydrashocker;2470496]Oh hell, just rebuild the top end!.......LOL......(While your there).......Ya right![quote]
Just saying that a plenum gakset job is basically rebuilding half your top end and it has to get done sooner or later.

Sounds to me the OP left the D at the shop right now, but I don't know what for. Just don't let him mess with the timing chain, that's an expensive job and like sharps said it's probably fine.