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Full boost but no power

Deviq

Deviq

New member
Need some help with my 2000 GTP. A couple weeks ago I replaced most of my gaskets. Did the lim, plenum, valve covers, and throttle body gaskets. Ran the car lightly for a hundred miles or so and changed the oil again.

Now that everything was done I ran some Seafoam in it and had some fun on the freeway. It ran better than it ever had. Had plenty of power and gas mileage seemed to go up also. I had it parked for a couple days and now it has no power in boost.

The car drives perfectly fine with just moderate throttle but as soon as boost starts to show on the DIC it just loses power completely. I've check all of the vacuum lines, the pcv valve, all wire connectors, and pulled a couple plugs from the front and everything looks fine. The car hasn't thrown any codes so have no idea where else to look, any suggestions? Thanks
 


That could make sense considering the seafoam might have loosened some crap that is now plugging the cat.

You can get an exhaust backpressure check at a shop. They'll hook up a pressure transducer where the upstream O2 goes and read the backpressure. That will tell you if you have a clogged cat.
 


unscrew the front 02, then put the pressure gague in there.

It should read less than 1 psi of backpressure. Rev the motor in park and see what the gauge does, if it spikes and go's above that psi, you have a restricted exhaust.
 
if you pull the front o2 sensor out, it could very well make a difference, but your air to fuel ratio might be so screwed up that you wouldnt be able to tell. worth a shot though.
 


Finally got a chance to mess with the car again. Pulled the o2 and went for a quick drive down the street. It seemed to be a little better but was really hard to tell. When I first started it up, it idled real rough. Almost sounded like it was misfiring. Nothing else is really sticking out so I'm gonna let the car cool off and pull all the plugs this time. Might as well check just in case, would hate to order a new cat and it ends up being a $5 repair.

Is the downpipe at zzp a decent option? Thinking close to stock as possible for now so a 2.5 downpipe with cat. Wondering since I keep seeing ppl suggest other places before zzp.
 
i got a magnaflow from zzp. it increased the performance quite a bit but for the first 200 miles it sounded like a fart can.
 
L36pro said:
i got a magnaflow from zzp. it increased the performance quite a bit but for the first 200 miles it sounded like a fart can.
Click to expand...

Magnaflow what?

Converter?

If all you did was replace the converter your ears are lying to you because a HFC with a factory catback isn't going to sound ANY different.
 
Bio248 said:
paul, dont even debate a 2.5" downpipe. you really want the 3".
Click to expand...

Getting ready to order the downpipe. Will the 3" downpipe bolt right on to the manifold or will I need a reducer? Also, should I get the ZZP gaskets or invest in different ones? Thnx.
 
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If your buying the "3" BOLT-IN DOWNPIPE"...you need nothing but new gaskets because it does exactly that...bolts right in to the factory rear manifold and catback.
 
Well... FML! The cat wasn't the only problem. I can tell car can breath better but more than half throttle is still killing the car. I'm getting a p0300 (Random Misfire) code and the car definitely feels like it but only at 50% or more throttle.

Maybe I cracked a plug, got a bad set of wires, not sure what else.. Anyone have any suggestions on where to start looking now? Btw, I've already done a tune up with plugs and wires, did the lim, plenum, and throttle body gaskets. I did pour half a bottle of seafoam in the tank when the cat got clogged but the cars been sitting with the same gas for almost a month. Could the gas have gone bad that quick? Its depressing putting all that work into it to be far worse than when I started.
 
if youre misfiring when going into the throttle it sounds like you've got an electrical problem. make sure all the plugs and wires are good, then start looking towards the coil packs or ICM.
 
Think I figured out the misfire issue. The last pin towards the driver side of the icm harness was bent. Straightened it with by putting a pen over it and no more misfires while driving again. But, same issue with losing power. This time while pressing on the gas during the trip I could hear something like a backfire coming from under the car. Still hunting but ran out of time today to do anything else..
 
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