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Gradual loss of power

gingerdude

gingerdude

Donating Users
Hey guys,

My 01 GP SE with 62,000 miles has slowly lost power over time. For example at take off I can push the pedal down half way and it basically acts like I'm hardly pushing it. It just feels like it chugs up to 2,000 RPM, but once you get over that it feels completely normal. It doesn't sputter or slip, it's smooth acceleration.

The power loss is evident on take off and on the highway no matter the gear. It literally feels like it has no balls anymore, but it has never tossed a code.

Everything that you would normally replace on a vehicle as routine maintenance like fluids, filters, wires, plugs have been done within the last 30,000 miles. I've also already done heads and intakes. I am the only one who has done any level of maintenance to the vehicle except for the basic oil and tire stuff. I got the car at 34k from my grandpa who took worked for GM so he took care of it.

I'm not going to be able to tackle the full tune up until September, so I'm hoping you all might have some advice on where to look.

My thoughts are:

1) Just needs a tune up. I put coppers in which were for 20k, yeah yeah I know, I don't have a garage anymore so it'll have to wait.

2) Fuel pump dying or fuel restriction, same as 1.

3) Clogged cat

4) Transmission taking a crap
 


I had a feeling you all would say that. But better than the trans, so I'll give the O2 sensor removal a shot.

If it is the cat it's going to be one hell of a time. When I did the heads and the intakes even my impact couldn't get the bolts out of the rear header. I ended up having to remove the rear header at the head and pulled the engine forward and the exhaust back as far as possible to work around it. Getting it back together was a huge b*tch.

Thank God this car unbolts at the cat. I did exhaust on my 94 Grand Am and it was all one welded piece. I was under there hack sawing and cussing for hours.
 
So question...

If it is the catalytic converter I'm assuming I want to replace it sooner than later? If I leave it too long can I destroy the engine? I'm just trying to figure out how long I actually have because I have to basically bum garage space from others to work now and I don't have access to one currently.
 
Yep, I'd get on it. If it's clogged it will get to the point where the engine may not want to run well, if at all. Heck, I'd drop a ZZP 2.5" catted downpipe in it and call it a day. Get's rid of the U-bend and is stainless as well. Just throw some copper gasket sealer on the rear exhaust mani. end and a little on the pipe end and bolt it in.

And soak down all the bolts/nuts with PB Blaster every day for a few days in advance. I'd bet those bolts will let go. I've actually taken the rear mani. bolts loose from up top with a long box wrench and some pipe on the end. Not sure if you can get to them like that on a 3.1L though.
 


Okay so I'm not really sure it's actually the Cat. I took out the O2 sensor and noticed no difference.

I realized that my loss in power is because it's misfiring in this RPM range... BAD. Like I'm talking 20+ misfires across all cylinders constantly on the scan tool only when between 2,000 and 3,000 RPM. If I accelerate slowly or very quickly as to not get into this range there are no misfires and it feels fine. And trust me I can definitely feel the misfires, they are unmistakeable. Weird part is that it does not misfire at all when in these RPM ranges in neutral.

If you look at my post history it has always had a slight misfire at idle, but now it's worse as well.

Also I noticed it tends to cycle the temperature up and down more often than normal. And KR is constant now.

I was able to do plugs, air filter, and fuel filter where I am, but Cat isn't doable right now. Plugs are NGK Iridiums gapped at .060. I put premium in which nixed the KR for the most part, but amped up the misfires.


Edit: Also given that it's misfiring this bad I'm likely forced to do the Cat anyways. But I don't want to toss a new Cat into a vehicle this is running this terribly. Would rather fix this first.
 
I'm giving up. Taking it up to the dealership in a couple weeks to determine what's causing the misfire. I'll fix it myself, but I'll let them diagnose since I have replaced nearly everything since I have gotten the car. Then I'll toss the new cat on.
 
Alright I replaced the Cat, O2 sensors, and the EGR valve. The EGR was a code that recently came up and I confirmed it wasn't sealing well. It runs MUCH better. Still has its usual misfire but at least it's drivable again.

Let's see what the dealership can turn up on the misfire...
 


I don't know if you ever resolved your misfire issue, but that unusual misfire could very likely be the beginning of intake gasket failure. The 3100's are prone to that as well. Just looking at the mileage and the age of your GP. The easiest way to tell is to spray brake cleaner around the intake manifold with it running. If the engine revs on its own there your issue. Also check your vacuum lines
 
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