Loss of power. What could it be?

[mntb]

Need some help diagnosing it at least narrowing down the list of possibilities.
2003 gmc envoy 4.2l swb, 222,xxx miles

Idles normal, revs in park like normal, driving nicely in the city like normal.
But when giving it more than 1/4 thottle, it will accelerate until it hits 2500rpms in any gear, then it looses power, falls flat on it face, it will go but slower than normal. If I push it, it will rev to almost 6k to get on the freeway. There Is a whole in the muffler, but the exhaust is abnormally quieter than usual.

I was thinking fuel filter, clogged cat, or fuel pump.
Replaced the filter. It was a little restrictive to blow through. So I eliminated that.
Had a shop manager drive it, said fuel delivery or clogged cat. Not much help.

Now I'm at fuel pump or clogged cat.
Any Thoughts, questions, suggestions welcome

Any way identify one vs the other?

Thanks in advance,
Brad

 

[Tiggerr]

Pull your upstream o2 sensor and see if it improves...if so it's the cat..
Fuel pressure regulator is a possibility too...

 

[budwich]

well, I am not sure a clogged exhaust system will cause you to "rev to 6000" and "put put" down the highway. That's a transmission system issue. What gear do think you were at 6000 rpm? Heck at 6000, I am doing over 65mph in 2nd.... and that's pulling a trailer.

get the torque app going and look at the "slip" data while you are travelling down the road.

 

[mntb]

I tried pulling the o2 sensor, a little improvement. Should the be a huge difference?
I might pull it again just to to sure.

Budwich,
I meant when on the highway in the event I had to pass someone or whatever it could rev that high if I downshifted, if I pushed it to do that.
The shop manager that drove it said if the cat was clogged usually it would restrict speed and rpms.

I noticed while driving today when under moderate accelertation, it would sort of surge (if that makes sense). Like it wanted to take off, but it's being held back.

Before this happened, when getting on the highway or under moderate to heavy acceleration, up to 2500rpms it was really slow and doggy. But 2500rpm and up, she would really wake up and just want to go. Kind of a dr. Jekyl, mr. Hide deal.

Is that normal for these 4.2l?

I have a code for the camshaft position sensor. it's not new. Ive tried cleaning it before but i think I needs to be replaced. If there is oil In the connector (vehicle side), does that need to be replaced as well?
Any Chance my current problem is the camshaft position sensor?

 

[midnightbluS10]

It's quite possible. Go pick up some electrical contact cleaner and spray out the connections, then let them dry. Add a small dab of dielectric grease and put the connection together. Only use enough dielectric grease to put a very light coat on the metal contacts. You don't want to glob it on.

Does it have an egr valve? If so, unplug the electrical connector and test drive it. See if it helps. If so, it's your cat. If not, I doubt it's converter related.

 

[Mooseman]

The 4.2 doesn't have an EGR.

 

[mntb]

Well, tried cleaning the contacts/connector for the camshaft position sensor.
Still no change.

The part that confuses me is why is the exhaust so quiet? The muffler has a small hole in it which makes it pretty noticeable. But now it's almost as quiet as if it doesn't have a hike in the muffler. The hole is on the rear edge for the muffler.
And the exhaust has a wierd smell to it. Kind of hard to describe. Kind of reminds. Me of starting a car on a cold winter morning (not 30 degrees like some may think, more like -30) to warm it up. And Kind of a burning smell.
Doesn't smell like rotten eggs or sulfer.

I forgot to mention (just dawned on me this morning) that a chunk of the cat (the honey comb internals) came out of the tail pipe a few months ago. Decent size. Not sure how it even made it out.

Maybe there is another chunk stuck somewhere? I do hear rattling from the muffler when idling.

 

[Tiggerr]

I don't think a chunk of cat is gonna make it to the tailpipe....

However the resonator is known to self destruct and blow chunks....
It's possible the muffler collapsed inside maybe... although I've never seen that on one of these trucks...

Time to drop the exhaust, I think and see what's up with it.....
I'm betting either obstruction in resonator or still could be the cat...

 

[mntb]

Previous owner cut off the coffee can resonator.
So as far as I can tell all that's left is the muffler or the cat. But how would chunk of the cat make it through the muffler?

I'm thinking that too. Just need to find the time.

 

[Tiggerr]

Being that you reported improvement when pulling the O2 sensor, I'm inclined to believe there's an obstruction in the exhaust somewhere....
like you said muffler or cat, one or the other since res is gone...
My money would be on the cat...
Sounds like you need a muffler anyway too...

 

[mntb]

Muffler is on the list of repairs.
I wanted something with a nice sound but not super loud. But haven't really found anything i like that Isnt super spendy.
It seems like Its a tall order to me the 4.2 sound good.
Probably just going to go with a walker soundfx for now, whenever the important stuff is taken care of.

 

[Mooseman]

Try hitting the cat with your hand and see if you can hear rattling in there. A chunk could make it through I guess. I'd be planning on replacing the cat.

 

[mntb]

I tried that. Sounds solid. Maybe there isn't any more loose pieces?
But I if I shake the exhaust from the exhaust top, i can here rattling around In the muffler.

 

[Mooseman]

You might be right. No code for cat efficiency below threshold?

 

[midnightbluS10]

The 4.2 doesn't have an EGR.

What's the big solenoid looking thing bolted to the head above the exhaust manifold?


Edit: nevermind. I completely forgot about the secondary air injection. I just assumed it was EGR because of its placement and the gasket, which looks similar to an EGR gasket. Sorry!

 

[mntb]

Moosman,
Actually yes. I believe it's a code like p0267. I read the codes but forgot to post which codes. There is an evap code which I believe is for the gas cap with no deal (rotted off).
But the code you said has been on for the few months. It's not new.

 

[Mooseman]

Well then, I guess your cat has bit the dust. Maybe it disintegrated and plugged up the muffler with that one piece that escaped.

 

[mntb]

Wonderful.
Any benefit to go cat-less? No emmisions here.
To replace the cat, does the transmission cross member need to come out or be dropped?
I found a full exhaust minus the manifold for $125 with 02 sensor. Not too far from me. From an 2004 swb.
My whole system looks kind of rusty. Previous owner wasn't big on underbody washes it looks like.

 

[Mooseman]

Advantages? A little more sound out the tailpipe, more pollution (but that's between you and your conscience), maybe a little less restriction. You will have to cheat the PCM by putting a spacer for the post-cat O2 sensor. You could use spark plug defoulers to do this or purpose built spacers like these:
https://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias=aps&field-keywords=oxygen+sensor+spacer

They trick the PCM into thinking the cat is working properly and keeps the CEL off.

You could just gut out the cat by punching a metal rod through it and using a shop vac at the other end. But for $125, I'd get that used one as long as the cat is good.

 

[mntb]

Those were the two options I was considering actually.

Space looks kind right to get the cat out over the crossmember. Any tricks or tips?
Or just support the trans with a floor back and drop the crossmember?

 

[budwich]

try cleaning the map sensor... actually check to see that the vacuum lines are good every where. use a "spray fluid test" if necessary.

 

[Chickenhawk]

Your cat is clogged, no question.

Now, the question is, why did it clog? A few months of running with the coolant temps below normal will do it.

So will a few MINUTES of running with with a flashing service engine light (indicating a misfire.)

Why not save all the drivers behind you the misfortune of making their eyes water every time you accelerate and just replace the cat. It is not too expensive. Cats are not there just to meet regulations that may or may not apply in your area; they are there to help save the earth for a future generation.

Drive behind a vehicle with no cat and you will instantly see what I mean about making your eyes water.

As for why it failed, if you can't remember any instances of severe misfire, it is likely coolant temps. Post a picture of your coolant temperature gauge and we can tell in an instant.

As this platform ages, loss of power at highway speeds will become more and more common. Years ago, we used to say, "Welcome to our forum. Clean your throttle body." Now it would be more appropriate to say, "Welcome to our forum. Replace your cat."

 

[Realism]

I agree with Chickenhawk here. It is more than likely your CAT was clogged and it only got worse when you had a chunk come out and gum it up even worse.

Make sure you fix the cause as well when you go to replace the CAT. As Chickenhawk states (and as I've previously experienced) running with lower than normal operating temp for a few months, aka thermostat stuck open, will cause your CAT to become problematic. Another possibility is running rich for too long causing your CAT to experience prolonged overheating. Could explain why you had a chunk of honeycomb.

 

[shovenose]

I really don't see the point in replacing the cat if you don't have to. I've owned several vehicles without cats (83 Chevy 3/4ton, 77 GMC Suburban 3/4ton) and sure while sucking on the exhaust pipe is not recommended they didn't really "smell nasty" or anything...

 

[Reprise]

+1 for that $125 replacement - if nothing else, you'll have extra O2 sensors / muffler, and there's a good chance the replacement will have fewer miles than what's on your truck now (and a working cat).

IMHO, it's more trouble to run without a cat & keep from throwing codes, etc. (see Mooseman's & Chickenhawk's posts above), vs. just replacing it. You can see opinions vary on that...LOL.

 

[midnightbluS10]

Your cat is clogged, no question.

Now, the question is, why did it clog? A few months of running with the coolant temps below normal will do it.

So will a few MINUTES of running with with a flashing service engine light (indicating a misfire.)

Why not save all the drivers behind you the misfortune of making their eyes water every time you accelerate and just replace the cat. It is not too expensive. Cats are not there just to meet regulations that may or may not apply in your area; they are there to help save the earth for a future generation.

Drive behind a vehicle with no cat and you will instantly see what I mean about making your eyes water.

As for why it failed, if you can't remember any instances of severe misfire, it is likely coolant temps. Post a picture of your coolant temperature gauge and we can tell in an instant.

As this platform ages, loss of power at highway speeds will become more and more common. Years ago, we used to say, "Welcome to our forum. Clean your throttle body." Now it would be more appropriate to say, "Welcome to our forum. Replace your cat."

I've never had 87 octane(or any standard gasoline) make my eyes water. Especially once burned. Never caused by my truck, either. And I've been without a cat for 7+ years. Then again, I'm more used to M1 & M5 methanol. Talk about eyes burning. Gasoline is like water compared to M1.