Two issues today, don't think they're related?

Dshow

Original poster
Member
Dec 7, 2011
68
Hi folks,
Towing the 21' boat to the lake today, I had two issues...
1) I tow in 3rd gear to keep trans temps down. I cruise ~70 mph @ 3k RPM. When I start going up a hill, it kicks down and jumps to ~4k RPM. Last season when it would do this, it was loud, so I take it out of cruise. This trip, when it kicked down, the engine made more noise than usual and there was a vibration until I reduced the RPM. Does that sound like a motor mount?

2) Going to the lake, I noticed the fuel mileage was worse than usual... ~9 MPG :eek: Coming back from the lake, we were on the interstate and I looked down and the Service Engine Soon light was on. It was a P0171. From the other threads, it sounds like that could be anything...? What are you thoughts on that and is it related to my back mileage?

Thanks- Dan
 

Voymom

Member
Feb 3, 2012
2,523
After looking at your truck, I realized you don't have a MAF sensor. But I would still inspect your truck for a vacuum leak. You could look at changing out the 02 sensor, the 171 I believe would be the sensor before the cat(in front). It's rare for both to fail at the same time. I'd also still check your fuel filter and fuel pressure. But I would do that last, as the computer should compensate for the reduced fuel volume.

The code still means your truck is running lean in bank 1, to much air coming out of the exhaust

This code can mean a lot of things could be in possible failure, but I think the vacuum leak is more common in these trucks. So I would inspect all your PCV hoses to start with, and move on to other possible things once that is done.
 

Sparky

Member
Dec 4, 2011
12,927
Hmm... reading lean, poor mpg, and louder...

Infamous exhaust manifold crack perhaps? Cracked manifold causes noise + leaks exhaust + sucks outside air, screwing with O2 sensor readings, which dumps more fuel to compensate for the supposed lean condition that doesn't really exist, causing it to actually run rich and burn more fuel, causing bad mpg, all while still leaking outside air and making the O2 sensor read lean...

Just an idea :undecided:
 

CaptainXL

Member
Dec 4, 2011
2,445
Dshow said:
Hi folks,
Towing the 21' boat to the lake today, I had two issues...
1) I tow in 3rd gear to keep trans temps down. I cruise ~70 mph @ 3k RPM. When I start going up a hill, it kicks down and jumps to ~4k RPM. Last season when it would do this, it was loud, so I take it out of cruise. This trip, when it kicked down, the engine made more noise than usual and there was a vibration until I reduced the RPM. Does that sound like a motor mount?

2) Going to the lake, I noticed the fuel mileage was worse than usual... ~9 MPG :eek: Coming back from the lake, we were on the interstate and I looked down and the Service Engine Soon light was on. It was a P0171. From the other threads, it sounds like that could be anything...? What are you thoughts on that and is it related to my back mileage?

Thanks- Dan

Sometimes the CPAS sticks the VVT which can leak exhaust gases into the cylinders causing a lean condition. Which could end up burning exhaust valves. I would replace your CPAS and give the engine a good flush. Use 5W-30 oil from here on out. Also replace O2 sensor in exhaust manifold.
 

Dshow

Original poster
Member
Dec 7, 2011
68
Thanks for the feedback. I reset the fault and its been off since then. I'm leaving for a trip so I will do some troubleshooting when I return. Thanks again!
 

Dshow

Original poster
Member
Dec 7, 2011
68
Update: So, the truck has thrown no codes since my last post so got busy with other things... Went on vacation over the 4th and towed the boat. The trip up was fine (except with rear window regulator went out so I have one on order.) On the way back, I had been driving about 45 minutes and all of a sudden, I couldn't keep speed on the interstate. When the accelerator was pushed, the engine would bog. I was lucky to get 30 MPH out of it. It was noon on Friday, 100+ degrees out, with the wife and 2 dogs... It would have been a bad scene to get stranded on the interstate so we found a hotel. I had my scan tool but the TB had no codes... I took it to the local Chevy dealer and they said my catalytic converter was plugged. Ordered the part and they installed it the next morning. We made it ~150 miles home that afternoon. I replaced both O2 sensors as well today (getting the one out of the manifold was a PITA, I ended up cutting the wires and using a regular socket). The mileage is much improved, before I'd be lucky to get 12 MPG, now I averaged 14.2.

Anything else I should look at? I don't want to replace another cat anytime soon, that left a mark on my checking account!!!!
 

CaptainXL

Member
Dec 4, 2011
2,445
Dshow said:
Anything else I should look at? I don't want to replace another cat anytime soon, that left a mark on my checking account!!!!

Exactly how much of a mark did it leave? A cat is about $90 for a good one and labor would be around $80-$120 for up to an hours worth of labor.

How long have you had this truck? It could be that if you just bought it within a year that the previous owner left the thermostat on when it failed. This is a big reason why cats go out.
 

Dshow

Original poster
Member
Dec 7, 2011
68
Let's just say I paid significantly more than the prices you listed, but with the wife, dogs, boat, and 100+ degree temps, I had to get it done. I've had the TB since new and it only has 70K miles. I got a thermostat fault about a year ago and replaced it.
 

CaptainXL

Member
Dec 4, 2011
2,445
Dshow said:
Let's just say I paid significantly more than the prices you listed, but with the wife, dogs, boat, and 100+ degree temps, I had to get it done. I've had the TB since new and it only has 70K miles. I got a thermostat fault about a year ago and replaced it.

There you go. it was probably already partially clogged over the past year and just got worse. When your mixture is enriched and engine can't expel he exhaust in good fashion then the cat will clog up faster, especially if you are towing. My .02

If it was the dealer you got it changed at then they probably replaced the entire exhaust pipe before the muffler. Yeah , I can see how that would cost more. They should have replaced O2 as a courtesy unless they mentioned that to you and you told them you would change it. Either way, glad to see your running again.
 

Vonhendon

Member
Dec 7, 2011
55
CaptainXL said:
Exactly how much of a mark did it leave? A cat is about $90 for a good one and labor would be around $80-$120 for up to an hours worth of labor.

How long have you had this truck? It could be that if you just bought it within a year that the previous owner left the thermostat on when it failed. This is a big reason why cats go out.

Where you find a CAT for $90 at?
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
Isn't there a 10 year 80k mile warranty on the cat? :undecided:
 

CaptainXL

Member
Dec 4, 2011
2,445
Wooluf1952 said:
Isn't there a 10 year 80k mile warranty on the cat? :undecided:

Yes there is. Good point. Shouldn't have paid a thing. I would call the dealer today dshow and see what's up.
 

Dshow

Original poster
Member
Dec 7, 2011
68
Great point, but it may be over 10 years by a couple of days, I remember I bought this right before the 4th vacation in 2002. I will check the documents I have.
 

CaptainXL

Member
Dec 4, 2011
2,445
Dshow said:
Great point, but it may be over 10 years by a couple of days, I remember I bought this right before the 4th vacation in 2002. I will check the documents I have.

That would really bite especially since it started acting up a month ago. I have heard of gm helping people out being close to warranty dates for other stuff so it's still worth fighting for. :thumbsup:
 

Dshow

Original poster
Member
Dec 7, 2011
68
I found document that say I bought it in June 03! Now I'm just trying to confirm how long the emissions warranty is... Keep your fingers crossed.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
It's 8 years and 80,000 miles and if it was in effect, the dealer should have volunteered that fact. I've heard of folks getting new PCMs within that time, but they often skitter out of paying for the cat claiming it was an owner-caused problem, not a defect in manufacturing.
 

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