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2003 chevy trailblazer_lt_ext
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Discussion Starter · #1 ·
A while back, I had gotten a some codes while freeway driving and towing my trailer. Mileage was horrible. I tracked it to a vacuum line I didn't connect after having the air box off. I also changed my fuel filter. The codes cleared on their own and haven't come back.

However, my towing mileage still sucks and it labors when getting up to freeway speed. It feels like its got power, but that something is using that power. It will kick into passing go and go fine if I really want it to. Problem is that normally for gradual acceleration I don't have to hit it hard. It dawned on me that it's behaving the same as it would if I had the A/C on while towing. My PS pump has always whined, but has been worse the part few months. At low speeds the steering's a little stiffer.

So, could the failing pump be binding enough to cause what I'm experiencing? I've never had a PS pump go bad, so I have nothing to reference. The problem is really not noticeable when I'm not towing. But even then my mileage is only about 14/15 in mixed driving. Down from 16/17.
 

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2008 gmc envoy_denali
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860 Posts
A while back, I had gotten a some codes while freeway driving and towing my trailer. Mileage was horrible. I tracked it to a vacuum line I didn't connect after having the air box off. I also changed my fuel filter. The codes cleared on their own and haven't come back.

However, my towing mileage still sucks and it labors when getting up to freeway speed. It feels like its got power, but that something is using that power. It will kick into passing go and go fine if I really want it to. Problem is that normally for gradual acceleration I don't have to hit it hard. It dawned on me that it's behaving the same as it would if I had the A/C on while towing. My PS pump has always whined, but has been worse the part few months. At low speeds the steering's a little stiffer.

So, could the failing pump be binding enough to cause what I'm experiencing? I've never had a PS pump go bad, so I have nothing to reference. The problem is really not noticeable when I'm not towing. But even then my mileage is only about 14/15 in mixed driving. Down from 16/17.
How much fluid is in your PS reservoir? My previous cars / trucks always whined alittle when the fluid wasn't at it's proper level
 

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2004 gmc
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26,436 Posts
Have you checked the air filter lately?

If your PS pump was absorbing even 2HP from the engine, that would be 1500 Watts it would have to be dissipating. A bad bearing could only absorb 1500 Watts for so long without overheating and being quite obvious.

Other reports of low power without codes showing up have been responded to by ideas like bad O2 sensor or restricted cat. Not sure if there's a consensus on the most likely cause.
 

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2003 chevy trailblazer_lt_ext
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968 Posts
Discussion Starter · #4 ·
Fluid level is normal and I check it regularly. When I bought it in '06, with 56k on it, the level was low and who knows how long the previous owner drove it like that.

I changed air filter in May. I thought about the 02 sensor, and I was going to replace it, its cheap enough anyway. Then I thought about the PS pump. It seemed logical and it needs to be replaced anyway. Its REALLY noisy. Its also not something that will break the bank. Yes, I'm concerned that it could also be the cat. That's probably the last step in the process.

Anyway, thanks!
 

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2003 chevy trailblazer_lt_ext
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968 Posts
Discussion Starter · #5 ·
Of course as I said the PS pump needed replacement anyway. So its nice and quiet now, but of course it didn't resolve the bogging. I replaced the front O2 sensor and that didn't help either. I had to take it to a shop to get it diagnosed. It took them a day to track it down, and they said it was the cat.

So I replaced the cat and rear o2 sensor today, and viola! All is well again. Well except that I'm nearly $500 poorer. I can't imagine what that would have cost to have it done somewhere. BTW, the cat was pretty easy to change. The hardest part was getting a torch head in the area where the top bolts are by the exhaust manifold.
 

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2004 gmc
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Thanks for the report, and statistical evidence that we're seeing more and more clogged cats. Any idea how the shop diagnosed it correctly to the cat? Or did they eliminate most other things, and that's what's left?
 

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2003 chevy trailblazer_lt_ext
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Discussion Starter · #7 ·
Roadie, it was the latter. They actually couldn't get it to bog down the first two times they drove it. Then it did so on the third time. They knew I had done plugs, fuel filter, air filter, cleaned the TB, and put the O2 sensor on. So they checked the fuel pressure, fuel regulator, scanned for codes, and checked the fuel injectors. All that's left at that point is the cat.

I can't be certain of course, but I suspect that the front O2 sensor was the cause of the cat failure. I had issues in May with code 0171 & 0172. Both "multi-cause" codes. So in troubleshooting, I didn't change the O2 sensor until two months later.
 

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2009 chevy
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6,513 Posts
I can't be certain of course, but I suspect that the front O2 sensor was the cause of the cat failure. I had issues in May with code 0171 & 0172. Both "multi-cause" codes. So in troubleshooting, I didn't change the O2 sensor until two months later.
I've gotten into the habit of changing the 02 when I change plugs. Most of the time, it's cheaper than the plugs and I believe 100k is pretty well the life expectancy.

I only had one cat plug, it was on an Olds with a 350. The car would work fine under normal driving; but when hot and when I need power, the car would bog down. Obviously, not able to breath.

Thanks for the update Doc :thumbsup:
 
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