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Old 12-06-2006, 05:29 AM   #1
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Well I think something may be wrong. I drove 140 miles from where I was on vacation back home and it was all highway. 100%. Now for some reason I got an average of about 22 mpg. I am thinking something might be wrong.

I was talking to John (DarkShadow) and he was informing me about how they use different blends of fuels for winter and summer. And that it is possible that the Winter blend, or otherwise the regular, less refined fuel, could be decreasing my overall gas mileage.

Or could it be that what WillWren said and that my Bosch Oxygen Sensor really is failing prematurely.

I have no codes, and the car is running just as well as it always has reguardless of the season.

Basic Tuneup Info - Amt of miles already on this item.
NGK TR55 Plugs - 8,000 miles
Autolite Professional Wires - 8,000 miles
K&N Drop in Clean - 3,000 miles
Bosch Oxygen Sensor - 20,000 miles

I run mobil one full synthetic oil and change at 2,500-3k and i use a delco oil filter

One thing i have never changed is the PCV filter. I don't know what it looks like or how to change it, but does this affect fuel mileage in any way?
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Old 12-06-2006, 09:43 AM   #2
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How fast were you going, how hilly was the terrain, and how trained are you at keeping the revs down?
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Old 12-06-2006, 11:55 AM   #3
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Diffrent Blends can and will affect Overall milage... I think you can easily loose as much as 10-15% in milage...

The worst milage I got was 13 city and 21 hwy..... That was after the Bosch O2 took a major crap...

John we have the same gear ratio, same exahust( pretty much ), cars in the same tune, about the same weight with the same options..

I'm lucky if my milage at its worst is 20 in town... I have done a 31 in it and that was not following the speed limit( I know you catch my drift here )....

A while back I knew a Service manager for a local dealership that had a 90 SE bonneville Loaded with the 2.97 gear ratio... He was tellime how much he and his wife loved that car... At the time it had 150,000 on it, and it still got 30-31 mpg when they took it on the road...

The 3.33 gear ratio is a drinker.. 16-17 city and 25-27 hwy would be the norm...

Wj regaurdless of the conditions you should be doing better than that...

As asked above tho... How hard were you on the car... What were the conditions? I'm quite sure you are running blended fuels right now... And was the milage drop sudden?

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Old 12-06-2006, 12:20 PM   #4
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On the road our 92 TranSport 3800 gets about 24 mpg so that is a "worst case" condition. OTOH Bonnevilles typically get 28-32 on the road. If no scan tool is available (BLM and integrator would give indications) and the car feels like it is running good otherise (no trouble codes or SES light) you might just try a new O2 sensor ((get the short body Delco AFS-20/ p/n 25162693) since one that reads lean can make the engine run over rich.
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Old 12-06-2006, 12:25 PM   #5
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Winter Blend KILLS your gas milage, and the interesting thing is that the winter blend is every where, not just in the states that get snow
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Old 12-06-2006, 12:27 PM   #6
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Quote:
Originally Posted by 1993 SLE
Winter Blend KILLS your gas milage, and the interesting thing is that the winter blend is every where, not just in the states that get snow
very true.

The last time i went to boostys to do my dash, i only got 27MPG on the highway for a 300mile trip.
I use to get 32-33.
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Old 12-06-2006, 03:22 PM   #7
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Quote:
Originally Posted by jr's3800
The 3.33 gear ratio is a drinker.. 16-17 city and 25-27 hwy would be the norm...
Last winter there was one fillup where I got 17-18 combined :o
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Old 12-06-2006, 03:49 PM   #8
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Quote:
Originally Posted by repinS
How fast were you going, how hilly was the terrain, and how trained are you at keeping the revs down?
I was going at about say..an average of 65? And there were no hills, I'm in wisconsin remember? As far as keeping revs down. I did NO redline starts or runs on the whole way back and when I did have to stop, I kept the startup relatively moderate.

The change was not what I would call drastic at all. It has actually been gradually decreasing over time. But yeah, I do know the Winter Blend can kill yah, but I'm not sure I was getting much better mileage this summer!

But I don't think anyone has answered the question about the PCV Valve...
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Old 12-06-2006, 03:56 PM   #9
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Quote:
Originally Posted by padgett
On the road our 92 TranSport 3800 gets about 24 mpg so that is a "worst case" condition. OTOH Bonnevilles typically get 28-32 on the road. If no scan tool is available (BLM and integrator would give indications) and the car feels like it is running good otherise (no trouble codes or SES light) you might just try a new O2 sensor ((get the short body Delco AFS-20/ p/n 25162693) since one that reads lean can make the engine run over rich.
On topic of the O2... my exhaust DOES smell rich at times. But for the most part the car is running fine, and not bogging down or anything, so it really couldn't be running THAT rich. I currently don't have access to a scan tool to look a little closer to see if it really IS the O2 acting up, but when I did have it on there about 9k ago, it showed it switching back and forth between lean and rich, therefore displaying a perfect mix.

IF I do replace my 02...I do know there are alternatives to Delco, that are much cheaper. How good are Denso oxygen sensors compared to a delco. There is one for only 14 and change at rockauto.com and thing is I really don't have alot of spare $$$, so I really don't wanna pay Delco'* premium prices if its not 100% necessary.
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Old 12-06-2006, 06:11 PM   #10
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Mine smells rich too, and kinda beating on my GX3 with 95% at 55mph yielded me 20mpg. And I am having problems with vacuum leaks... so it could be better. But so far i have 120mi on the first 1/4 of a tank.

And to answer your question about the PCV valve affecting fuel economy, yes. Very much so. All you have to do is remove it [located right behind the alternator, isn't too bad to pull out], and shake it. If it rattles, it'* fine, if not you need a new one.
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