Another question about gas mileage.

I've made a few posts in this group before and got some very good advice, so here's the question;
Recently purchased '95 Chevy High Top Van (G-20) with 350 motor (at
least that's what the label says inside the engine compartment). Not sure about the transmission model, although it has overdrive (automatic, of course).
I've changed the rotor and cap, added new spark plugs, and advanced the timing as far as I dare. Also changed the O2 sensor ($60 just for the sensor, ouch!).
This thing starts quick and runs very smooth, no misses or pings, but the spark plugs DON"T have that 'tan' color you get when your burning the right fuel mixture, which makes me suspicious. Instead they are nearly WHITE, which means its running too lean, and seems to confound the mystery (at least to me).
Now the biggest problem. It only gets 11-12 mpg, and that's on the highway. Around town it gets 10, maybe 11 (I've checked it twice). I know this is a high top, so they tend to be a little heavy (4800 curb weight last I checked) and not the most aerodynamic of vehicles, but I've owned vans with 350"s before (it's been a few years) and I don't remember the mileage being _that_ bad.!!
Or am I asking for too much!??
Sorry about the long post, Just wanted to make sure you had all pertinent info.
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I run a 95 GMC High Top myself. It also has a 350 and a 4L60E trans (same as yours probably) with a 3:42 rear gear in mine I get a high of 16 highway and about 14 around town.
--
Steve Williams

<Millwright snipped-for-privacy@webtv.net> wrote in message
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Mill,
If you were running lean you'd have ECM DTC's, great gas mileage, high operating temps and a shitload of pinging. The brown deposits are usually soot from cooked oil which has slipped past the valve guide seals and/or rings. White plugs and shitty gas mileage would have me looking REAL close at the head gasket<s> on the affected side. Are both sides affected or just one? All plugs are white or just a few? Do you use any fuel additives?
Doc

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<Doc wrote: Mill, If you were running lean you'd have ECM DTC's, great gas mileage, high operating temps and a shitload of pinging. The brown deposits are usually soot from cooked oil which has slipped past the valve guide seals and/or rings. White plugs and shitty gas mileage would have me looking REAL close at the head gasket<s> on the affected side. Are both sides affected or just one? All plugs are white or just a few? Do you use any fuel additives? Doc>
Hi Doc;
No, I don't use ay fuel additives, just regular gas (no high test).
ALL, the plugs are white, no brown deposits.
I would suspect the head gasket too, but, there's no water in the oil, and vice versa, so I didn't do a compression test. The engine runs VERY smooth. Engine temp stays normal.
The engine sets no codes. The exhaust system is working the way its supposed to (i.e. no leaks. not clogged) but it does smell a little rich when cold, but goes away once the engine warms up.
I've driven this thing _hundreds_ of miles, already (to the east coast and back), and the mileage is better at 70 than driving at 60,!!! but still only 11 or 12 to the gallon. That's right, if I drive slower (60) the mileage gets worse (10 mpg, sometimes less).
The only odd thing is that I can smell raw gas when I open the air cleaner (again, that makes me wonder, but, I can't see any leaks).
In the service manual, they list the Fuel PR as a possible cause. What do you think? I don't want to start 'just throwing parts' at this problem, but, I'm getting desperate (sp?) at this point. I've had that engine bonnet off so many times in the last six weeks I've lost count. (lol).
Tomorrow, I'll be taking apart the TB and changing the FPR, what else can I do?
But, I still don't know what's really wrong with this van. Any help you guys can give would be great.
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Very interesting! My 91 K1500 recently had a gas mileage reduction...I've not checked the plugs, but I too have that raw fuel smell from the throttle body. Strangely, I've replaced the FPR about a year ago in a TB rebuild...what else could be going on??
b
<Doc wrote: Mill, If you were running lean you'd have ECM DTC's, great gas mileage, high operating temps and a shitload of pinging. The brown deposits are usually soot from cooked oil which has slipped past the valve guide seals and/or rings. White plugs and shitty gas mileage would have me looking REAL close at the head gasket<s> on the affected side. Are both sides affected or just one? All plugs are white or just a few? Do you use any fuel additives? Doc>
Hi Doc;
No, I don't use ay fuel additives, just regular gas (no high test).
ALL, the plugs are white, no brown deposits.
I would suspect the head gasket too, but, there's no water in the oil, and vice versa, so I didn't do a compression test. The engine runs VERY smooth. Engine temp stays normal.
The engine sets no codes. The exhaust system is working the way its supposed to (i.e. no leaks. not clogged) but it does smell a little rich when cold, but goes away once the engine warms up.
I've driven this thing _hundreds_ of miles, already (to the east coast and back), and the mileage is better at 70 than driving at 60,!!! but still only 11 or 12 to the gallon. That's right, if I drive slower (60) the mileage gets worse (10 mpg, sometimes less).
The only odd thing is that I can smell raw gas when I open the air cleaner (again, that makes me wonder, but, I can't see any leaks).
In the service manual, they list the Fuel PR as a possible cause. What do you think? I don't want to start 'just throwing parts' at this problem, but, I'm getting desperate (sp?) at this point. I've had that engine bonnet off so many times in the last six weeks I've lost count. (lol).
Tomorrow, I'll be taking apart the TB and changing the FPR, what else can I do?
But, I still don't know what's really wrong with this van. Any help you guys can give would be great.
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I have never had a pre-Vortec 350 that got much better mileage then you are talking about. I have a '96 now and the power and mileage have both increased quite a bit. In fact I wouldn't consider a pre '96 GM product with a 350 again. I think you may be looking at 12-15 mpg at the very best....

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my TBI 350 in my 88 K2500 gets 15-16 MPG city, my '98 C2500 work vehicle w/ a Vortec 350 gets the same mileage, though it has a bunch more power. unless a van has a diesel in it, it will get abysmal mileage, not much you can do about it.
-Bret

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