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Old 10-08-2020, 12:33 PM   #141
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Default Update on 1995 Chevy

Our 1995 Chevy Roadtrek 190 Versatile is the last year of the old style Chey van chassis with the last year of the TBI 350. We have been getting 10.5 to 11 MPG and also had hot soak vapor lock problems. After some troubleshooting I found that it had low pressure. We replaced the fuel pump which cured the vapor lock and I was pleasantly surprised to find that the fuel mileage jumped to 12 to 12.5 MPG. That may not sound like much but it's a 14% increase so I'm quite happy. The van also has one of the old school pellet catalytic converters so now I'm thinking about upgrading that to a newer higher flow converter to see If I can get up to 13MPG.
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Old 10-08-2020, 02:17 PM   #142
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Our 1995 Chevy Roadtrek 190 Versatile is the last year of the old style Chey van chassis with the last year of the TBI 350. We have been getting 10.5 to 11 MPG and also had hot soak vapor lock problems. After some troubleshooting I found that it had low pressure. We replaced the fuel pump which cured the vapor lock and I was pleasantly surprised to find that the fuel mileage jumped to 12 to 12.5 MPG. That may not sound like much but it's a 14% increase so I'm quite happy. The van also has one of the old school pellet catalytic converters so now I'm thinking about upgrading that to a newer higher flow converter to see If I can get up to 13MPG.
Weird on your MPG. My average over the last 70k miles is about 13.4 pulling a 6x10 cargo trailer at 2500 libs loaded at about 62-65 mph.

My total weight all kitted up and road ready is right at 11,000 lbs, according an Oregon weigh station. It seems a bit weird that your mpg is that low, unless you're really gettin' it down the road and/or it's all city driving.

I would wonder of a cat cleaning would help. I know that it really helped my RT run stronger after doing it. RT info in signature.
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Old 10-08-2020, 02:25 PM   #143
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Old 10-08-2020, 02:54 PM   #144
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Our 1995 Chevy Roadtrek 190 Versatile is the last year of the old style Chey van chassis with the last year of the TBI 350. We have been getting 10.5 to 11 MPG and also had hot soak vapor lock problems. After some troubleshooting I found that it had low pressure. We replaced the fuel pump which cured the vapor lock and I was pleasantly surprised to find that the fuel mileage jumped to 12 to 12.5 MPG. That may not sound like much but it's a 14% increase so I'm quite happy. The van also has one of the old school pellet catalytic converters so now I'm thinking about upgrading that to a newer higher flow converter to see If I can get up to 13MPG.

My guess is that 1995 5.7 throttle body setup is very similar to the 4.3 TB we had in a 1989 S10 Blazer. I was pretty unimpressed with the TB injection although it was typical of the technology at the time. TB infection is really just a carb setup with fuel sprayed in at medium pressure, usually on a the throttle plate. While it can meter fuel a bit better than a carb, they normally don't use an atomizing venturi like a carb does, so fuel dropout can be and issue. Our 4.3 also had a single plane intake manifold that gave very poor fuel distribution. It was very obvious of the problems when I would pull spark plugs and they showed very large cylinder to cylinder balance based on the color and amount of deposits. I did check good and even on compression across the cylinders and didn't use any oil, so almost certainly mixture and distribution.



Unfortunately, there isn't a whole lot you can do about the fuel issues unless you change the setup to port injection which is neither easy or cheap to have done. A hard core DiY person could put a a later TPI setup on it and do the right tune to match the van, and I would guess the mileage would increase quite a bit. I put a modified TPI based, programmable, setup on a twin turbo 340 CID Dodge I built after running a finely tuned carb setup and the mileage went up a bit, but not a lot, as the carb and intake were very well dialed in. The 600hp, 3800# vehicle was up to about 22mpg compared to a factory 340 carb setup, no turbos, that got about 12mpg.


There used to a be a modified throttle body, that ran the fuel through a venturi like the carb, but used the stock medium pressure injectors, but I doubt they are still available. You might be able to find an aftermarket manifold that does a better job, though as they would probably be a drop in with a carb manifold and adapter. Some thing like an Edelbrock Performer dual plane is a very good setup for efficiency with good balanced distribution.


Changing the catalytic converter may help some, but may not also. Sometimes changes like that don't really have an affect on the fuel input, but would probably increase high load performance.


Pulling the spark plugs to look at them is often the best place to start to get a feel for what kind of things may or may help for mileage. Even at best, I wouldn't expect to get much beyond 14-15mpg on the high end with the pre LS engines like the 5.7. On an older vehicle, gaining a bit of increase is probably cost prohibitive in most cases.
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Old 10-08-2020, 03:00 PM   #145
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On my trip home from picking up my new to me, well broken in, 2008 RT210V, before oil change, ATF change, and service, we averaged 15 mpg. That was NC, Va, WV, Md, Pa into Western NY state.
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Old 10-08-2020, 03:52 PM   #146
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Weird on your MPG. My average over the last 70k miles is about 13.4 pulling a 6x10 cargo trailer at 2500 libs loaded at about 62-65 mph.

My total weight all kitted up and road ready is right at 11,000 lbs, according an Oregon weigh station. It seems a bit weird that your mpg is that low, unless you're really gettin' it down the road and/or it's all city driving.

I would wonder of a cat cleaning would help. I know that it really helped my RT run stronger after doing it. RT info in signature.

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That's why I pointed out that my 95 has a TBI motor. That engine was introduced in 1987. The Vortec motors introduced in 1996 were a substantial improvement.
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Old 10-08-2020, 04:56 PM   #147
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Unfortunately, there isn't a whole lot you can do about the fuel issues unless you change the setup to port injection which is neither easy or cheap to have done. A hard core DiY person could put a a later TPI setup on it and do the right tune to match the van, and I would guess the mileage would increase quite a bit.
...

There used to a be a modified throttle body, that ran the fuel through a venturi like the carb, but used the stock medium pressure injectors, but I doubt they are still available. You might be able to find an aftermarket manifold that does a better job, though as they would probably be a drop in with a carb manifold and adapter. Some thing like an Edelbrock Performer dual plane is a very good setup for efficiency with good balanced distribution.
GM makes a TBI intake manifold that bolts to the Vortec heads so you can upgrade the heads and keep the TBI injection and computer. That and a set of junkyard heads would not be terribly expensive. I doubt the stock TBI tune would be anywhere near optimal and I'm just not terribly exciting about spending hours logging data and burning EPROMs. It's literally been decades since I've actually touched an EPROM burner.

Since an upgraded converter is relatively cheap and I'd want that anyway I'll probably start with that and the salad bowl air cleaner mod. After I retire and finish all of my other incomplete projects I may get around to a head swap. Or if my 401K does well, maybe just a van swap.
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Old 10-08-2020, 05:34 PM   #148
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GM makes a TBI intake manifold that bolts to the Vortec heads so you can upgrade the heads and keep the TBI injection and computer. That and a set of junkyard heads would not be terribly expensive. I doubt the stock TBI tune would be anywhere near optimal and I'm just not terribly exciting about spending hours logging data and burning EPROMs. It's literally been decades since I've actually touched an EPROM burner.

Since an upgraded converter is relatively cheap and I'd want that anyway I'll probably start with that and the salad bowl air cleaner mod. After I retire and finish all of my other incomplete projects I may get around to a head swap. Or if my 401K does well, maybe just a van swap.

If a Vortec swap and TPI swap was in the cards, you would probably ahead for time and hassle by just shopping for a complete TPI setup as there lots of them around and you probably get a truck one with computer and harness. Those engines weren't nearly as integrated into everything else like they are now, so that is a pretty common swap in older pickup. TPI tunes can be purchased for a couple of hundred dollars for custom or you can get a live tuner and do it on a laptop. I have tuner for our 2007 LQ4 van engine and it works well. I will be getting a different one soon for the very specific LT1 gen2 engine in my 96 Buick Roadmaster wagon. It is a very specific one for that engine only and I will need it when I rebuild an upgrade the engine this winter, even though my changes will be minor. It will also get a rear gear change, so that will also change stuff the will need to be tuned.
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Old 10-09-2020, 05:29 AM   #149
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I don't mean to throw water on the discussion. I believe that conserving fuel is good for the environment and our use of resources. But the difference, given 30k miles traveled of 15mpg and 25mpg is 800gal. At $3/gal that's $2400. A sizeable savings. But if we're talking about an older rig costing $10k and a new one costing $70k (or more) the cost itself to break even is significant for most owners.
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Old 10-09-2020, 12:11 PM   #150
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I don't mean to throw water on the discussion. I believe that conserving fuel is good for the environment and our use of resources. But the difference, given 30k miles traveled of 15mpg and 25mpg is 800gal. At $3/gal that's $2400. A sizeable savings. But if we're talking about an older rig costing $10k and a new one costing $70k (or more) the cost itself to break even is significant for most owners.
^^^This is the true bottom line.
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Old 10-09-2020, 12:58 PM   #151
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^^^This is the true bottom line.

Yep, as I said earlier, for most older vehicles in it cost prohibitive to do major changes for a couple mpg. If it is a resto that will be kept a while and is not being limited to payback calculations, then it is often worth it for the satisfaction. The latter category is where my old Roadmaster falls, no way it will be back while I am alive, but it will be nicer to have so doesn't matter. Kind of how much fish cost per pound by the time you figure all the money you spend to catch them. Write it off to being a hobby.
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Old 10-09-2020, 01:00 PM   #152
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It depends on how I drive my Promaster B+.

When I am in a hurry, holding a near constant speed of 70-75 MPG across varying terrain and in traffic that requires frequent acceleration to pass I get around 11.5 MPG

If I try to conserve gas and use a combination of very slow acceleration and allowing the speed to vary by 25 mph as I as ascend hills (and slow), then descend them (and speed up) I have seen up to 15 mpg over a full tank of gas. I find this type of driving tiring and not particularly polite to others as I can end up going quite slow near the top of long hills.

On cruise control (which on the PM annoyingly allows the speed to vary by +/- 5 mph, or 10mph total) the van will get between 12.5 and 13.5 mpg depending on terrain.

Unlike GallenH I will actively try and throw cold water on this discussion!

In the end, the difference between 11mpg and 15mpg is a very trivial part of the overall cost of RV ownership. We drove around 10k miles on our unit this year (which was a lot for us and included a cross-country trip). This mileage difference adds up to less than $600 for the year at the very most, and less than half that under the actual blended driving conditions we experienced. Compared to depreciation, repairs, camping fees, tolls, dining out while traveling, etc this is a rounding error. It just doesn't make sense at these levels to even include it in the decision making process of either the purchase or operation.
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Old 10-09-2020, 02:47 PM   #153
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I agree that mpg’s are a small part of the cost of ownership. One thing that does matter is range. It’s annoying when you have to fill up multiple times during a day’s drive.

There are also so many variables in load, driving conditions, and data collection methods that comparisons are difficult.

For the record,
2014 Chevy Roadtrek 190P, 6.0L, 6-speed automatic

18.8 mpg at 65-70 mph solo, empty, on 2300 mile drive from MD to AZ.

15.3 mpg round trip average on 1300 mile round trip to CA, fully loaded, towing a 1600# Scamp trailer, four people on board, 60-65 mph.

Both were calculated using fuel purchased and miles driven. Those were the only two times I took the trouble to keep records.
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Old 10-09-2020, 03:33 PM   #154
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Both were calculated using fuel purchased and miles driven. Those were the only two times I took the trouble to keep records.
I have a similar Chevy model. My dash computer mpg is at least 5% optimistic.
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Old 10-09-2020, 05:39 PM   #155
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IIRC mine was off by about 0.5 mpg, or around 3%. The computers are getting better over time, I suspect.
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Old 10-09-2020, 07:29 PM   #156
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IIRC mine was off by about 0.5 mpg, or around 3%. The computers are getting better over time, I suspect.

Most of the newer cars I have seen for quite a while now seem to have speed read 1-2mph higher than actual and odometer is similar, so makes the mileage look better. The trip computers errors are most likely do to the flow sensor accuracy and linearity as the computer part of it is very, very easy. Finding affordable flow sensors that are accurate even in the low flow end of the use range is very difficult. It is also possible that they are using just the specs for the injectors and pulse width to calculate the volume, and that could be even less accurate, I think. When I had my old Escort checked for mileage when it was nearly new, the dealer had a very high end flow meter that they put in the fuel line to measure actual flow, and it spit out the cumulative mileage and instantaneous.
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Old 10-09-2020, 07:31 PM   #157
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I like it best when mine shows 99.9mpg while coasting downhill after a reset.

Booster, you are correct. My speedo is very close but usually 1-2 mph higher than what my Garmin shows. A little cushion to prevent speeding tickets as well.
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Old 10-09-2020, 07:42 PM   #158
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I like it best when mine shows 99.9mpg while coasting downhill after a reset.

Booster, you are correct. My speedo is very close but usually 1-2 mph higher than what my Garmin shows. A little cushion to prevent speeding tickets as well.

That 99.9 is really infinitely, I think, because according to Scangauge it means to engine has gone to full fuel shutoff. My old Buick, which doesn't have full shutoff shows in the 40-60mpg.
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Old 10-09-2020, 09:47 PM   #159
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...The trip computers errors are most likely do to the flow sensor accuracy and linearity as the computer part of it is very, very easy...
When I said "the computer" of course I meant the whole system, including the sensors that provide the input data. The results seem to be getting better in newer vehicles in my personal experience.
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Old 10-10-2020, 11:39 PM   #160
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2019 Coachmen CrossFit 22C.Ford transit 350 dual rears, 3.7 liter gas. 200 miles today, 16.2.
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