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argo 09-14-2014 03:51 PM

1992 Caprice Wagon Fuel Economy Project
I have been lurking on this forum for a while and have seen a few mileage discussions regarding these cars, or similar ones, and there is quite a mixed consensus about their efficiency potential. I rescued this particular car from my parents. I actually drove this car to high school back in 1992. The car had been sitting mostly and relegated to spare car duty. I wanted a backup family car for my 1992 Diesel Suburban, so I offered to buy it. My parents gave it to me because I always fixed it for them for free. So the price was right but the old girl needed some help.

Nobody would ever accuse the LO3 5.0L (305 TBI) V8 of being a rocket in a 4500 lb car, especially when pulling 3.08 gears, but it was particularly sluggish when I brought it home and it had no heat and it only managed 13 MPG. I gave it a tuneup, replaced the thermostat (I installed a 205* unit instead of the factory 190* thermostat), I replaced the worn out O2 sensor and re-calibrated the TPS down to 0.62v at idle to make the computer run the engine a little leaner. I also replaced the tires with Yokohama Geolander HT/S tires in the LT 215-75-R15 and run them at the full 50 psi. This doubled my fuel economy to 26 mpg highway on a trip to Disneyworld with the family on a 2,100 mile round trip. Around town it is averaging about 20 MPG. I recently took a trip to building supply liquidator in Readding PA to buy replacement windows for my house and despite the weight of 10 windows (2 of which ended up on the roof rack) it averaged 23.1 MPG for the trip. I can do better, but since I try to keep with the flow of traffic and generally cruise at 5 MPH over the limit I think these numbers are reasonable as a starting point. Since I live in a rural area and sometimes need to travel on unimproved roads, lowering the car is not an option. Also, as a mechanic/shop teacher I always travel with about 100 lbs of tools in my traveling tool box. I intend to modify the TBI unit for more efficiency by installing smaller injectors and boosting the fuel pressure to compensate because higher pressure with smaller injectors should provide better atomization. I plan to use the injectors for the 4.3L V6 and a pump for an LT1. I might convert to a 6.2L diesel like my Suburban has. I custom built that for fuel economy and get 27 mpg with the Sub. Stay tuned...

spacemanspif 09-14-2014 06:05 PM

Welcome that is a very noble plan for the often unappreciated caprice wagon (I call those cars rolling caves because of all the space they have). Being a shop teacher you have more tools and tech skills than most of us here. You should develop a kam back, air dam and maybe side skirts out of some aluminum sheet metal. The kam would help with your over-the-limit speeds and the dam might as well. Looking foreword to seeing pictures and/or progress on the "cave", you are doing great already!

101Volts 09-14-2014 06:22 PM

Hey I am aware these cars have great potential for higher fuel efficiency regardless of their size, It looks like maybe you're the first here who will be heavily modifying one of these whales and finishing it. I have a Wagon too but it isn't as aerodynamic as the 1991-1996 Whale type. Someone on here a while back was going to convert one like your own to Diesel but didn't finish, I'm sure you can get 30+ HWY with a Diesel and Manual Transmission. You got a good start, I'd like to see more on subject of Wagons!

P.S. I once got 28.56 on a HWY trip in a 2000 Caravan. That's a lot lighter than the Wagon you have but the EPA does rate it at 19 Combined, whereas the Wagon is at 18:

argo 09-14-2014 08:41 PM

Thanks for the positive support! There is a person on The Diesel Place who did a 6.2L conversion to a Roadmaster wagon and it was doing over 40 MPG Imp. Which would be about 35 MPG US. The main issues are time and funds. Both are limited. I am going to "fuel" around with fuel pressure and injectors first. I'd like to also get involved with burning chips if I can source the equipment cheap enough. I think with better fuel atomization, more EGR, and a more aggressive spark table I could squeak 30 out of it. If you look into the history of the TBI engines you find that the last 2 years they were produced, The TBI 350 in the trucks used smaller injectors and higher fuel pressures. That was a stop gap measure to pull the TBI trucks through the tougher emissions regulations unt they went with the VORTEC CFI unit in 1997. GM never came out and said it, but what other practical reason was there for the sudden change during the engine's twilight years?

Also for anyone with one of these engines, the single wire O2 sensors don't last too long. They are cheap so don't skimp. When you change plugs, change O2 sensors too. You can't trust them once they hit 30,000 miles. For $25.00 why take chances?

If you think about it, the LO3 has the architecture for a fantastic fuel economy engine. The small ports, with the high swirl chambers, the smaller bore with less chance of fuel condensation on the walls, the long stroke for good low rpm torque... The much maligned 305 is a simple, reliable and adequate V8 for family cars. It is capable of good fuel efficiency and adequate performance. The reasons it is perfect for this assignment are the same reasons hot rodders throw them away in their quest for performance. I will keep you posted on the mods as they happen. In my quest to "improve and modify" myself I am trying to commute by bicycle a few days each week so I don't rack up as many miles as I used to. I suppose it would be unethical to add the 40-80 miles a week I cover by bike to my fuel economy calculations! :) If I get close to or exceed 30 MPG I will leave the car alone except for maintenance. I won't bother with a diesel conversion for 5 mpg. With the price difference between regular gas and diesel fuel, I would never see the payoff.

Also another thing on the maintenance list is a timing chain and gears. The factory ones get sloppy at about 100,000 miles and I am at 101,000 now. So probably in the spring, that will get done.

jcp123 09-14-2014 09:11 PM

That's about on par for a wagon that size if not a little better. FE regs killed wagons like these, shunting American buyers into SUVs.

argo 09-15-2014 12:24 AM


Originally Posted by jcp123 (Post 445444)
That's about on par for a wagon that size if not a little better. FE regs killed wagons like these, shunting American buyers into SUVs.

I think it was the minivan that did that. It was a fad that displaced the wagon then fizzled out leaving no other option but SUVs. Also, consider the stalwart European manufacturers that still offer wagons that nobody in America will buy, like BMW, Volvo, Mercedes, VW, even non Europeans like Subaru and Mazda. Their wagons are niche market vehicles in the USA despite being volume sellers in Europe and Asia. I can cite my wife as an example. We have a Suburban because she didn't want a station wagon. I was going to do the diesel swap to an 88 Custom Cruiser I had found with a beautiful body but a blown Olds 307. She wanted no parts of it. So I found the next best thing, a 2wd Suburban with a knocking 250,000 mile 350 and a slipping 700R4, and did the diesel swap to it instead. FE regs didn't do that. Further, I do better than most minivans on fuel economy. My brother in law has a Honda Odyssey and gets 25 mpg and that's with premium. I do 26 on regular. Besides, think how awesome a modern version of one of these could be with a variable displacement 5.3L LS or a Ford Country Squire with an Ecoboost V6 from the F-150. There is no doubt they could be in the low to mid 30s, and with a baby Duramax or Powerstroke they could be in the 40s.

101Volts 10-04-2014 04:09 AM

So, Do you have any news on the Wagon? It's been almost three weeks since the last post.

argo 11-12-2014 08:18 PM

No new news to report. I have been swamped with shop work and senior projects. Also we are trying to get the shop NATEF accredited and I have been putting in a lot of hours getting the shop upgraded. I can report that my average MPG is about 22 MPG overall. I have not done any highway trips of any significant distance. This is mostly a 50/50 mix of stop and go and rural highway driving. I am looking forward to knocking out the timing chain in the spring. I will keep you updated... I am excited but unfortunately I have more enthusiasm than time.

101Volts 01-21-2015 04:54 PM

Over two months and a week later...

How's this going?

The_Jed 01-21-2015 09:23 PM

Do you have any pics of the car?

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