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  • TDC - Technical Questions & Answers - October 2004

TDC - Technical Questions & Answers - October 2004

Questions and Answers

Bruce Caldwell
Oct 1, 2004
Best Buys
I drive a '92 Chevy 1/2-ton shortbed pickup with the 305 V-8 and 700R4 automatic transmission. I would like better fuel economy, but I need to keep costs reasonable. If you had this truck and about $500 to spend, what would you do?
Jay Allumbaugh
via e-mail
A: We would first make sure the engine was tuned to factory specs. Items such as new spark plugs, wires (if necessary), and air and fuel filters are too reasonably priced to ignore. You need to be at the factory baseline before embarking on any upgrades. We'd have the transmission checked if there was any evidence of late shifts or upshift problems. Automatics have been known to have stuck-throttle-valve problems in these trucks between 1990 and 1992. If the transmission is staying in a low gear unnecessarily long, that's wasting fuel. We would check tire pressures and alignment.
Then we would invest in a high-performance air filter such as a K&N unit. The next place we would spend money would be on the exhaust system, such as a high-performance after-cat system. If there was enough money, we'd also consider headers and an upgraded computer chip.
Save The Cat'
Like probably every other truck owner in the country, I'm very concerned about runaway gas prices. I didn't buy my F-150 for its fuel economy, but these recent price hikes have me scared. I'm looking for inexpensive ways to improve fuel economy. I know I could buy an awful lot of gas if I spent a thousand dollars on parts that promise better fuel economy, so I was wondering if I could improve mileage by eliminating the catalytic converter on my truck? If I did that, would I need to recalibrate the fuel-injection system?
Randy Haynes
St. Louis
A: Don't remove your catalytic converter. It's against the law and it won't improve your mileage or performance. Replacing a clogged or worn-out converter will restore performance, and you can replace the stock converter with an emissions-legal performance catalytic converter. The idea that catalytic converters are a performance deterrent is one of those automotive urban myths. It fits right in with those stories about the gas companies squashing a carburetor that runs on water or one that gets 100 mpg. We haven't heard of an updated version with a fuel-injection system that uses water, so maybe that myth has died. If gas companies had access to a water-based fuel system, they could make so much money that they wouldn't care about selling gas. If your truck has well over 100,000 miles on it, or if you suspect a bad converter, you can do a simple check at home. When the converter is totally cold (such as in the morning), hit it with your fist. If it sounds like there is a lot of loose debris, chances are excellent that the converter is failing. Take the truck to a muffler shop for a professional diagnosis.
Photo 2/3   |   tdc full Up
Full Up
I've been paying more attention than ever to rising gas prices. When I drive by a station with significantly lower prices, I stop and fill up. My problem is that the gas gauge on my '91 Dodge Ram pickup doesn't go all the way to full. I don't want to waste or spill gas by overfilling, but I want to squeeze in as much bargain gas as possible. Could the tank have an air bubble or a clogged vent? Do gas gauges wear out especially early on Dodge trucks? My truck has the 5.2L V-8 and automatic transmission if that makes any difference. Thank you.
Jack Myre
Corpus Christi, Texas
A: Dodge makes an improved gas gauge sending unit for your truck and similar-era Dodge Dakotas; the part number to ask for is 52017992. We hope you're just topping off at low-priced stations when you drive by them in the course of your daily travels. If you venture very far out of your way to buy less-expensive gas, you may be fooling yourself about the actual savings. Saving an extra few cents a gallon, or even 10 cents a gallon, can be as much an emotional savings as an actual one. We tend to get emotionally involved with gas prices. Milk and dairy products have shot up recently, but you don't hear about people driving around searching out the cheapest milk prices. Some simple calculations about the extra miles or extra minutes it takes to search for cheap gas can quickly show that it doesn't take much of a detour to void any potential savings.
Using the right grade of gas is a better way to save on fuel costs. Don't use premium unless the manufacturer specifies it. If your truck runs fine on regular and doesn't ping, use it. Regular is usually 20 cents less than premium and 10 cents less than the mid-grade gas. Some things that can consistently save more money than searching for the lowest gas price include keeping your tires properly inflated, having your alignment checked, keeping your air filter clean, not carrying unnecessary weight, planning your route with the least amount of stops, using cruise control whenever possible, and not making unnecessary trips. If you'd like more information about fuel costs and related subjects, there are several Web sites that you may find interesting:
Tire Tricks
I've been running around with a set of Boyd Coddington 19x8-inch Spyders mounted on P225/35R19 Nitto tires on my '03 Chevy Blazer. I drive more than 100 miles to and from work six days a week. The Blazer gets acceptable gas mileage, but with the recent skyrocketing gas prices, I'm looking for anything I can do to improve my mileage figures. With work and general around-town driving, I'm putting on more than 3,000 miles a month. I kept the original 15-inch wheels and P235/70R15 all-season steel-belted radial tires. I was wondering if my fuel economy would improve if I went back to the smaller wheels and tires until gas prices come back down. Is there any benefit to switching wheels and tires?
Troy Smolke
Escondido, California
A: It's possible that you might see some minor gains by going back to the original wheel and tire combo, but, then again, you might not. The first consideration is the height of each set. If the two sets are the same height/diameter, the old narrower-tread tires could offer a small advantage. You can probably run the old tires at higher inflation levels without getting a totally jarring ride. Greater air pressure means less rolling resistance, which translates to better fuel economy.
It's also possible that the new tires are slightly taller than the old ones. If that's the case, you've effectively raised the gear ratio (made it numerically lower), which, given your long freeway commutes, could equal improved fuel economy. You should measure both sets to determine if there is a height advantage.
The most definitive way to ascertain which set is best is to run each set for a week and keep track of fuel economy. For the comparison to be fair, you need to do similar driving with both sets. You might want to refuel on the way home from work each day to eliminate any after-work variables.
As Seen On TV
I've noticed a number of products that claim to boost fuel economy being advertised on cable TV shows. The products sound pretty enticing, although the exact mileage improvements seem a little vague. Supposedly, the devices create a vortex effect that improves fuel atomization and helps engines to be more fuel-efficient. At a hundred bucks or less, it seems like one of these devices could pay for itself rather quickly. My skepticism stems from the fact that these devices seem to be available only on TV and not in local stores. I've always been leery of products I couldn't inspect before I bought them.
I drive an '03 Chevy Suburban with the 8.1L gas V-8. It's a lot of engine and a lot of truck, so a several-miles-per-gallon improvement sounds almost too good to be true. Is it?
Mark Pearson
Medford, Oregon
A: The old adage is, If it seems too good to be true, it probably is. People seem more reluctant to return something bought on TV than if they bought it in a conventional retail outlet. Also, it's much harder to return something to an ethereal post office box address. It seems as though questionable marketers thrive on this difficulty of complaining about unsatisfactory products.
Whenever there is a fuel-supply or cost problem, these wonder devices seem to appear as quickly as gas prices rise. Lately, that translates into a lot of mileage-making miracles. We don't know which vortex-style devices you've been tempted to buy, but the Environmental Protection Agency's National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan, has tested more than 100 of these mileage-improvement devices. The organization's conclusion was that they don't work. Whenever there is a fuel-related crisis, miracle fuel additives also seem to proliferate. This isn't to say that all additives are bad, but the Federal Trade Commission has taken numerous enforcement actions when false mileage-improvement claims are made. A product might clean fuel system components, but the company can't claim improved fuel economy unless it can prove it. When it comes to cleaning fuel injectors, the surest course is to have them professionally cleaned.
If you choose to spend money on "miracle mileage" products, ask yourself: If the product is so great, why isn't it national news? An affordable product, whether mechanical or chemical, that significantly increased fuel economy would be front-page news. Don't compound the added expense of rising gas prices by buying questionable products.
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One-Sided AffairQ: I have a '90 GMC 1-ton pickup with twin saddle tanks. Each tank has its own gas filler. That means I have to fill one tank and then drive to the other side of the pump to fill the other. Is there a way to make it so I could fill both tanks from one side?
David Kossuth
via e-mail
A: There are crossover conversion kits for trucks such as yours. They have a pipe that runs between the two tanks. The problem is that the pipe goes on top of the tanks. That means the filler-neck locations need to be raised so the gas cap is at the very top of the gas-filler door.
We installed one of these kits on a Chevy dualie and found it to be slower than filling the two tanks separately. The problem was that gas backed up too easily in the crossover pipe. The gas nozzle would sense that the tank was full and shut off. We would balance the nozzle as far out of the filler neck as possible and it would still shut off repeatedly. We couldn't leave the nozzle alone; we had to constantly nurse the gas into the tanks. When you're talking about 40 gallons of gas, that can take a long time. We ended up removing the crossover pipe. One thing you might consider is looking for a local gas station with extra-long hoses. Then park at the end pump and you should be able to reach both gas-filler doors.
Trans Plans
Is there anything I can do to my automatic transmission to improve fuel economy? I have an '88 Silverado. I've done the standard air filter, exhaust system, computer-chip improvements. I'm happy with the extra fuel economy, but I'd like more. What about a rearend gear change?
Bob Sanchez
A: A shift-improver kit that allows the transmission to shift quicker and crisper can give you a slight mileage gain. The idea is to make the shifts more precise so there is less slippage. The shift characteristics will be harsher, but people who drive modified trucks usually like that. A gear change could improve mileage if you currently have lower-than-average gears. Going to a higher (lower numerically) gear will allow you to run freeway speeds at a lower rpm. If you go too high with the gear ratio, you run the risk of negating mileage gains because you'll have to keep downshifting to maintain speed.
Crank Call
I'm trying to assemble a low-dollar 350 small-block V-8 for my '71 Chevy C-10 project. In order to save money, I've been buying parts at swap meets and on the Internet. The best block I have is an '87 casting, but the best reciprocating assembly is from an '84. I'm 99 percent sure of the years.
I would like to use the crankshaft, rods, and pistons from the earlier engine in the newer block and with the corresponding cylinder heads. My problem is that the crank is the so-called two-piece design, while the block is the one-piece rear-seal design. Is there any way I can use the earlier crankshaft and related parts in the newer block, or do I need to keep looking?
Lee Swanson,
via e-mail
A: Regarding the two styles of crankshafts, you can go one way, but not the other. Fortunately, you want to go the correct way.
The '85-and-earlier cranks are known as the two-piece style. The rear seal is in the block casting and rear main bearing cap. In 1986, GM changed to a one-piece seal design. The rear seal is housed in an aluminum adapter that attaches to the block. The two-piece seals were known to leak oil, so the new design was conceived to reduce those leaks.
You can't put a newer-style crankshaft into an earlier block, but you can put your preferred early reciprocating assembly into the '87 block. GM makes a two-piece rear-seal adapter (PN 10051118).
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