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  • TDC - Technical Questions & Answers - January 2004

TDC - Technical Questions & Answers - January 2004

Your Questions

Bruce Caldwell
Jan 1, 2004
Tanks A Lot
I recently bought an '81 Chevy shortbed Fleetside pickup at an estate sale. The deceased owner bought the truck new. Apparently, the truck was seldom used, or not used much in the last several years, because the odometer read only 58,400 miles. The truck was parked in an old, unheated garage. Almost everything is in excellent condition, except that the truck wouldn't run.
The fact that the truck wouldn't run was to my advantage as that made the price very attractive. I had the truck towed home, the gas gauge was on empty; it will run briefly on starter fluid. The engine compartment smells of very old, varnished gas. The gas tank reeks of bad gas. I'm certain that bad gas is why the truck wouldn't start.
My question involves the gas tank. I'm sure that the current tank is full of sludge. I don't see any obvious signs of rust on the outside of the tank, but I'm concerned that there could be rust inside. Even though I got a great deal on the truck, I'm on a budget and would like to fix the tank as inexpensively as possible. Can you tell me what my options are? Also, what should I do about the fuel lines and the carburetor? Thanks for your help.
- Russell Smoot, Rockford, IL
A: Prolonged storage can cause gasoline to go bad. The problem is amplified when the gas level is very low. It's best to store a vehicle with a full tank of fresh gas. There are gas additives, such as Sta-Bil, that help stabilize the gas, but obviously the original owner didn't use any. Given the near-empty tank and big temperature fluctuations during the time of storage, the situation was ripe for condensation and rust, turning the old gas into a sort of petroleum sludge.
You need to clean the whole fuel delivery system. There are several options. It's possible to save the old tank; you need to drain and flush out the old gas. To do this correctly, you need to find out the regulations in your area for disposing of hazardous waste. When dropping a gas tank, let it down slowly so you don't break any lines or wiring that might still be attached. A tank with several gallons of gas can weigh more than you might imagine.
You might be able to find a shop that still boils out old gas tanks. You probably won't find this service listed in the Yellow Pages, but try calling a couple well-established radiator repair shops; it's a relatively inexpensive service. The shop should be able to tell you if there is too much rust inside the tank or if there are any leaks.
If the tank isn't in too bad shape, you can get a do-it-yourself gas tank sealer kit from the Eastwood Company. The different chemicals in this kit allow you to clean out the old gunk, etch the metal for good sealer adhesion, and coat the insides of the tank with a protective sealer. The sealer forms a barrier between the fuel and any imperfections in the tank. Eastwood offers a two-part urethane glue product that can seal pinhole leaks on the outside of the tank. The company also has a zinc spray coating to protect the outside of the tank from rust.
You may be able to find a better gas tank at a wrecking yard; the same basic gas tank was used for many years in GM pickups. You want a tank from a recently wrecked truck to avoid the same old sludge that's in your tank. A more expensive, but still very reasonable, solution is to install a new reproduction gas tank. Mail-order companies such as J.C. Whitney offer factory duplicate tanks in either 22-gauge steel or rustproof polyethylene. Prices for your truck are in the $130 to $180 range, depending on the type of tank. The company also sells replacement tank straps, which are a good idea.
Regarding the carburetor and the fuel lines, they need to be thoroughly cleaned, too. A carburetor repair shop should be able to tell you whether the carb can be rebuilt or whether you need a new one. You might be able to find a good used carb at a wrecking yard.
The steel fuel lines may be salvageable, but any rubber sections or connectors should be replaced. We have successfully cleaned old fuel lines by plugging one end and spraying as much carb cleaner as possible into the other end. Then we plugged that end and let it sit for a day or more. Afterward, we unplugged the ends, let the cleaner drain into a suitable container, and forced out any remaining cleaner with compressed air. That was followed by more carb cleaner and compressed air from each end of the line.
No Slow Blow
I know lots of people complain about not having sufficient air conditioning, but my problem is that the air-conditioner blower doesn't work at slow speeds. The air conditioning in my '90 GMC Sierra Extended Cab seems to be all or nothing. It blows fine on high, but not at the low speeds. Lots of times I just want a gentle breeze, not a hurricane. How can I fix this problem?
- Phillip Griffey, Williamsport, PA
A: You probably need a new blower relay. The connections and relays related to the heating/air-conditioning system can become oxidized or develop burned contacts, especially on older vehicles; this can affect the operation of the A/C unit. Sometimes you can tap the relay (not too forcefully) with something such as a small rubber or plastic-tipped mallet while the unit is on at low speed. If the blower suddenly starts working correctly, you have corrosion or a faulty relay.
Pinging In My Ears
My '99 Chevy Tahoe has developed an annoying pinging at relatively high rpm ranges (3,000 to 4,000 rpm). The problem occurs more when I'm towing my personal watercraft, but it also does it when the truck is empty. The engine is the 255hp 5.7L V-8 backed by the four-speed overdrive automatic transmission.
I'm the second owner of the truck, and I bought it at a new-car dealership's used-car lot, so I don't know how the truck was used before I bought it. I've put about 30,000 of the 64,000 total miles on the vehicle. The pinging has been getting more and more noticeable over time.
I've done a few modest upgrades in the hopes of improving performance. I'm pretty sure the pinging has become worse since I added things, but then maybe I've just noticed it more now that the truck has more miles on it. I added a high-performance, open-element air filter and a performance exhaust system. I installed some hi-po spark plugs, too. I'm obviously frustrated by the pinging, and I'm also concerned that it might be causing some internal engine damage. Can you help me get rid of the pinging, or is it just something I have to endure?
- Bob Krzyzanowski, Riverside, CA
A: Pinging, or detonation, isn't something you should have to endure. It's a very common problem and a subject that generates a lot of mail. In some instances, there are problems that are relevant to specific makes and models, but in most cases, the causes and cures are pretty universal.
To troubleshoot a problem such as this, you need to do a little detective work. It sounds like you have a general idea when the problem started, but not a specific time. The problem with pinging is that it usually starts out small and gradually increases; severe pinging rarely happens overnight. Given the gradual increase, the problem was probably occurring before it became so evident as to annoy you.
Since you did make some mechanical changes, it would be best to undo the changes (especially the air filter and the spark plugs) in order to get the engine back to its factory condition. Undoing the exhaust changes isn't practical or necessary.
Any equipment incompatibility is more likely to involve things such as an open-element air filter, an aftermarket mass air meter, or different heat range spark plugs. Yes, most quality aftermarket parts are carefully designed to work with your engine, but you never know when some modification might upset the computer calibration enough to cause pinging. The goal of getting back to stock is to eliminate as many variables as possible.
A common source of pinging problems is fuel with an insufficient octane rating. You didn't specify what grade fuel you're using, but the engine was designed for standard unleaded. Try switching to 91-octane premium fuel, maybe even with some added octane booster. Switching fuel grades will be most noticeable if you run the current fuel as low as possible so the tank is 90 percent or more premium.
If a couple tanks of premium fuel with some octane booster don't solve the problem, look to mechanical problems such as clogged fuel injectors. Generally speaking, your truck has pretty low mileage for a clogged injector, but that doesn't mean that couldn't be the problem. Injector problems are more common on engines with more than 100,000 miles on them.
You didn't say if the spark plugs you installed were hotter or colder than the OEM plugs. You could try going one heat range colder with a factory-style spark plug. If your engine has been running rich, it could have carbon buildup problems, which can lead to pinging. If some of the simple suggestions don't stop the pinging, you will need to take the truck to a competent shop for a more thorough diagnosis.
You may also want to check to see if an aftermarket computer module was installed by the previous owner. Sometimes, these chips have timing curves that are a little too aggressive to run with 87-octane fuel. We've also heard about pinging problems with the new LS-1 based engines, which required a computer upgrade to fix the problem. Another source of the problem could be the block-mounted detonation sensor. Also check your spark plug gap; anything more than 0.045 inches could lead to pinging.
These early Vortec motors are also notorious for having intake manifolds that get polluted with carbon from the EGR recirculation through the manifold. This has a tendency to gum up the inside of the manifold and could lead to fuel distribution problems, causing a lean condition, which can lead to pinging.
Photo 2/3   |   tdc 1981 Chevrolet Pickup
Photo 3/3   |   tdc 1990 Gmc Sierra Extended Cab
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