Fuel stabilizer best for longer-term storage

Hey there, time traveller!
This article was published 11/12/2009 (5818 days ago), so information in it may no longer be current.

QUESTION: A quick question re: storage of vehicles. I currently add stabyl to my Miata for winter storage but we are now also storing our full-size Tahoe for about four months. My husband thinks it does not need any fuel stabilizer since it is short-term. It will not be started until we take it back out.

ANSWER: The longer you store a vehicle, the more fuel stabilizer will help. Your Tahoe is only being stored for four months and could be stored without adding stabilizer, although it wouldn’t hurt. Stabilizer will help the old stored gas run better in your engine after a few months. A lot depends on where it is stored

I usually suggest storing a vehicle with a full tank of fuel. This prevents condensation from occurring inside the fuel tank during temperature swings. However, if the vehicle is in a location where the temperatures are fairly constant, I then leave it with only about one-quarter tank of fuel and fill it with fresh fuel when I take it out of storage, so stabilizer isn’t needed then. Don’t forget to fully charge the battery and disconnect the cables before you leave.

 

QUESTION: I own a 1997 Mazda SE B4000 truck with 118,000 kilometres. Last year, the dreaded check engine light came on. My code reader indicated codes P0171 and P0174, both banks running lean. In addition, after the vehicle reaches operating temperature, it begins a rapid surge at idle. There is no specific amount of time after reaching operating temperature. It could be immediate or 15 minutes later. Also while surging, if I place it in drive, the surging seems to stop. However as soon as I place it back in neutral or park, the surging resumes.

My research on the Internet suggested replacing the MAF sensor. Did that, same codes appear, as well as the surging. Installed three new O2 sensors. No change. Replaced catalytic converter, new fuel filter, PCV valve, new plugs and wires. Replaced upper intake manifold gasket, fuel rail gasket and throttle body gasket.

ANSWER: An air leak is the most common cause of this type of vehicle problem. It creates a lean fuel mixture that is then sensed by the oxygen sensors and sets trouble codes for a lean mixture. A lean mixture would make any surging worse, but the surging may be caused by a different problem. Let’s look at sources of air leaks you may have overlooked.

First, check for an air leak at the o-rings around each fuel injector that seal the injectors to the intake manifold. They don’t leak often, but you have looked at most other sources.

Another place to look would be at the charcoal canister purge valve and hoses. The charcoal canister stores fuel vapours from the fuel tank and slowly lets them into the intake manifold so they can be burned as the engine runs. A faulty control valve, called the purge valve, would let too much air and vapours in, creating the lean mixture. Block the purge hose temporarily to see if this corrects the problem.

A faulty mass air flow (MAF) sensor is a common fault. You have already replaced one, but I have seen faulty new units. Unplugging the electrical connector at the MAF allows the computer to substitute a value. If the engine runs better, the MAF is a suspect.

The idle surge may be caused by a throttle stop screw that has been adjusted too low. Normally this screw is not adjusted, but if it is worn or someone has turned it, the throttle plates will be closed too far.

I think you are close to fixing the problem. Just a little bit more should do it.

Jim Kerr is an experienced mechanic, instructor and member of the Automobile Journalists’ Association of Canada.

kerr.jim@sasktel.net