Engine Problems FAQ

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Frequently asked questions about engine performance problems. The answers to these questions should give you a decent idea as to where to start in diagnosing your engine's behavior problems.


My engine isn't running as smooth as it used to at idle, but it runs fine at anything off idle.

-This is a common symptom of a vacuum leak. A vacuum leak is air that enters the engine downstream (after) the airflow meter or carb. This causes the air/fuel mixture to lean out, which is when there is a higher air to fuel ratio. Remember, ideal mixture ratio is 14.7 lbs of air to 1 pound of fuel. Too much air will result in incomplete combustion and misfires.

To remedy the problem, visually inspect the rubber intake boot between the airflow meter and engine and check for perferations that would allow unmetered air into the engine. If this checks out fine, look for damaged or disconnected vacuum lines. If those check out, then you can take a can of brake or carb cleaner and spray it around the throttle body and all intake manifold gaskets with the engine running. When the rpm's smooth out, you have found the source of your leak. If your vehicle is carburetted, then chances are the gasket between the carb and intake manifold is leaking.

Two other common sources of false air are stuck open EGR valves, which allow exhaust gasses to get drawn into the intake manifold and choke out the engine because of the inert gas; and old PCV valves. PCV valves can be tricky to diagnose because of their design. In some cases, a loose oil filler cap, or dipstick can be the cause of the leak. Some vehicles are impossible to start if the oil filler cap is even cracked open, SAABs are notorious for this.


Will I get more power from my engine if i use jet fuel?

-No. In fact, you could actually do more harm than good by using jet fuel in your car. Jet fuels do not vary that much from regular gasoline. Their main difference is the additives in them. Jet fuels use de-icers to keep the fuel from freezing at high altitudes. Because of the way a turbine engine works, it generates much higher combustion temperatures and burns these additives off. Your engine may just end up with deposits from these additives which will inevitably rob you of power. If you want more power from your fuel, switch to premium or find some race fuel to add to your tank.

Why is it bad to buy a low mileage older car?

-People are always looking for that low mileage classic car that granny drove 2 miles to church and back every Sunday, every week since it was new. While these cars do fetch a higher price and are a rare find, they are more than likely in worse condition than the same year car that travels 7,000 miles a month.

Stop and go traffic is torture on every single part of a car. When the engine is at idle, it is not igniting the fuel mixture completely. This results in fuel wash on the cylinder walls. Over time, it can deteriorate piston rings, which will result in oil consumption. Along with this, the blow-by gasses from combustion settle in the engine oil and begin breaking it down. These gasses are substantially lower, to non-existant during high rpm operation seen during cruising speeds. Therefore, vehicles subjected to stop and go traffic (in town driving) on a consistent basis will need their oil changed more often then a vehicle that logs 30,000 miles per year. It is in these grocery carts that synthetic engine oils would be ideal, because they resist chemical breakdown much better than mineral oils.

Rubber engine seals, such as the valve cover gasket, valve seals and guides, crank and cam seals and other gaskets/seals, are actually conditioned by the engine oil. If the engine is allowed to sit, and no oil ever reaches these seals, they will dry out, crack, and end up leaking much much sooner than an engine that is constantly moving. I cannot tell you how many 60,000 mile, 6 year old engines i have resealed for this reason. On the other hand, I have seen a few 8 year old, 200,000+ mile engines looking like they did when the rolled off the showroom floor. While all these seals are cheap to buy, they are not always cheap to have installed.

The loads imparted on an engine to get it moving are far worse than the loads needed to sustain a cruising rpm. When you accelerate, fuel is dumped into the engine and richens the mixture (less air, more fuel). This creates a more violent detonation process when the mixture ignites until the engine reaches it's cruising speed. If you have ever listened to your engine when you leave a stop sign, it sounds much louder than when at cruise.