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Fuel Starvation-The Signs & Consequences - Tech Scene

Apr 9, 2007 SHARE

Editor's Note- Tech Scene is a new column in Turbo magazine where the staff will answer technical letters that need more highly detailed explainations. Tech Scene may also be harnessed to perform quick tests of products or introduces new technologies to our readership.

Tech Scene: I'm having trouble with my car and I'm about to give up on it. I own a 1996 Subaru Impreza Turbo GT 2.0 4WD. I know this car is not available in the United States, but my problem could happen to any car. I bought a larger turbo from an Australian company called Turbo Smart and it is specially made for my car. Now the problem is when the engine is under full acceleration, it hesitates and detonates. According to the air/fuel ratio meter that I just installed, my car is running too lean (I need more fuel), so how can I fix the problem? Is it the injectors or fuel pump or fuel pressure regulator? If it's injectors, then that's a problem; I couldn't find any company that sells upgraded fuel injectors for my car. If it's fuel pump, there is a company that sells fuel pumps for my car, but there wide choice of possibilities and I'm confused. Should I buy the solid-state electronic fuel pump or interrupter electrical fuel pump? And if it's the fuel regulator, there are a lot of them, so which one do you recommend any size? I know my situation is very complicated but I hope you can help me. Thank you. Note: I have installed an air induction kit and exhaust system in addition to the turbo.Abdul Nasser Al-RayesVia Internet

In the three years I have been the tech editor for Turbo, I have read the question above and similar ones pertaining to fuel starvation nearly a thousand times. This is the perfect opportunity to address this question in our new Tech Scene column.

It does not matter if you own a Honda or a Saturn, fuel starvation can occur if proper fuel enrichment issues are not addressed when modifying your engine. It would be a dream for performance enthusiasts if every aftermarket performance product we installed would bring immediate optomized power gains to your engine. Unfortunately, we don't live in a fantasy world; in reality, many aftermarket products require proper fuel and ignition tuning to fully realize their power-producing potential. For example, in our HKS Super AFR article, we were still able to extract additional horsepower from a normally aspirated B16A engine that was only lightly modified with an air filter, exhaust and header. We are positive we would be able to extract even more power from the engine if it was more heavily modified. On force-fed engines, the issue of fuel starvation is even more critical; detonation can grenade the engine in a matter of seconds, depending on the severity of the detonation. As more horsepower is extracted from a powerplant, tuning becomes ever so crucial.

One of the best investments an enthusiast can make is by purchasing an air/fuel monitor. Although we don't expect you to go out and get a $5,000 Motec air/fuel monitor and install it in your vehicle, there are some cost-effective solutions. There are some units that run in the $100 to $200 range which are not as accurate as the Motec, but should do fine for most performance advocates. The key is to install the unit prior to making any modifications to the engine.

After the air/fuel monitor is installed, use a notepad and mark down at each 500-rpm interval what ratio the factory engine is running. As you start to install each performance product on your vehicle, see how it affects the air/fuel ratio. With a fuel computer, you can tailor the fuel curve to re-match the factory readings. As more performance products are installed, it is more likely you will have to re-tailor the fuel curve for optimum power and reliability.

In Abdul's case, we are not sure how much boost is being run but recommend turning the boost pressure back to the factory setting. He should then see if the vehicle still detonates or is running lean on the air/fuel monitor. If it does either, we recommend installing an aftermarket piggyback fuel computer like the A'PEXi Super AFC, HKS Super AFR or Field fuel computer. With the piggyback unit installed, you will be able to richen the fuel curve and prevent the detonation from occurring. If the piggyback unit is not capable of curing your lean air/fuel ratio, you will need to purchase some larger injectors. RC Engineering sells larger injectors for nearly every possible engine. Make sure that when you install the larger injectors, you trim the injectors' duty cycle at idle so it does not idle poorly or, worse, wash the oil off the cylinder walls and destroy your engine. We doubt you will need an upgraded regulator or fuel pump once you install the fuel computer and injectors. If you want to be on the safe side and install an upgraded pump, find out the rating on the factory pump, which is usually rated at liters per hour (lph) or gallons per hour (gph). Then use the specification to choose a fuel pump that is one size larger than yours. You should be able to find a drop-in, in-tank pump once you have the correct specifications. Good luck with your Subaru build-up, Abdul. A'PEXi (714) 685-5700, HKS (310) 763-9600 or RC Engineering (310) 320-2277. -Robert Choo

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