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Tuning a Carbureted Street Rod Engine - Part 1 of 2

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spacer Tuning A Fuel Injected Engine

By: Henry P. Olsen

Keeping a kit-car with fuel injection running well takes more than just changing oil, spark plugs and installing a clean air filter. If you want your car to run it’s best and not leave you stranded along some backroad where your cell phone has no reception for you to call for help or a tow truck, here are a few hints on how to properly tune your car to help prevent a breakdown. First, when you are using an engine and computer from a “donor” car or converting a existing vehicle into a “clone car”, one of the first things to know is what year and model car did the engine come from and if possible, keep track of the original vehicle’s VIN# (vehicle id #). The VIN # tells a computer scan tool the year, engine size, production date plus much more information and this data will help supply you or the technician repairing your car the information needed to access the computer codes and data.

Fuel Filters and Electric Fuel Pump Life

Fuel filters are often overlooked as a tune-up related item. A plugged filter can cause many problems; among them are vapor lock and/or a lack of power due to a lack of proper fuel flow. A plugged fuel filter may shorten the fuel pump’s life by having to force the fuel through a plugged filter. One way of checking that the fuel system is able to supply the engine with enough fuel is to read the engine computer’s data stream by using a computer scan tool. An engine computer scan tool can supply the long and short term fuel trim readings (the amount of time the fuel injector is supplying fuel); or on earlier systems, the injector on time which can indicate the engine has a fuel supply problem, that can be caused by low fuel pressure, a dirty fuel filter, or dirty fuel injectors. An electric fuel pump has a life of 80,000 to 100,000 miles, if you have a lot of miles on an in-tank electric fuel pump replace it to avoid having a break down miles away from your tools or a friendly mechanic.

Codes and Data

When you are updating a hot rod to use a newer OEM computer controlled fuel injection system it is a good idea to use a scan tool to read any computer trouble codes that are present. The reason for knowing trouble codes is because when using a newer computer controlled engine in an older car you may not use all the components, such as the exhaust recirculation valve, fuel evaporative system, etc. that were used in the original vehicle but disabled or disconnected on your car. A good scan tool can also be used to read the data the computer is using to determine the amount of fuel and ignition timing needed by the engine. If the trouble codes found are not deemed relevant to your application, keep track of them as well as making notes on the data such as the long-term fuel trim (a command given by the computer to make the air/fuel mixture richer or leaner). If you have any computer or fuel injection problems in the future you will have a reference or baseline of the data when the car ran well. The data that you can get by reading the scan tool can indicate if the fuel system is supplying enough fuel for the engine; we have seen cases where the fuel injection system being used was from a 5.0 engine and therefore could not supply enough fuel for the larger displacement engine being used.

Scan Tools

There are many engine computer scan tools available, from simple code readers that can just read engine trouble codes that will tell you the type of problem you have to a scan tool such as the units the car dealers use. A simple code reader will tell you if you have any trouble or fault codes, but the lack of any trouble codes may not be enough to trouble shoot the problem that you have now or prevent a problem by noting impending trouble codes. A basic scan tool such as OTC/SPX’s Mind Reader or palm top unit are inexpensive basic scan tools that can supply you with the computers input and output data, this data can be of great help in maintaining your system as well as supplying data that can indicate a problem in the making. The next level of scan tool is a unit such as the Genesis from OTC that has a data base called pathfinder built into it. The advantage of a scan tool with a system like pathfinder built into it is that it can supply you with trouble shooting info on codes and the proper readings for the inputs and outputs, thus providing a path to follow in diagnosing the vehicle. This along with basic bi-directional control of some computer outputs is more than enough capability for most repair shops. A unit such as a Tech 2 (GM vehicles) / DRB3 (Chrysler vehicles) or a NGS / New Generation Star (Ford vehicles) are the scan tools that the car dealers use, can give you data along with more advanced bi-direction capabilities that a professional trouble shooter/technician needs. Many of the Ford fuel injection engine computers (example: the very popular1986 and later Ford 5.0 HO V-8 engine) only have fault codes available through a scan tool. The way to access the computer input and output data is to use a break out box that goes inline between the computer and its wiring harness, this allows you to read the data by giving you access to the data at each computer connection/pin.

Cleaning and Maintaining Clean Fuel Injectors

Part of the maintenance of a fuel injected engine is the care of the fuel injectors, the fuel injectors get “dirty” with age and use, and the heat of the engine can turn the fuel into varnish and gum restricting its flow. A product such as Techron from Chevron can do a great job of cleaning and maintaining a fuel injector when used as part of any tune-up, but if the injectors are plugged it may take a stronger method of cleaning. There are other methods of cleaning fuel injectors, such as using a high strength fuel injector cleaning chemical that is run just through the fuel rail and the fuel injectors, the system we use most is available from OTC/SPX tool company. The most accurate method of checking fuel injectors for spray pattern, flow volume and for leaking involves removing the injectors and cleaning and flowing them on an ultrasonic fuel injector cleaner / flow bench such as the unit we use from ACE Electric/ANSU. This method allow us to observe the fuel injectors spray pattern and measure the flow volume of each injector, thus allowing us to be sure the fuel injectors all flow the proper amount of fuel.

Sensor Maintenance

Oxygen/o2 sensors are a tune-up item that many mechanics ignore, they have a life of 30,000 to 100,000 miles depending on the driving and engine condition. The oxygen sensor signals the computer if the air/fuel mixture is too rich or too lean in order for the computer to properly adjust the mixture. As the o2 sensor goes bad, it will slow down in its reaction rate or give false readings causing the air/fuel mixture to be incorrect. The air charge sensor and coolant temperature sensor are both used by the computer to determine proper ignition timing and air/fuel mixture. The mass airflow sensor (if used), tells the computer how much air the engine is using. If the mass air flow sensor goes bad, gets dirty or gets fouled by oil film, the computer will get a incorrect reading of the amount of air being consumed by the engine. If the mass air flow readings are inaccurate the computer will not be able to command the correct air/fuel mixture. Any bad or faulty sensor will not supply the computer with the correct reading; thus the computer will not send the correct commands to allow the engine to operate, as it should. As with any computer, the engine computer must have the correct input data or it will not run right, garbage in garbage out.

Ignition Scopes

Using an ignition scope to check the condition of the ignition system can be very helpful in diagnosing and preventing many ignition problems. Modern electronic ignition systems are very sensitive to voltage spikes caused by bad spark plug wires; never pull a spark plug wire off to check for ignition output. The voltage spike can damage the ignition module; the effects of this may cause the ignition to fail immediately or sometime down the road in the middle of nowhere. Almost any ignition scope will do a great job, but on newer engines using distributorless ignition or coil on plug (a ignition coil mounted on each spark plug), a more modern unit such as the unit we use the Vision Premier from OTC/SPX tool may be needed to do the job. A good ignition scope can be used to check ignition output, the voltage required to jump the spark plug gap, cylinder balance (the % of power each cylinder is producing), and starter cranking amps per cylinder; this info can help in checking the engine and ignition system condition. One hint in trouble shooting spark plug wires is to spray a water mist from a spray bottle onto the plug wires while in a darkened area, if the engine runs rough or you see a spark jumping to ground it is time to replace the plug wires.

A modern fuel injected engine used in a street-rod can supply you with a great running reliable power plant when it is properly tuned and maintained. Having a history of any computer trouble codes and the computer’s data will not only help you in any future repairs, but also if you break down on the road; having this information will give a repair shop the information they will need to do any repairs in less time and expense. A low cost tool that should be in the glove box of any car is a simple voltmeter; my favorite is a pocket voltmeter from otc/spx that has retail price of under $40.00. Having a voltmeter handy has saved the day for me many times by helping to point out a blown fuse, relay or any low voltage problem. The proper tools make the task of how to trouble shoot any problems that may come up in the future much easier to solve and help take some of the mystery out of repairing a fuel injected hot-rod.

OTC/SPX Corporation
655 Eisenhower Dr.
Owatonna, MN. 55060

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San Bruno, Ca. 94066

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Burlingame Ca. 94010 650 343 4860 on car service and repairs