FiTech Install

1972 Oldsmobile Cutlass Supreme

This article walks you through some pointers for installing a TBI fuel injection system in a classic carbureted engine. A FiTech system was used, but other options are available as well, by Holley, Edelbrock, MSD and others. The challenges between each will be slightly different, however the concept will remain the same.

One universal constant with these types of projects is that there is alot of bad information floating around, and the instructions aren’t that great, so hopefully this will help.

Let’s Begin

First, some Q&A, based solely on my opinion:

Q: Is fuel injection better than carburation?

A: Yes

 

Q: Is fuel injection more reliable than carburation?

A: Potentially, yes. This depends on how well you do the install. For example, do you use quality wiring techniques and power sources? Quality wiring and clean power are essential for FI.

 

Q: Is fuel injection more powerful than a carb?

A: In theory, both can yield the exact same power. In reality, a self learning FI system will optimize better unless you have your carb exactly dialed in for every altitude and weather scenario you are in. Of course, this depends on your FI tuning as well.

 

Q: Is fuel injection easy to install?

A: Yes, but this depends on your approach. Completely swapping tanks will require fuel system work that adds complexity, but this is the most reliable approach. There will be a good bit of custom wiring, with no specific instructions for your application.

 

Q: Is fuel injection safer than carburation?

A: Yes. There are less leak points and less gasoline above your exhaust manifolds, and therefore less chance of fire.

 

Q: Should I do it?

A: Yes. Unless you aren’t in the mood for a project, can’t afford the downtime, or you’re focusing on originality.

 

Q: Are any mods required other than the FI itself?

A: Probably. Your distributor must be compatible. You must have clean power and grounds. You may need to make intake manifold changes (probably not though). Optimization may be available, for example you wont’ need that old exhaust crossover to heat your intake manifold anymore. You won’t have a Choke anymore. Throttle cable changes may be required. You may convert to electronic timing rather than your distributor.  You must have a fuel return line, and many old cars don’t. O2 & coolant temperature sensor install. No exhaust leaks upstream of the O2 sensor. Fuel Filter for FI. The list goes on. You’re really creating a whole new animal to work with and optimize.

 

Q: What’s the cost?

A: My total cost was $1,500, doing all of the work myself. The unit itself was about $1k. This depends on your scope.

 

Q: How long did it take?

A: 1 week.

 

Q: What tools are required?

A: Basic hand tools. A welder for the O2 sensor bung (or shop). Soldering iron, crimper and terminals for the wiring. Volt Meter. Torque Wrench. Thread sealant and fuel system parts (tubing bender/possibly flaring tool/tubing cutter/hose/tubing/couplings/etc depending on your design).

Theory

This is the nickel tour, but if you’re considering this project you probably already know what’s written here. So skip it if you don’t care. If you want something more advanced, let me know! Fundamentally, a carburetor (carb) and fuel injection (FI) use completely different approaches to fuel delivery.

Fuel is supplied to the carburetor and deposited into a bowl up to a certain level. A float in the bowl stops the flow of fuel when it is full, and the fuel pump only needs to supply enough fuel pressure to maintain this level, and keep the float up (around 4-7 psi). When a cylinder in the engine moves down on the intake stroke, it creates a vacuum in the intake manifold as it pulls air into the engine through the carb barrels. A carburetor uses the venturi effect of this air moving through the barrels to pull fuel through small openings (jets). The size of these jets controls the air to fuel ratio, and adjusting this can be done by replacing the jets or orifices with larger or smaller sizes. Other carb circuits such as accelerator pumps, chokes, and a secondary set of jets or barrels allow the carb to respond to various conditions, such as sudden acceleration or cold starts, and they can be tuned by replacing them and adjusting them in various ways. How does a carb control idle speed? It Doesn’t! You tell the carb how much air to deliver at idle (set screw), and based on this airflow and the fuel delivered by the resulting venturi effect (jets or idle circuit), a certain RPM is achieved. It is not “Controlled” at all. Meaning, if you applied a load on the engine (putting an auto trans in gear for example), the rpms would drop. This is different with FI.

Fuel injection on the other hand does not rely on engine vacuum at all to deliver fuel. It also doesn’t have a fuel bowl to supply the fuel. Instead, fuel injection relies on sensors to tell a computer when the engine needs fuel. To replace the choke, the computer needs to know if the engine is warm or cold. It does this with a coolant temperature sensor. If cold, the computer makes the same adjustments a choke would with a carb, enriching the mixture to allow easier start and smoother idle. It can also keep the idle speed elevated when cold. How? Fuel injection relies on high pressure fuel (58 psi or so, depends) to supply on/off valves called injectors. These injectors open and close when voltage is applied with a solenoid.  The computer controls the air to fuel ratio be telling the injectors how long to stay open. Longer open time = more fuel delivered. This is called duration/injector load. The computer knows how rich the fuel is by using an oxygen sensor in the exhaust. If the sensor reads alot of oxygen, it knows that more fuel would be needed to achieve the desired ratio. Also important is When the injectors open. If the injector opened during the exhaust stroke, that wouldn’t be particularly helpful would it? It needs to open at a certain time on the intake stroke to allow the fuel to be pulled into the cylinder. The computer needs to know the position of the pistons to open the injectors at the correct time. It can do this based on a position sensor on the crankshaft or camshaft, or it can do this based on your ignition timing, since the spark plug also needs to fire at exactly the correct time. This FiTech unit uses the ignition pulse to tell the computer when the engine is at TDC. If you have a V8, it then knows that there will be another intake stroke every 45 degrees of rotation (8 cylinders/360 degrees).

Fuel injection controls idle speed by firing the injectors, and controlling the airflow, unlike a carb. There is a motor called an idle air control valve (IAC) which opens to increase airflow, which causes the O2 sensor to read more oxygen, which tells the computer to open the injectors longer and allow more fuel into the engine. The computer opens the IAC to achieve a certain RPM, and the RPM is known my measuring how often it seens a pulse from your ignition system or crank/camshaft position sensor. 1 crankshaft sensor pulse per minute = 1 RPM right? This is a huge improvement over a carb, since now the RPMs can be configured and automatically controlled by the ECU. If it’s hot or cold, high altitude or low altitude, etc, it doesn’t matter, since the computer can use the IAC and sensors to maintain exactly your desired RPM.

When the injectors open, it is essentially creating a hole in your fuel supply system which reduces the available pressure. To overcome this, the pump supplies more pressure than the injectors need. A regulator allows some of the fuel to bypass the injectors and return to the tank, maintaining a certain regulated pressure. When the injectors suddenly open, the regulator closes to allow more fuel pressure to remain in your fuel rail which supplies the injectors. If you didn’t have this feature, the computer would never achieve its target air to fuel ratio, since every time it opened the injectors for a certain amount of time, the fuel delivered would be different because the supply pressure is different. This is why a return fuel line and quality regulator is critical for a FI system. The heavy reliance on all of these systems and sensors is also why quality power supply and wiring is so important for FI.

Requirements

Fuel system design

Your fuel system must be able to supply enough pressure AND volume for fuel injection, and have a return. There are a few ways to do this. Your system must also be rated for whatever fuel you’re using, however all of the systems I’ve seen can be used with any fuel. It really depends on your fuel lines and pump more than the system itself. One huge benefit to FI is that is measures the exhaust gas O2 ratio directly, and therefore can automatically adjust for differences in fuel quality.

Fuel Pump:

1. In-line booster pump
2. FiTech fuel command center, or similar.
3. Fuel tank/cell designed for an in-tank pump and return. – Best

The fuel return is low/no pressure, so there are some options.

1. You already have one – Done.
2. Use your old vapor vent line for a charcoal canister or similar if equipped. You can then vent the tank locally with various techniques, but remember that gas explodes.
3. Run a 3rd line – Best

Fuel Filter:

1. You need 10 microns or finer. The lower the better for injectors.
2. The filter must be downstream of your pump.
3. The filter must be changeable/accessible.
4. The filter must be rated for your supply pressure. (58 PSI in my case, but some pumps are up to 100 psi).
5. Consider an OEM filter in fuel injection service, since they are easily sourced and and cheaper. For example, a filter from a 99 Chevy Silverado.

Fuel Pressure regulator. Many systems like FiTech’s come with a built in pressure regulator.

1. Must regulate to your injectors/system requirements.
2. Must be downstream of your fuel pump and on the supply line.
3. Some regulators are integrated into the pump. This is fine if it’s the design.

Fuel Lines:

1. Must be rated for your supply pressure, INCLUDING your clamps/connections.
2. Must be clean to below 10 micron after the filter.
3. Must not have kinks or pinch points.
4. Must not leak
5. Convert your system to AN braided hose and fittings – Best

A stock fuel system is probably steel and low pressure rubber hose, and could have corrosion. Fuel injection supply, especially after the filter, must be CLEAN. Either clean your old rusty lines, or run new ones. Ensure they are large enough to supply the fuel required for your horsepower as well. My requirement was 3/8″. Your return can be one size smaller than your supply. Also make sure you buy Fuel injection hose or better.

 My Approach

Add up how many couplings, unions, hose ends, and length of braided hose you will need. It helps to draw your system’s design on paper. Order a couple extra feet and ends for the unplanned issue, or for future maintenance. You will also need a tubing cutter and bender. I used a dremel tool with electrical tape to cut the braided lines, but remember that you must not allow debris into your injectors.

Note: Swagelock and automotive AN fittings usually have different pitches and are not compatible. Automotive are 37 degrees while industrial/plumbing fittings tend to be 45 deg.

My design

Fuel Supply

Supply-

• Tanks Inc fuel tank with in-tank Walbro pump and sending unit supplies fuel pressure.
• AN braided line at tank connects to stock 3/8″ steel line.
• 3/8″ line was cut near/under passenger seat along frame rail to install in-line fuel filter. A 2″ length of braided line was used to connect fuel filter to hardline.
• Fuel filter discharge has short 2″ braided section to new custom bent 3/8″ hardline, which runs up the firewall behind the transmission dipstick. Mounting clamp was used to secure the hardline to the firewall (available at Harbor Freight). Be careful of exhaust heat in this area.
• Braided section connects firewall mounted hardline to the FI unit.

Return –

• Braided line leaves the FI unit and runs above the transmission bellhousing.
• This connects to the new aluminum 3/8″ line above the frame rail on the passenger side.
• Aluminum line runs to fuel tank in parallel to the stock 3/8″ steel line, and terminates.
• Braided AN hose connects the aluminum hardline to the fuel tank return.

Vent –

• Because I ran a new return line, my vent line remained stock. I retained my charcoal canister and vent line, which really helps with garage gas smell.
• NOTE: MAKE SURE your vent line connects to the highest vent port available on your tank. Otherwise, when you fill your tank with gas, the level could be high enough to send liquid fuel through your vent line and fill your charcoal canister, resulting in being kicked off the drag strip. …Not that I would know.

If you take this approach, your new sending unit and pump will probably be universal, and you’ll need to cut the sending unit level arm and fuel pump supply and return hoses. The pump and sending unit come with instructions. Measure twice, and cut once. Follow the instructions. When you cut, don’t cut near the sending unit resistor or the tank openings because of the debris.

Fuel Pump Wiring

I used all stock sending unit wiring. Only fuel pump wiring needed to be run, since the old design was an in-block mechanical pump.

For my automotive high-current wiring, I only use original and authentic Packard 56 series style connections. They are stronger, longer lasting, and look completely OEM. You can buy them online in a big kit (Amazon or terminal supply company), your stores won’t have them. Delphi style connections would work too (the newer sealed pin-style connections on newer GM vehicles), but they won’t be era-correct looking. Remember that the reliability of you FI system almost completely depends on your wiring quality and routing.

10-gauge wire was connected to new 56 series terminals at the FI unit and run inside the car, under the carpet, to the trunk. From in the trunk, I ran the wire along the routing of the stock sending-unit wiring to the pump. The ground ran from the pump to the body above the rear axle and was bolted in with a sheet metal bolt.

The FiTech unit has an internal relay to drive the fuel pump. Not all units do. If yours doesn’t, you need to also add a relay kit to the system somewhere. Summit’s fuel pump relay kit seems to be fantastic quality for the cost (I bought one).

Sensors

Finished Install

First Impressions

Install went fairly well. Most of the work was converting the fuel tank in my case. I turned the key, and had a crank but no start condition.

Troubleshooting resulted in a ignition noise fault. This ignition pulse controls injector timing, so this is no good. I also had an IAC fault.

The IAC fault was caused because one of the harness connectors wasn’t plugged in. Stupid mistake that it took me all too long to realize. Make sure every single wire is routed correctly if you’re getting a fault.

The ignition noise error was very difficult to diagnose. Every time I called FiTech support I got a different answer, and every call was a 30 minute hold time.Long story short, FiTech’s tech support tries to be helpful, but it’s really quite bad. The most disappointing call was when I read the error code the FiTech unit was giving me to them over the phone (P0303 or something).  Support replied that they need me to tell them what that means since they don’t have a list…WHAT!?!?

So, you’re on your own with troubleshooting and tuning if you buy FiTech. Know that upfront.

I have a MSD Blaster coil connected to a MSD ready-to-run billet distributor. The ignition noise fault was caused by connecting Fitech’s signal wire to the coil negative, even though this is what the instructions said to do. I instead routed it to the distributor’s tach signal wire and the noise fault disappeared.

The other common source of noise is an improper FI unit ground. If your gasket or bolts (think paint/coatings) prevent a good ground, you will have any number of issues. I ran a ground wire from the Fitech unit bolt straight to the battery. Ditto with the 12v supply.

One thing I learned is that the FI unit is extremely sensitive to the BASE timing setting matching your actual base timing. This means timing with no vacuum or mechanical advance. Idle quality and power both correlated with how close this setting was to actual, and when it was 5 degrees off the car would barely run. The FI unit doesn’t care if your base timing is 10 or 15 degrees BTDC, but it does care that the setting matches your actual setting. This makes sense, since the FI unit is using this setting to determine top dead center, and therefore when the injectors need to fire to correlate with the intake stroke of a cylinder.

Here’s a list of the troubleshooting that followed to try to get this thing to run.

Document every default setting before you change it! Otherwise, you may need to do a complete factory default reset and lose all of your tuning.

Problem: No Start. Ignition noise fault and IAC motor fault.

Troubleshooting: Plugged in IAC motor. Moved FiTech unit’s ignition wire to the distributors tach wire instead of coil -. Grounded FI unit body with direct line.

Result: Noise fault and IAC fault cleared, still not start.

Problem: Crank but no start. Discovered it would start if I depressed the gas pedal while starting.

Troubleshooting: Tightened primary throttle adjustment screw until IAC counts read in the recommended range (3-10). Move the screw 1/4 turn at a time. Default is the tip of the screw just touching the throttle arm plus 1/4 turn.

Result: Unsuccessful.

Troubleshooting: Increased Cranking IAC in the unit settings (larger value). This adds more air/throttle.

Result: Unsuccessful.

Troubleshooting: Matched ignition timing to ECU timing more closely (within 1 degree)

Result: Almost starts by itself. Definitely idles better if throttle is used to start.

Troubleshooting: Increased Cranking fuel in the unit settings. There are 3 different settings, one for each temperature range. I moved all fuel settings down to 0 (richer) from the defaults.

Result: Some success. Engine starts after a number of rotations.

Troubleshooting: lowered cranking fuel (richer) and Increased IAC another smaller step.

Result: Success! Starts in 2 rotations or less.

 

Current state: engine runs great on fuel injection. I am having issues with pre-ignition and a ticking valve train that is preventing a thorough test and tuning. I then discovered loss of compression in cylinder 3 (See Post Here) which required pulling the engine. In total, I have around 600 miles on the fuel injection and I loved it during that time.

Even with a cylinder down, the fuel injection idled MUCH better than the carb. I have what I would consider a hot street cam.

MPG increased from what I guess to be 10-12 highway/city combo to 15-17 mpg highway. Pretty good for a 455 BBO. It’s hard to tell with so few miles.

I can’t wait to get the engine reinstalled and start some tuning fun. There is alot of functionality in these units to control exactly what you need to, however since they are self-learning, you don’t need to get everything exactly right if you don’t want to.

LEFTLANEBRAIN