Fuel Injection for your Vintage Engine
You’ve probably seen the ads for aftermarket fuel injection systems at very reasonable prices. You’re likely wondering if these systems really work as advertised and whether it’s worth the money to do the upgrade. We’ve been installing the aftermarket throttle body injections systems and we’d say the answer is “ Yes” to both questions but with some disclaimers. We’re not endorsing one brand over another. The goal of this article is to provide an overview of this technology so you can make an informed decision.
Carburation vs. Fuel Injection
Carburetors have been around since the dawn of the internal combustion engine. They are still used today in many applications because they work. Applying modern technology to carburetor design has made them very dependable and more precise. If you keep the dirt out of them and don’t let fuel evaporate in the bowl, you’ll rarely have a problem. When they do act up, you can frequently “limp” them home. If something goes wrong with your electronic fuel injection you’ll need a tow truck. However, things rarely go wrong with modern EFI.
The problem with carburetors is that it is difficult to get everything perfect. Because of their design, you just can’t compensate for every situation with the adjustments you have available. You end up with compromises. The settings that work best in summer won’t be ideal for winter. The settings that give you max power may not be ideal for sitting in city traffic. The ability of fuel injection to adjust for changing conditions is what makes it so desirable. You get instant starting under all conditions, great cold engine drive-away and maximum fuel efficiency under all conditions. If done properly, fuel injection also eliminates the dreaded “vapor lock” encountered with carbureted engines.
Vapor lock has been a problem for ages. It is caused by fuel getting too hot and vaporizing in the lines. Fuel pumps are designed to move liquids, not vapors. Once the fuel begins to vaporize the flow essentially stops. This was a problem decades ago and is actually worse now. The new ethanol spiked fuels have a lower boiling point than pure gasoline. It doesn’t have to get as hot for the fuel to begin vaporizing. With fuel injection, the fuel in the lines is under considerable pressure which effectively raises the boiling point. For cars that aren’t used regularly, fuel injection can really improve driving experience. No more sludged- up carburetors, no more long battles to get the engine running after it’s been sitting for weeks, no more hot restart problems. Now that the prices for fuel injection have come down so much, it’s really worth considering.
What are these new systems ?
The new compact systems that look like carburetors are essentially a take-off on the original throttle body fuel injection systems used by the OEM’s in the 80’s and 90’s. Like some of the original versions, they’re designed to bolt in the place of a carburetor. They’re relatively simple devices consisting of a throttle body, injectors and the electronics. The computer controls have come a long way in both sophistication and in size. The engine control modules (ECMs) are housed inside the throttle body itself making for a nice clean installation package. In the “old days” the processor was large and fragile which meant it had to be mounted elsewhere in the car.
The systems have been around for a few years now and are offered by several companies, including some well known brands like Holley. The throttle body systems used to be a bit pricey which made the decision to switch a little harder. A couple of years ago a company called Fitech entered the market with a system that retailed for around $900. This got a lot of people’s attention especially when you consider that a new carburetor will run in the $400-500 range. It also got the attention of the competition. Some of the big name companies dramatically reduced their prices to compete with the new kid on the block. Overall this was a huge break for the consumer. We now have multiple brands to choose from that are an excellent value.
There is one snag with these new systems; fuel supply. Like modern cars, these systems require a high pressure fuel delivery system. We’re talking roughly 60 psi. If you have a carburetor, your mechanical fuel pump is only providing around 5 pounds of pressure. As a result, you will need to upgrade your fuel system. Keep in mind that 60 psi will challenge your older plumbing and you’ll quickly find the weak spots.
There are a few options for upgrading your system: buy a new tank and electric fuel pump package, retrofit your old tank with an electric pump or purchase a stand-alone fuel supply system like the Fitech Fuel Command Center. Please note that I did not include plumbing an in-line electric fuel pump into your old fuel lines as one of the options. Granted it looks like a cheap and easy solution but it will create problems.
Electric Fuel Pump Basics
For everyday automotive applications you typically need an electric pump to generate the high fuel pressure needed for fuel injection. Electric fuel pumps are great at providing pressure if they are receiving a good supply of fuel. What they are really bad at is sucking fuel out of a tank. They have very weak suction and have to be “gravity fed”. The instructions for every electric pump specify this. In other words, the pump has to be below the bottom of the fuel tank with no restrictions in the line in order for gravity to provide a supply of fuel. The pumps also require a certain level of cooling. This is one of the reasons why the OEM’s submerge the pumps in the gas tank. If you simply plumb an electric pump into your existing fuel line, the pump will have to draw fuel out of the tank, which it’s not designed to do. It will work when the tank is full and the temperatures are cool. As the tank level goes down it becomes harder to draw the fuel from the tank. The pump will get hot (made much worse in hot climates) which will heat the incoming fuel. The pump is struggling to pull the fuel in to begin with and now the fuel is getting heated which makes it want to boil. Eventually the pump will just cavitate and you’ll end up with a case of vapor lock. Starving the pump out of fuel will also cause the pump to burn up over time.
Our strategy is to stick with what works. Virtually every modern car has an in-tank pump feeding the fuel injection system because it works so well. Expect to spend as much as $600 for the parts to convert to an in tank pumping system. This does not include labor. If your tank is old and hasn’t been relined, this would be a good time to start with a fresh system. You’ll need good lines and connections from the tank to the FI unit. Don’t expect simple hose clamps to work long term. Any hose sections must be rated for fuel injection pressures. Old style carburetor fuel hose will burst.
Simple set-up, anyone can do it in their driveway…..
OK, so you’ve decided fuel injection is for you. You’ve read all the ads and been to the web sites. It sounds like all you have to do is bolt the unit on, hook up a few wires, answer a few questions then step back and be amazed. Can this really be true? I’ll give that a yes and no.
This part really is pretty simple. It’s no more difficult than swapping a carb out. You may have some minor complications connecting the throttle and transmission cables to the FI unit. It all depends on what you’re starting with in terms of cable ends. You can buy adapters for just about any scenario. If you know 12V wiring, the electrical hook-up is also simple. You’ll need to do a little plumbing to get fuel to the unit. These units require a return fuel line. Some carbureted cars already have a return line on them which greatly simplifies this step. If not, you’ll need to run a new line back to the tank and also have a provision on the tank to dump the returning fuel. We like to make the installation clean and simple. We only have a single line running to the engine compartment. We make our own return loop system that hides away under the car near the tank. This also helps to keep the fuel supply cooler.
The FI units also require an O2 and ECT (engine coolant temperature) sensor which are provided with the kits. You’ll have to tap into one bank of your exhaust system to install the O2 sensor. We always weld in a threaded bung but the kits come with an adaptor that can be held on with hose clamps. Either way you’ll still be making a hole in your exhaust. The ECT sensor threads into one of the water ports on your engine. If you have the heating system hooked up and are running a temp gauge, you may find that you don’t have any places left to thread the ECT into. If this happens you’ll need to utilize a T fitting or a new water outlet neck that has an extra port on it.
Advice on Fuel Pressure
We’ve found that these units are sensitive to fuel pressure variations. The target pressure is usually 58 psi. We’ve found that the processors really have trouble with a 10 psi variation. The ECM can’t trim the fuel enough to compensate for the pressure change and the system goes into a continuous “hunting” mode. We haven’t tested variations less than 10 psi yet. The units don’t have any internal pressure monitoring system and there are no pressure ports to hook up a test gauge. We highly recommend that you install a gauge close to the EFI unit when you are doing your initial plumbing. If you’re not getting the target fuel pressure when you initially cycle the pump, don’t even bother trying to start up the system. Locate and correct the pressure issue first. The start-up will go much better if the ECM doesn’t have to un-learn a bunch of bad data.
The Initial Start-up
Here is where things can go south. The units are pre-programmed and are self learning but only to a point. You answer some questions about the engine on the little display screen, hit the key and cross your fingers. Sometimes it works, sometimes it doesn’t. That doesn’t mean the systems are bad. On the contrary they’re really impressive. The problem is that the programmers can’t factor every possible engine set up into the software for the initial start. They do a great job of covering a wide range but it may not include your exact set-up.
If you have a no-start condition they provide some basic instructions to try to get you through it. However, you do need to have some knowledge of fuel injection. Do you know what short term fuel trim is ? Fuel injector pulse width ? How about idle air controller steps ? If you do then you’ll have the engine purring in no time. If not, you‘re probably in for a struggle. The engine will frequently start-up. If it runs at all, the self learning will kick in and get things functional. You may still have a range of drivability issues that have to be manually programmed out. If you have a thorough knowledge of fuel injection it won’t be a problem. There are adjustments in the programs for most drivability scenarios. If you don’t have this knowledge base it will get frustrating. Knowing what to adjust, how much and which direction to adjust can become an aggravating trial and error process. The manufacturers all have tech support lines and there are support forums for the major brands. However, if you don’t fully understand how FI works, you may have trouble translating their advice into a running engine.
Here’s how I would summarize this conversion technology:
As with most vehicle upgrades there are additional costs to do it right. It’s not just a $500 up-charge over a carb swap. It’s more like a $1000 – $1500 up-charge just for parts due to the fuel system requirements. That doesn’t mean it’s not worth it. Engines run fantastic with this new technology, even ones with wild cams. You’ll enjoy your vintage car more than ever and you can dial in your desired level of performance and economy. Some parts of the installation are simple, some parts not so much. Getting the programming perfect requires a decent knowledge of FI technology. You can dodge all the obstacles by having a reputable shop do the installation and programming for you. Of course this will run up the cost of the conversion. If you’re getting ready to do a restoration on your vehicle that will require a new fuel tank and carb, this conversion is a no-brainer. The labor costs are already in the build. You’re basically just paying a little extra for upgraded parts. If you’re restoring an older fuel injected vehicle with primitive control systems, these new stand alone FI units are a dream. You can use the original fuel supply system and you’ll now have an EFI package that you can easily program and monitor yourself.