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1986 Dodge Custom 100 Pickup w/ 318cid Engine

Is it cost effective in terms of gas savings to change out the carburator intake manifold and install a fuel injected intake manifold on this pickup? Can it even be done? The pickup is in very good condition and I would keep it anyway.

Unlikely, you’ll probably never recoup the intial investment of an EFI setup in fuel savings. You’ll likely spend $1200-$3000 on it depending on how nice a setup you want. The fuel savings won’t be huge, maybe 2 MPG at best.

It took me years to come to the conclusion that it is best to make what came with the vehicle work as designed,rather than modifying the system.

If you are doing this work for personal enjoyment or a way to demonstrat your skills then I support your efforts.

I do have a personal experience where a major modification worked for the better. I replaced the 305 V-6 in my 65 GMC pickup with a small block,worked out good.

It might be cost-effective if;

  1. the carb is trashed and needs a rebuild anyway
  2. you can get the parts you need at a salvage yard
  3. you do the work yourself and assume that your time is worthless or this a your hobby

Check at on a Dodge (truck) forum and I bet you can find someone that has done it.

If you’re wanting fuel injection you’re going to need a lot more than a fuel injected intake manifold.

Throw in wire harness, fuel pump, fuel lines, ECU, a few dozen other items along with modifying most vacuum lines and cables, etc. also.

There are some simplified add-on FI systems but they’re expensive; as in a couple of grand.

A “fuel injected intake manifold”? Do you mean a Throttle Body Injection system?

Clearly, multiport is out of the question…at least this question. That would require new heads that would take injectors at the intake ports and tons of plumbing. That leaves TBI. TBI needs some system to tell the injectors how often and/or how long to open (pulsewidth) or…like in the days of old, the days of vacuum operated injection systems…how much to open.

Let’s assume you’re talking electronic fuel injection rather than vacuum operated. That’ll be operated by a computer adjusting the injector’s “pulse width”, the width of each pulse when the injector is open.

Now you need a computer. And that computer needs some signals to run through its program to determine how wide to make th injector pulses. It needs to know the engine’s operating conditions and what you the driver are demanding. It needs to know the engine speed, the amount of air moving in vs. the amount the pistons are trying to draw in (the mass airflow and the vacuum via the manifold’s “absolute pressure”). It needs to know how much you the driver are asking (the position of the throttle). It needs to know the temperature of the engine.

So, you’re talking about adding a throttle body injection setup, a crank or cam speed sensor, a mass airflow sensor, a manifold absolute pressure sensor, a throttle position sensor, a temp sensor, a computer to make sense of all these, and a program to allow the computer to do something with the sensor. And upgraded replacement parts that will physically accept these senors. You can’t plug a MAP sensor into a manifold without a hole. For TBI you can theoreticallly live without cranks position data and without an oxygen sensor, so I’ll skip those.

Can it be done? Yup.
Would it be fun and educational? Yup.
Would it be cost effective? No way.

Personally I’d get it all “up to snuff” and keep it in original configuration.

TBI swaps are usually done to improve power and since TBI doesn’t really have that much of a fuel economy advantage over a well-tuned carburetor the fuel savings are usually minimal.

Some of the aftermarket carburetors are designed for, or can at least be tuned for, better fuel economy. Even this probably isn’t going to be cost effective unless the carburetor is shot anyways.

One cheap and easy thing you can do is switch over to a manual choke. If you do a lot of shorter trips, that will majorly improve your overall mileage.

Thanks for the reply. I’ll leave it as is.

I converted my 86 K5 with a 350 to fuel injection. My fuel economy went from anout 13 to 15mpg. I use the truck for off-road use, so my motivation was more than just fuel economy. The carb didn’t like steep hill climps and it cought on fire once:)

The cheapest way to do this is strip the entire system from a newer truck that has fuel injection. On Chevy?s it?s easy if you use olde TBI setups or MPI. You want the wire harness, ECU distributor and all related sensors. You also need to upgrade the fuel system:

  • the entire fuel system has to be re-plumbed for larger fuel lines (3/8in ID min)
    -high flow EFI fuel filter
    -any rubber fuel lines need to be rated for high pressure, SAE J30 R9 is the stuff you want
  • you need a high flow EFI fuel pump (mine’s external, and I retained the factory sending unit) Walbro makes a nice pump
  • larger return line to the tank
  • you may have to drill a hole in the top of the tank and install a bulkhead fitting for the return line

Actually you can get aftermarket port FI systems for popular V8s. The fuel injectors are mounted in the intake manifold runners just before the heads. There is a throttle body but it’s only used for air metering.

In any case, converting this engine to FI is a costly proposition. The OP’s making the right decision: leave it as is.