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Converting to Fuel Injection


Updated 8-15-01

This is by far the most popular thing on my web site. I get e-mail questions almost every other day on this, and I'm happy to answer them. I've had the unit for almost 2 years now, and all is well. I also added more technical info to the last page on how to tune the ECU, wire with MSD ignition, and combat the infamous "CB interference monster" as well as other FAQ.
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Click Here to see Installation Manual pages


My Jeep has a AMC 304 V8 engine with a 2 barrel carburetor on it. It's as it was from the factory. It works well for "normal" driving, but has the usual problems that carbs. are known to have. It likes to kill when you bounce the Jeep too much, and sputters going up steep grades. Although these are bad things, the driving force (pun intended) behind doing this conversion is the need to cross the Rocky Mountains for my annual pilgrimage to Moab! I've gone there in two different vehicles before, but both were newer, with fuel injection. If you've never crossed the mountains before, let me tell you, It's HELL on your truck! If your vehicle has reasonable power at low altitudes, it will feel like a Yugo at 12,000 feet. I live at 740 feet above sea level, so when I took my 4.0 Liter Explorer over those big hills, it was all I could do to keep 50 MPH sometimes! Certainly, the altitude change would cause major havok with my carbureted motor, and since I'm no expert at fiddling with carb adjustments, I don't want to spend three days playing with the thing as I try to get out west. My solution is to convert to fuel injection using a Holley ProJection setup.


Choosing a brand of Fuel Injection.
I chose to use the Holley ProJection system, simply because I have used their stuff before, and have always been satisfied. I didn't compare features or anything else worthwhile, I just trust that they have a good product that will function properly. I did read stuff on the internet about people who converted their 6 cylinders with a Howell brand TBI and had less than good results. I have also seen articles in which people have used the Holley system and have had problems with CB interference and after-market ignition systems. I thought, I'll be the judge of that.

Selecting the Model.
In the Holley catalog, they list a unit designed to work with the AMC small block. The model number is #502-20. It has a 2bbl throttle body for engines with up to 275 horsepower. They also offer a Closed Loop Thingy that uses an oxygen sensor to regulate the fuel mixture when conditions change. I want that too, that way, when I cross the Rockys I don't have to continualy adjust my settings. Unfortunatly, the Holley ProJection unit doesn't just bolt onto my factory two barrel intake manifold. It requires a 4 barrel intake manifold, and the Holley catalog suggests using a dual plane design for best results. Well, "best results" is what it's all about, so I went in-search-of.

Here's what the #502-20 consists of.

I checked prices at Blakely Auto Parts, a local parts store that's only a couple of blocks from my work. Their price for the TBI (Holley #502-20) is $1,075.00 and the optional Closed Loop Thingy or CLT (Holley #534-54) is $123.75. I also checked with Jeg's and their prices were much better. The TBI and Closed Loop Thingy was $650.00 together! Now I like to buy stuff locally when I can, but as you can see, the price difference was too great. I ordered the stuff from Jegs and got it in a couple days.

The Intake Manifold Search.
This has turned out to be the toughest part of the whole deal so far. When I talked to a guy at Holley, he suggested I contact Offenhauser. Their phone number is (213)225-1307. Offenhauser offers a Dual Port intake (Cat #6057-DP) that is a dual plane design and accepts a four barrel carb. They also offer a EquaFlow intake (Cat #5917) that is a single plane design. Since Holley suggests I use a dual plane design, the EqualFlow is out. That leaves the Dual Port. The Dual Port design has completely isolated airways between the main and the secondary airways of the carb. Since I'm putting a two barrel throttle body on it, I don't think the Dual Port design will allow much fuel to reach the secondary airways, so it's out too. (See Dual Port picture) Now I turned to Summit Racing. The guy there suggests an Edelbrock intake, Cat #2131. Summit quoted me a price of $165.95, but they were out. I went to Edelbrock's Web Site and checked it out. It's perfect! It's a dual plane, and it shares airways for main and secondary. It's all mine. Click Here to see the info. I then called JEG'S mail order, and they had the intake in stock at $163.00 (including freight :-). Just to confirm your suspisions, I need a four barrel intake, and I'm putting a two barrel throttle body on it! Go figure.

On to Installation!

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