DIY EFI Part II - continued

Shortly after publishing Part I of DYI EFI we completed the exhaust work and fired up the motor. The initial reaction was all smiles. The motor fired up on the first turn of the key - one of the immediate benefits of fuel injection. Even more astonishing was that the engine idled with our relatively lopey (226/232 degrees duration and .572 lift) non-EFI designed camshaft. Unfortunately the celebrations were short lived as the first of our problems came as the engine came up to operating temperature. A large pool of coolant developed under the engine and forced us to shut the engine down. A quick inspection revealed the Cometic headgaskets were leaking - a problem not uncommon with multi-layer steel (MLS) head gaskets. MLS gaskets require mirror like surface finishes on the cylinder head and block deck to seal up properly. Any slight surface irregularities are channels for water to seep out of when pressure builds in the cooling system. We took our chances using the gaskets since we were not about to pull and disassemble the motor to have it resurfaced. So the final score was MLS gaskets 1, FordMuscle 0. We succumbed to more downtime and eventually replaced the headgaskets with standard Fel Pro graphite coated head gaskets (part number 8548 PT1).

That's not oil an oil leak but rather coolant. The Cometic head gaskets unfortunately didn't seal up resulting in a water leak between the rear coolant passage.

We thought installing Cometic MLS head gaskets would be a wise decision since we ultimately planned to reinstall the supercharger. Unfortunately these gaskets require a freshly machined mirror-like deck surface to seal properly. We gambled, and lost, using them as a replacement gasket.

By the time we got the head gaskets replaced and were ready for our second try at proving the EFI conversion our appetite to drive Project 67 was voracious. We hadn't taken the car to track in over six months and were getting antsy watching the summer evening track sessions pass us by on the calendar. With a turn of the key the inline fuel pump primed and the engine came to life with the swiftness and predictability we expect of fuel injection. At operating temperature we confirmed the replaced headgaskets had solved the coolant leak problem and we were looking to be in good shape for the first road test. After easing it down the street to the first open section of road we slowly started bringing the rpms up. The throttle response was crisp and acceleration smooth up until 3,500 rpm. That's when the engine acted as if it was hitting a rev-limiter and popped and sputtered. A couple more tries in different gears confirmed that we had a fuel or ignition problem rearing it's ugly head at exactly 3,500 rpm. Defeated again we rolled back to the garage for more troubleshooting.

Fuel Pump Cavitation
One of the things we noticed after our initial test drive was the inline fuel pump had gone from virtually inaudible to a shriek so loud that it could be heard over the exhaust system. Since this was such an obvious change in characteristics we suspected fuel pump failure or cavitation as being the likely cause of our 3,500 rpm engine cut out problem. Cavitation is a condition when a liquid, in this case fuel, vaporizes at the pump entry and forms voids or cavities of air. As the bubbles collapse they release energy and force pressure against the pump rotors.

Cavitation is generally is due to fuel temperatures getting too hot or too low pressure feeding the pump - both condition affecting the vaporization point of a liquid. The loud whining sounds and drop in fuel pressure are signs of cavitation and require correcting for proper operation. We suspected that our pump cavitation was due to too small of a filter before the pump. The 40 micron filter, while perfectly able to prevent the smallest of contaminants from entering the pump, proved to be too small to allow enough fuel to be drawn through at the rate required by the pump. We changed to a 100 micron filter, which also has a significantly larger filtering area, and that solved the cavitation problem. Our hopes were raised that we were finally ready to roll.

We learned that the inline fuel pump was cavitating due to the insufficient pre-filter area (top), causing a pressure drop before the pump and thus heating up the fuel. We swapped to a larger filter with a cartridge element. This cured the cavitation problem and made the pump whisper quiet. Note that the larger filter uses a 100 micron filtering element while the smaller is 40 microns.

The fuel system consists of a Mallory 255lph inline fuel pump with 100 micron prefilter and 40 micron post filter. We modified the stock sending unit with a -8AN fitting and ran -8AN hose to the fuel rails. -6AN line returns fuel back to the tank.

Back to Basics
Perhaps it is a variation of Murphy's Law, but one of the lessons that always seems to repeat itself regarding automotive problems is that it will either take a very long time to find the simplest problem, or that it will take no time at all to find the most complex one. We're certainly headed that way with our Project '67. We would never have suspected cavitation had it not been for the horrendous sounds emitted by the pump. So while the fuel pump is now quiet and pressure is constant, we still have the engine breaking up at 3,500 rpm. In hindsight we should have suspected ignition but then we would be dealing with the cavitation problem now.

So at the time of publishing this article we've gone through just about every ignition component except the spark plugs. We've swapped out, for trouble shooting purposes, the plug wires, distributor, TFI module, coil and computer. The problem still exists and all that remains now is to pull the spark plugs and check for a cracked insulator or perhaps a collapsed plug gap. We know, some of you are wondering why we'd save for last something as easy as pulling and checking eight spark plugs. The answer - remember those Dart heads with the goofy plug angles? It turns out you can't get a spark plug socket over the plugs without removing the headers. It's an example of how great design is worthless without basic functionality.

There, we've revealed to you our shortcomings. While we don't expect to set any trends in the world of automotive enthusiast media at least you know FM isn't sugar coating these projects to make you think we have some superior skill sets you don't. We're certain that this problem will be resolved soon, and when it is we'll be back on track with dyno testing and installing the supercharger.