By C.Asaravala

If you were anywhere near Northern California the last week of September you probably heard a big whooshing sound at about noon on the 29th. That was my huge sigh of relief as our Project '67 Mustang was unstrapped from the dyno rollers. Nearly six months after embarking on an EFI conversion project we finally had a running car - and one that runs surprisingly well too.

It all began back in February when we decided to ditch the carburetor and install a Ford EEC based fuel-injection setup from Mass-Flo EFI. We had grown tired of trying to tune the carburetor to run with the Vortech supercharger we had installed late last year (see the "High on Carbs" series) . We knew that for ultimate tuneability, and driveability, we'd have to convert to a computer controlled system whereby we could infinitely adjust timing and fuel delivery.

Mass-Flo's stealthy EFI system is based on hiding the mass-air meter in the air cleaner.

It didn't seem like too tough of a job. As we detailed in Part I, the conversion can really be broken down into three main sections -fuel system, electrical and hardware. The Mass-Flo kit comes with a custom wiring harness for early Mustangs (you could use a harness from a 5.0L donor car but you'd have to deal with unnecessary emissions sensors, etc.) With the harness and computer in place we installed the carbureted Victor Jr. manifold, modified for fuel injectors. On top of it goes the throttle body and Mass-Flo MAF sensor. It's a pretty slick setup that allows use of a standard air-cleaner giving the impression of a carbureted motor to the unsuspecting eye.

Unfortunately we hit some turbulence in what otherwise seemed to be a very straightforward path to EFI. As we reported in Part II the motor fired up immediately and the computer had no problem idling the somewhat aggressive cam. The problem reared it's head when we tried to drive the car. At 3500 rpm the engine would hit a wall. In fact it felt so much like hitting a rev limiter that I checked the car and engine bay several times to see if there was some rpm limit module that I had installed and forgotten about. The solution wouldn't be that easy.

We spent every available hour trying to troubleshoot fuel and ignition. Over the course of a month we swapped out the MSD box, coil, distributor, plug wires, plugs and even the computer. No change - run the motor up in neutral or in gear and it would break up at exactly 3500 rpms every time. We initially thought we were on the right track having identified cavitation in the fuel pump (see Part II for details). We tracked the problem down to a insufficient filter size before the pump which was restricting flow. Unfortunately swapping the filter out to a larger one didn't resolve the 3500rpm breakup, though it did resolve the cavitation.

Reaching out to the masses
That's where we left off in the last issue. We suspected at this point that the problem had to reside in the wiring but we weren't sure where. Was it a defect, a bad sensor, a short, or some mis-wiring on our part? We were running out of motivation and ideas and decided to reach out to the online enthusiast community for help. We posted our problems on several tech forums and asked for ideas. Then we sat back and hoped someone out there would produce a solution.

The purple wire is the "TFI Start" circuit. This circuit applies 12V to the TFI module upon cranking and the computer in turn retards timing to facilitate faster engine starting. Our goof resulted in the timing being retarded continuously such that the engine wouldn't run past 3500 rpm.

After a couple weeks Wade Chamberlain, who goes by the handle FFR Cobra on the Corral.net and other forums posted a response which looked to us as being the key to unleash this engine. He suggested that we likely had one of the wires to the distributor TFI module connected to a full-time 12V source, when in fact it should only receive 12V during cranking. He explained that this circuit in the EFI wiring serves to retard timing while engine cranking for faster starting. If the circuit is seeing 12V while the engine is running in effect the timing is being retarded. This made perfect sense, since in fact the 3500rpm break up felt more like a rev limiter then it did a misfire or fuel starvation issue. Wade also added that this is a common mistake when guys convert older vehicles to fuel injection because it is easy to assume that the only connection ever requiring 12V during cranking only is the starter.

The next morning we moved the wire over to the starter side of the ignition relay and fired the motor up. A single stab of the accelerator pedal is all that it took to realize the weeks of frustration were over. The motor reved beyond 3500 for the first time, and now we were in business.

To Mass-Flo's credit their instructions clearly indicate that the purple TFI wire is supposed to connect to a cranking 12V source. We even marked it properly in the above image which we ran in Part II. However we misinterpreted this to mean 12V during cranking and running. Again, we assumed that there couldn't possibly be a circuit, other than the starter, that needs 12V only during cranking. My bad.

Simply connecting the wire to the starter activation side of the solenoid resolved the problem.