Editorial

Basic Tools to test EFI properly.

Proper testing for any engine problem means being able to control the circumstances surrounding the problem, duplicating the conditions as best as possible, and understanding how your test equipment and the engine interact. This only comes with experience with working with both items on a regular basis.
In our example, the customer complaint was that the motor would stall when idled for extended periods of time. Usually on a hot day. Although vapor lock is a hard thing to duplicate, this was exactly what we thought we had to do on the onset.

step one

So our first step was to hook up our Dyno and other test equipment and verify for normal operation and any fault codes, before we started our testing. (No fault codes were found.)
Bringing the engine to full operating temperature and running the text book tests was next. (All checked out fine.)

step two

One of the first things we noted was that the heater hoses that ran to the cabin were wire-tied to the mechanical fuel pump but, we left these in place until we could verify if they had any effect on the operation of the fuel system.

After an hour of running at varying throttle settings, we decided to just let it idle and covered the engine with a blanket to keep it nice and warm during the tests. (everything seemed fine at this point.) What happened next started our quest for the answer.
After about a half hour of idling in gear the motor stalled. Our fuel rail pressure gauge showed almost no pressure and the VST tank was low on fuel. Our next step was to check it see if our mechanical fuel pump was part of the problem or not. We installed an additional fuel pressure gauge to the VST fuel feed line. (Note that we use clear hose for our fuel gauges as this lets us see the quality of the fuel we are getting.)

As mentioned in the intro to this article, (and to make a long story short) we re-routed the hoses to the heater and found this did not solve the stalling problem. We then pulled the mechanical fuel pump, found gas in the sea-fuel pump lube cavity and installed a new fuel pump.

The final result was a consistent fuel pump reading of 6 to 7 psi and an engine that ran for over an hour and a half with proper readings and without stalling.

End of story.