| 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. After some basic tests, Our next step was to check current service bulletins and we contacted tech support for any information they might contribute. "That engine doesn't have a vapor-lock problem" they said.
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So our next 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 all the text book tests was next. (All checked out fine, again.)
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One of the things we noted was that the heater hoses that ran to the cabin heater 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. First, we had to duplicate vapor-locking.
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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.)
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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.
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The 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. However, we noted excessively high pressure in the VST tank after shut-down. Loosening the vent cap on the VST would release the pressure but obviously, we still had the potential for vapor-lock. Which now occurred at about 20 to 30 minutes after shut-down. [Even with the motor box open and in the shade.] At this point we made numerous calls to tech support who denied a fuel cooling kit was available for this engine.
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End of story. Not quite... After extensive research, and the boat owner bitching out Sea Ray customer service, it turned out that Mercruiser did make a fuel cooling retro-fit kit for this engine to cool the fuel. [just like newer versions of this engine] After kit installation... Vapor locking problem solved. Why Mercruiser originally denied the existence of a fuel cooling kit, which cost us three days of testing... is up for speculation.
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