HPDI surging

[TomD]

I removed a pair of 92 Yamaha 200s and replaced them with a set of 01 HPDI 200s.
After a few minutes of WOT on the test run the Stbd eng starts to drop down, and surge back up to speed. This happened several times. Each time it would go lower, behaving just like a fuel pump issue on a carb engine. I slowed both engines and brought them up to speed again. Each time I did this the interval to failure was reduced.
I then grabbed the primer bulb and began squeezing. The engine immediately responded and came up to speed. I see this engine has a pair of LP pumps to feed the VST. I then replaced both pumps and ran the boat again. It behaved exactly the same way. This boat has two seperate fuel systems (filters lines tanks) so I swapped lines and ran the boat again to no avail. I only had time to vacuum test the fuel system at the filter. There was less than 2 in. Hg drop. I did not have time to check it at the fuel pump, as it began raining.
Any light you could shed would be greatly appreciated.

[Hamfisted]

Did you check the long vertical fuel filter under the hood? Does the boat have Racor fuel/water separators installed? If not, it should. The HPDI's are very sensitive to fuel contamination. There's a tire valve on the top of the VST pump to check fuel pressure there, should be around 30 psi or so. There are three fuel filters under the hood. If the motors were run many hours without a Racor I'd suspect one or more of them are clogged up. Do you have a service manual for the motor?


Mike