2003 hpdi surging

[forester]

I have an 03 250 hpdi that has an intermittent surging problem. Mostly in the 2500 rpm to WOT range. Will idle fine. I can run sometime 10-15 miles and never misses at all and then the next run it surges for a mile or so and then straightens out. This is over a couple tanks of non-ethanol fuel so bad fuel should not be a problem. I have replaced the fuel lines from the tank, the bulb, the water separator, plugs and the low pressure fuel pumps. Its been about 75 hours since all of the filters have been changed. Any ideas on what else to look for. Motor has about 375 original hours.

[MichAngler]

I had a similar issue with my 05 and I did a lot of the same work

Low pressure pumps
primer bulb
standard filter in the canister
plugs
lines
and I have a 10 micron separator between tank and motor that was replaced as well

It wasn’t until I replaced the filter in the VST tank and the separator just above the VST tank that I finally solved my issue

Might try taking it to an authorized Yamaha service center and have them plug it in and see if it’s kicking any fault codes and see if they can figure it out

[jdwo2212]

Mine also was in the vst when i experienced it this year. Had to do filters and in my case replace vst pump. My mechanic was able to test by swapping a vst unit off his motor to mine. So i got lucky that way. Great mechanic tho! :)