My walbro has been great for 6 mos. About the fp going away a cruise you might want to check your fuel filter if you have not already done so. Good luck.

 

replaced filter twice in last 2000 miles. No help there.

 

I hope you have it figured out by now. FYI the reason I mentioned the fuel filter is that when I installed the 392 in mine the pressure at the output of the filter was 16 - 17 at idle and I could pull it down to about 13 or so. I have a big line kit and changed the filter when I changed the pump. I must have picked up a load of bad fuel at the first fill after the install because the pressure started jumping around up to as much as 20 and then it would drop to 12. This was at cruise. Double checked the filter by looking at it and it looked ok but maybe just a hair dark. I was ready to pull the Walbro and start bad-mouthing but on a whim stuck a new filter in it. It's been fine since. My fuel pressure tap is at the output side of the filter and I still can't figure why a bad filter would cause the pressure to go above what was expected but that's what happened. It's been normal since - 5 or 6 months - probably 5k miles and no glitches.

 

I havent figured it out yet. My FP is tapped on the inlet at the VP-44. I dont have the big line kit from filter to VP-44. I am really thinking that its bad fuel. But it has happened everytime I drive it for the last 3 weeks. Have used 2 different diesel truck stops. One of which I always use, was when it started happening. This last tank is from a different place. 3 tanks in total since problem started. Bret

 

You mentioned that your Walbro setup is from Glacier Diesel. You might check the poppet style pressure relief valve to see if anything from the fuel has caused it to stick open. During the high flow condition at startup it will allow more fuel to bypass and then when you increase demand for fuel at cruise it could be sticky enough to not close. If that's the case the fuel pressure should go right back up to normal when you take the load off the engine. I think that is the reason for my wierd pressure fluctuations and once I installed a new filter the pressure never got high enough to cause the poppet to stick. Just a possibility.

 

Yeah I thought about that, or possibily the bypass valve at the VP too.