Fishjager

I put a FASS 95 HPFP on my truck about six weeks ago. It read 18-18.5 in the beginning. Now it is down to 15.5-16.5. Is this normal? This is at idle and cruising down the freeway.

Twodiesels

I have the same issues. Mine used to idle at 17 consistently but now it is erratic. I had the fuel pressure checked manually and it was at 19. So I dont now what the deal is. I am not sure if the fass is going bad or if the guage is bad.

Fishjager

Maybe DieselDan will see this post and help us both out. I hope it is not any thing serious. I wonder if the FASS system fails, do you have to ship them the old one and wait for another one to come? That is a long time to be without a vehicle.

crobtex

My old style HPFP (FASS II) started out at about 25 psi and has settled in at 19. Normal according to DD.

Twodiesels: If your fuel pressure was reading OK on a seperate, external gage, I would think that you probably have a gage problem.


I'm sure Dan will chime in here.

Diesel-Dan

Fuel Temp can have a bearing on pressure. Staring in the cool morn, pressure might read a bit higher than the hotter afternoon. Mine drops about 1.5 PSI from morn to afternoon.

From my seat here.....i have seen tons of gauges cause issues. I’m not passing the buck, just stating fact. If I get a fuel pressure issue call here, the first words out of my mouth is “Have you confirmed the gauge to be reading correctly against a known working gauge?” You would not believe the issues this one question filters out.

Check your gauge out first. If you have an isolator (Don’t get me started on these! Haha) I would highly suggest rebleeding both sides out. I have seen Edge Juice with Monitors read low only under WOT for some reason. Not all, but enough to mention. I had a guy double check his with a mechanical gauge and it was 7 PSI off under WOT.

Im not saying we don’t have our issues….but confirming the gauge will make sure our issue is legitimate.

In both of your cases, I don’t see any issue with your pressures. Different restriction on different trucks (AND fuel pressure gauge calibrations) might show different readings. If you are over 15-16 PSI consistently, I wouldn't worry about it.

Fishjager

Crobtex,DD thanks for the reply. I just got off the phone with the place I purchased the FASS. They told me a guy in the shop had the same issue. DD I think you hit it on the head. The shop told me to drain the anti freeze out of the isolator and fill it with silicone spray instead. There seems to be and issue with anti freeze as a buffer. I will try the silicone next. Thanks again for the reply.