I noticed the other day that my fuel pressure gauge was reading high. I replaced my lift pump last year. And from day one it has read 12 idle, 10 cruising 8 WOT. Well I noticed that once everything was warm ( 45 mile trip ) I looked down at my gauge and it was pegged above 15 at idle. I haven't noticed it driving down the road, due to daylight and I have no lights on the gauge. I have checked the connections and all seem OK. When its cold It's at it's normal psi of 12. Any ideas on what this could be?
Thanks,

Kimrey

 

Probably the by-pass valve stuck closed for a bit.
Mine did that once, looked down and saw 18 psi , shut down, & restarted, and it's been good ever since.

 

Kimrey:

The consistency of diesel fuel (oil) changes with temperature changes, therefore you will see a pressure change on your gauge.

I have a 1993 Dodge diesel and have being using a vacuum gauge on a Racor filter since purchasing it. The Racor is filtering the fuel pre lift pump. Also I have a 2002 DD and use a pressure gauge which is reading the pressure post OEM filter.

On the vacuum gauge I see a higher vacuum during cold weather than when the ambient temperature is warm. On the pressure gauge the reading is lower when the temperature is cold but rises as the ambient temperature rises during the day. This change also is seen when running a long distance as you mentioned in your message and the reason being is as your fuel is bypassed back to the fuel tank, it warms up and the consistency changes.

 

Thanks guys. It must have been the by-pass valve. Yea when it's cold fuel is slower, but as it warms up it becomes more fluent. But I have never seen it that high. I know that's not high compared to other people, but I was going by what it has been reading since the install of the pump. Thanks for the replies, I was just worried that something might be wrong.

Kimrey