Rail pressure fluctuates

[Greg Moser]

I have a 2005 with 122,000 miles, original owner no mods. I have religiously replaced fuel filter every 15,000 miles. I have a gauge on the low pressure side and a gauge on the rail. The low pressure always reads 8-9, which is perfectly fine. The issue I am seeing is when I am on the highway, steady speed I will see the rail pressure drop and then come right back. Sometimes it happens so quickly you don't notice anything is wrong, other times you feel like a miss. I have no issues starting, I don't notice any smoke on startup. This is intermittent, it started last week and does seem to be getting worse. I removed the FCA and sprayed wd40 in it to see if things would improve, but did not seem to make a difference. It appears to idle fine, has anybody had an issue like this? It seems that most problems with the FCA occur during idle, any help on this would be greatly appreciated.

 

[Ozymandias]

Use a scanner to proof your gauge! I was fooled by a brand gauge lately into thinking my transmission is bad.
If the sound of the engine doesn't change at all during these gauge jumps, more then likely the gauge is wrong.

 

[Darkbloodmon]

If the gauge checks out find, start with the small stuff first. FCA/Rail Relief Valve.

 

[Greg Moser]

Use a scanner to proof your gauge! I was fooled by a brand gauge lately into thinking my transmission is bad.
If the sound of the engine doesn't change at all during these gauge jumps, more then likely the gauge is wrong.

I am pretty certain the gauge is correct, I noticed when the gauge does jump I can hear I guess what everyone refers to as a fuel knock. Also I have also heard that if the fca does not rattle when shaken it is bad, not sure how true that statement is. Thanks for all suggestions, I am assuming an edge scanner is the type of scanner you are talking about?