Fuel Pressure Gauge Fluctuates

[Doug07]

1977 Lance. the Fuel pressure gauge fluctuates(bounces back and forth) while engine is running. MX says the pressure is solid at the spider ( distribution point) and reads correct pressure. He also doesn't think its the gauge, as he can work on the system and it will stay solid for a few trips the start to bounce again. Note: turning on the electrical fuel pump doesn't effect the gauge reading. Also, both original and JPI700 fuel flow gauges read normally.
In advance, thanks for any input

 

[flyguydon]

 

[sierrakilo99]

 

[Lgiroux]

 

[BGFYankee]

 

[kaos32d]

 

[BGFYankee]

 

[otterf18]

 

[flyhigh]

 

[sierrakilo99]