fuel pump question

[stevek]

hey eric I have TT340 pump put in about a month ago. The proble im seem to be having is after about 6 runs my fuel pressure guage was set at 40# with hose on seems to start to drop down to about 35#. the first time it went down i parked it and found out that i had a lot of pressure in fuel tank and fuel tank verry very hot also, so after opening the cap a few times to let pressure out i found the charcoal can line was plugged.cleaned out now very little pressure now in tank, i took pump out all looked good but stills drops, possible i weakened pump, adj fuel press reg seems ok , any thoughts, thanks

 

[Eric Stage I]

I see this quite often (with any pump) when the car heats up. Sometimes it's a fuel pressure gauge issue (reads different when hot). Other times it can be a voltage thing. Usually you have more voltage at the alternator when cold, which increases fuel pump output. If your return line is slightly restrictive, then this extra pump volume can cause higher pressure at idle when cold, then it drops as the alternator volts drop down when hot. My own car shows ~15.0 volts at the alternator when dead cold, then drops to maybe 14.0 volts when it warms up.
If you're losing pressure under boost, then it could be a pump issue.

 

[stevek]

ok thanks, ill try different fuel guage and see what it reads,do you know what kind of fuel sending unit i can hook up to power logger to read pressure better,and should the hot wire plug with 2 connectors on it get warm afterr awhile.