Confused about fuel pressure problem?????

[67coupe]

Just got a new liquid filled fp gauge. Was working on car today and noticed that after it ran for a while the fuel pressure had dropped. Started at 36 psi and after 20min was at 30 psi (both readings with no vacuum). I searched the threads and found this.

Dropping Fuel Pressure Ghost Expelled!!!!

I just figured out what was causing my mysterious fuel pressure drop so take note so it won't cause you the grief it caused me! Would you believe it was not dropping at all. It seems that liquid filled fuel pressure gages are not recommended under the hood when exposed to heat! The "bourbon tube" that expands when the fuel pressure hits it, is connected to a spring that moves the gage needle in the positive direction. When a gage is filled with a liquid the heat causes the liquid to expand and collapse the "bourbon tube" causing the gage needle to move in the negative direction hence the falling fuel pressure. I used a liquid filled gage because they dampen the needle so it will not bounce under the mechanical fuel pressure spikes. My advice is to stay far away from liquid filled gages if you are putting them under the hood!​

Is this true? Can anyone confirm it? Or, do I need to look at the pump?

Btw, pump is stock with 88,000 mi.

Thanks

 

[HISSIN50]

who said that? im curious (i take different data from different folks with more creed than others). it sounds pretty credible, and i think i have read that before (no personal experience), so it sounds good to me. i wonder if you iced the gauge and then re-did the situation from earlier, if it would read consistant? or put a diagnostic gauge on the schrader and try it again.
interesting stuff.

 

[SHAGGY87]

I'd replace the fuel pump, that fixed my pressure drop probelem.

 

[vikingpower]

i got a Nordskog dig guage plugged into my BBK adj. and it the reading isnt very consistent, Im happy with it staying between 40-45 and have to settle with it wandering. as long as you arent leaning out dont worry about it. But definitely get rid of the stock fuel pump...

 

[67coupe]

Thanks for the replies,

I don't remember who posted it. It was a thread with no replies. I started it again 5 hours later and the pressure was again reading 36. I just got out of college and have many plans for this car and a bigger pump and lower gears are first on the list.

I don't think I'm going lean, it pulls very strong to 5000 rpm. But, that is my only concern. I was thinking if it drops 6 psi from cold to hot idle, how much does it drop at WOT.

I searched the internet to try and find any information confirming this theory and did not find any. I will try to borrow a friends guage and try to repeat the situation. I was basically wondering if anyone had a similar experience or could confirm this guy's theory. As soon as I borrow a gauge I will follow up with my results.

thanks again.

 

[jerry beach]

You are taking readings with the vac line off the regulator. That simulates wide open throttle to the regulator. So it should only drop with the line connected. Your regulator maybe be going south. Pinch the return line and see if the pressure goes up. This usually indicates a bad regulator and good pump if thats the case. I replaced my reg. for the heck of it with an adjustable model when I put in new injectors. I have a Holley, it was $65 and had to be ordered in the next day at the local parts store.

Try a different guage too, or ice it like Hissin suggested.

Come to think of it I have no vacuum hooked to mine. Its been that way for years. I think its supposed to have it, but I didnt put it back. Seems to make no difference running at 40 psi all the time.