NFB - Help with 98 pontiac

[Gary94Formula]

My Dad's Bonneville with the 3800 v6 non/SC started dropping fuel pressure late Friday. We have a gauge on it and it will run around 42 pounds, then it just drops to 12 pouds or so and it stalls. You don't even have to cycle the key, you just take it out of gear and hit the starter and it gets fuel pressure again and your on your way. The only thing he has done is filled the tank with gas Friday. A coupe of friends one being a school mechanic and another being a GMC truck mechanic are stumped. We have ran the thing pretty much all weekend and yesterday it was just idleing and the fuel pressure kept going up and down. We shut it off to put in on the lift this am. we started it up and let it run for 2.5 hours today and it's was fine. We then drove it for another hour and nothing. This thing was run for 3 hours Friday night and was having issues. We had it running for over 12 hours yesterday with issues... We have the new Snap-on MODIS tech unit on it and nothings showing up...
The only difference is the gas was getting down to a 1/4 of a tank or so. We are stumped ...

Any ideas?

Thanks in advance
Gary94Formula

[TraceZ]

My Dad's Bonneville with the 3800 v6 non/SC started dropping fuel pressure late Friday. We have a gauge on it and it will run around 42 pounds, then it just drops to 12 pouds or so and it stalls. You don't even have to cycle the key, you just take it out of gear and hit the starter and it gets fuel pressure again and your on your way. The only thing he has done is filled the tank with gas Friday. A coupe of friends one being a school mechanic and another being a GMC truck mechanic are stumped. We have ran the thing pretty much all weekend and yesterday it was just idleing and the fuel pressure kept going up and down. We shut it off to put in on the lift this am. we started it up and let it run for 2.5 hours today and it's was fine. We then drove it for another hour and nothing. This thing was run for 3 hours Friday night and was having issues. We had it running for over 12 hours yesterday with issues... We have the new Snap-on MODIS tech unit on it and nothings showing up...
The only difference is the gas was getting down to a 1/4 of a tank or so. We are stumped ...

Any ideas?

Thanks in advance
Gary94Formula

put a voltage meter on the pump. Put the meter where you can see it while driving. If the voltage dropps when the PSI drop, it is most likely the relay. If the voltage does not drop, it is the pump.

You might just want to replace the relay and filter and see if that fixes it. If not, it is time for a new pump.

[Gary94Formula]

That's pretty much our next plan of attack. We had hoped to do a voltage and a amp test on the pump Sunday, but the thing never burped...

Thanks.
Gary94Formula

[Gary94Formula]

Update on this... We sound the pump to be bad. We couldn't prove it, but the problem hasn't occured in 2 weeks or 500+ miles. It's on of those jobs, when it started with the pump, but the sending unit was starting to rust, so we replaced that along with the gas tank. We don't want to do that job again.