tee-boy

iTrader: (8)

Background: Bought my 98 TA WS6 3 mo ago. Took to track a week ago and couldn't get below 14.6 even when hooking. Got back from track and changed plugs, wires, fuel filter, cleaned K&N. Went back to track last night improved to a 14.1. Still too slow for this car. My 60's are decent at 2.15 but can't break into 13's or exceed 100mph.

So I decide it has to be a fueling issue (too lazy to do a compression check at this point). I check fuel pressure w/o engine running. It seems good at 54 lbs (very minimum for these cars). I start the engine, and the needle on the pressure guage starts vibrating really fast b/w 60 and 70 lbs constantly. Pressure is supposed to drop w/ engine running. What could this be?

ss1

iTrader: (32)

Is it a stock pump, or Racetronix pump & harness? You should probably post a little info on your setup.

tee-boy

iTrader: (8)

Set up is stock. Fuel Pump is stock.

Old Geezer

iTrader: (3)

Key on, engine off results in lower voltage to the pump. Engine running, the alt is now in the picture, and the voltage rises. [Hopefully, anyhow.]
Also, if the ecm does not see cranking rpm, the pump will time out, and may not get to full psi in the short time it's on.

tee-boy

iTrader: (8)

Let me restate the issue:

I check fuel pressure w/o engine running and key on. It seems good at 54 lbs. I check again with the engine running, and the needle on the pressure guage starts vibrating really fast b/w 60 and 70 lbs constantly. Pressure is supposed to drop w/ engine running. What could this be?

Old Geezer

iTrader: (3)

Me stating I can read???

ChevyChad

iTrader: (50)

Your stock fuel pressure is supposed to be 58psi. It will fluctuate a little with the engine running (between 58-60). So, your pressure is not "good" at 54, it is low. Why do you think the pressure would go down with the engine running??? It should stay the same, but it will go up as stated above because your pump is getting more voltage from the alternator.

tee-boy

iTrader: (8)

According to Hayne's manual, 1998 and later V8 FP should be 55-60 psi. Engine running at idle should decrease by 3 to 10 psi. Of course the same manual says that if fp doesn't drop w/ engine running, to apply vacum to the regulator. This would be hard considering that the regulator, from what i read on this site, is in the gas tank.

ChevyChad

iTrader: (50)

stock pressure on mine was about 58 at idle, and 60 at part throttle...

something is definitely fishy tho if you are seeing 70 at idle. You sure your gauge is accurate???

tee-boy

iTrader: (8)

No I'm not sure, but it's brand new. What worries me is the needle moving eratticaly b/w 60 and 70 psi w/ engine running. The car is running 14.15's at 100mph w/ 2.15 60's. I read everywhere that a 98 WS6 is a mid 13 car. I'm guessing that I am not getting fuel at the top end but not sure.

tee-boy

iTrader: (8)

Well, figured this one out. I retruned th FP guage for a new one. Pressure is at 60 w/ engine on. Cheap as tools they make these days.