I have the denso pump for the twin turbo supra. When fuel pressure gets to 45 pounds it drops off and of course start to get knock so I get out of the throttle. I had another denso pump that I put it and it does the same. When I put the second pump in I noticed that the wire going to the positive lead on the pump was about ready to break on the connection. I figured that was the problem. It might have gotten a little more pressure maybe 50 pounds but it drops off. I have the racetronix harness connection and it is hotwired. I don't see how it could be the pump since both act the same way. I have the translator plus with the extreme chip. Any advice what to do. Do these pumps pull more voltage than other pumps and maybe I'm not getting the voltage to it?
Need help to figure out why fuel pressure at wot drops off
- Thread starter Mike70gtx
- Start date
I'll check regulator tomorrow. (Where do I apply the pressure to the regulator? Please explain a little more) Then I'll check voltage. If I remember right I have always been a little low on voltage reading through the scanmaster. Maybe my dual spray alky has been compensating for some fuel shortage.
DaySleeper
Member
- Joined
- Jul 27, 2010
You might check the fuel filter.
Update. New regulator and still have same problem. I thinking I could have a low voltage problem. My scan master shows 12.1 volts and when I try to go wot, it goes down to about 11.1 volts. I have 19 volts at battery, !9 or more at the back of alternator, the same at my relay in the trunk and 18 or more the harness connection by gas tank going to fuel pump. I do have the racetronix wire connector to fuel pump. First of all can my voltage be that high? I have always had low numbers on scanmaster voltage. The fuel pressure makes it to 50 pounds and then drops off. Any ideas what to check next?
Turbo1dr
9 Sec Wanna-Be
- Joined
- May 25, 2001
If you actually have 19 volts at the battery then it should explode soon. Might want to test it again with another meter.
You could have an internal fuel leak inside the fuel tank. Make sure the hose connecting the pump doesn't have a hole in it that only leaks above a certain pressure.
You could have an internal fuel leak inside the fuel tank. Make sure the hose connecting the pump doesn't have a hole in it that only leaks above a certain pressure.
the pump is run by the voltage applied to its 2 terminals. the negative connection needs to be a solid, low impedance path back to the engine block or battery.
High positive voltage will do little if the negative side of the 'loop' has issues.
Bob
High positive voltage will do little if the negative side of the 'loop' has issues.
Bob
I have most of the casper electronics stuff to for battery, starter, alternator, etc. I have had motor out so many times I'm sure I have my main grounds good. Is there a way to check the negative starting at the pump and working back. (like ohm meter or something). Could this dense pump take more voltage than my old walbro?
- Joined
- Nov 30, 2009
Just because you changed regulators does not eliminate that it is getting the boost signal. With the car sitting ignition on (not running) jump the pump to turn on and stay on apply 15 to 20 psi to the vac line that goes to the regulator . Fuel pressure should rise 1 for 1 ,if it does you have a leak in the line and are not getting boost signal to the regulator, just like QUIP'6' said earlier, plus it's a whole lot easier to do than dropping the tank again. Sam
If pressure rises to a point and then drops off,your fuel supply is insufficient. At your power level,a volt booster might get you there,otherwise it's time for a double pumper. Use only AC Delco. I've seen as much as 6 lbs of pressure loss with other brands. Pressure falling is pump. Again,I think more voltage might get you there and it is beneficial to spark output.
Please explain how or why I put air pressure to the regulator? Doesn't it use vacuum to adjust the regulator? Do I just take a small blow gun and apply pressure to where the vacuum line goes on to the regulator? Also can I just do this while it is idling and see if I can get to 70 psi fuel pressure?
- Joined
- Nov 30, 2009
Your vac lines all turn into positive pressure lines unless there is a check valve. So when you go into boost (+ pressure) that vac line to the regulator gets pressurized and adjusts the regulator for more FP . This is when we say FP should rise 1 for 1 with each lb. of boost. So just put a known pressure under 20 psi to the regulator with a compressor or a small hand pump (Mity Vac) and see if FP rises (43psi base + 15 psi you apply = 58psi on gauge) and holds as long as the applied pressure is there. Good Luck Sam
- Joined
- May 28, 2001
Time to do a volt drop test on the entire car......
Chuck, could you explain how to do a volt drop test and what will it show me?
Checked voltage with different meter. I was 14.09 at alternator and 13.98 at battery. Even with bad tester the numbers should be consistent at least at the plug in by gas tank. Why so low through scan master?
This statement makes me think that you don't have your fuel pump hot wired if this is true you'll increase your pumps pumping ability greatly by installing a hot wire and volt booster. Again,you have a fuel delivery problem.
Yes I do have a diy hotwire setup. I believe it's 10 gauge (maybe 12) wire from alternator to relay in trunk. I might have a foot or two of stock wire where I spiced into at the trunk. Then the new racetronix plug from sender to connector by bumper. Do not have volt booster.
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