:cheers: We are talking '88 l98 :D

Decided to do some tests this afternoon. Here's what I cam up with

1) Key on...instantaneous (no hesitation) 42 psi
2) 2sec, pump shut down...40 psi
3) engine start, cold idle...38 psi
4) engine warm idle ...34 psi

5) Step on gas (warm, 34psi), instaneous (barely touch pedal) brief run up to 36 psi...immediate return to 34psi
6) 34 psi right up to 2500 rpm and holing for a time at 2500

7) off throttle, slight gain

8) return to idle...34 psi

Did this test as part of looking into mild pinging problem on hard accelleration. According to the book, 34 psi is minimum.

Are you all running closer to 38?

Thanks

Jack

 

i will try my best...but have you tried to replace the fuel filter and check the voltage on the fuel pump? :confused:

 

Those numbers are similar to what i got and i seem to have no performance problems. :cheers:

 

Sounds like a fuel pressure regulator spring going south. Install an adjustable regulator and set your own pressure. The pinging could also be an indication of the engine leaning out. Good Luck.. :chevy

 

Your numbers look good. What you need to know, is what happens at WOT. Tape the fuel pressure gauge to the windshield, and drive hard. Pressure should climb 6 pounds or so as manifold vacuum spoils, and stay at about 38psig the entire time your foot is planted on the gas. No fluttering about - just rock solid.
My pinging was cause by a faulty fuel pump that could not keep pressure up under the conditions stated. I replaced it - no problems anymore.

 

Hey Jack....I agree with the comment above as it sounds like the fpr is crapping out. With the loss of vacuum (upon accleration), the spring in the fpr should apply more pressure to the diaphram causing a RISE in fp off idle. Check it a WOT and get back to us.


[Modified by ittlfly, 6:16 AM 10/29/2003]

 

:cheers: Thanks Guys

If I am feeling better, I will try to get back into it this weekend.

I did get, about a momentary two pound increase at the split second the TPS would have begun to engage, but it dropped immediately back to 34. I expected the increase, but I expected it to last longer.. I ran it up to 2500 in neutral and it stayed at 34


Thanks again

Jack

 

[QUOTE] :cheers: Thanks Guys

If I am feeling better, I will try to get back into it this weekend.

I did get, about a momentary two pound increase at the split second the TPS would have begun to engage, but it dropped immediately back to 34. I expected the increase, but I expected it to last longer.. I ran it up to 2500 in neutral and it stayed at 34

You should maintain the higher pressure once the vacuum drops at the fpr. Do you have any fuel in the vacuum line from the fpr? That would be a clue.


:D


[Modified by ittlfly, 1:20 PM 10/29/2003]

 

Remember that the pressure increase is due to load, not RPM. Even if you rev the motor to 6,000 RPM at idle, there will be no lasting fuel pressure increase. You have to be driving to keep a low vacuum condition for more than an instant. Duck taping the FP gauge to the windshield works very well. Worse case you may need a passenger to read it for you.

George

 

Ditto.

Jake

 

Since I don't know the numbers for a 88 I can't be sure, but 42 sounds okay. If you have a stock regulator there should be a vacumn hose from the reg to the plenum. This reduces pressure at idle. You don't need to drive the car with a guage on your windshield. - Just pinch the vacumn hose closed and measure your pressure.

 

Skippy
Pinching the vacuum hose does nothing. Vacuum stays in the regulator.
Pinching the return hose will only tell you the maximium pressure the pump will deliver, not the max volume. A pump needs to deliver about 40psig while it is suppling perhaps 40 gallons/hour. You must drive the car to test that. It is common for pumps to develop output leaks back into the tank, where they can still deliver pressure into a dead volume, but cannot keep up with the huge fuel demands at WOT. A leaky or poor fitting output damper will cause a pump to fall on it's face at WOT, but will pass your test.

George


[Modified by George West, 10:19 AM 10/30/2003]

 

Almost; it does a little something.

Pinching the vacuum hose leading from the regulator to the plenum will show the pressure when no vacuum is going to the regulator. It is the same thing as removing the vacuum hose and plugging it, which is the recommended way to set fuel pressure.

So if you have your fuel pressure is set at, say 45 psi (vacuum hose attached), when you pinch the hose the pressure will increase at a ratio of about 1 psi for every 2" if vacuum the engine pulls.

My engine pulls 14" of vacuum, so my pressure increases 7 psi with no vacuum.

At WOT, however, vacuum does not fall to zero on most engines; there is usually 1 to 2 inches of vacuum still being created in the engine. Looking at that data on a dyno graph is one way to tell if there is a need for greater intake flow; such as going with a larger carburetor.

Correct: it doesn't show volume, just pressure. In the 1/4 mile engines I use to build we'd always check fuel flow volume using the oil gallon bucket trick.

Don't forget, shen correctly installed, fuel pressure on the TPI is vacuum referenced. So when you blip the throttle, vacuum momentarily drops resulting in a fuel pressure increase. When vacuum returns to normal, the pressure drops back to it's previous position.

Check it out for yourself. Attach a vacuum gauge to the engine and watch both the fuel pressure gauge and vacuum gauge as you blip the throttle. They'll move in sync, but in opposite directions.

One last point, when an engine is first started, the vacuum reading should be a tad lower than when it is completely warmed up. The rings will be sealing better at normal operating temperature, resulting in a higher vacuum reading. Another reason to make sure the engine is fully warmed up and in closed loop before going in for emissions testing.

Just my thoughts.
Jake


[Modified by JAKE, 11:28 AM 10/30/2003]

 

If you have the stock tune on your car I bet it's your pump.
I also agree you must test the pressure at WOT under a load(while driving)
How many miles are on your pump?

I replaced my pump with the Racetronix kit. Nice set up and come with a Walbro High pressure pump. I had a pinging problem and found that my pressure dropped under WOT. I believe it should stay around 40 at WOT.

 

Jake

Not to beat a dead horse, since we all know what you mean, but............

No matter how hard I pinch my vacuum line going to the fuel pressure regulator, it does nothing. When I remove it - well that does increase the pressure, as you would expect. Unless your regulator is leaking through the diaphragm, pinching the vacuum line does nothing at all, except prevent the regulator from following subsequent intake manifold vacuum changes. All you do is trap the pressure that is already in the regulator.

But you knew that. I'm just being ****.

George