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Running lean

old_man said:
The regulator actually is designed to keep the fuel pressure constant compared to the pressure inside the intake. That makes the injector action constant over different manifold vacuums.
Click to expand...

ain't that what I said?? maybe I didn't type as clearly as I thought:cheers:
 
only specs printed (that I am aware of) are as I posted in the first post:

30psi at idle and 39psi w/out vacuum on the regulator-- this would show that the regulator is capable of compensating for engine conditions that would alter vacuum anywhere from idle(highest vacuum) to WOT and full load (zero vacuum)
 
It would be nice to be able to drive the vehicle and read the fuel pressure under real world conditions. I did this with a supercharged Miata that I had. Vacuum/boost gauge ziptied to one wiper and fuel pressure gauge to the other. Found out it didn't have sufficient fuel under a load.
 
I agree it's valuable to know how it's operating in a real world environment. Insufficient fuel volume at speed will cause all sorts of driveability issues. The only problem is trying to determine what's correct and what's not. The only "specs" I've seen show the high point and low point with no vacuum samples in between. Assuming it's a linear increase, and you've got a vacuum gauge connected, you would be able to see correlation and assume it's functioning correctly. I do agree that values outside of 31-39psi would be an easy sign of failure, though.
 
The way it was explained to me years ago by my buddy at Jeep Engineering is that the "running" fuel pressure is the higher number and without full vacuum it pretty much stays there during almost any time except idle. With vacuum applied to the FPR, pressure is decreased for good emissions, idle quality and coasting. So, the FPR's intended use is to reduce, not increase fuel pressure. Now, if you have forced induction there are Auxiliary FPRs which increase fuel pressure proportionately with boost.
 
Shorty said:
I agree it's valuable to know how it's operating in a real world environment. Insufficient fuel volume at speed will cause all sorts of driveability issues. The only problem is trying to determine what's correct and what's not. The only "specs" I've seen show the high point and low point with no vacuum samples in between. Assuming it's a linear increase, and you've got a vacuum gauge connected, you would be able to see correlation and assume it's functioning correctly. I do agree that values outside of 31-39psi would be an easy sign of failure, though.
Click to expand...
i understand what you are saying, but when you disconnect the vacumm line all your checking is to see if the regulator is working properly. but yet the vehicle is still not under a load. so its not an accurate reading.
 
Shorty said:
I agree it's valuable to know how it's operating in a real world environment. Insufficient fuel volume at speed will cause all sorts of driveability issues. The only problem is trying to determine what's correct and what's not. The only "specs" I've seen show the high point and low point with no vacuum samples in between. Assuming it's a linear increase, and you've got a vacuum gauge connected, you would be able to see correlation and assume it's functioning correctly. I do agree that values outside of 31-39psi would be an easy sign of failure, though.
Click to expand...

It's not a linear increase. It really only reads full vacuum or loss of full vacuum. It's more like an on-off switch. The spec is for with full vacuum at idle or without full vacuum at idle. It's intention is to reduce fuel pressure at idle or decel, not increase pressure with load.

I'm all for driving the rig with the fuel pressure gauge hooked up.
 
XJRunner said:
how much pressure should I be getting at the rail?
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I'll go back to the original question^^

it was answered as it was asked-- I understand that under load AND at speed, the pump may not be able to supply sufficient volume to satisfy the necessary pressures. I was simply attempting to answer the question asked without entering a debate over methods of "outsmarting" the factory recognized test.
 
Shorty said:
I'll go back to the original question^^

it was answered as it was asked-- I understand that under load AND at speed, the pump may not be able to supply sufficient volume to satisfy the necessary pressures. I was simply attempting to answer the question asked without entering a debate over methods of "outsmarting" the factory recognized test.
Click to expand...

I understand that and you are correct.
I would like to see this test be done at road speed and under loads. This could possibly be an underperforming fuel pump issue which can't be detected at idle using the factory tests. Under load, as volume drops and is insufficient, the pressure will also drop.
I'm not trying to beat up on you. If I were, it would be much more obvious. LOL.
 
Shorty said:
I'll go back to the original question^^

it was answered as it was asked-- I understand that under load AND at speed, the pump may not be able to supply sufficient volume to satisfy the necessary pressures. I was simply attempting to answer the question asked without entering a debate over methods of "outsmarting" the factory recognized test.
Click to expand...

the original question was that his vechicle was running lean..... and im not debating i'm just trying to help diagnose a problem.
 
cruiser54 said:
Then hook up a fuel pressure gauge and go for a ride while viewing the gauge under real world driving conditons..
Click to expand...

yes thats the only real true way to check the fuel pump off your list of lean conditions. whens the last time you changed your fuel filter?
 
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