ErnestSw

With reference to the PET illustration 107-15 there is one "diaphragm damper" (# 5) shown at the front of the engine and one shown on the driver's side at the rear (# 3). There is a "pressure regulator" (# 4) shown on the passenger's side at the rear.
Questions:
What do the "diaphragm dampers" do and could their failure result in a rich condition at high RPMs?
What does the "pressure regulator" do and could its failure result in a rich condition at high RPMs?
I understand that the Rising Rate Fuel Pressure Regulator is installed on the driver's side of the intake. How does this relate to the above devices?

ErnestSw

bump

jeff jackson

the "diaphram dampers" are there to smooth and dissapate fuel surges and tthe natural pulsation of the pressure in the fuel rails as the fuel pump operates, and injectors are fired. The pressure regulator, is to regulate overall fuel pressure, ans is located on the return line to the fuel tank. Hope this helps.

ErnestSw

Thanks Jeff. I'm still confused as to why the pressure regulator is not replaced by the RRFP.

jeff jackson

It IS replaced by the Rising Rate FPR...the dampers remain the same, the FPR is swapped out in this mod.

toofast928

Fuel dampner is used to prevent "hammer" noise in the fuel rail. Similar to water pipes in the house. I deleated the fuel dampner because it could cause a fuel restriction.

ErnestSw

Apparantly I was given some misinformation and the fuel pressure regulator is indeed the one that's replaced.
I ASSUME that the fuel pressure regulator DOWN REGULATES the fuel pressure. In other words, it reduces the maximum pressure produced by the fuel pumps to the proper operating pressure.
If that is the case, could a failure of the pressure regulator cause an rich running condition?
Here's the scenario:
Hi revs, increased fuel pump pressure, rich condition.
Somebody please correct me if I'm wrong.

sublimate

I don't know if it's accurate to say it DOWN REGULATES the fuel pressure.
The FPR is on the return line to the tank. If there was no FPR (or it failed open) then there be next to no fuel pressure at the rails - almost all the fuel put out by the pump would dump right back in the tank. If the FPR failed closed then the pressure at the rails would build to the stall pressure of the pump (very high) and the engine would run very rich (probably not even idle).

A RRFRP closes off the return line (raises the fuel pressure) more at higher rpm (higher manifold pressure acutally, I believe) than at lower rpm. Generally they're used with forced induction. Adding one to a NA engine could easily make it run too rich at high rpm if it raised the pressure too much.

a4sfed928

The main purpose for the fuel pressure regulator is to maintain the same pressure differential across the injector nozzle tip. If the pressure in the fuel rail was to remain at a static pressure then at idle when the intake manifold vacuum is high there would be a larger pressure differential across the injector pintel than when the throttle was stabbed wide open and the intake manifold vacuum is low. In other words its function is to maintain the rail pressure at some value above manifold pressure no matter what value the manifold pressure is at.

FlyingDog

At atmospheric with no vacuum, fuel pressure is 55psi. With full vacuum at idle, fuel pressure is dropped to 47psi. If you have a vacuum leak, you will run very rich at low throttle settings, but it will correct at higher throttle settings.

https://rennlist.com/forums/showthre...highlight=rich

Jim_H

But it should be adjustable. I'm still not clear on whether you actually have a RRFR...

ErnestSw

I don't have an RRFP. I do have a rich condition at WOT as documented on a dyno.

So the stock fuel pressure regulator is on the return side of the loop from the pump back to the tank and the vacuum connection is to a feedback loop that allows the maintennence of an adequate pressure differential when the manifold pressure drops at WOT.
Is it possible for a stock fuel pressure regulator to fail in such a way that it provides too much pressure at WOT?

I just read dr Bob's post stating that "If there's a vacuum leack at the FPR the car will run rich".

But Matt seems to rule that out at WOT.

FlyingDog

If a diaphragm fails in a damper, it could pump fuel into the vacuum line which goes to the intake and makes the car run rich. I'm not sure which would outweigh which... vacuum pulling fuel in at idle or increased fuel pressure pushing fuel not at idle.

ErnestSw

Matt,
Wouldn't running fuel into the intake cause a RICH mixture?

Jim_H

Since the guru's aren't around much on the weekends I will throw out the first thing I would check. Please note I will even post a to myself. Anyhoo I would check my air filterand make sure it hasn't gotten a bunch of crud in there somehow . Maybe you sucked a roll of paper towels in there...