Peter F

Hi,

I was testing my fuel pressure regulators and dampers with a vacum tester to see if they hold pressure.
The dampers show no movement on the needle after ~30 minutes of vacum applied.
The pressure regulator lost half of the vacum after 15 minutes, there is no fuel or anything visible when pulling the vacum line.
Is this normal or do I need a new pressure regulator?
I have a random issue with the engine starting to run rough, I have a fuel pressure meeter on the rail and at idle it shows~48PSI normally with a steady needle.
When the rougness occures the pressure is down to 42-44PSI and the needle flickers back and forth with the idle speed.

Appreciate some help here.

Thanks/Peter

Mike Frye

Peter,

I don't know what you're supposed to be seeing with the vacuum tester, but if you're intermittently losing pressure and it's coinciding with roughness, it could be something simple, like a clogged fuel filter or failing fuel pump (or more likely fuel pump relay/connections) couldn't it?

How old is your fuel filter?
Does the car sit for long periods of time?
How old is your gas?
Does the car take the winter off and now it's getting ready for spring?

Sorry more questions than answers. It's what I do.

Peter F

Hi NJSharkFan,

no problem with additional questions, appreciate your input here
Yes the car has been sitting over winther but had the same issue last Year.
Both fuel pumps and filter has been replaced last Year.
Recently filled the tank with new gasoline.
LH is new from John Speake and so is the MAF.
I have been tseting with the spanner and get no error codes at all.
This leads me to beleive it is fuel related since that will not show up in the spanner test.

Thanks/Peter

mark kibort

the fuel regulator shouldnt hold any vacuum. that is determined by the throttle body port. as soon as the vaccum is gone in the manifold, the vacuum is gone in the fuel regulator. the pressure the lines keep, is determined by the fuel pump check valve. if you want to check to see if its a fuel regulator issue, pull the vacuum line off it entirely, then see if the car stumbles during idle. if the fuel regulator is tied to the incorrect vacuum source it could exhibit what you are seeing. (ie vacuum booster, vacuum reservoir, etc)

If you are just applying a vacuum to the vacuum side of the regultor, and its falling after 30min, could it be the connection? if it leaks, then of course, what would replace the vacuum would be fuel, or the case around the vacuum side only would be leaking, in which case, that would not be a concern.

mk

John V

Peter,

I think I understand what your saying... your checking to see if the vacuum side of the dampers & regulators are leaking and thereby effecting fuel pressure dynamically. The fact that your regulator leaked down to 15" hg does indicate a very very small leak BUT, the leak may have been in your test setup, the hose connection OR the regulator. Even if it was the regulator, the fact that it took 15 minutes to loose 14" hg makes any such leak insignificant as far as contributing to your original problems. By that I mean, the regulator might still be bad or sticking, but the probelm is not related to a "vacuum leak" of such minimal proportions within the regulator.

Peter F

Hi Mark,

I have been scanning the old threads that I could find on testing the dampers and fuel pressure regulator.
What I could find was two tests, first pull the vacum line and check for any fuel seeping out, this is not the case.
Second advice found was to apply vacum to each of the dampers and regulator one by one and see if they hold vacum.
Dampers do not leak any vacum when tested but the regulator drops half of the vacum in 15 minutes.
The fault is intermittent but has started to show more and more frequently.
Not sure how to proceed to cure the problem.

Thanks/Peter

Peter F

Exactly John, what i see is that the regulator losses half the vacum in 15 minutes.
(So 300mm HG is down to 150mm HG after 15 minutes)
Dampers still show 300 mm HG after even 30 minutes.

Thanks/Peter

mark kibort

You are talking about a total NON issue. the fact that they loose (or the test fitting) vacuum over 15mins, doesnt matter. the vacuum supply is constant and infinite, any slight leak, the throttle body vacuum can conpensate for. meaning, if it looses vacuum over a 15 min period, you are talking about a system that provides vacuum instantly and replace any small leak,instantly. Plus the only real purpose of the throttle body driven vacuum on the regulator, is to pull back fuel pressure at idle and off throttle.
the pressure of the fuel is at near 50psi and the vacuum is either ambient or near zero . so, if there was an isssue, it would be fuel leaking out of the diaphram into the vacuum area.

Mk

Peter F

Thanks Mark,

I hooked up the tester againg and it doesnt leak now so the FPR can be ruled out.
Big question now is what to try next

/Peter

the flyin' scotsman

Peter............considering the amount of work you've put into the fuel system what have you done with the ignition?

Main components:

Coils, Distributor caps and rotors, spark plugs and all wires.

Peter F

Coils new this winter, Distributor caps and rotors, spark plugs and all wires replaced last Year.
So pretty much have been done here as well.

/Peter

the flyin' scotsman

ok...............do you have the stock cats on the car? if so is it possible they're plugged.

How are all the vacuum connections?

Peter F

X-pipe with new race catalysators from last Year with new O2 sensor.
Only thing I can think of in the ignition circuit that has not been replaced is the ignition amplifiers in the fornt left side.
But if they were faukty I guess it should be showing when testing with the spanner.
When tesing the ECU's I get no errors at all.
When tesing the actuators the WOT switch test report time out so that is going to be replaced.
But that should not give issues both on idle and coasting I guess?
I have just gone trough all the vacum and fixed two fault vacum activators in the dash which was leaking.
The blue/black valve at the brake booster has been replaced and the intake has been off last Year and all rubber under was replaced including gaskets.
If I remove a vacum line at the x near the booster i get a loud hiss even after 30 minutes of shutdown.

/Peter

the flyin' scotsman

When the engine runs rough is it cold, warm or both?

Peter F

Most of the time it happends after a short moment of driving.
But sometimes it is directly when starting the engine as well so it does not seems to be related to hot/cold only.

/Peter