I don't know how many times an in car fuel pressure gauge has saved my engine from running lean....

With an FSE regulator, two examples inexplicably after a while started dropping the pressure under full load so that the engine ran lean. I could confirm this with the in-car wideband and the fuel pressure gauge.

Now with an SX regulator, the fuel pressure has for no apparent reason on close inspection, recently dropped from 3.3 to 3.1 bar. This is enough to get the mixture on the lean side of what I want and the knocklink sparkly. I can't see any explanation for the drop, the fuel pump is recently new, but without the gauge I would not have known.

It seems we potentially engineer in unreliability when we use an outboard fuel pressure regulator that is adjustable, even one of good quality like an SX?

I'll keep an eye on the fuel pressure, but I have to say, fuel pressure has been my biggest engine threatening variable that has gone off on multiple occasions or needed a tweak.

 

John, they are very valuable, its probably the only thing i lift off for!

Have you checked the piping to the rails, and reg. If they have been on and off a few times, they could be buggered

 

Piping is pretty good and recent, it is push fittings that look insubstantial, but are rated to 12 bar IIRC and haven't leaked, and hose rated to decent pressure. No leaks/kinks etc.

I wonder if the temperature has changed it, but I would think an SX regulator should be fairly impervious to that.

 

Never had any probs with temp change from my SX reg. Did you use thread lock on the FPR or make sure it was securely locked?

 

John, I have to buy an FSE or maybe an SX with engine mounted gauge soon.
Are you saying that the pressure dropped gradually, ie over weeks, or over a few minutes?
Does the stock FPR change just as much, but you can't see it under 'stock' Subaru condititons, ie no fuel gauge to compare.
You can get a liquid filled gauge to dampen the reading, but if the gauge is not so damped is it sticky hence variable readings?

If the pressure can change by, say 5% of nominal (setting at mapping date) shouldn't the map be set high/low to accommodate such a variation howsoever caused?

I have no answers, just questions I'm sorry to say, but fuel/pipe temperature must play a part and much more remotely the volts feeding the pump. A hard volt drop will change the pressure to the FPR, but smoothing that out is exactly ewhat it is there for! Do Walbro's run at 12v or 9v (to the motor)?

911

There is a £100 ticket between the FSE and the gauged SX, so which one?

 

Pay the extra for the SX! I had an FSE and it started to play up after around a year! Replaced it with the SX now. As John has said, he has had 2 FSE ones fail on him IIRC, and many others have had faulty units too. It seems they are OK on very lightly modded cars, but struggle when boost is around the 1.3bar area +
Is damaging your engine worth risking for an extra £50 ??

MEF seems to have a few for sale lately for £150!

 

Sold!
It was mef's deal I was thinking of in answering this thread.
Thanks, 911

 

Weather permitting, I should be fitting a fuel pressure gauge this weekend. What do any of you recommend for any min or max values I should be setting for my warning light to come on? It is a SPA gauge btw.

Damian.

 

Not gonna bother putting my FSE on then ..... guess i'd best go for an SX to save my engine not pennies.

 

£100 difference between FSE and an SX?? think your buying from the wrong supplier.....................more "deals" around than you'd know..........

alyn - asperformance.com

 

Damian, depends what your fuel pressure is set at?

 

FSE state quite clearly that their FPR is intended for aplications up to 5 bar. For the SX I think it is 6 bar. So it depends how much fuel pressure you want to run over boost. For instance if you plan to run and map for 3.5 bar over boost then you need fuel pressure of 5bar at 1.5 bar of boost. Remember this is set up with the vacum pipe disconnected.
Not many cars run fuel pressure guages in the cabin but on an engine running on ten tenths it is important. I had a problem which took weeks to cure and in the end I am not totally confident I ever found the real cause. The car is fitted with a SPA digital FPR which is very accurate and quick. While running hard, mapping at Bruntingthorpe, Bob detected a momentary lean spot. It was barely discernable. It was not consistant. It was there on full load from time to time. It coincided with a drop in fuel pressure from say 5.6 to 4.9 bar all within half a second and back to 5.6 bar. Unpredictable and momentary. I think knock was recorded sometimes.
I did all sorts. Changed to a bigger Bosch pump, replaced fuel lines, drilled holes in the fuel cap, borrowed another SX FPR from RCMS, ran full tank, half tank and any other tank you want. I had a bullet in line fuel filter and swapped that for the O/E and the problem stopped.
My conclusion was that the horizontal filter was trapping air bubbles out the fuel and they were passing in a slug from time to time. Still not sure that was really what was causing the problem but without the SPA FP Guage the problem might not have been solved.
Hope this is helpful.
Anybody want to buy a cheap bullet filter with spare cartridges?

 

Steven, I hadn't threadlocked it, but the locknut needed a spanner to loosen it.

I think it happened over the course of a day as I usually at least glance at the AFR gauge when first booting it to check it is richer than my preferred AFR, and it wasn't today, but about 0.4 AFR points leaner, normally it is very consistent indeed. Then I looked more closely at the fuel pressure and saw it was 0.2 bar less than what I'd mapped it for. This tallies up roughly with the change in AFR, and correcting it sorted it. Previously it has been very consistent. Why it changed I don't know. I do now occasionally have a lean spot sometimes with knocklink sparkle that wasn't there at variable areas from 5800 to 6600 RPM approx, you can just see the wideband go lean by 0.5 AFR points, but it isn't reproducible. I'll keep an eye on it, and maybe renew the fuel filter if it seems to be a problem, although it is an OEM one it is not recent and has had methanol and NF through it previously.