Modify stock FPR?

[decathect]

I know that in the Honda world this has been done...

I know most of you will suggest that I get an aftermarket one. However, for my own purposes, and for the sake of argument, I am wondering if it would be possible to maybe drill a small relief hole in the inner piston of the FPR to relieve the excess pressure from a walbro 255? Right now I think my pump is overrunning my stock FPR and the pressure is too high.

Would this at all be possible? Has this been done before? VFAQ out there about it? (ha, I looked but didn't find one).

THanks!

 

[decathect]

THis is what i'm referring to:

The Old One - Energy Dynamics : Articles

Anyone tried this? I may have to give it a whirl, if its even possible.

 

[jeffo]

If I recall, our stock FPR's aren't constructed exactly like that. The restriction on a stock DSM FPR is the orifice that the fuel must go through after it has gotten past the seat, as it tries to exit the return line. I tried to drill the orifice out, many years ago, but whatever steel they made it of is VERY tough, and all I did was burn up drill bits.
http://www.dsmchips.com/~keydiver/restriction.jpg
keydiver

 

[JayRolla]

1g FPR's dont get overun by the 255lph. I have ran one in two cars and no issues at all on stock FPR. Its the 2g FPR that gets overrun easy. Sometimes a 1g will get overrun if the spring is real weak.

 

[decathect]

well, my low fuel trims are at like 88%... The medium and high are fine, but it seems to be getting a lot too much fuel on low throttle.

I will be installing a fuel psi gauge soon to verify this exactly... at this point its just a strong suspicion.

 

[decathect]

If I recall, our stock FPR's aren't constructed exactly like that. The restriction on a stock DSM FPR is the orifice that the fuel must go through after it has gotten past the seat, as it tries to exit the return line. I tried to drill the orifice out, many years ago, but whatever steel they made it of is VERY tough, and all I did was burn up drill bits.
http://www.dsmchips.com/~keydiver/restriction.jpg
keydiver

so you tried to drill a hole straight thru, right as the fuel from the delivery pipe makes a left turn?

 

[jeffo]

so you tried to drill a hole straight thru, right as the fuel from the delivery pipe makes a left turn?

I don't remember, its been too many years, but if I recall the orifice is not positioned as shown in that diagram. I think I was able to drill it through one of the fuel ports. But it was a waste of time and drill bits.

1g FPR's dont get overun by the 255lph. I have ran one in two cars and no issues at all on stock FPR.

This is so NOT true! I had the RRE Denso 165lph pump on my GVR-4 and it overran the stock FPR, rewired or not. I had the same fuel pressure, vacuum hose on or off. Just because you *can* tune around it with an AFC doesn't mean its right. Have you looked at the orifice size of a stock FPR? I have, and it is ridiculously small. There's no way it can bypass the full flow of a 255 pump at idle or low load. "If the spring is weak" has nothing to do with it, and shows that you obviously don't understand how an FPR works. If the spring was weak you wouldn't get a base pressure of 37psi, it would be lower, as the spring sets the base pressure. Increasing the spring pressure raises the fuel pressure, and less spring pressure allows the valve to open sooner, causing LOWER fuel pressure.
keydiver

 

[JayRolla]

Welll I did learn something about FPR's, thanks.

Its hit or miss, I have never had an issue or a few others I know. Most do not get overrun. Ive used n/a's also with no overrun. I have perfect AFR's and fuel trims within 5%.

To the OP is the fuel pump rewired? I have not rewired my fuel pump and that may be enough to cause the overrun.

 

[decathect]

not rewired.

 

[jeffo]

I have perfect AFR's and fuel trims within 5%.

1) FPR overrun doesn't affect openloop/WOT AFR, and
2) A LOW TRIM that is removing 5% fuel would be 80, the lowest the trims can go, which proves you did have FPR overrun. 5% extra fuel on top of 37psi base pressure would be only an extra 4psi at idle and light cruising, which is VERY easy for a 255 pump to achieve. I'm not saying that lots of people don't do it and get away with it, especially with the fueltrims helping out, or if they have an AFC to tune around it. But, the 1G FPR does get overrun by a 255 pump, which is clearly evident by just watching the pressure gauge while connecting the vacuum line. If it doesn't drop 7-9 psi, it is being overrun.
keydiver

 

[decathect]

thanks for all the help jeff. I may pick up a spare FPR to experiment with this.

 

[JayRolla]

1) FPR overrun doesn't affect openloop/WOT AFR, and
2) A LOW TRIM that is removing 5% fuel would be 80, the lowest the trims can go, which proves you did have FPR overrun. 5% extra fuel on top of 37psi base pressure would be only an extra 4psi at idle and light cruising, which is VERY easy for a 255 pump to achieve. I'm not saying that lots of people don't do it and get away with it, especially with the fueltrims helping out, or if they have an AFC to tune around it. But, the 1G FPR does get overrun by a 255 pump, which is clearly evident by just watching the pressure gauge while connecting the vacuum line. If it doesn't drop 7-9 psi, it is being overrun.
keydiver

Negative. I know openloop is not affected. Lo trim is at 0-4% positive, not negative. Ohh I do have a fuel pressure gauge on my fuel filter. Its solid at 37psi and raises to around 45 when removed. Again I know its not being overrun.

 

[decathect]

wait, why does FPR overrun not affect open loop? Confused about that.

 

[jeffo]

Once the engine actually starts consuming large amounts of fuel, not as much of it needs to be returned to the tank, so overrun is usually not an issue. I'm sure there are exceptions, like a rewired 255 pump with stock 450cc injectors at 10psi, but for the most part overrun isn't an issue at WOT. Also, since the fuel pressure rises 1:1 with boost the fuelpump volume is actually dropping as boost goes up, also reducing the likelyhood of overrun.

 

[1timehondalover]

I overran a stock 1g fpr with a 190lph. It worked fine on my 680cc injectors but had massive pressure when I switched to 1050's.

 

[decathect]

Hrm, what should warm idle fuel pressure be? Mine is right around 36-37 psi. Doesn't seem too bad...

 

[steve]

Its solid at 37psi and raises to around 45 when removed. Again I know its not being overrun.

That's really high for a turbo manual. It should be 37 with the hose off and about 28 with the hose on at normal idle at sea level. Since your vacuum in the Springs is going to be lower the pressure will be higher.

 

[decathect]

looks like i need a little pressure relief Looks like i'll be looking into this mod after all.

 

[dsmfa9nutter]

1g FPR's dont get overun by the 255lph.

I've only heard of people not overrunning the stock fpr with a 255 on the internet (and we all know how true everything is on the internet), I've seen numerous examples of it actually overrunning a stock fpr in person. I chalk this up to be an internet myth that seems to circulate all over the dsm world.

 

[decathect]

yeah, these things get propogated by people who don't know what they're talking about

Its kindof amazing how bad info can spread so rampantly. It makes doing research on the internet very tricky. I usually try to find a bunch/all agreeing opinions before I believe anything I read.

 

[steve]

Its kind of amazing how bad info can spread so rampantly.

What's amazing is how easily incorrect information becomes "fact" and how hard it is to squash them with correct information.

 

[decathect]

Update:

I drilled a relief hole in the stock FPR, size 0.04". It brought the fuel pressure down from about 40 psi to about 34 psi... I might drill the hole out a tad bigger to get it back to stock levels.

Good mod for anyone with a walbro and overrun FPR.

 

[decathect]

The only downside to this that I think i'm finding is that the car takes a long time to start now, since the fuel pressure is so quickly bled off through that relief hole in the FPR.

 

[steve]

It took me a while to catch that what you did was drill a hole to cause the FPR to leak fuel past the regulator.

What the factory does on other cars with larger pumps is implement a two step voltage source (two speeds) for the fuel pump to keep it from overrunning the FPR off boost by dropping the voltage and then feeding the pump full voltage while boosting.

 

[EclipticalGS]

That 2 step voltage trigger would be kinda hard to make. Id just get a afpr for cheap unless you wanna be the furst or whatever to use ## 1g