Adjustable Fuel Reg Problems.

[DanielH]

Hey guys having troubles with my fuel system.

I have an rb25det in a VS commodore with 300rwkw, all built and tuned myself.

I have always been running a cheapo eBay fuel reg, and never had a reason to worry about it with years of running a stock rb20, now that it's tuned I have noticed a problem with having to have a very steep fuel map, and only just being able to get enough resolution on the map to have somewhat reasonable cruise AFR's and enough fuel on full boost.

I did some troubleshooting with a good fuel pressure gauge, and have found that my fuel reg does not drop fuel pressure at idle by more than 1psi, observed by removing the vac line while its running.

The other interesting thing is that going onto full boost (21psi) the fuel pressure only increases by 10psi.

Naturally the first conclusion I came to was a shitty cheap fuel reg is my issue, so I changed on a sard reg (not sure if genuine or not, I've had it kicking about for about 5 years) and retested and it behaves EXACTLY the same!

I expect never to get a good drop in pressure at idle because im running big cams with a big overlap, as a result I don't pull much vacuum at idle (6 in-hg roughly), but I'd of thought I would see more going on than 10-11psi difference between idle and 21psi of boost.

Here is the basic mod list:

Stock rebuild with forged pistons, stock compression, cams etc etc

Greddy copy intake

High mount turbo setup, gt3076

Nistune ecu

HKS fuel rail

GTR injectors

walbro 450lph pump intank, running factory wiring, triggered by ignition.

Stock 8mm hard lines from tank.

The reg has a direct free flowing hose 30cm long straight off one of the bottom ports on the greddy intake, tested and proven.

Have I got 2 shitty regs that both behave exactly the same, is this somehow normal or could I have an underlying issue elsewhere?

Thanks in advance!

Edited January 18, 2015 by DanielH

[GTSBoy]

Check voltage at fuel pump when under load. Factory wiring might be strangling it.

[R31Nismoid]

Yeah sounds like fuel pump.

Begs the question though, stock fuel reg is more than adequate for your application. You can push another 100rwkw before you'd need to think about changing it.

So keep that in mind if you have issues with it later on, go back to stock.

[chiksluvit]

Got a stock fuel reg adaptor for external mounting if you wanted to try that. Having also used the generic fpr, I haven't experienced any problems with it either

[DanielH]

I never thought about using an adaptor to mount a stock reg, bit hard otherwise with running the hks rail and top feed injectors, I might have to hard wire the pump with some better wiring and see if that helps

[KiwiRS4T]

There's at least two tutorials on this site on how to directly wire it. (oops may not directly relate to your Holden). But yes I'm still using the stock regulator - more reliable then many (of course not all) aftermarket regs.

[scotty nm35]

Where is the vac line connected?

The Walbro pumps require 20 amps, so make sure your direct power feed is sufficient (40 amp relay at least)

They also flow massive amounts of fuel, if your return line is restricted (most cars are) you will have issues running low fuel pressure. What was the base pressure by the way?

[DanielH]

Connected to one of the vac ports on the greddy plenum with a dedicated hose.

well if I set the pressure to 40psi with pump on, engine off, it jumps to 43 psi with engine running with/without vac line connected, kind of backs up the restricted return line theory as the pump will run harder with the alt charging, gonna be even worse when I change my alternator for one that charges properly if that's the case!

Edited January 20, 2015 by DanielH

[Badgaz]

43psi is what you want though isn't it? and the return line should cope with the amount of fuel being bypassed at idle.

[DanielH]

No what I want is for the pressure to drop at idle/vacuum and increase 1:1 with my boost pressure, I'm having a hard time getting my fuel map right, it's not lean enough at low load with the map zero'd (as low as it will go) and its only just maxing out the injectors/getting good afr's on boost with the map on the highest figure.

[Badgaz]

have you tried changing the injector scaling at idle so it achieves the correct lambda and then correcting the rest of the map?

[DanielH]

That's what I have done, as I said I have got the full boost portion of the map right on the highest value that can be used in the nistune, I can't scale the map any lower.

I can confirm I had a power supply issue and probably a return line restriction because I have rewired the pump with its own direct power supply/relay and its jumped from 40psi base pressure to 60psi

[DanielH]

And it won't go any lower ^^

[Badgaz]

i'm not talking about the map values i'm talking about the injector sizing value.

[GTSBoy]

i'm not talking about the map values i'm talking about the injector sizing value.

Yuh, but it's still the same problem. For whatever his K value is right now, he has the idle section zeroed out (and can't get any leaner but needs to get leaner) and he has the upper end of the map at max enrichment (and therefore can't get any more fuel into it and may need to do so). So if he were to change K up or down he would only improve one or the other of those two and make the other one worse.

[Badgaz]

But maxing the injector not the value as i understood it at the top end of the map.

[DanielH]

The injection multiplier (K value) is the one main correction for everything, injector/maf size, fuel pressure etc. etc. all effect this value, it is used to get everything in the ballpark and then the fuel map gets you going from there, if I get the reg working perfectly or close to it the fuel map should be easy to get right, with room left on the map.

Later commodores use a quick-release fuel line fitting which turns out has quite a restrictive end on the fitting, I drilled that out and I can get 50psi with pump on/engine off which is probably good enough.

I'm going to run it on the dyno again and see how the fuel pressure behaves and if its better, redo my fuel map, I'm much happier with how the pump is running now that it's rewired!

Thanks for the help so far!

Edited January 21, 2015 by DanielH

[scotty nm35]

I found a 4mm return line restriction is the minimum requirement for a 460 Walbro, I had to drill the Vac generator in the evo tank to pass enough back (so I could run 35psi at idle) If you are still having issues, try dropping the return into a bucket and see if the pressure drops, then work your way back. If the return line is squashed or crimped under the car it will restrict similarly.

Remember, when the decel fuel cut occurs the pressure will raise higher, and probably leave you with a slight rich spike when the injectors kick back in. Drill more than you need.

[DanielH]

I found 2 restrictions (holdens quick release fuel line fittings) which had about a 4mm hole in the end, I drilled those out to 6mm on both fittings which helped with the high pressure, but the reg is still not creeping high enough on boost.

I have got my fuel map to the point where it's usable and it will do for now, powercruise is on Saturday and I have too much other stuff to do before then. After that I may be able to do some more testing and figure it out.

Interestingly the fuel pressure spikes to 75psi before settling to 70 the way I have it at the moment, base is 60. But this is pointing towards a possible flow issue, I would think? As boost comes on the reg is applying more restriction to the fuel rail but the injectors suddenly start to swallow a whole lot more fuel.

[scotty nm35]

If you can't drop the pressure to 35psi at idle, there is still a 2mm restrictor in the line somewhere. Check in the tank, the quick release fittings are fine and not the problem. Anything smaller than 4mm you need to drill out