external fuel pressure regulator question

Z

zooracer

New member
I have a non-adjustable fuel press. reg. on my swift that is permanently attached to the fuel rail. My car runs lean, so I am going out to buy an AEM universal fuel press. reg. to install inline with my stock regulator and rail.
I was going to install it in the return line to the tank, after the stock rail/regulator.
Will this help with my lean condition?
And, is this proper install? Is it okay to leave the stock regulator on and functioning? I've heard different opinions on this one...
Also, the AEM unit runs about 170, and I would have to find AN 6 nipples for it to hook up my fuel lines to. Anyone know of a cheaper, but still adequate unit (preferably one here in the U.S.)
Thanks
matt batson
 
You can use 6mm hose directly into the -6 nipples on the regulator. No need for - line.

If you leave you stock regulator in position, you new one will do nothing! Remove the stock unit, cut in half just below the rolled joint removing all the internals, and weld/braze a plate over the top. That way you have the stock unit straight through and the aftermarket can work. Good Luck, Chuck

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Chuck Baader
#36 ITA E30 BMW
Alabama Region Registrar
 
We discussed removing the OEM regulator over on the Mazda forum and there are 2 strains of thought:
1. Since you can use an aftermarket regulator (and pump) and it won't work right w/o removing/disabling the OEM one, you can necessarily do so [one guy was even talking about fabricating a custom fuel rail]; and
2. No where do the rules say anything about removing/disabling the OEM regulator so you can't.
No. 1 makes logical sense but, as we all know, . . .
This needs to be clarified.


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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
Okay, I understand about cutting the regulator off and removing, but will have to take it to someone to weld a plate on.
I was hoping to leave everything on the car as is, and untouched.
This would make it easy for me anyways.
I mean , if it will work without going through all the trouble of removing the rail, cutting it, and taking it to someone for welding, then I would rather just leave it all installed and just use the AEM regulator to help pull more fuel through.
But, if it will not work with the stock one installed, then thats another matter altogether.
 
If the stock regulator remains, the AEM will do nothing because the pressure is being regulated before the fule gets to the AEM. While I understand the rule interpertation, there are regulators that sit on the rail just like the stock one that are adjustable. They just cost more and are not as reliable...go figure!! Chuck
 
Carburated and fuel injection are very differnet animals. Carbs are down stream of the regulator where as fuel injectors are up stream. Most electric fuel pumps for carburetor use have built-in pressure regulators. These are usually set at 3 to 7 psi to prevent over riding the float and flooding the carb. Therefore the regulator is mounted before the the carb.
Fuel injection systems are realtively high pressure systems. In order for the system to operate properly the injectors need a steady flow of properly presurized fuel to atomize and spray the correct amount of fuel into the manifold. Therefore the pressure regulator MUST be after the fuel rail. If you mount the regulator in front of the fuel rail the injectors will be in the low pressure return flow, and probably won't even run. On most OEM fuel rails the factory regulator is in the return port of the rail.
Adding an aftermarket regulator with a higher pressure setting in the fuel return line will effectively negate the factory regulator. If you wish to lower the fuel pressure below factory setings then the factory regulator would need to be disabled.

I hope this is clear as mud.

Chuck
ITA Fiero #34
 
Chuck, I think you got that last sentence backwards since the added reg. would be after the stock unit. Therefore, it would have no effect if set above the stock unit. If set below the stock unit, it would reduce rail pressure assuming you are using largen injectors...also not legal. Chuck
 
if first regulator is set to 30psi and 2nd is set to 35, the fuel exiting the first regulator will back up til pressure reaches 35-all the way back to the pump. If the regulators are risng rate (manifold vacuum modulated) then you should send a vacuum signal to both because fuel pressure will vary in each over a range of 10psi or so. Until you raise your setting by more than that amount, the 1st regulator, without a vacuum signal, will predominate at idle/part throttle, making the sytem richer in those areas and lessening the range of load compensation.

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phil hunt
 
Ok, so here it is.
I have a lean running motor. If I add this AEM regulator, by splicing it into the return line, will this help me get more more fuel at WOT?
I assumed that even with the stock regulator in place, it would get me more fuel at WOT. Am I wrong?
thanks for all the help
 
if the swift has a vacuum modulated regulator (most likely) then you should also use an adjustable vacuum modulated regulator downstream of it to raise the range of fuelpressure which will uniformly richen the engine over all circumstances in a linear fashion. If the stock regulator is vacuum modulated and you add a fixed rate adjustable regulator, the engine will run richer at full throttle in proportion to the amount you raised the full load pressure, but it will run even richer at lower loads and idle because the engine menagement is calibrated/programmed to work with a regulator that lowers the fuel pressure depending upon manifold vacuum (rising rate regulator keeps the pressure diffence between the fuel rail and the injector nozzle constant and eliminates manifold vacuum from influencing fuel flow).
Doing this should reap huge returns in fuel tuning and get you 90% of the way to nirvana. Expect to find that when you get top end (peak HP)fueling right by raising pressures, that low end area (peak torque) will be somewhat rich and a tradeoff. Total nirvana is found in chip tuning where a non-linear adjustment can be made.

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phil hunt
 
Ok, great. My stock one is vacuum referenced, and the AEM is too. Along with being adjustable.
One more quickie is, where do I find the male AN -6 fittings so I can fit my fuel lines?
 
Originally posted by zooracer@Aug 8 2005, 01:03 PM
Ok, great.  My stock one is vacuum referenced, and the AEM is too.  Along with being adjustable.
One more quickie is, where do I find the male AN -6 fittings so I can fit my fuel lines?
[snapback]57929[/snapback]​
Click to expand...
 
most auto parts stores and hardware stores will have brass nipples, AN/NTP tapered pipe. If not-truck shops/truck parts stores will surely have them OR: spend big bucks for aluminum ones at a recers stor OR: just put in NPT/hose nipple and use good quality 7mm id fuel injection hose (BMW or VW/
audi) and mini-clamps. I'd take the last option.
 
Hey Matt,

Quit fooling with the fuel injection, bolt on a pair of Weber Sidedrafts and come play in GP! :023:

I'll help you tune the Webers.

MC :eclipsee_steering:
 
Originally posted by pfcs@Aug 5 2005, 10:32 PM
if first regulator is set to 30psi and 2nd is set to 35, the fuel exiting the first regulator will back up til pressure reaches 35-all the way back to the pump.
Click to expand...

Ummm . . . unless I've totally forgotten my rudimentary introduction to fluid dynamics . . . in this scenario, the pressure at the fuel rail woud be 65psi. Pressure regulators assume output side to be at 0, so a 30 behind a 35 would add 30 to the perceived 0 - which is really 35.
 
Ok guys, I assume (bad thing) that all regulators are basically the same. Fuel pump producing 30 to 100 psi fuel pressure. Fuel line from the pump to the fuel rail. Fuel injectors feed from the fuel rail by either diret connection or delivery tubes. Fuel flows from the pump through the line into the fuel rail and then encounters the pressure regulator. Regulator has an inlet passage, a diaphram with a pressure spring setting on it, an adjustment screw on top the spring to vary the pressure, most OEMs don't, (some have multiple presurized outlet ports,) and the return port. The diaphram remains closed until the fuel reaches the desired pressure at which point the diaphram is pushed off it's seat allowing fuel to flow out the return line. Since the injectors are using some of the fuel that is flowing through the rail the pressure will pulsate, and the diaphram will open and close rapidly to maintain a constant pressure. On GM products (the only brand I have hands on expierance with) the vacuum port is on the spring side of the diaphram. and is only effective during closed throttle conditions. If you remember your basics, vacuum is lowest in a normally aspirated engine during wot. Vacuum is highest during high rpm closed throttle. On the GM products the vacuum port is used to dump fuel pressure during high speed rapid decelleration to prevent overly rich exhaust from going into the catalitic converter. I just purchased a Mallory modle 4305M pressure regulator, and reading the data sheet that came with it says "This regulator is equiped with a vavuum compensation port that can be used to momentarilydecrease fuel pressure at idle and part throttle." Low vacuum such as during wot acceleration have no effect on the fuel pressure regulator. Most aftermarket regulators use the same port for vacuum or pressure sensing. On turbo/super charger systems bleed pressure is used to actually increase the fuel pressure by pressurizing the spring side of teh diaphram.


No Chuck I do not have it backwards. The highest pressure regulator in the system will control the fuel pressure up to that point. Factory regulator set at 30psi followed by an aftrermarket regulator set at 45psi equals all fuel in system at 45psi. second regulator overriding the first. Factory regulator need not be removed to get desired 45psi. If the desire is to reduce the fuel pressure and you have the OEM regulator in place at 30 the add an aftermarlet regulator set at 25psi pressure up to the OEM regulator will still be 30psi, the fuel between the OEM regulator and the aftermarket regulator will be 25psi. The engine will still see the factory setting of 30psi. If you desire to lower the fuel pressure below the factory setting, the OEM regulator must be removed, or at least the aftermarket regulater must be installed in front of the OEM regulator.

Chuck
ITA Fiero #34
 
if pumps are installed in series, pressure capacity is additive; if in parrallel, volume is cumulative. not so for regulators. that said, I'd prefer to see the stock regulator eliminated anyway-its just another thing to go wrong/confuse a diagnosis, etc.
 
oops. Shot myself in the foot. delete the last half of the last sentance. For pressure lower than OEM the factory regulator MUST be removed.

I agree Phil, but the rules nerds say it must remain.

Chuck
 
hey mark, glad to hear about your newfound speed with your VW.
Funny how just when you thought you had a car developed to the hilt, there is something else you can do and gain like 4 seconds a lap!
I am definitely planning on moving up to production, just not right away.

I can barely afford to race in ITB as it is, so moving up to GP will break the bank.
The biggest expense I can see is the tires in production, as they cost more and dont last as long.
But, after I win the ARRC next year I will probably be able to afford the move up.
B)
matt batson
 
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