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Old 01-25-2014, 12:07 PM   #1
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Exclamation Insight on fuel delivery, fuel pressure, and related

1994, Naturally aspirated, plan to keep it that way, for now its just a daily street car
rebuilt block, but has 2000 heads, intake manifold, injectors etc..
Megasquirt ecu, AEM wideband o2, AFR gauge already

Ive got wayy to low fuel pressure. like 18.9psi constantly, maybe it twitches up to 20psi sometimes...this reading is based off the digital gauge in my tuner studio. also the car has always had lean running related issues and a twitchy AFR reading, unsteady idle, random cutting out on the highway

Just ordered a new walbro190lph fuel pump kit, new fuel filter and an new adjustable fuel pressure regulator.

Im good for the install of the pump and filter, but having a hard time finding a solid write up on how to install the new regulator and adjusting it to proper pressure just for normal daily driving (naturally aspirated) use.

Any insight here?
What pressure, in psi should i be shooting for?
also any link to a good write up or install video of the regulator would be much apreciated
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Old 01-25-2014, 12:13 PM   #2
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Does your ecu actually measure fuel pressure or did you just randomly check a gauge in TS?

Sounds like you need more tune and less fuel pumps.
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Old 01-25-2014, 12:34 PM   #3
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Quote:
Originally Posted by Oscar View Post
Does your ecu actually measure fuel pressure or did you just randomly check a gauge in TS?

Sounds like you need more tune and less fuel pumps.
Yes it measures fuel pressure. Its a megasquirt PNP gen 1
running the newest version of tuner studio MS
i also have a vacuum line tapped into a vaccum vs boost gauge in the cab
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Old 01-25-2014, 12:37 PM   #4
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Unless you have an electronic fuel pressure gauge feeding a signal to your MS, it's precisely measuring jack ****.

You need to tune the car.
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Old 01-25-2014, 12:39 PM   #5
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Where did you plumb the fuel pressure gauge into the system and how is it connected to the MS?

Agree with Oscars statement above.
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Old 01-25-2014, 12:45 PM   #6
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Quote:
Originally Posted by EO2K View Post
Where did you plumb the fuel pressure gauge into the system and how is it connected to the MS?

Agree with Oscars statement above.
OK. So i guess tuner studio is not properly measuring my fuel pressure. then why am i getting a reading? the needle on the gauge moves a bit and is reading 18 psi.
does the car not have a wired fuel pressure sensor that sends a signal via 0-5v to the ecu?

Edit!
The fuel pressure regulator that i am installing has a gauge mounted directly to it. will that not be a sufficient way to measure the pressure at least at idle??
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Old 01-25-2014, 01:11 PM   #7
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if you want to measure fuel pressure, and have an aftermarket fuel pressure gauge with 1/8npt port, you can buy a 0-5v 0-100psi fuel pressure sender off ebay for $28 and wire it to megasquirt. I've done that and it works great.

Pressure Transducer or Sender 100 PSI Stainless Steel for Oil Fuel Air Water | eBay

Otherwise the reading in megasquirt is just out of thin air
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Old 01-25-2014, 11:51 PM   #8
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Quote:
Originally Posted by soviet View Post
if you want to measure fuel pressure, and have an aftermarket fuel pressure gauge with 1/8npt port, you can buy a 0-5v 0-100psi fuel pressure sender off ebay for $28 and wire it to megasquirt. I've done that and it works great.

Pressure Transducer or Sender 100 PSI Stainless Steel for Oil Fuel Air Water | eBay

Otherwise the reading in megasquirt is just out of thin air
OK. got that and thanks by the way.
But still im not positive on the fuel pressure that i need to run when I install this adjustable fuel pressure regulator, and how to mount it. it has like 4 outlets
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Old 01-26-2014, 12:04 AM   #9
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I don't really see the need for an aftermarket fuel pressure regulator.
The stock one should be able to do just fine with your practically stock engine.

Edit:

Or an aftermarket fuel pump for that matter.
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Old 01-26-2014, 01:10 AM   #10
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I run 80psi on NB injectors. More pressure is good for atomization
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Old 01-26-2014, 02:05 AM   #11
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The MS is probably reading noise or feedback voltage it the circuit or something, just ignore it if you don't have an actual fuel pressure gauge setup. Also check out the MiataTurbo Wiki for all the answers to all the fueling/injector/pump/regulator questions you could possibly come up with.

...except the one about plumbing in your adjustable regulator. The manufacturers instructions should be followed in that case.
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Old 01-26-2014, 09:01 AM   #12
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like they said, you MS is not reading a thing, you need a pressure gauge on the car. You could always rent a fuel pressure tester from your local auto parts store to check. And save your self money on a aftermarket regulator and gauge. Odds are its your tune, bring it to a dyno and have someone experienced tune your car.
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