fuel pressure gauges only go to 100 psi. DOH! - Miata Turbo Forum - Boost cars, acquire cats.

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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 03-04-2008, 05:23 AM   #1
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Default fuel pressure gauges only go to 100 psi. DOH!

What's the point of a fuel pressure gauge if it stops at 100 psi?
I was thinking of getting a FP gauge since I'm going to be running a rising rate FPR, and according to the DIY FAQ, with the way the Greddy kit comes out of the box at 5 psi and the 12:1 FPR I'm going to be running 110 psi. Yea, that's high. Yea, that's technically above what the fuel pump should be running... so if the pump isn't able to do it and isn't supplying the full pressure I'd like to have a FP gauge to know the motor isn't getting as much fuel as it should be. One problem - every gauge I've found goes to 100 psi!!! WTF...

Question: does having a wideband AFPR gauge eliminate the need for any fuel pressure gauge? I plan to get the LC1 eventually...

I was going to do a nice hood-mount with a gauge pod/cup on the hood... would be cool and useful if I could find a guage that'd actually have a useful range....

-Ryan
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Old 03-04-2008, 06:09 AM   #2
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The reason you wouldn't want to run more than 100 psi... Fuel lines bursting and causing engine bay fires. Stuff like that...

You wouldn't need a fuel pressure gauge if you got a wideband. Just tune it by AFR and not max fuel pressure. It's much safer that way anyways.
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Old 03-04-2008, 06:36 AM   #3
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I know that it's far better to run larger flowing injectors and therefore needing less pressure to attain X amount of fuel. My point is that the Greddy kit COMES like this - anybody who buys the kit and installs it should be hitting 110 psi by the math.

Yes, a wideband allows you to tune the car to attain the proper A/F ratio. Doesn't really apply here as the greddy kit has no tuneability. My question is more, should I have both the wideband A/F and a fuel press. gauge so that I can know exactly what each are at? especially since the greddy kit demands alot of fuel pressure out of the box.

My point of considering a FP gauge is that if the FPR or the fuel pump fails, I can see that on the gauge immediately - instead of finding out by some terrible noise or the motor seizing...

-Ryan
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Old 03-04-2008, 09:06 AM   #4
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you might be able to see if the FP drops, but surely still have no clue what your AFR is. it may be 12:1 or 11:1 or 10:1 or 9:1, you have no clue.

if you need a gauge, find a local hydraulics shop and give them $7.
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Old 03-04-2008, 09:19 AM   #5
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The stock pump can only put out 75 to 80 psi nomatter what ratio your fpr is..

and if your fuel pump fails suddenly, the engine will just turn off, no harm. Now if it slowly decreases fuel pressure, youll run way lean.
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Old 03-04-2008, 09:21 AM   #6
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Unless you replace the stock FP with a high pressure one, the GReddy kit as designed will only take your FP to the pump maximum of 80psi.

I have found that a boost gauge and FP gauge mounted next to each other will form a set pattern of increase that will suddenly get your attention if it changes.
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Old 03-04-2008, 11:04 AM   #7
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Your looking autoparts stores I bet. As said, find your local hydraulic/rubber supply store... most carry a product line from Dixon. Put you city in the place in your Profile that asks for it and I can probably recommend a place.

When I was running high fuel pressure, I simply replaced all my rubber fuel lines with brand new rubber (from same hydraulic shop) rated to 300psi.
The lines are real easy to reach. There are a couple coming out of the fuel pump assembly on top of the tank, and a couple small ones at the fuel filter... and then whatever you've got in the engine bay. It's about $8 worth of hose. For peace of mind.

Also, your same hydraulic/rubber shop should have mini-tbolt clamps... DON'T USE CRAP WORM CLAMPS!!! They come in boxes of 12 or so... don't forget to put those clamps on the fuel filter and on the assembly at the tank on the feed line.

I was running over 130psi of fuel pressure on my OEM 15yr old hoses before I got smart and replaced them... lucky I didn't have any fires. Then I got bigger injectors and could turn pressure down under 100psi.

Get yourself a set of 1.8injectors or even some Toyota 305-330cc's... for sale in the classifieds all the time.
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Old 03-04-2008, 11:39 AM   #8
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Having said that I fully agree with the wideband AFR recommendation, here are some affordable pressure gauges that read > 100 PSI:

120PSI, NOS brand: http://store.summitracing.com/partde...5&autoview=sku

150PSI, Autometer brand: http://store.summitracing.com/partde...5&autoview=sku (there are many different styles of this one)

Both of these are mechanical, so either outside-mount or they'd need an inline isolator.
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Old 03-04-2008, 06:12 PM   #9
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sooo... the 12:1 disc the greddy comes with is pretty much a joke, huh? I mean, even at low low boost it pusher the fuel pressure higher than the pump can supply it...

I'm adding a MS and wideband down the road - I'm just trying to get a reliable setup for the first 6 months or so on the base psi before I add the parts to go higher...

-Ryan
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Old 03-04-2008, 07:29 PM   #10
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Quote:
Originally Posted by ThePass View Post
sooo... the 12:1 disc the greddy comes with is pretty much a joke, huh? I mean, even at low low boost it pusher the fuel pressure higher than the pump can supply it...

I'm adding a MS and wideband down the road - I'm just trying to get a reliable setup for the first 6 months or so on the base psi before I add the parts to go higher...

-Ryan
Yes, it was engineered for the base kit that bolts on for a few psi and CA Carb. If you go to a higher output pump, you need to swap out discs.
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