Fuel Pressure Monitoring
 

How is everyone monitoring fuel pressure?

I came VERY close to blowing my car up on the dyno the other day because of a lack of fuel pressure under boost. I'm looking in to solutions now.

In cabin fuel pressure gauge. Autometer sells them for $180-220. I use this one:
http://www.autometer.com/cat_gaugede...gid=2526&sid=3

if you don't have a fuel reurn system, get one of the fuel adapters for a nitrous kit. It has a 1/8" npt port on it. hook your gauge to that port.

I don't have room for another guage. Has anyone seen a device that warns of low fuel pressure with a dummy light or even an audible notification?

you could go with some thing like this:

http://www.autometer.com/img/products/3239_d.jpg

thenm buy the 30 psi pressor sensor and set the warning light to come on if pressure drops below 30 psi.

the problem is that fuel pressure is very dynamic, especially when you have a 1:1 ratio regulator. you cant really put a warning light on it unless you just pick a pressure like 30psi like he said about. problem is, if your pressure even drops 4-5 psi below where it should be at any given moment, you have problems.

What I would like to do is set up a light to turn on if under 58 psi (my setpoint is 60). It would be nice, also, if I could change the reference point based on boost. :)

It really sounds like you should consider switching one of your gauges out and replacingit with a fuelpressure gauge.

If you have a fuel return system with a 1:1 regulator, your fuel pressure will fluctuate at least 20 psi. about -10psi (approx. 20 in.Hg of vaccum) at idle to + whatever your boosting. if you are boosting 10psi...then, you'd have a 20psi differential.

I think you should get a a defi BF gauge or autometer nexus. both of these have warning and record functions.

I'd recommend the cyberdyne because it has a hi and low memory recall along with a low pressure warning (flashing display), but I don't think the pressure transducer is accurate enough on the cyberdyne. It seems slow to react.

This is the problem I frequently run in to, because I don't want ANY guages. I have a boost guage and an A/F guage now, but neither can be seen while driving. They are only there for speriodic checks (they are under my armrest in my center console of my '04 G35 coupe). My car is my daily driver, and I strive to keep it looking as stock as possible, as to not draw unwanted attention from people who may see/ride in my car

you are a handy guy.

make a gauge pod like mine for the G. People think it's stock. I even had an Infiniti dealer ask me if I'd make more of them. it took me about 2 hours to do this. By using a defi d-gauge, I was able to mount the gauge from behind, giving it more of an OEM look.


http://i7.photobucket.com/albums/y28...5/DSC_0025.jpg

http://i7.photobucket.com/albums/y28...5/DSC_0037.jpg

Usually the fuel pressure drop is caused by over-loosening your FPR adjustment screw, or a vaccum line that is dislodged, or you are in the process of running out of gas. :) Before a dyno session, I always blip the throttle, to insure that fuel pressure is, in fact, rising.

I simple in cabin fuel pressure gauge is a good idea, so you can make a quick visual check while making your dyno pulls. One other note: with our very sensitive siphoning systems, its a good idea to refrain from WOT pulls when your fuel tank is less than 1/4 full.

Hope that helps.

This is a very good point, Sharif.

Most people are not aware that when setting your fuel pressure at idle, there is a point where the fuel return system cannot flow enough thru the return line to get the pressure to go all the way to zero. It will bottom out around maybe 40ish depending on your exact circumstances. If you continue to lower the set screw behind what it can flow at idle, when you start to burn more fuel by driving the actual pressure will fall to the setscrew setting. The symptoms of this will be the idle pressure being higher then your cruising pressure - assuming equal plenum vacuum when both samples are taken (if using 1:1 setup).

Ineteresting that I NEVER thought about gas level. I was below a 1/4 tank. I am not above a 1/4 tank, I'll make some runs on my way home from work to monitor my A/F.

Things I have thought of -

Possible bad pump - tired pump not able to product full output (2 year old pump)

Bad regulator - Not sure how a regulator works, but there must be at least one moving part (spring?) that allows more liquid to flow when there is less resistance (higher duty cycle).

Fuel filter - restrict flow

Not enough gas - Sharif is smart.

Quadcam, I love that guage setup, IF I change anything I'll go that route.

In the mean time, I've came up with a plan to combat all my issues.

I ordered a fuel pressure sending unit that I plan to interface with a dedicated, custom, controller. I'll have a programmable low set point that will flash a yellow LED when fuel pressure is below setpoint. I will then disconnect my boost reference port on my regulator and retune my car. I don't need the boost reference anymore now that I have a UTEC, but I never eliminated it.

If anyone has a good reason why I should leave the boost reference on I have a few extra MAP sensors laying around that I could use to automatically adjust my 'low fuel pressure' setpoint to rise and fall with boost/vacuum.

Boost reference is important for an FI car. Otherwise, you are loosing actual pressure at the injector tip, even though your regulator is set at a fixed pressure. So definately keep the pressure line attached to your reg, so that your fuel pressure will rise 1:1 with boost.

I can't fix that by increasing my duty cycle under load?

All this talk about fuel systems, what's the deal with CJ Motorsports? I called and said there # was disconnected. Trying to get there stage 1 kit.

You can...however, you have to significantly increase duty cyles beyond what what be considered a more linear relationship to RPM and boost, as you have to add additional fuel to compensate for the pressure loss.

You may also find, that even with a larger injectors, you will be reaching duty cycles that are pretty darn high. Lastly, your car will start and idle better with the vaccum line attached, is it will actually reduce fuel pressure and flow for you, to help start and idle the car more cleanly.

CJM manufactures the kit. You can purchase them through CJ, or their authorized dealers. We have them on sale until Dec 15th for $899 shipped.

Sorry, we moved the office and the number on the page is wrong. The new number is 630-270-5457. That is a cell phone that we are using for business for now. If it works out for us, we will keep it, otherwise we will do some phone wiring in the new building.

Of course, we have several dealers as well, essentially every sponsor of the forum here.

OK, thanks guys.