Im going to start logging fuel pressure

[AutoMods]

kinda nerdy but I'm excited to start logging fuel pressure. picked up this sensor for $30 . need to find out why my car is running lean sometimes under full throttle while other times it doesn't.

Could be anything since my whole fuel system is new (e85, injectors, new dual pump custom setup, new lines/filter) . I wouldn't think this would be likely but maybe my fuel tank can't keep enough fuel around my dual internal pumps. plus I'm needing a lot more fuel in general so my fuel rails and smallish regulator might be having trouble.

Its nice to be able to log stuff like this with tuning software. Can't imagine taking my car to get dyno tuned and then never looking/logging whats going on with your car. or even worse a mail order tune :(


Brand new pressure transducer.
Input: 0-100 psi.
Output: 0.5V – 4.5V linear voltage output.
Works for oil, fuel or air pressure. Can be used in oil tank, gas tank, etc.
Accuracy: within 2% full scale.
Thread: 1/8” NPT.
Wiring connector: water sealed quick disconnect. Mating connector is included.
Wiring: Red: +5V. Yellow: ground. Green: signal output.

179

[slow ride]

Ryan, are you still running the factory fuel rail?

[AutoMods]

yea stock rails. I do have an in dash fuel pressure gauge with peak hold but its hard to watch when driving. Pressure should be 58psi + 10psi for boost. Peak hold/recall does show 68 psi but that doesn't mean it didn't hit peak and then back down near redline. Tried to have greg watch the gauge but we kept losing traction in 4th gear and then the gauge flutters because boost flutters with traction loss and I have to lift the pedal some. I'm going to try to put the boost down to 6psi so I can keep traction and see if it goes lean at 6psi.

I'd throw the mt's back on but I have to raise the coilovers and i'm kinda lazy. just need to buy some nice radials

[AutoMods]

wasn't 100% sure what the formula was to make my tuning software convert the voltage to psi so did a test and here is what the 0-100psi sensor output

voltage-----Air Compressor Gauge-----1.5" Liquid Gauge
--------------------------------------------------------
1.47v-----30psi-----24psi
1.91v-----40psi-----35psi
2.36v-----50psi-----46psi
3.57v-----80psi-----77psi
4.35v-----100psi-----97psi
4.48v-----???-------100psi

Not sure but I'm guessing the 1.5" liquid gauge was more accurate because it is 0-100psi vs the air comp gauge was 0-200. Also note the 1.5" gauge and sensor was at the end of a 50 foot air hose so not sure if there would be a pressure drop there.

Anyway looks like the formula may be psi = (voltage-.5v)/.04 .

180

[AutoMods]

here is a log of my fuel pressure with my pump running but car off (tuning software can do that) . Pressure goes up and down about 6psi. although with the car running and driving it does smooth out a little probably because more fuel is being consumed and less returned by the regulator. Base pressure is 58psi and it seems to cycle 55psi-61psi most of the time

click here to view the log
184


Anyway so far it appears that my fuel pressure is where it should be and I think my lean issue is not due to lack of fuel up in the rail

[SLVR7]

Just because there is pressure doesn't mean there is volume, don't rule out lack of fuel yet.

[AutoMods]

I would think a lack of volume would cause a drop in fuel pressure

[SLVR7]

Not always, I've had plenty of vehicles pass a pressure test but have no volume, happens on gm vortec motors often.

[Batwood]

Not always, I've had plenty of vehicles pass a pressure test but have no volume, happens on gm vortec motors often.

x2.

Last fuel pump I did in a 4.3 only gained 2-3 psi on the gauge. And it was within spec before, but wouldn't run.

[AutoMods]

if you pressure test a vehicle at idle, that requires very little volume and so yes it could pass a psi test at idle and not produce much volume. But if you tested that same car/setup at wot under high volume requirements, the psi would drop if the pump isn't putting out the volume it should be. Your tests probably do not allow you to drive the car and view psi but my sensor does allow me to test fuel pressure on the go at wot under high volume requirements .

[SLVR7]

I tape the fuel pressure guage to the winshield and drive it. I'm not saying that is your problem, just don't rule it out yet. I'm running e85 with 10000cc's worth of injector at 78% duty at 90psi, I've been through lots of fuel issues, you might be suprised what can happen.