Fuel pressure not constant

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dakotaprerunner
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Joined: Mon Mar 29, 2010 9:41 am

Fuel pressure not constant

Post by dakotaprerunner »

Hello everyone,

Here is a screen shots from two different logs on my newly MS3X'd truck. The factory manual for this dodge says I should have around 50 psi at the rail. Any thoughts?
elutionsdesign
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Re: Fuel pressure not constant

Post by elutionsdesign »

Other than a lack of context, no. Need the entire log posted as many factors come into play. Depending upon where the injectors discharge is huge, for example. And the screen shot "seems" to be noisy but if the y-axis is only a couple of psi maybe not.
Graduate of EFI University.

I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
dakotaprerunner
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Re: Fuel pressure not constant

Post by dakotaprerunner »

Sorry for the lack of detail. I was trying to post in a hurry before dinner. The Y axis is from ~38 to ~60. I'll increase the sensor lag and smooth out the signal. I keep trying to upload the log file but the forum says that there is a file size limit... I'm thinking that the problem is more hardware related than MS3X related. I think my stock in-tank pump/regulator needs to be replaced. Just curious if anyone else has seen a similar situation where the fuel pressure is has a 20 psi increase over 15 or 20 minutes of driving. I'm also going to try hooking up the pressure transducer to a pump and FPR on the bench and see if i get a constant reading.

Connor
piledriver
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Re: Fuel pressure not constant

Post by piledriver »

dakotaprerunner wrote:Sorry for the lack of detail. I was trying to post in a hurry before dinner. The Y axis is from ~38 to ~60. I'll increase the sensor lag and smooth out the signal. I keep trying to upload the log file but the forum says that there is a file size limit... I'm thinking that the problem is more hardware related than MS3X related. I think my stock in-tank pump/regulator needs to be replaced. Just curious if anyone else has seen a similar situation where the fuel pressure is has a 20 psi increase over 15 or 20 minutes of driving. I'm also going to try hooking up the pressure transducer to a pump and FPR on the bench and see if i get a constant reading.

Connor
Not unless the pump does pressure control or has a load reducer setup, doubt it in your case.
Plot your battery voltage as well. Might correlate.

Long logs get huge. zipping them up does wonders, but has its limits.
If on MS3 you can limit what you log on the sdcard... usually to increase the log rate.
~400hz is doable.
Always doing things the hard way, MS2 sequential w/ v1.01 mainboard, LS2 coils. 80 mile/day commuter status.
billr
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Re: Fuel pressure not constant

Post by billr »

Get a log of the pump with engine not running, use "fuel pump test", that will show if noise on that sensor line is increasing due to spark or injector operation.
ol boy
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Re: Fuel pressure not constant

Post by ol boy »

Just a thought... is the regulator vacuum referenced to the intake? If it is then under idle conditions the pressure we be reduced to keep the 50psi across the injector. At WOT to pressure will come up to 50 psi as the intake is at zero psi. You still get your 50 psi across the injector. If it was boosted then you'd see the fuel pressure increase with boost. 10 psi boost will need 60 psi to keep the same delta across the injector.
306 SBFord, Torquer II EFI intake, 60 lbs injectors, 8 LS2 coils, VS Racing 7668 turbo, 4R70W, MS3x fw1.4 w/built in trans controller.
piledriver
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Re: Fuel pressure not constant

Post by piledriver »

"...manifold referenced FPR"
Good call.

A short zipped up log and msq would probably provide quick answers rather than WAGs...
Always doing things the hard way, MS2 sequential w/ v1.01 mainboard, LS2 coils. 80 mile/day commuter status.
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