2009 Escalade - takes a while to start but idles and drives perfect

[Alvin]

In the video the fp dropped a psi or 2 which my screen shot shows. Boost drops off a little to pull the delta back in my favour.
You'll need to dig into this when you have time. You should see what I'm claiming is 100% accurate. The GMW standards document I have for the fpcm also backs up my claim. The reported fuel pressure is based on an internal calculation which models the fuel pressure drop in the fuel system. Raw sensor volts tell the real story.

Do you happen to know y=mx+b for that fuel pressure sensor?

[hjtrbo]

Do you happen to know y=mx+b for that fuel pressure sensor?

Yes, psi = (27.809 x Volts - 20.717) + (baro - MAP)

And the excerpt from GMW 8774. I can't attach the whole doc here, DMCA and all.

[Alvin]

Yes, psi = (27.809 x Volts - 20.717) + (baro - MAP)

And the excerpt from GMW 8774. I can't attach the whole doc here, DMCA and all.

I understand. Sounds like the FPCM will always estimate lower FP than actual as it is only "subtracting a calculated fuel line pressure loss"

There is no chance you are accidentally having your Baro updated because of boost? I don't know your setup but there are plenty of GM OS's that will update the baro to some higher pressure after seeing boost the first time per drive cycle.

I will test this out. But I'm going to test calculated pressure vs reported pressure. I'm going to leave injector delta P out of the equation.. Just RAW what pressure is vs. what pressure is reported to be.

[hjtrbo]

I will test this out. But I'm going to test calculated pressure vs reported pressure. I'm going to leave injector delta P out of the equation.. Just RAW what pressure is vs. what pressure is reported to be.

Will be good to see what you find. E67 factory LSA. The N/A Holdens I've played with don't show the issue. Unknown if it's flow rate or OS dependant. But it's something to add to the memory bank if one comes along one day logging a horrible reported fuel pressure drop. Verify with a mech gauge and switch over to logging sensor volts instead.

[Alvin]

I happen to be on the dyno right now with a FPCM equipped car 2010 camaro.

I had to use a different scalar/offset than you did. What I did was measure voltage at a about 27psi and another at 58 then just did basic algebra to come up with y=mx+b I attached my math so that you can try it.. but i bet best results would be to calibrate the next one on your own with what you got.

Anyway for this example.. reported matches a manual calculation of what it should be. Not saying it's impossible for some OS or situation to be different.. this is just what I found.

math.pngresults.png

[hjtrbo]

Be good to see what you get when a 2013-15 ZL1 turns up at your door that consumes north of 600g/s of air.

[AZ03Cobra]

I had some time during the week to work on it. I tried taking up to half of the startup fuel out and no change. I did decide to toss a new fuel pump in, just because the stock one had 140K on it and I really didnt want to worry about a 15 year old pump on a boosted setup, plus I wanted a stock core to build a dual pump setup out of. That didnt change anything (the car did seem to idle/drive smoother, but it was probably just in my head). I also tried bumping the fuel pump prime time to 4 seconds to see if I could cheat using that until I got around to pulling injectors, but that didnt help either. I have FIC 850s in there and the driver side 4 are easy to get to, the passenger side I will have to yank the blower, so fingers crossed if it is a leaky injector pintle, its on the driver side. Truck runs perfect otherwise, sits right at 11.7 AFR at WOT, trims are stable, idle is great. I did fix the injector table, but im thinking its probably mechanical at this point since quick restarts are perfect.

[Alvin]

It's been a long time since I've seen one.. but a injector that drips will cause a hard start.

I don't know where we are at.. have you mechanically verified fuel pressure while trying to crank.

[AZ03Cobra]

That?s the plan for this week, I?ve just been so busy with work I wasn?t able to make it to the speed shop to grab a gauge. I may just get one on Amazon, but figured it?s not a bad idea to have on the fuel rail anyway.