High fuel pump pressure after reflash

[fido]

Hello,
quite recently I've been tuning Camaro with LS3, Camaro ZL1 with LSA, Corvete ZR1, all of them with upgraded injectors and I had the same problem - after ECM flash, on idle, I'm getting very high fuel pressure (around 450kPa), even when I command 350kPa for low/normal flow. It slowly descend to my commanded value, but sometimes it takes about 5 minutes until that I'm really on my commanded AFR, as injectors can't keep correct fuel amount under 1ms IPW. This problem disappear later on and after another engine start, it's pushing my commanded pressure. Anyway, it slows down idle/low load tuning, as I have to wait couple of minutes until fuel pressure settle down. Why it happens? It even differs from car to car and even the time for settling down is different.Sometimes it takes even 15 minutes to settle pressure down.
Another problem I discovered is that ID injectors sucks, when it comes to short pulse. It's just not possible to fine tune them. I'm getting spread +/-10% AFR on 0.5-0.8ms injector pulse width in the same MAF cell! In connection with above mentioned problem it renders them as waste of money as you expect to spend some more $ on their price and save something on dyno renting, but it's not the case when you spend 2 hours more to fine tune idle :bang head:
It happened 3 times and it really bothers me. Is there any trick to avoid this strange fuel pump behavior?

best regards, Fido

[GHuggins]

This must be part of the rich after flash issue we all fight? All part of the ecm's "self" re-initialization or relearn process.... Never thought to check fuel pressure. Curious though... Is the actual fuel pressure this high or just "shown" this high?

[10_SS]

as Ghuggins said.. you are def seeing higher injector pulse than what is reported in the scanner... see Post 89 in the link below. Now if your seeing higher fuel pressure also.. anythings possible.... Basically what happens is the calculated Intake Valve Temp data creeps to around 300? when running, Then gets reset to coolant temp after flash/reset/batt disconnect and then the ECU adds fuel for whatever reason, but it doesn't need it, and this added fuel isn't part of the reported scanner Injector Pulsewidth, but it does show up on a scope of the injector signal. Now, if the coolant temp is below 150ish.. then no added fuel occurs. That post should be made a sticky, called "Rich After Flash".

http://www.hptuners.com/forum/showth...er-Flash/page5

[fido]

Thank you for pointing me there. Anyway I'm sure that problem is caused by fuel pressure so I added my comments. Continuing there:
http://www.hptuners.com/forum/showth...243#post404243

[schpenxel]

This must be part of the rich after flash issue we all fight? All part of the ecm's "self" re-initialization or relearn process.... Never thought to check fuel pressure. Curious though... Is the actual fuel pressure this high or just "shown" this high?

That's what I was about to ask..

[10_SS]

If it was fake and just shown high, or really high pressure, then either way I would expect a decrease in measured Injector PW to compensate which would endup in either correct fuel or lean fuel if it was "Fake". I have a feeling since it's a ZL1, then just a different strategy to get richer AFR after flash/reset. This means the car will run rich when WOT right after reset/flash.. I'm thinking safety strategy for whatever reason. Still would like him to measure actual injector PW. See what's actualyl happening. If no change in PW.. then it's just GM's way of finding other ways to add fuel.

[fido]

If it was fake and just shown high, or really high pressure, then either way I would expect a decrease in measured Injector PW

I commented it in another post in "rich after flash" theme. Yes, it's really the high pressure, as IPW is shortened, but with big injectors is 0.5ms IPW too short (or Short pulse adder data are wrong). Either way, there is not solution for that...except just waiting until fuel pressure descend to my commanded value.

[schpenxel]

I flashed my e38 Escalade earlier and logged commanded fuel pressure and fuel pump PWM immediately after. Pressure stayed at 58psi and PWM stayed constant as well, 95% I think it was. This is a non PWM fuel pump model so it behaved as expected