Cadillac CTS-V Forum banner
41 - 60 of 83 Posts

·
Premium Member
2014 CTS-V Sedan A6
Joined
·
1,393 Posts
So I was able to flash my FPCM without paying extra - I guess HP Tuners took pity on me, or I managed to make enough revisions to my tune over the years that I unlocked a bonus level!

Anyway, I finally got rid of my CEL from the Dsteck Aux pump. @adam112 ran a dedicated relay when he helped me install his amazing fuel hat, and I got the CEL every time I hit boost for a Fuel pump secondary circuit low voltage due to the relay (P0231). Although I disabled the code and even FPCM reporting altogether in the ECM, the code would persist - the FPCM has many of these codes duplicated onboard, and only when I disabled the FPCM DTC reporting did the CEL finally disappear!

It also looks like JAustin's fuel pressure tweaks bought me a little extra headroom on the supply side - so far it looks like the rail pressure dip that's commonly reported has been minimized. The dip is still there, just not nearly as severe. I suspect there is more to here as my FP starts to ramp back up at higher RPM but I'm not quite sure what to change. It probably has something to do with one of the fuel flow rate vs voltage tables (or similar).

Fun fact: with the 9.55 / 3.0 pulley ratio, I'm hitting almost 19psi in 65*F ambient. yay!

Have you changed out the pressure relief valve in the fuel pump basket? That little fucker opens up at 68'ish PSI. Tom and I are about to change ours out so we don't have FP issues at the track this spring. Trying to find a weekend to knock them out.
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #42 ·
Have you changed out the pressure relief valve in the fuel pump basket? That little fucker opens up at 68'ish PSI. Tom and I are about to change ours out so we don't have FP issues at the track this spring. Trying to find a weekend to knock them out.
I haven't. I will if I need to upgrade the fuel lines (I keep thinking about that Kong dual pass lid!).

You happen to have a link or part number to the replacement part?

Sent from my SM-G991U1 using Tapatalk
 

·
Premium Member
2014 CTS-V Sedan A6
Joined
·
1,393 Posts
  • Like
Reactions: random84

·
Registered
Joined
·
173 Posts
How are you guys dialing in idle without cats and stock cam? My eyes burn from the exhaust fumes in the garage on a cold start. For now i just turned off the high idle on a cold start and it helped for sure.
 
  • Like
Reactions: loweredd

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #46 ·
How are you guys dialing in idle without cats and stock cam? My eyes burn from the exhaust fumes in the garage on a cold start. For now i just turned off the high idle on a cold start and it helped for sure.
Your cold start fueling is probably rich AF. I think we posted above about leaning out commanded EQ relative to valve temperature - start there first

Sent from my SM-G991U1 using Tapatalk
 

·
Registered
Joined
·
510 Posts
no cats will always have some issues, u could try some EOIT to help a little more fuel get into the chamber and not straight out the exhaust on cold starts but u wont fix all of it especially without cats, also u dont want to delay EOIT too much for cold either as it needs the warming valve to help it, if fuel is equaling commanded just shift the OL commanded EQ a little closer to stoich until it starts to not idle well when cold and then go back to a good idle, when i was starting on ethanol i found it quite good even close to stoich which burns hotter then a richer mix so helps warm up also
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #48 ·
This is JAustin's post from page two showing some of the tables you should look at (one for 93 and one for ethanol).

Stoich would be 1.0, so yeah... you can probably cut this table by 40% from stock values (closer to 1.00) and solve a lot of your problems - which is the stock cold-start dumping fuel into the cylinder and exhaust to heat things up. Don't forget to turn off Cat light-up settings in the spark tables also. Posting up a tune file might actually help us see what you've changed or not.

A stock cam probably doesn't need to mess with Exhaust Overlap Injector Timing (EOIT) IMHO, given what else could be changed. If you do, don't mess with it over 1200 RPM. I haven't bothered personally, and I am running a bit more cam. :D

 

·
Registered
Joined
·
510 Posts
A stock cam probably doesn't need to mess with Exhaust Overlap Injector Timing (EOIT) IMHO, given what else could be changed. If you do, don't mess with it over 1200 RPM. I haven't bothered personally, and I am running a bit more cam. :D
little trick with the EOIT if u can delay it in mid and up top enough that it keeps a good burn but enters in a less atomized state it then takes longer to ignite and burn thus it can help get some more timing into it without knock more so for petrol but ethanol also, i dont like to be injecting much past BDC tho on boosted, if u want to do a test zero out the normal rpm eoit table if not already, set the normal ect take 20 off whole table, then the boundary set idle upto 1536rpm to 520 then set the 6144rpm and above to 560 and interpopulate from the 1536 to the 6144 see how that goes/feels if u see any richer then normal then ur getting more in the chamber so thats fuel u can remove if u keep the changes and it should feel a bit stronger
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #50 · (Edited)
So I've been messing with the Fuel pressure and FPCM settings. I believe I have figured out that the OEM settings are all bass-ackwards. Using the data log here, pay attention to the commanded and actual Fuel pressure on the bottom of the chart.

151013


There are two increases in actual (and desired) FP with excellent correlation: my baseline FP is ~50psi, which is what most of us see driving around town. Ordinarily, when we floor it we see a jump into 70psi - but not here. There is an intermediate step up to 60psi before I eventually see 70psi. This intermediate mode - where the ECM is pulling duty cycle to bring actual fuel pressure DOWN to the commanded 60psi - is what I believe I have been seeing all along.

What's happening is that my fuel flow rate (in lb-hr) is so low under normal driving, that we are typically in "Low Flow" mode in the tune (50psi). Most bolt-on cars will use enough fuel that when you mash it, your flow rate jumps so much that you simultaneously clear the "low flow" mode threshold, bypassing the normal FP mode (60psi) altogether and going straight into high flow mode (70 psi); so it looks like in stock form our commanded fuel pressures jump from 50 to 70 psi.

Only after altering my "high flow" upper range did this manifest into that "fuel pressure dip" I see when on Ethanol - due to the vastly altered fuel flow requirements:

151016


Note, that modifying the "High flow" tables does not actually change your flow rate - it just changes WHEN the pre-defined line pressures are commanded. I believe that when we hit the "High Flow" threshold, that triggers 100% pump pulse-width as well as the higher line pressures. In my case, the flow rates were such that I was winding up in "Normal" mode in the middle of a pull commanding 60psi, and the ECM was pulling pump duty cycle to bring actual line pressures down to this level. I am going to adjust these values so that I jump straight into High Flow mode and see if that dip disappears - but so far, I've seen that "High Flow" mode and 100% pump duty cycle are triggered specifically by the calculated fuel flow rate.

So in reality, raising these thresholds doesn't seem to actually do anything, other than changing (delaying) when the ECM actually command maximum line pressure. In actuality, we want to LOWER the High Flow threshold to get there earlier in our runs, as that should command 100% pump DC by default along with higher line pressure (obviously, you can modify the desired line pressure for each mode). Thus, I am going to LOWER my high flow Upper limits so that I trigger the High Flow fuel pressure earlier - whether on pump or ethanol - and monitor to see if FP DC is still being pulled or if it stays at 100% - or in other words, my theory is that the primary difference between "Normal" and "High Flow" modes is that "Normal" mode allows pulse-width modification and "High Flow" mode doesn't? I hope to verify this soon.

Logging fuel flow reveals that I am in the double-digits for fuel flow until essentially boost, when it skyrockets into the mid-300 lb-hr and up rates. However, if one was so inclined, by drastically changing the threshold values for each, you could use lower fuel pressures when idling or under light throttle, ramping up as you get to WOT for better atomization - or even run 70psi all the time by adjusting the trip thresholds for whichever mode you wanted to run.

So how do we actually improve pump flow? Aside from ensuring you're in High Flow mode for boost, and making sure we're not commanding so much pressure as to be overriding the integrated pressure relief (68-72psi?), generally speaking that's where adjusting (increasing) your Openloop Duty Cycle and Openloop DC Multi tables for the flow and pressure values may have benefit. For now, I suspect that properly adjusting the flow modes will hopefully solve my problem - but I have increased the Openloop DC tables slightly in previous tunes FWIW.
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #51 ·
Success:

High Flow mode commands 100% duty cycle. So for max pump output, you want to LOWER your High Flow upper threshold.

I changed mine to 300 lb-hr just as a round number, and my log shows going into "Normal" mode at 60 psi early in the run, with pump duty cycle being modulated, and as soon as I hit 300 lb-hr the line pressure increases (overshooting commanded) with 100% pump DC. This occurred almost 1k RPM earlier than the run I posted above, solely due to High Flow upper limit adjustment.

151023


It can be hard to see, but the Fuel Pump Duty Cycle (white, second-to-bottom frame) steadily drops down to 50% duty cycle in "Normal" mode @60psi, as the ECM tries to match the commanded FP. As soon as my flow trips the High Upper threshold, it pegs to 100% DC and does not drop down. The tapering of fuel pressure towards the end of the pull is due to consumption, pump DC remains at 100%.

151024
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #52 ·
I also increased the fuel pump duty cycle in relevant areas by ~5% and slightly adjusted the Open Loop DC modifier to get closer to "1.000" at 15 volts, which is where my system voltage hangs out. This table may reflect limitations to the factory pump flow rates versus aftermarket pumps like the DW300, so I'd suggest small changes and monitor for progress. But I suspect aftermarket pumps could see some real benefit here.

151052
 

·
Premium Member
2014 CTS-V Sedan A6
Joined
·
1,393 Posts
Well, this is amazing information. Lower the high flow limits in the FSCM to get the computer to trigger high flow mode sooner?
 
  • Like
Reactions: Blades1_99

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #55 ·
Well, this is amazing information. Lower the high flow limits in the FSCM to get the computer to trigger high flow mode sooner?


:D


Sent from my SM-G991U1 using Tapatalk
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #56 ·
Yup, a short 4th gear pull - I'm definitely pushing through the regulator in the middle of the run, but the pump duty cycle is dialed in (bottom of the display):
151086
 

·
Premium Member
2014 CTS-V Sedan A6
Joined
·
1,393 Posts
What numbers did you wind up going with?

Awesome data log BTW. I love the fuel pressure line there. I also dig the Fuel Flow log.

Awesome!
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #58 ·
What numbers did you wind up going with?

Awesome data log BTW. I love the fuel pressure line there. I also dig the Fuel Flow log.

Awesome!
Yeah, I couldn't tell if you were being sarcastic (or not) above - but I could have sworn the conventional wisdom was to raise the High Flow thresholds, so I wanted to correct that notion here. You were spot on with the duty Cycle vs voltage changes.

Although now, because I am getting 100% duty cycle sooner, I would not have need to change the voltage vs flow duty cycle tables - though the DW pumps certainly like it. On factory pumps, I suspect it might be more limited in use.

Right now, I have left it at ~300lb-hr flow rate just because that corresponds well to the lowest RPM range for each shift. I think I will lower it even further, so I get High Flow at ~3k RPM no matter what - I'll just have to keep an eye on rail pressure. I suspect that lean area early in the run is a side-effect of the pump DC being modulated.... or it could just be my tune.
 

·
Registered
Joined
·
510 Posts
I suspect that lean area early in the run is a side-effect of the pump DC being modulated.... or it could just be my tune.
have u done much with the transients ? u could bump that up like 10% whole table impact factor see if it helps, the transients dont affect steady state only during throttle/map movement
 

·
Premium Member
Joined
·
17,761 Posts
Discussion Starter · #60 ·
have u done much with the transients ? u could bump that up like 10% whole table impact factor see if it helps, the transients dont affect steady state only during throttle/map movement
I already messed with transits to where it richens up on tip in. The lean condition persists for some time where I suspect it is a delay between the fuel pump DC modulation and the injector pulse width compensation - but you could have a point there.

I see the lean condition mostly when pump DC is not 100%. But, it's worth taking another look at. Part throttle can be so tricky!

Sent from my SM-G991U1 using Tapatalk
 
41 - 60 of 83 Posts
Top