Actual rail pressure higher than desired (not at idle)

[Chevy1925]

here is an interesting one.

So ive had a rattle upon hitting the throttle from a stop or when hitting the throttle from a coast off boost like after a long downhill. its been there for quite some time but never been my top priority to look into, specially cause i only really notice it in higher elevation where the stock turbo spools slower. After my trip to silverton and back, im looking into this as it gets real annoying pulling passed or starting from lights sounding like an old 7.3.

here is a screen shot of my rail issue


it will do this every time. if im easy with depressing the throttle, it can get it to follow nicely and it wont rattle. Nothing as far as tuning in for my rail is different than stock. i have stock lb7 regulators in each pump and the valley one is new but it rattled just like this prior to that change. idle rail will hold perfect and cruising it will hold perfect, its only the initial throttle tip in from normal acceleration.

thoughts? i thought maybe lift pump pressure too high but figured that would cause it to run high rail all the time, specially at idle which isnt the case. maybe my second pump controller is going bad or not right?

 

[duratothemax]

IMO, a goofy 2nd CP3 controller is the most likely case. Have you played with B1010 at all?

 

[Chevy1925]

no i have not, i did a long time ago when i was trying to diag a bad FPR but put it back to stock after confirming that the FPR was bad. i read some old threads about Mika doing that on DP back in 07 but i wasnt about to start dabbling in it till i asked. his thread was the closest i could find but still not the same issue i have

 

[THEFERMANATOR]

Try logging actual VS desired rail valve current and see how far apart they are from each other. If they are a good bit apart, I would look closely at your 2nd CP3 controller. Otherwise you could adjust the B1010 to bring the desired back closer to actual so it doesn't spike up on you. And it's worth checking your supply pressure to make sure that isn't it.

 

[Chevy1925]

ill log that on the way home today and see what we get

 

[DAVe3283]

Try logging actual VS desired rail valve current and see how far apart they are from each other. If they are a good bit apart, I would look closely at your 2nd CP3 controller. Otherwise you could adjust the B1010 to bring the desired back closer to actual so it doesn't spike up on you. And it's worth checking your supply pressure to make sure that isn't it.

^^ This.

But, don't necessarily give up on the 2nd CP3 controller if the actual current is way out. You will probably have to add a good bit of current to the table at the lower part (where the throttle tip-in happens). The stock table is expecting one pump to start to dump fuel, but in reality, two pumps start to dump fuel. This causes the overshoot. The LB7 rail pressure algorithm is somewhat brain-dead, and that table needs to be really close for things to work right.

If you feel really adventurous, you can start messing with the PID parameters for the algorithm. But like I said, it is brain-dead, so don't expect it to respond like a normal (industrial/commercial) PID loop will, IMO.

 

[hondarider552]

James if you are still having this problem when I get my truck back you can try my cp3 harness, or Steves.

 

[Chevy1925]

The only pids I found to log are commanded rail current and desired rail current. Both seem to follow the same path (see pic, they are the bottom left cell), nothing to log "actual"

 

[THEFERMANATOR]

They should follow each other at first, but the ECM should begin to correct after the rail pressure actual doesn't follow desired. It can take some time for the ECM to alter the rail valve current to bring rail pressure into check. Look at your logs and where the rail pressure is high add some rail valve current to reduce pressure. I know it took some time for me to get my rail valve current tables correct when I swapped in a LBZ CP3. Worked fine for my small tow tune, but on my big tune I had to change it some for it to follow semi closely.

 

[Chevy1925]

Well I bumped mA up by 50 from 1000-6000, then bumped 7000 up by 25. I'll see where that goes. What's strange is if I have the scan up and have the area high lighted I'm looking at, the b1010 table will just stay at the top 1500 value and not move even with the selection in the scan tool on where desired rail current is 1150

 

[THEFERMANATOR]

Theres a PID for total fuel flow you have to log in order for the log to follow in your tune file. Can't remember which one right now(been awhile since I had to rescale one), but it figures in total fuel flow to the engine as well as fuel returned when the injectors fire, and CP3 return for cooling. From your log though I would be looking at your dual CP3 controller. If you look, where it goes over desired the rail valve current is staying pretty flat while your pressure is fluctuating up and then slowly back down. In one spot I see where the pressure went up, then down, then back up and down again while the rail valve current and demand stayed pretty flat. If the pressure was foolowing directly inline with the rail valve current, I would say a simple rescale would fix it, but your log is showing fluctuations and deviations from the current table which would make me think theres a problem in the control circuit like a poor connection or in your case the 2nd controller. By raising your MA it should help it to stay on the lower side and not spike as much.

From my logs I did before, the areas it sounds like your spiking in are the 3000-5000 areas. 12000+ is pretty much WOT, and idle was in the 1500-2500 range for flow. 2000-6000 was the cruise areas. Because the tables works off of total MM of fuel flow, it varies alot with RPM's and load.

 

[duratothemax]

The LB7 rail pressure algorithm is somewhat brain-dead, and that table needs to be really close for things to work right.

If you feel really adventurous, you can start messing with the PID parameters for the algorithm. But like I said, it is brain-dead, so don't expect it to respond like a normal (industrial/commercial) PID loop will, IMO.

x2

 

[Chevy1925]

well adding that much mA made 0 difference, acts exactly the same. im gunna try lowing lift pump pressure after work and see if that helps. i really need to get a gauge in the truck for it....

Ferm, i think i know what PID your talking about. i think its labeled "fuel rail pressure flow" or something along those lines. it graphs it via MM3. ill throw that in the log as well and see what i find.

thanks Ben and Dave for the info.

Brian, if it werent such a bitch to get the FPR plug out of the regulator, i would have gone to steves and stole his for a few min. if diag starts pointing that way, i may have to deal with it and swing over there. thanks buddy

 

[DIESELMAFIAPER.LB7]

Shit it take like 30 seconds to get to that plug on mine maybe if you had big boy turbos and not gay stocker stuff

I'd swap the controller though

 

[Chevy1925]

Shit it take like 30 seconds to get to that plug on mine maybe if you had big boy turbos and not gay stocker stuff

I'd swap the controller though

You shut your whorish mouth :angel:. putting the actual plug in the FPR isnt bad, its plugging the pig tails together from the factory wires to the PPE wires. i need three hands and two pairs of needle nose pilers

 

[DIESELMAFIAPER.LB7]

You shut your whorish mouth :angel:. putting the actual plug in the FPR isnt bad, its plugging the pig tails together from the factory wires to the PPE wires. i need three hands and two pairs of needle nose pilers

Put your g string on and get it done already

 

[Chevy1925]

dropped my lift pump pressure all the way down (backed screw all the way out), made no difference other than the little lope i would get coming to a stop is gone, which i figured would stop that.



i found the commanded fuel rail pressure flow PID and it is the light blue third from the bottom on the left side. im having trouble rescaling the graph so you cant see alot.

guess next is swapping boxes or should i try adding more mA to the FPR current?? im not sure whats concidered "alot" of current

 

[DIESELMAFIAPER.LB7]

Mine starts at 1650 iirc then I made it linear down to 100 and works well for me

 

[JoshH]

Keep adding mA until it stops doing what it's doing or won't run. My $.02

 

[Chevy1925]

Lol sounds good. Thanks josh and jake