LBZ-Odd Rail Pressure Drop

[killerbee]

Very strange issue. The rail pressure will fall off to 85mPA with no explanation, using reasonable PW and rpm. I swapped to an older tune and got rid of this problem to a normal 140mPA rail drain. So the problem is not hardware, but in the tuning. Yet this log shows desFRP not fluctuating from 180.

I though someone might have already flipped the switch i did (I have no idea at this point) and has seen this already. Any leads appreciated.

Here is the log. There is a very obvious and descript knee when this happens, but doesn't appear to be correlated to anything obvious. Thanks

[bballer182]

you have a log of a tune that doesn't do that?

that is interesting to say the least. I would have expected that around 2700 2800 uS and up but not at 1700. that what mine was doing before the lift pump was installed.

[Dozerboy]

I lose RP even on small tunes the first time for the day I get on the throttle hard in my truck. And it will hold a much larger PW after that one time.

[bballer182]

I lose RP even on small tunes the first time for the day I get on the throttle hard in my truck. And it will hold a much larger PW after that one time.

fuel temp issue?

[horsehaulin]

Is this truck running a lift pump?

[killerbee]

no lift pump.

Yes I have a log, 5 minutes after this one using an older tune, even more PW, that loses pressure to only the usual 140mPA, relatively normal.

This one falls flat and hard in a straight line to that floor around 85mPA. It did MIL once with rail pressure code, but not on todays logging experience.

My initial thought was the same as most would think...hardware issue. But it doesn't appear to be, if I can improve it with a tune change.

[vortecfcar]

Fuel pressure relief valve.

[killerbee]

It is shimmed.

But the reality is, a hardware cause is ruled out at this point.

[vortecfcar]

But the reality is, a hardware cause is ruled out at this point.

Have to play devils advocate here. I don't think you've ruled out hardware. I don't think you could without logging regulator function to establish that the fuel pressure algorithm isn't chasing the low actual pressure.

Nick

[killerbee]

I am open to ideas. I don't know exactly what you are saying Nick, but I'm all ears.

A similar tune with PW that is 100us higher, resulted in a 135-140mPA FRP.

[vortecfcar]

Consider that the higher pulsewidth tune may have not pushed quite as hard on the hardware system and not pushed the valve open.

Try lowing your commanded fuel pressure to 21k or so on the offending tune and see if it still pukes.

Nick

[killerbee]

ok, I see what you are saying.

do bosch 180mPA (vs 160) rails run higher incidence of FPRV issues, in your experience?

[vortecfcar]

I see it at least as often on the Bosch trucks as I do on the LLY's. Of course, I tune many more Bosch trucks than LLY's.

Suffices to say that it happens. :)

Nick

[JoshH]

I very seriously doubt that the FPRV is opening. Every time I have logged an FPRV opening it is a sharp drop of pressure, not a gradual fall, and I have never seen it on an LBZ or LMM. What did you change between the two tunes where one was doing it and the other wasn't? I wouldn't be surprised if the answer to your problem is found in table B1015 or B0720.

[killerbee]

Josh,

are you saying that you have seen a boschism where desfrp is not trying to drive actfrp?

FWIW, those 2 tables are essentially identical in each tune.

[JoshH]

The 1015 table is based on total fuel quantity and controls the fuel pressure regulator. If it doesn't see enough fuel flow, it will not open up the regulator. From what I can tell, you are running almost twice as much pulse width at your indicated fuel quantity than the stock tune. If you haven't modified table B1015, the regulator may not be able to open enough to maintain desired fuel pressure. Is there any particular reason why you are changing the pulse width table so drastically in that area?

[killerbee]

I will look at that also. Thanks for the suggestions. I assume your suggestion is to lower those values in 1015.

[duramaximizer]

I would also say to look in 1015 something about that says there could be more behind the seens running FRP into the ground besides the desired FRP.

Unless it's possible that something is messing with 1007?

[killerbee]

I didn't log baro, but assuming it is not malfunctioning, it should be a non-issue with a 0 multiplier. 1006 is a strange table. Gotta wonder why it is set up so negatively for altitude in the moderate fueling areas.

[killerbee]

Here is a quick differences summary. Most are minor changes.



Comparison summary: 10:35:07 pm, Thursday Apr 29, 2010

Calibration comparison between 138hp.tun and 640Torque_low smoke_0000.tun.
*Values that differ by more than 0.100000% are considered different.


B0701 "Base Idle Speed" -2.0800 "Different from row 12 to row 24 inclusive."
B1115 "Pedal Position to Desired Torque" -9.2920 "Different from cell: 0,0 to cell: 13,15 inclusive."
B1102 "Torque Based Fuel" 5.7250 "Different from cell: 0,1 to cell: 22,22 inclusive."
B1113 "Torque Based Fuel Med Altitude Adjust" 2.3633 "Different from cell: 0,0 to cell: 22,22 inclusive."
B1114 "Torque Based Fuel High Altitude Adjust" 8.5498 "Different from cell: 0,0 to cell: 22,22 inclusive."
B1117 "Maximum Fuel Quantity vs RPM" -62.0000 "Different from row 1 to row 19 inclusive."
B1120 "Engine Overtemp Torque Limiting" -13.6068 "Different from cell: 0,0 to cell: 15,9 inclusive."
B1121 "Intake Temp Torque Limiting" -6.2663 "Different from cell: 12,7 to cell: 15,15 inclusive."
B1122 "Torque Fuel Limit RPM Conversion" -36.6800 "Different from cell: 0,0 to cell: 15,15 inclusive."
B1127 "Cranking Torque Reference" 8.0000 "Different from cell: 0,0 to cell: 14,15 inclusive."
B0720 "Main Injection Pulse" 4.4833 "Different from cell: 1,1 to cell: 15,19 inclusive."
B0797 "Main Injection Mixture Limit RPM" 67.5000 "CAL: 600 <-> ALT: 6000"
B0793 "Main Injection Rich Mixture Limit" -2.0000 "CAL: 1.000 <-> ALT: 0.920"
B0794 "Main Injection Lean Mixture Limit" -40.0000 "CAL: 3.000 <-> ALT: 1.400"
B0795 "Main Injection Mixture Limit" -39.5000 "Different from cell: 0,0 to cell: 15,15 inclusive."
B9101 "Pilot Injection #1 Quantity (A)" 5.0000 "Different from cell: 1,1 to cell: 22,20 inclusive."
B9102 "Pilot Injection #1 Quantity (B)" 5.0000 "Different from cell: 1,1 to cell: 19,20 inclusive."
B9103 "Pilot Injection #1 Coolant Adjust (A)" 4.2500 "Different from cell: 0,0 to cell: 22,22 inclusive."
B9104 "Pilot Injection #1 Coolant Adjust (B)" 4.2500 "Different from cell: 0,2 to cell: 22,22 inclusive."
B0908 "Timing Base, (A)" -21.6406 "Different from cell: 0,0 to cell: 22,22 inclusive."
B0909 "Timing Base, (B)" 3.1771 "Different from cell: 2,0 to cell: 22,22 inclusive."
B0956 "Timing ECT, No P2 & P3, Low Altitude" -15.8203 "Different from cell: 0,0 to cell: 22,22 inclusive."
B0957 "Timing ECT, No P2 & P3, Low Altitude Multiplier" -5.0018 "Different from row 0 to row 4 inclusive."
B1201 "Timing Base, No Pilot #2 or #3" 5.2200 "Different from cell: 0,0 to cell: 22,22 inclusive."
B1204 "Timing Coolant Adjust (A)" 4.0000 "Different from cell: 0,3 to cell: 11,22 inclusive."
B1205 "Timing Coolant Adjust (B)" 4.0000 "Different from cell: 0,3 to cell: 7,22 inclusive."
B1206 "Timing Coolant Multiplier (A)" 45.4545 "Different from row 5 to row 6 inclusive."
B1207 "Timing Coolant Multiplier (B)" 45.4545 "Different from row 5 to row 6 inclusive."
B1118 "Maximum Torque 1 vs RPM" -13.5500 "Different from row 14 to row 16 inclusive."
B1119 "Maximum Torque 2 vs RPM" -7.2850 "Different from row 13 to row 13 inclusive."
B1128 "Barometric Pressure Torque Limit" -18.7360 "Different from cell: 11,0 to cell: 12,15 inclusive."
B1501 "EGR Control" N/A "CAL: Enable <-> ALT: Disable"
B1001 "Fuel Pressure Base" 2.4140 "Different from cell: 2,0 to cell: 19,14 inclusive."
B1002 "Fuel Pressure ECT" -1.0000 "Different from cell: 0,0 to cell: 5,5 inclusive."
B1014 "Pressure Maintain Fuel Limit" -20.0000 "Different from row 7 to row 9 inclusive."
B2204 "Desired Boost Levels, EGR Off, High Altitude" -29.2667 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2207 "Desired Boost Levels, EGR On, High Altitude" -30.6889 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2205 "Desired Boost Levels, EGR Off, Med Altitude" -27.7333 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2208 "Desired Boost Levels, EGR On, Med Altitude" -27.3778 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2206 "Desired Boost Levels, EGR Off, Low Altitude" 13.9556 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2209 "Desired Boost Levels, EGR On, Low Altitude" 13.9556 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2216 "Desired Boost ECT" -3.6000 "Different from cell: 5,1 to cell: 13,7 inclusive."
B2217 "Desired Boost Coolant Temp Multiplier" 33.3333 "Different from row 0 to row 5 inclusive."
B2214 "Turbo Vane Target Position, EGR Off, Low Altitude" -30.3467 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2215 "Turbo Vane Target Position, EGR On, Low Altitude" -26.5991 "Different from cell: 0,0 to cell: 22,22 inclusive."
B2224 "Turbo Vane Target Position Maximum, High Altitude" 15.0024 "Different from cell: 4,0 to cell: 15,15 inclusive."
B2223 "Turbo Vane Target Position Maximum, Med Altitude" 15.0024 "Different from cell: 4,0 to cell: 15,15 inclusive."
B2222 "Turbo Vane Target Position Maximum, Low Altitude" 15.0024 "Different from cell: 4,0 to cell: 15,15 inclusive."
B2237 "Turbo Vane Target Position Maximum, Cold Start" 9.6313 "Different from cell: 6,5 to cell: 15,15 inclusive."
B2225 "Turbo Vane Target Position Minimum" 59.9976 "Different from cell: 1,0 to cell: 15,15 inclusive."
B2231 "Turbo Boost Control Fuel Enable" 12.5000 "Different from row 10 to row 11 inclusive."
B2232 "Turbo Boost Control Fuel Disable" -9.5000 "Different from row 10 to row 22 inclusive."
C0802 "P0107 Error Time" -1.2214 "CAL: 10.00 <-> ALT: 2.00"
C0804 "P0108 Error Time" -1.2214 "CAL: 10.00 <-> ALT: 2.00"
C0809 "P0106 MAP / Baro Mismatch Time" 27.4809 "CAL: 20.00 <-> ALT: 200.00"
C0811 "P0045 Error Time" -1.3740 "CAL: 10.00 <-> ALT: 1.00"
C0813 "P0045 Error Time" -1.3740 "CAL: 10.00 <-> ALT: 1.00"
C1802 "P0192 Error Time" -2.2595 "CAL: 15.00 <-> ALT: 0.20"
C1804 "P0193 Error Time" -2.2595 "CAL: 15.00 <-> ALT: 0.20"
F0101 "Fuel Level Sensor Primary" -2.1167 "Different from row 0 to row 23 inclusive."
F0301 "Main Fuel Tank Size" -0.6333 "CAL: 26 <-> ALT: 25"
F0303 "Combined Fuel Tank Capacity" -0.6333 "CAL: 26 <-> ALT: 25"

[vortecfcar]

The 1015 table is based on total fuel quantity and controls the fuel pressure regulator. If it doesn't see enough fuel flow, it will not open up the regulator. From what I can tell, you are running almost twice as much pulse width at your indicated fuel quantity than the stock tune. If you haven't modified table B1015, the regulator may not be able to open enough to maintain desired fuel pressure. Is there any particular reason why you are changing the pulse width table so drastically in that area?

It looks like the regulator is doing just fine shortly before the pressure drop. There's no sudden increase in fuel demand to coincide with the drop. It looks like the truck is just accelerating smoothly when it suddenly drops pressure (although it's hard to gauge time without a log). A poorly designed B1015 table would have a difficult time finding desired fuel pressure. This truck found pressure and then lost it.


Also, consider that at 2800 RPM, the regulator is allowed to chase fuel pressure as much as it wants per table B1060. I'm not saying it's positively a relief valve, but I've never seen a situation where the truck didn't make achieving desired rail pressure it's number 1 priority with regard to fuel pressure. It seems hardware related.

Here's picture of a log from a stock LBZ Kodiak I tuned (rather diagnosed) yesterday that is having similar issues (no shim or lift pump). It sinks to about 35mPa.

Nick

[killerbee]

It looks like the truck is just accelerating smoothly when it suddenly drops pressure (although it's hard to gauge time without a log). A poorly designed B1015 table would have a difficult time finding desired fuel pressure. ...

Here's picture of a log from a stock LBZ Kodiak I tuned (rather diagnosed) yesterday that is having similar issues (no shim or lift pump). It sinks to about 35mPa.

Nick


1.6 seconds from peak to bottom.

The kodiak looks much the same. Let us know how that develops with hardware changes, or if tuning changes help.

[Dozerboy]

fuel temp issue?

I don't think so since I normally don't get on it until its warmed up but worth looking into.



Screen Shot
Normally the truck falls on its face and won't shift. During this run the truck felt a little slow but kept on pulling. No lift pump and does it on a new fuel filter too. You can see I did a run right after this one and no drop at all.

[killerbee]

Fuel temperature is the key property toward predicting fuel pump cavitation for the diesel hydrocarbon. It helps define NPSH that must exist to avoid loss of prime do to "boiling" gas conversion of the fuel. The hotter the fuel, the more lift pump pressure required to keep the liquid state and maintain the same flow.

Notwithstanding another intervening software explanation, this is what explains the precipitous pressure drop by the pump, unless the fprv is opening. I think Nicks suggestion of reducing desfrp is an attempt to determine if the fprv is opening?

[killerbee]

a lift pump resolved the issue.

it is odd though: after resetting codes or ignition, the first high throttle run loses pressure. Subsequent runs maintain.

[vortecfcar]

it is odd though: after resetting codes or ignition, the first high throttle run loses pressure. Subsequent runs maintain.

Glad you to hear you got it sorted out.

Does this sentence still apply with the lift pump?

Nick

[killerbee]

Yes. I think this was mentioned by someone earlier in the thread also.

[killerbee]

I wanted to test the idea we discussed by using a 150mPA cap, but the pump would not support flow while off. Got the code just cruising down the street. 80/35 mPA disparity in des/act with the pump off.

A lot of people are installing lift pumps without providing a one-way check bypass. He is going to be stranded if the pump dies, no real power.

[bballer182]

I wanted to test the idea we discussed by using a 150mPA cap, but the pump would not support flow while off. Got the code just cruising down the street. 80/35 mPA disparity in des/act with the pump off.

A lot of people are installing lift pumps without providing a one-way check bypass. He is going to be stranded if the pump dies, no real power.

Used a non-flow-thru pump, huh?:doh2:

Definitely wouldn't do that without having a bypass...