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2005 LLY u7185 Fuel Pressure Issue with tune?

Predator support for GM diesel vehicles

Moderator: mikel


Posts: 15
I've got a 2005 LLY that is being monitored with a U7185 v.9r07 and I'm seeing some really strange values for desired fuel pressure. When the key is turned on the desired fuel pressure is up a bit over 4,000psi but when you start it the desired fuel pressure value decreased to 3072psi when the truck is warmed up. The highest desired pressure that I have logged regardless of stock tune, or 80hp tune is 16,000psi. Note that the actual fuel pressure is very closely mirroring the desired fuel pressure and the FPR was replaced two years ago. I'm curious to know if there is a problem with the logging software portion of the Predator or the PID for fuel pressure not displaying accurately? Now that I've had the predator in the truck I'm also seeing these values when I take it out and have it back to the stock tune. I'd really appreciate some help here. Given that these trucks are supposed to reach up over 23,000psi at WOT and maintain 5-6,000psi at and idle, the values that I am seeing for desired fuel pressure are very concerning to me. If it were actual pressure that I was having and issue with I'd be searching for a mechanical cause, however that's not the case.

I also noticed that the desired pressure turns to a -9,xxx psi value at times when driving the truck. Why would that occur?

I've attached a couple of logs.


Posts: 15
Is it possible to monitor the throttle position related PIDS with he predator? That would be really helpful .


Posts: 52507
Location: DiabloSport World Headquarters

the tool simply displays what the ECU reports :)

the 9xxxx value is likely a case of the value changing faster than the refresh rate of the tool, but it should look OK in the log itself...

I have to say, I dont actually see any issues here. Does the truck run right?
Does it make good power?
is it throwing any codes??
Mike Litsch
Powerteq Customer Service Manager
Diablo Tech support by phone:
561-908-0040x4
M-F 8:00 AM to 5:00 PM EST


Posts: 15
mikel wrote:
the tool simply displays what the ECU reports :)

the 9xxxx value is likely a case of the value changing faster than the refresh rate of the tool, but it should look OK in the log itself...

I have to say, I dont actually see any issues here. Does the truck run right?
Does it make good power?
is it throwing any codes??


The -9xxx value does appear in the logs which leads me to believe that even if the refresh rate of the tuner can't keep up with it in realtime display, then it's also logging that inability to refresh quickly enough.

The truck is not making "good power". It's down from where it was before. It does throw the occasional P1093 code. I'm not insinuating that the predator is the cause, but merely trying to rule out some issues. My assumption was that as Diablosport says they test these tunes on a dyno etc when they are developed I thought there would be some familiarity with the fact that stock fuel pressure values at idle are 5-6,000psi and that WOT/High RPM values are supposed to be right around 23,200. So the issue that I have is that the pressures are not high enough, which in turn affects the injection fueling, power etc. If you aren't familiar enough with the stock parameters of the truck, then I'm a bit puzzled as to how the tunes are written. To produce the extra power called out in your tunes, you would need the CP3 injection pump and the computer to work together to pull from the tables in the ECM and produce the needed injection pressures.

So if I'm understanding correctly, you can't offer any insight into what kind of fuel pressures I should be seeing with your tunes, you haven't ever had any reports of the software not accurately reporting the ECM outputs, and your silent on whether or not the Predator has the ability to monitor the Throttle position PID that the tuner puts out?

All I'm after here is trying to establish baseline figures for diagnosis, some of which are being obtained with your product, and baseline figures with your tunes installed for comparison, and trying to determine if I can monitor one of the most basic PIDs out there.

Did you have a chance to look at the logs?


Posts: 52507
Location: DiabloSport World Headquarters

you see it in log playback in DV, or on the tool?
Id expect it onthe tool, not in Dataviewer.

If there are no throttle PIDs in the tool, use a laptop with Dataviewer and live stream the data, you'll get a much larger list of PIDs to choose from.

I'm not our diesel tuner, thus I dont have any specific data as to how much pressure you should be seeing at any given time.
The tunes do command extra pressure to help make power, but thats not where all the power comes from.

I'll see if our Diesel tuner may have some time to chime in here and help you out a bit more.

Thanks
Mike Litsch
Powerteq Customer Service Manager
Diablo Tech support by phone:
561-908-0040x4
M-F 8:00 AM to 5:00 PM EST

Buck02

kai1414 wrote:
I've got a 2005 LLY that is being monitored with a U7185 v.9r07 and I'm seeing some really strange values for desired fuel pressure. When the key is turned on the desired fuel pressure is up a bit over 4,000psi but when you start it the desired fuel pressure value decreased to 3072psi when the truck is warmed up. The highest desired pressure that I have logged regardless of stock tune, or 80hp tune is 16,000psi. Note that the actual fuel pressure is very closely mirroring the desired fuel pressure and the FPR was replaced two years ago. I'm curious to know if there is a problem with the logging software portion of the Predator or the PID for fuel pressure not displaying accurately? Now that I've had the predator in the truck I'm also seeing these values when I take it out and have it back to the stock tune. I'd really appreciate some help here. Given that these trucks are supposed to reach up over 23,000psi at WOT and maintain 5-6,000psi at and idle, the values that I am seeing for desired fuel pressure are very concerning to me. If it were actual pressure that I was having and issue with I'd be searching for a mechanical cause, however that's not the case.

I also noticed that the desired pressure turns to a -9,xxx psi value at times when driving the truck. Why would that occur?

I've attached a couple of logs.


Idle is suppose to be around 3500-4500 psi.

The Stock injection CP3 pump with stock rail shim is good for 22500psi for an LLY stock CP3 pump.

If you are running into rail issue and have a stock plunger return you may want to plug it or shim it. If you have shimmed already you may want to check the return line and your plug isn't seated in the rail completely. That will cause the code you are seeing.

If you are only seeing 16000psi at WOT then the CP3 cant keep up with commanded or the rail is returning fuel causing the low rail pressure code.


Posts: 15
[

Idle is suppose to be around 3500-4500 psi.

The Stock injection CP3 pump with stock rail shim is good for 22500psi for an LLY stock CP3 pump.

If you are running into rail issue and have a stock plunger return you may want to plug it or shim it. If you have shimmed already you may want to check the return line and your plug isn't seated in the rail completely. That will cause the code you are seeing.

If you are only seeing 16000psi at WOT then the CP3 cant keep up with commanded or the rail is returning fuel causing the low rail pressure code.[/quote]

Out of curiosity where are you getting your idle and WOT psi figures from?

Either way 3072 psi of Desired pressure is not within spec nor is 16,000psi of desired at WOT. What I'm trying to get across is that I am not having any issued with actual fuel pressure so the FPRV and the actual function of the CP3 don't have anything to do with it. Rail pressure is not a problem, as it follows the desired rail pressure value very closely. The problem that I am having is that the desired values are very low all the way through from idle to WOT, both in stock form and with any of the tunes I install from the U7185. I'm guessing that the P1093 has to do with the -9xxx values that I am seeing and it's subsequent departure from actual pressures triggering the code. I've done a bottle test and the FPRV is not losing any fuel and logging the data shows that I am not losing actual fuel pressure.

Could you give me an idea of what the tunes in the predator require for desired pressure at idle and WOT if they are changed from stock form. That's what I'm trying to understand, is what values I should be seeing from the tunes vs what I am actually seeing. If my values are off in both stock form and with your tune, I can pretty effectively rule out anything tune related and start trying to track down a mechanical cause.

I'll try to live stream with Dataviewer and see what I can find. I appreciate the time and suggestions.


Posts: 52507
Location: DiabloSport World Headquarters

pressure at idle is not going to be changed in the tunes...
Mike Litsch
Powerteq Customer Service Manager
Diablo Tech support by phone:
561-908-0040x4
M-F 8:00 AM to 5:00 PM EST


Posts: 15
I understand if you won't give exact numbers but could you please confirm that your tune pressures are at least equivalent to stock OEM tuning at WOT?

Buck02

CP3 Pressures tables are not changed from stock. Injector Pulse and timing is changed which will cause pressures to fluctuate to more commanded fuel. Basically causing the cp3 to work harder.


Posts: 15
Interesting. It was my understanding that the ECM pulled the desired pressure from the pressure table solely as a function of RPM and throttle position. If the injector pulse was lengthened and the timing changed I could see that working the CP3 harder in terms of actual delivery and actual pressure, but don't see it affecting desired fuel pressure at all. Really appreciate the info. That would lead me to believe that I must have a sensor, perhaps the APPS that is supplying an incorrect reading. If you'd be interested in closing the loop, I'll let you know what I find when this gets resolved.


Posts: 15
So here's an update guys. Using the latest tune revision and Dataviewer 3.3 with a GIGAWARE serial cable I've narrowed down the problem to the data logging of the predator/Dataviewer. I swapped in a brand new APPS and the same values of 76.50% throttle position exists with both APPS. I then probed the 5V source and the signals both at the pedal and at the ECM. 5V reference signals are all good. Grounds are all good. My signal voltages at the pedal and at the ECM are right in the allowable spec range. Here's where the problem is. The APPS 2 and APPS 3 voltages that are displayed by the Predator/Dataviewer are off by around 1.0V each. There is no dedicated PID for the APPS 1 voltage, but normalized throttle position PID continues to show 76.50%. Given that I know the actual values in the truck are correct and significantly different from Predator, it leads me to believe that there is a problem with your software for the Predator and or Dataviewer. Given that the fuel pressure values etc that I was seeing a problem with are all derived from TPS and RPM, it would stand to reason that the software is not displaying those correctly either. Any reccomendations or suggestions?

It's now coming full circle a bit that the one other person that I saw that had this exact same problem said that he was logging with a predator and a dealer ECM reflash/recalibration didn't fix his problem, because he still saw it when monitoring with the predator. I'd like to keep using it, but right now I don't have much confidence in the software.

I'd really love some support on this one guys.


Posts: 52507
Location: DiabloSport World Headquarters

do you have access to any other scan tool to verify the data?
Mike Litsch
Powerteq Customer Service Manager
Diablo Tech support by phone:
561-908-0040x4
M-F 8:00 AM to 5:00 PM EST


Posts: 15
mikel wrote:
do you have access to any other scan tool to verify the data?


I have an appt with the local dealer to hook a Tech2 up to the truck on Monday.

I have already verified that the readings in the Pred/DataViewer are not correct by taking actual voltage readings at the ECM, mid harness connector, and pedal with a voltmeter and comparing against the OEM specs for the acceptable range. I've ruled out the harness, ECM 5V reference signals, and APPs as culprits.

Still seeing that 76.50% throttle reading from the normalized throttle % PID.


Posts: 15
Had the truck scanned with a Tech2 at the dealer today. They verified all of my findings that all parameters of APPS etc were within spec. It also further confirmed that the values being displayed with the predator and data viewer are not correct. There is a problem somewhere with your software or firmware that is not allowing the U7185 with the most current update to properly interpret the PID's from the truck. I can tell you for sure that at the very least the desired fuel pressure values and the APPS voltages and the normalized TPS as a % are way off. I'm not sure if its an issue with unit conversions or what the problem is, but it's not right. Thoughts?

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