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Discussion Starter #1 (Edited)
I figured it was about that time again to "give back" to you guys. We cant express our appreciation for you guys running our tuning and representing our product. So I feel I will make a little post on how to do basic diagnosis on your truck using your EFILIVE V2 or AUTOCAL. Regardless if you purchased from us, or any other tuner... This information should be beneficial for you. Feel free to add whatever you wish!

Here we go...

The best way to diagnose issues with your vehicle, is to first understand how the ECM interprets the data from the sensors, and then applies voltage for the desired fuel/air.

Lets start with the beginning of the puzzle, the MAF sensor. The MAF sensor is what calculates how much air your vehicle is taking in, which then allows the ECM to tell the fuel system how much volume to allow. EFILIVE uses the units of MM3 to represent the fuel volume in our trucks. At Idle, typically we will see roughly 40 grams/sec calculated by the MAF sensor and roughly 10mm3. It is safe to say 10mm3 divided by 8 injectors= each injector putting out roughly 1.25 mm3. When looking at balance rates, it is also safe to assume the ECM is looking for 1.25mm3 per injector to determine a perfect balance rate of "zero". Zero as in the fuel rate note being positive or negative of 1.25mm3 per injector. This volume of fuel is achieved by 2 things, Fuel injector "on time" (Duration) and Fuel rail pressure supplied by the CP3. The on time is how how long the injector is held open in microseconds. The Rail pressure is the PSI made by the cp3 into the rails.

The Cp3 determins how much pressure to make by its "regulator".. This regulator is sent a voltage which is then calculated by the ECM to PSI. "zero" volts will send the CP3 wide open on pressure (hints why you hear of a dual cp3 kit losing its ground and going to max pressure from time to time).. Remember there are other limiters involved that are in place to keep the cp3 alive (such as mm3 per sec, fuel flow upper base, ect.) so just changing voltage or desired fuel rail pressure does not mean you will always get what you command..:thumb

So now that you see the very basics of the process of the ecm (yes i left how torque based fuel and many other tuning aspects ect. as this is not a "tuning thread") we can now look at common issues and how the "average guy" can diagnose them.

MAF- Lets say the truck is laggy on the bottom, or has some type of surge or just feels like it isnt getting the proper fuel and we see rail pressure actual following desired. The next place to take a quick look is the MAF sensor in grams/sec or lbs/min... I use grams/sec so lets go with that. As you get on the accelerator, your commanding more fuel which requires more air for a proper AFR. When you come off of idle (40 grams/sec) and come into the throttle you should see grams/sec go up. On a LBZ/LMM for example, at WOT you should see at least roughly 350 grams/sec. If your truck is feeling laggy or surgy, take a quick look at your log and see if grams/sec is fluctuating or if it is coming up in a linear fashion. If you see a drop or a surge in grams/sec start with the basics. Look for EGR commanded and if it comes off of "zero" and opens, then you will sometimes see a drop- this could indicate a faulty EGR valve. Another scenario could be a boost leak, or the most common A DIRTY MAF SENSOR! Understand that if the MAF fluctuates, so will fueling because the ECM will not allow the truck to fuel any more than the limit set by the maf sensor. Some tuners set this up differently, but the majority will have MAF enabled properly.

Rail pressure- Scenario 2.) Your going WOT (or under strong load) and the truck feels as though it falls on its face. Generally, when this happens the truck will set a code such as a P0087. This can be caused by many different things. The most common denominator for sudden rail loss is the fuel filter being dirty! I tend to change mine every 5k miles..but thats just me. Not always, but many times the drop from the rail losing pressure through a faulty valve (04.5-2010 dmax) (FPRV=fuel pressure relief valve) looks like a very harsh sudden drop in the log many times dropping to, or lower than 11,000 PSI. Another test for this is the "bottle test" in which you can use the search up there and find out easily how to do. If this be the case, its under 60 bucks to pick up a Race valve, or you can simply shim it. Search is your friend :neener.
Now lets say the valve checks out "ok" and its time for further diagnosis.. The ECM has what is called "thresholds" and what this is the limits and the amount of time the Actual Vs. desired mismatched to determine if the ecm needs to go to limp home and/or throw a code. These thresholds can be modified with EFILIVE, but remember dont band-aid hard part issues with tuning. BAD TUNING CAN ALSO CAUSE ISSUES. Bad injectors can cause low FRP and a bad cp3 can cause low rail pressure. A 06-2010 dmax commands 26k FRP at WOT, on a truck with under roughly a 100hp tune, the stock cp3 should have no issue keeping up unless it is in bad condition. On a 01-05 dmax the rail should be right up of 23k. LB7s are notorious for injector issues so if you are having rail issues there, I would not overlook that as being a issue even if the balance rates were ok as balance rates do not always detect leaks, large drips, ect. Rail pressure at idle should be around 4300PSI, if you are having a "surge" at idle, look at your desired vs. actual and see if it is fluctating.. If so, lift pump pressure may be too high, or very likely a bad fuel pressure regulator.

Also note that tuning plays major key into low rail issues if the tune is commanding more fuel than the stock fuel system can keep up with. I recommend ask your tuner to look at your datalogs and tell you what is going on. As professional tuners, they should know how all the sensors work, and every basic thing i just told you. Big duration can cause a low rail pressure issue. Not to mention low rail pressure (i consider low more then 3500PSI of desired) is very inefficient and many times can cause a truck to smoke, lose power, and get bad fuel economy. Low rail pressure is also hard on the CP3 and injectors, so make sure to not "band-aid" these types of issues to save a buck, cause likely it will cost you in the long run.

If there is anything else you guys would like to ask, feel free to do so. I hope this gives just a basic understanding of how your truck looks at fuel and air and the basics on how the sensors work. If you do not know how to work the scan tool, i recommend downloading the tutorial i have in my link and checking out how to datalog, build maps, and create dashboards ect.

Thank you again everyone for all your business and cheers to 2013! :drink:gearjamin:D
 

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Nice write-up Kory, I went ahead and stickied it. It might be good to try to keep it clean, so please only comment if you are asking something or adding something.
 

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Great info, this is why I joined this forum. I have my problem listed in the LB7 powertrain section if you would care to look at it but I will ask you my EFI Live questions directly here. Truck starts,runs, great just seems to laydown at 60mph max boost is 16psi used to make 26psi. new MAF, MAP, FICM, fuel pressures on top of each other.

1) I have an autocal with dsp5 setup on it and I would like to be able to view my data logs because I am not getting enough "free" answers from my tuner. Is there a way I can see my own logs without buying V2?
2) I had different tuner look at my logs and he is telling me that my MAF and "demanded" fuel looks good (maybe slightly rich) but i am not making the boost/power to match and there is no black smoke (not a boost leak) any ideas?
3) will the low boost cut fuel back? could I really be that rich and have no black smoke?

Thanks,
 

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Awesome post. Just picked up a v2 and ordered tunes through Willie today for this very reason! Cant wait!

Not too many other tuners willing to spend their time to write stuff like this up , def helps the average joe efi user like me


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Discussion Starter #7
Great info, this is why I joined this forum. I have my problem listed in the LB7 powertrain section if you would care to look at it but I will ask you my EFI Live questions directly here. Truck starts,runs, great just seems to laydown at 60mph max boost is 16psi used to make 26psi. new MAF, MAP, FICM, fuel pressures on top of each other.

1) I have an autocal with dsp5 setup on it and I would like to be able to view my data logs because I am not getting enough "free" answers from my tuner. Is there a way I can see my own logs without buying V2?
2) I had different tuner look at my logs and he is telling me that my MAF and "demanded" fuel looks good (maybe slightly rich) but i am not making the boost/power to match and there is no black smoke (not a boost leak) any ideas?
3) will the low boost cut fuel back? could I really be that rich and have no black smoke?

Thanks,
Who is your tuner?


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IdahoRob with ATP trucks. I am not trying to run anyone through the mud, they are a good company and were very helpful and I am sure the tunes will work great if I could ever solve this problem. This is an unusual problem that can't really be blamed on their tuning so they stopped offering free answers (I ask a lot of questions! because I am usually good at diagnosis, but I can't "see" into the ECM as well as they can and I don't have intrest in writing my own tunes) and offered to try fix the problem with their hourly rate and me driving the 600 miles to get my truck to them.
 

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Discussion Starter #9 (Edited)
I would trust what they have to say... They are very good in what they do!

The autocal is likely set up to data log and use the scan tool 7.5 to view the data. If the autocal doesn't already have the pids loaded then use it as a pass through device with 7.5 and select Duramax imperial for your PID list. Maybe Dustin will chime in here shortly and help you out too!


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Great info, this is why I joined this forum. I have my problem listed in the LB7 powertrain section if you would care to look at it but I will ask you my EFI Live questions directly here. Truck starts,runs, great just seems to laydown at 60mph max boost is 16psi used to make 26psi. new MAF, MAP, FICM, fuel pressures on top of each other.

1) I have an autocal with dsp5 setup on it and I would like to be able to view my data logs because I am not getting enough "free" answers from my tuner. Is there a way I can see my own logs without buying V2?
2) I had different tuner look at my logs and he is telling me that my MAF and "demanded" fuel looks good (maybe slightly rich) but i am not making the boost/power to match and there is no black smoke (not a boost leak) any ideas?
3) will the low boost cut fuel back? could I really be that rich and have no black smoke?

Thanks,
Sounds like a possible bad turbo or boost leak as with the LB7 we can not control boost directly due to it being a fixed vane charger.

may also want to check your wastegate as that is a common problem to start leaking.
 

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I cannot view my own data logs, however, as memeory serves while looking at my cts I was getting ~450gm/s. If the turbo and or wastegate was going bad would the lack of boost (MAP) pull fueling out? or would it continue to pour in fuel according to the MAF. seems to me if the MAF reading is on point the compressor side of the turbo is good? Is there a way to test the turbo/wastegate? I have pressure tested the compressor side with no leaks. FYI this all started when i deleted my EGR. Thanks so much for your help guys!
 

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Discussion Starter #13
When deleting egr and issue all if the sudden happened there is likely a leak there. I bet you would see grams/sec drop when it occurred.


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wouldn't the truck blow black smoke with a boost leak? Or does the MAP scale back the fuel to match boost?
 

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Great information Kory thanks.
To data log just plug autocal into truck, drive, then autocal into computer for results, right?
 

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Wow, thanks for this. I got my autocal from a local shop just in case I needed some more answers and I'm finding out much more here!

Thanks
 

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So how can I tell if my lift pump pressure is too high?
 
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