New EFI user trying to diagnose intermittent low power on LB7

[kst8engineer]

Last night I logged data using EFI for the first time on my LB7. I'm trying to diagnose an intermittent low power issue on it. My initial thought was that the suction side of my cp3 might be getting weak, so in an attempt to diagnose it, I logged RPM, throttle position, desired fuel rail pressure, actual fuel rail pressure, fuel rail pressure (I'm not sure what the significance of this parameter is compared to the other FRP's), and boost. I was surprised to see that my desired and actual fuel rail pressure fell right on top of each other, so I believe that would rule out a fuel starvation issue.

One thing I did note though, was that I see a big difference in boost between a run when the truck pulled stronger versus a "weak" run. On the weak runs, I was only seeing a few pounds of boost over atmospheric.

I'll post the .efi log files tonight from home. In the meantime, does anyone have any thoughts on what would be a likely cause for a low boost situation? Leaking boost line? Bad wastegate actuator?

Thanks in advance

[kst8engineer]

Hopefully these file attachments will work... Here are the log files -- two runs that were very poor accereration, and two that were moderately better.

10138
10139
10140
10141

[Big D]

Any mods? Stock Tune?
Need more data to be logged to get the full story.
log these pids:
CALC.ACTBOOST
GM.FRPACT
SAE.MAF
GM.BARO2
GM.BOOST
SAE.ECT
SAE.RPM
SAE.IAT
SAE.MAP
GM.FUELQ_MAIN_DMA
GM.MAINBPW
GM.MNINJTIM
GM.DMAX_TRQ_DMA
GM.BOOST_DMA
GM.TP
SAE.VSS

Log the data using the pids above and get back to us. There are too many variables to make a attempt at a low power situation without more information especially data.

[kst8engineer]

Only mods are are a 4" downpipe-back MBRP exhaust and a Banks hot-side boost tube. I'm currently running the stock tune. Thanks for the recommendation on which PID's to log. I'll capture more data and post back again.

[kst8engineer]

I logged a little more data this morning, so hopefully this will help. I wasn't able to capture the PID calc.actboost as it was showing that it was unsupported when I created the PID selection file, but for some reason it is showing as supported now. Anyway, here are the logs. Thanks again.

10152
10150
10151

[Big D]

check for a boost leak, there maybe a ripped boot. make sure the waste gate acuator is linkage is connected. use some pliers and try to actuate the wastegate. you should not be able to move it.
Your fueling is being limited proably becuase of a boost which limits the MAF therefore the airflow values are not being achieved.

[kst8engineer]

check for a boost leak, there maybe a ripped boot. make sure the waste gate acuator is linkage is connected. use some pliers and try to actuate the wastegate. you should not be able to move it.
Your fueling is being limited proably becuase of a boost which limits the MAF therefore the airflow values are not being achieved.

Big D - thanks for the recommendations. I'll check those items tomorrow and see what I find.

[kst8engineer]

I just got done looking all of the boost tube connections over. The clamps are tight and the sleeves appear to be properly engaged over the boost tubes and intercooler ports. I noticed a small bit of damage to the outer surface of the sleeve on the lower end of the hot side boost tube, but it appears to just be in the outer layer of the wrap material on the sleeve. I don't know how sensitive these sleeves are in terms of nicks / scratches to know whether it's bad enough to cause a leak.

I tried to move the wastegate actuator linkage, but it feels solid, and the linkage appears to be hooked up properly. It looks like the rubber line/hose that feeds boost to the wastegate actuator is only about 6"-8" long running from the actuator to the outlet of the compressor side of the turbo. I read some other posts on Duramax Forum that were talking about the wastegate actuator being run by vacuum rather than boost, and that the computer altered the duty cycle of a solenoid to control how much vacuum got fed to the wastegate actuator, allowing the computer to control boost. Does my LB7 use a more basic boost-actuated wastegate without computer control?

http://i16.photobucket.com/albums/b4/kst8engineer/04Dmax/IMG_20110319_125310.jpg

http://i16.photobucket.com/albums/b4/kst8engineer/04Dmax/IMG_20110319_125210.jpg

[kst8engineer]

I had a spare sleeve, so I decided to replace the damaged one and see if that was the problem. After I got the damaged sleeve off, I could see that the damage was considerably deeper than you could see on the outside. I also found another crack all the way through to the inside of the sleeve, so I installed the new one. I took it for a drive after church today and found out that replacing the sleeve didn't cure the problem. I haven't had a chance to log data after replacing the sleeve, but it's on the list of things to do.

[Big D]

The wastegate is boost controlled. It uses exhaust pressure and boost psi to open the internal gate to limit boost on stock fueling to around 22 psi. Do a trouble code check with the scan tool and tell us what codes there are. If you can download the tune in the ecm and post it up, there maybe something different. There's always a chance of the charge air cooler leaking.

[kst8engineer]

When I display current DTC's, I only see one:

DTC U1000 ---H--CS

When I display all DTC's, I get the following list:

ABS C0040 M-PH---S
PCM P0101 ---HX--S
TCCM(/ABS U1000
PCM P0700 ---HX--S
DIC U1000 ---H--CS
TCCM(/ABS C0550 ---
TCCM(/ABS B0790 ---
TCCM(/ABS B2725 ---

The current tune is attached.
10160

[THEFERMANATOR]

I see a P0700 code, but no trans codes. Also I see a U1000 which sounds like your reduced power may be a communications issue with the TCM or TCCM. There is a bulletin out for the C0550 code which involves a flash update for teh TCCM due to it not waking up when the key is turned on. If the ECM doesn't see teh transfer case module, it could cause a reduced engine power situation. Also the P0101 is a MAF performance code which is fairly common on tuned trucks(I turned mine off as I didn't feel like rescaling the MAF to get rid of it).

[kst8engineer]

This evening I removed and inspected each boost tube sleeve, cleaned up the connections, and reinstalled each one. I took it for a drive and verified that the problem still wasn't fixed. After that, to rule out the possibility of a bad wastegate actuator, I used vice grips and a scrap piece of rubber hose to temporarily crimp the boost line leading to the wastegate actuator. I took it for a drive again after doing this, and it's still the same. Most of the time, I only get 2-4 psi boost, but on occasion, something changes and I'll build up to 12-14 psi boost.

I was lucky enough to be able to catch one of those on a data log, so I'm hoping that information might be useful. In the log file, at frame 268, something changed and the boost started building. It built up to 12-13 psi and held it, so it's leading me to think that a boost leak isn't the problem. Like THEFERMANATOR noted above, I'm getting a P0101 MAF sensor performance code. Could an incorrect MAF sensor reading be limiting fuel, and do the MAF sensor values in the attached log appear normal (especially those prior to frame 268)?

P0101 "Mass Air Flow (MAF) Sensor Performance" PHC ($10) "Powertrain Control Module (PCM)"

Here's the log file that shows the change beginning at frame 268:
10167

[kst8engineer]

I cleaned the MAF sensor this evening and took it for a drive afterwards, and to my surprise, it seems to have made a big improvement. I'll try to log data tomorrow evening to see if the problem is fixed.

[Big D]

Looks like you found your problem. If there has been a K&N filter in the box the oil could have saturated the element in the meter and cause your issue. the P0101 is a dead give away and will limit fuel if it is not giving feed back.


I cleaned the MAF sensor this evening and took it for a drive afterwards, and to my surprise, it seems to have made a big improvement. I'll try to log data tomorrow evening to see if the problem is fixed.

[kst8engineer]

Looks like you found your problem. If there has been a K&N filter in the box the oil could have saturated the element in the meter and cause your issue. the P0101 is a dead give away and will limit fuel if it is not giving feed back.

We bought the truck with 120k miles and it was completely stock. 25k miles later the MAF sensor started acting up, still with the stock air filter. I don't know in particular what caused the MAF sensor to be contaminated, but I'm glad it's fixed now. I went ahead and flashed the truck this evening with two DSP tunes from Rob Coddens, and it's running great. Thanks to Big D and TheFermanator for all your help!