Sporadic Fault Codes….

desrtdog

desrtdog

Senior Member
Joined
Nov 15, 2020
Posts
290
Location
TX
I am currently traveling with “The Dominic” (2010 BB Vision; 6.7 Cummins ISB; Allison 2500). Changed both fuel filters on Wednesday, prefilling both before installing and took it out for a 20 min drive to get it up to temp - ran fine.
Drove from Houston to Kerrville Friday - 260 miles, no problems, except for one issue where the bus stalled when started (after a rest break) and put into Drive. After arriving, had the same issue when the bus was started after being shut down - i.e., stalled when shifted from N to D….both of these cases the bus was still warm…in both cases, I hit the manual prime pump at the low pressure filter and managed to get it started/moving, in the latter, I let it sit for a couple hours before doing this.
My initial thought was that maybe there was some air still in the fuel system, and that when the engine was warm, perhaps this exacerbated the issue. However, this afternoon I took it out to fill the tank and run by the store, leaving it running while I was in the store (maybe 10 min). After pulling onto the main road, the bus lurched as if it was stalling again, so pulled over, shut down, pulled error codes: FMI 2 / SPN 101 (fault code 1942 - Crankcase Pressure - Data Erratic, Intermittent, or Incorrect) and FMI 2 / SPN 627 (fault code 4429 - Power Supply Lost With Ignition On - Data Erratic, Intermittent, or Incorrect) both Historical, not Active … did the fuel pump thing and was on the way again in 5 min…back on the main road, it did the same thing again and the power was severely lowered as I limped back to the hotel.
Let the bus sit til after dinner, then went and looked again at fault codes…had one active at “key on” FMI 7 / SPN 2633 (fault code 3616 - Engine VGT Nozzle Position - Mechanical System Not Responding or Out of Adjustment)…started the bus and idled for several minutes, and on starting the code went to Historical… (As a side note, I did get this same code about a month back, but not accompanied by the loss of power that I got this afternoon.)

So now here’s the question: is it possible that a dirty crankcase filter could be causing the 1942 and 3616 fault codes?? ….or something else….

I’m planning to change the crankcase filter tomorrow (have a new filter and not entirely sure how long ago it was changed - not since I’ve had the bus, so 4-1/2 years min). Will also try to check the connectors for the turbo actuator and crankcase pressure sensor (if I can get them apart), but would appreciate any input…
 
I would clear all the codes and see if this one comes back.
FMI 2 / SPN 627 (fault code 4429 - Power Supply Lost With Ignition On - Data Erratic, Intermittent, or Incorrect) both Historical, not Active

Any kind of power loss will make any electronic system go wacko...causing other codes/issues.
We had another member having intermittent issues with the TCM as so did I.
turned out if as a failing pigtail fuse holder in the batt box.
I would go there first.

If the fuse is loose or if one leg is discolored, that would need immediate attention. Not saying this is your issue but this scenario could cause your intermittent issues, other issues maybe like this one you listed.... (fault code 1942 - Crankcase Pressure - Data Erratic, Intermittent, or Incorrect)
 
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I have looked for said fuse holder at the batt box before and could not find one … no smaller gauge wires coming from the box … will look again later this morning.

Was asking about the ccv filter because both the turbo and pressure sensor are in that area - crankcase has a vent to the turbo …
 
I have seen other BB busses where they actually use circuit boards in their electrical systems. not sure about yours. best way to find out, have you ever tried getting your wiring diagrams from the BB website?

anyway, in a pinch, if nothing else (filters) seem to get the job done, you could try finding the ecu power wire at the ecu, try following it back to see where it goes OR find the power wire, strip the insulation back about an inch and attach a new fused power wire to the old one, without cutting out the old one.

You would in effect be piggy backing or adding another power wire in parallel to the original power wire.
It shouldn't cause any issues with back feeding. The ecu will only see a new clean power wire and dismiss the old wire.

Later down the road you can do a proper fix. This of course is assuming that my guess is correct.

I honestly do not see how a plugged up filter would cause the ecu to loose power or cause erratic data from a sensor. at worst the motor might smoke or run ok but at a power loss, but this is just my guess. If you get it going again, clear the codes from the ECU if possible. If a loss of power to ecu shows up again I would feel that I am guessing in the right direction. If you want to PM me your vin I would be happy to look into the BB website for a wiring diagram.

The other easy troubleshooting elimination thing I would do, remove the crankcase filter and do a short run, monitor how she responds. If that was all it was then simply get a new filter....
 
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Google search -> 6.7 Cummins VGT cleaning
To address a potentially stuck or coked-up 6.7 Cummins VGT (Variable Geometry Turbocharger), you can try cleaning the turbo, which involves removing and rebuilding it, and recalibrating the actuator.

Here's a more detailed breakdown:
  • Why Clean?
    Clogging of the VGT vanes with carbon buildup can lead to reduced performance, misfires, and potentially stuck vanes.

  • Cleaning Process:
    • Removal and Rebuild: The most thorough approach involves removing the turbocharger, disassembling it, and cleaning the vanes and housing.

    • Actuator Recalibration: After cleaning, the actuator (which controls the vanes) needs to be recalibrated to ensure proper operation.

    • Vane Stuck Open or Closed: If the vanes are stuck, you may need to unplug the VGT solenoid and tap the turbo to free them, or leave the solenoid plugged in and tap the back of the turbo.
  • Preventative Measures:
    • Regular Maintenance: Follow the recommended maintenance schedule for your 6.7L Cummins, including changing the crankcase vent filter and cleaning the EGR valve.

    • Fuel Quality: Use high-quality diesel fuel to minimize soot buildup.

    • Avoid Extended Drain Intervals: Regularly drain and change the engine oil to prevent sludge and contamination.
  • Common Problems:
    • Stuck Vanes: A common issue with VGT turbos, often caused by carbon buildup.

    • Excessive Oil Consumption: Can indicate a failed bearing or other issues within the turbocharger.

    • Mechanical or Electrical Faults: Other potential problems can include actuator failures or electrical issues.
  • Professional Help:
    If you're not comfortable with these procedures, it's best to seek professional help from a qualified mechanic.
This video demonstrates how to clean a diesel VGT turbocharger:
 
@desrtdog,
I'll be away from the computer so just give me a call if I can help out in anyway....
 
So, pretty sure I am dealing with an electrical gremlin. I got 7 miles up the road from Kerrville on Monday when the bus shut down…would restart, but when I dropped it into “drive”, it stalled. Spent a couple hours on the roadside checking battery connections and other electrical connections under the bus; called a shop I talked to earlier in the day and told them I was going to try to make it over to them…started the bus, turned around and it ran fine all the way in (about 30 min), as well as while they were checking it out on the computer…
Could find nothing really obvious, so left it overnight for them to take for a drive in the morning, plus do a couple of other small things while they had it …. On their test drive Tuesday, could not replicate the issue…were supposed to take it out again yesterday evening, but that did not happen… waiting to hear back today…

Thinking electrical because the code it was throwing on Monday was the FMI 2 / SPN 627…

More to come…
 

  • In Cummins diagnostics, an FMI (Failure Mode Indicator) value of "2" indicates that the data is "Erratic, Intermittent, or Incorrect". This means the sensor or system is not providing a consistent or reliable signal.

    Here's a more detailed explanation:
    • FMI (Failure Mode Indicator):
      FMI codes are used in conjunction with SPN (Suspected Parameter Number) codes to pinpoint the nature of a fault.

    • FMI 2 Meaning:
      An FMI of "2" signifies that the data received by the Engine Control Module (ECM) from a specific sensor or system is not reliable. The data is either fluctuating erratically, intermittently failing to provide a signal, or simply incorrect.

    • Possible Causes:
      • Sensor Issues: The sensor itself might be faulty, damaged, or have a loose connection.

      • Wiring Problems: A short, open, or damaged wire in the sensor's wiring harness can cause intermittent or incorrect data.

      • System Problems: The system the sensor is connected to (e.g., aftertreatment system, turbocharger) may be malfunctioning, leading to erratic sensor readings.

      • ECM Issues: In rare cases, the ECM itself might be experiencing a problem that causes it to misinterpret sensor data.
 
So picked up the bus this afternoon and drove the 30 miles (mostly uphill) to Fredericksburg without a single issue.
Talked to the mechanic before I left, and he said that he cleaned a few connectors and checked cables. They also had it out on a couple of drives and were not able to replicate any issues. Don’t know if possibly something was reset by plugging in to the insite software or maybe something resolved in the poking around. Will look at the schematics a bit more after I get home… Got a 230 mile drive home tomorrow, so fingers crossed it goes without a hitch…
 
Ok so after going thru all those useless diagrams...would you believe your service manual is also listed there!
volume 2, I printed the pages for you, 4, highlighted the power wires to the ECM.
The wiring looks straight forward. Goes thru 1 relay and 2 fuses. You have 1 common power stud and one common ground stud.

Here's the diagrams and don't know if you got the other doc I talked about, stress testing wires.
Keep me updated...
 

Attachments

  • Porchdog bus wiring -ECM.PDF
    1 MB · Views: 2
  • electrical_circuit_testing.pdf
    215.9 KB · Views: 5
@ewo1 - can’t tell you how many times I’ve looked at the vantage site and skipped right by the “reference” tab, going instead directly to the wiring diagrams…funny thing is that I had downloaded the service manual in pieces from the Central States Bus website, but did not bother to check through the Body Electrical section for essentially the same wiring diagram I landed on from the wiring diagram section. Thanks!
As mentioned in your note to me, I’ll check the relay and fuses when I get to the bus later today…
 
So here’s where things stand….
On Thursday, had the bus out for a test drive following some troubleshooting…ran good for about 20 min, then service light came on with chive error codes 1117 and 0435, and oil pressure indication on dash showing zero. Shut bus down the restarted; oil pressure indication back and error codes moved to inactive.
On Friday, I pulled and cleaned all the ground connections on the engine (2) and firewall (1); checked each battery (voltages at 12.70 / 12.68 / 12.69; checked continuity of the + and - power wires to the ECM (light bulb test => good); replaced the 5 amp fuse for ECM ignition wire, and procured but did not install a new relay for the ECM ignition fuse block. Ground wires looked ok before wire brushing, although the large post at the firewall had 4 different wires on it and there was some paint on parts fo the lugs…

Today, I backprobed the ECM ignition power wire through the firewall connector (ok); loosened and cleaned the alternator ground wire; pulled the connector on the oil pressure switch and sprayed the terminals with electronic cleaner and checked resistance spec on the pressure switch - spec is < 10 ohms, it was zero…Then took the bus for a 30+ minute drive with no issues…

So, problem solved or not??… will have to see do a bit more driving to see…maybe the ground wire cleaning, maybe the new fuse?? More to come…
 
As I was reading about your issue, it feels like it could be wiring, specifically the contacts. I think you are on the right trail. Hopefully it doesn't come back.
 
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