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Tim
Tim, Foreman
Category: Heavy Equipment
Satisfied Customers: 356
Experience:  23 Years Heavy Equipment and Truck Repairs Shop and Field in the Minning and Construction Industry
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cat c7 engine starts and runs fine. develops intermittent miss

Customer Question

cat c7 engine starts and runs fine. develops intermittent miss under load and no load conditions. acts like air in fuel. replaced filters. ran fuel line directly to transfer pump from bucket of fuel. no leaks in fuel system. exhaust temps. read normal. cylinder cut out seems equal. no codes..any ideas?
Submitted: 5 years ago.
Category: Heavy Equipment
Expert:  Tim replied 5 years ago.

Hello, welcome to JA, my name is XXXXX XXXXX try to help... Couple questions, any smoke when it cuts out? do you have cruiz control, and has it ever had the miss in cruiz? does it ever miss when not moving and just throttling up? sounds like you have ET or a scanner? Also, please include engine ser# XXXXX reply...

 

 

Tim

Customer: replied 5 years ago.

no smoke when it cuts out,never tried it in cruise,does cut out moving or not,original complaint was that the truck would barely go more than 8 miles an hour then it would just take off like a rocket, I test drove it. it was never that bad but i could feel a miss mostly upon take off then engine would clear up. I've since given the truck back for local deliveries only until it gets worse, so I do not have engine serial# XXXXX

mike

Expert:  Heath replied 5 years ago.
Hello my name is XXXXX XXXXX i would enjoy helping you with your question. First thing you need to do is ck your engine oil and see how dirty it is because the injectors on that unit are oil pressure actuaited and oil pressure makes them fire. If the oil cks good you need to take a plug out of oil rail on the drivers side of the engine and ck oil pressure coming out of your Huey pump the pressure at full rpm seating still should not fall under 28 Lbs if all cks good you need to then ckd for any medal in the same oil rail if there is medal present the huey pump then has failed and you the need all injectors and pump changed. Hope that helps you with your problem and if you have any more question fill free to ask and thank you.
Expert:  Tim replied 5 years ago.

Hello mechanic mike, Thanks Heath for the input... on a intermitten miss like you have explained that only happens sometimes , I would not go changing the heui dirty oil / diluted oil would be causing problems more constant, and if the Heui was pumping metal you would be parked..and i would not condem any Heui with out plugging into it and checking accuation pressures, and what the ECM is seeing.. any ways, with out the ser# XXXXX had to use a a typical ser# XXXXX here is your trouble list for intermitten cut out... the reason I asked if it does it in cruiz is because if it doesnt, then you will want to focus on the throttle position sensor...let me know

 

  • Diagnostic codes

     

  • Electrical connections

     

  • Engine monitoring

     

  • Electronic system

     

  • Accelerator pedal position sensor

     

  • Vehicle speed signal

     

  • Power train data link

     

  • Fuel supply

     

  • Torque limit switch

     

  • Low injection actuation pressure
  •  

     

    Tim

    Customer: replied 5 years ago.
    Tim, will i be able to continue this diagnosis with you. once the the truck returns to my shop in the next week?
    Expert:  Tim replied 5 years ago.

    Hello... Yes sir you can!!! Just reply back when you are ready...

     

    Talk with you then,

     

    Tim

    Customer: replied 5 years ago.
    Hey Tim, got that c7 back. ser#KAL28667 Truck hesitates so bad at times it will not exceed 8 mph. driver pulls truck to side of road shuts ign. off waits 5 mins. starts truck and it will run fine for an undettermined amount of time. as for cruise truck haas to run at 35 mph before you can engage and if you've made it that far odds are it's running fine or only hesitating slightly. driver says"all our c7s hesitate from a stop though" this company uses biodiesel
    Expert:  Tim replied 5 years ago.

    Ok,your ser # XXXXX the same list I gave so lets start with a couple checks., no check engine lights correct? this has brand new fuel filters?. . when sitting at a idle... no problems correct?

     

     

    Full throttle nuetral with foot pedel does it miss or cut out??

     

    If you , turn on the cruiz switch and with out the pedal, use the accel switch to throttle up any problems??

     

    Do you have a reader or Cat ET? or access to it if so the things we need to check is fuel position to fuel rate.. and quite a few other things..

     

    Tim

    Customer: replied 5 years ago.
    we have a prolink which i believe reads fuel rate to fuel position not sure. yes cruise switch accelerates smooth to 1400 rpm. try to duplicate with foot feed engine cuts out. throttle signal does not fluctuate but i don't know how fast refresh rate is on a prolink. graph the signal line to ecm with graphing meter?
    Expert:  Tim replied 5 years ago.

    Ok I am really leaning towards the TPS now if it doesnt cut out with the cruiz accel, but does with the pedal... so if you were to take it for a drive and use the accel switch for a throttle, I wonder if you could get top speed with out issue.. Check the plug real well at the pedel, also make sure its comming all the way up..( no dirt jammed under the back of it)

     

    any ways lets go the the next step see if you can do the following with your prolink.. i am not familar with prolink on cat.. because I have ET..try this..........

     

    Monitor the fuel position, the rated fuel limit and the FRC fuel limit.

    While the vehicle is operating under full load, the parameters should meet the following conditions:

    • The fuel position is equal to the rated fuel limit.

       

    • The fuel position is less than the FRC fuel limit.

    Let me know..

    Tim

    Customer: replied 5 years ago.
    Tim, New scenario swapped tps with known good from kal29160 c7, test drove no problems. got back to shop engine would miss upon excelerating with no load at about 1500rpm increased throttle to gov. @ 2600rpm engine misses horribly feels like its running out of fuel frc=112 fuel del.=104 fuel rate=158 checked fuel pressure 70-72psi good flow engine temps cyl 1-4 well over 600 deg. 5 &6 200-250 i'm sure I losing 5&6 held throttle @ 100 percent for atleast 2 min. while all this is happening start to lose rpm down to 1500 like running out of fuel but guage shows 70-72 psi flow still good inj press 3775psi inj. rate shows 50% smokin' like a mother......havin' fun yet ...i'm not....lol!
    Expert:  Tim replied 5 years ago.

    Ok .. so sounds like we may have corrected one issue of a few issues with the TPS.. your fuel rate is higher than the frc so the next step is the following. you already checked the rate and pos..

    read 4 and do 5 also make SURE you are not getting a code when the miss is happening..

     

     

    1. Connect Cat ET to the cab data link connector.
    1. While the problem is occurring, check for diagnostic codes that are related to the boost pressure sensor and the atmospheric pressure sensor. If a diagnostic code is found, refer to Troubleshooting, "Engine Pressure Sensor Open or Short Circuit - Test".
    1. Monitor the fuel position, the rated fuel limit and the FRC fuel limit.

      While the vehicle is operating under full load, the parameters should meet the following conditions:

      • The fuel position is equal to the rated fuel limit.

         

      • The fuel position is less than the FRC fuel limit.

         

      If the fuel position is equal to the rated fuel limit and the fuel position is less than the FRC fuel limit, the electronics are operating correctly.

    1. If the fuel position is not equal to the rated fuel limit and/or the fuel position is not less than the FRC fuel limit, perform the following tests in order:
    1. When the engine is off, place the keyswitch in the ON position. Check the boost pressure on the Cat ET status screen.

      When the engine is off, the boost pressure should be 0 kPa (0 psi).

     

     

    Check the above first...then if its OK and your prolink will do a injector cut out test check that...

     

    I will be off work and home in about 2 hrs...

     

    Tim

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