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  1. #11
    Bobtail Member
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    You say you had a rebuilt controller put on the turbo? This is an ISX CM870 correct? They use an air actuator to move the sliding nozzle. I have also had new turbos that exibit symptoms of the cracked shroud plate. Shroud plates are easy to check if you are competant and careful. I also have no interest in the aftermarket tuners as it always creates more troubles than its worth. Also im a Cummins tech and they will not let me do any warranty repairs on tuned engines. That being said, check the intake and exhaust for shellacking. The boost sensors plug up with carbon due to the same problem that causes the oil filter to plug and give you low engine oil riffle pressure fault codes. Low oil pressure is not a symptom you should overlook on an ISX, it will lead to a catastophic failure. The ISX is built with tri-metal bearings and there is no room for error in the oil system, you WILL lose a bearing or oil pump without the proper oil delivery. Now, the ISX cm870 and cm871 engines suffered from retarded injector camshaft timing and unless its corrected or checked you will be plugging up filters and fouling your intake and engine internals. I am sure this also is the cause of broken rings on the cm870's. It is a fairly big job to check the cam timing but it makes a hug difference in performance, MPG and engine durability. Any time you have low oil pressure codes, verify with a mechanical guage and if its ok.......check the pressure drop across the filter. Checking for pressure drop is easy and a quick way to tell whats going on. Remember to use only Fleetguard extended service oil filters as they help to resolve some of these problems. Cheers, Ed


  2. #12
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    Quote Originally Posted by Heavyd View Post
    I have no experience with tuned ECMs, but that is a big mystery that may be behind some if not all of your problems. I would go back to who ever tuned the ECM with what ever software they used and make sure it is correct for your application. Something may be amiss in the programming. Once the software have been checked and verified, then go onto hardware stuff.
    thanks . It was pulling poorly , ( compared to what I remember ) , and getting poor fuel mileage , before the Tune. The miss has been there for some time.
    I don't think it's the tune .
    Pulled the intake pressure sensor. Looked ok. A little carbon , but not enough to stop it up.

  3. #13
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    Quote Originally Posted by coastrider View Post
    You say you had a rebuilt controller put on the turbo? This is an ISX CM870 correct? They use an air actuator to move the sliding nozzle. I have also had new turbos that exibit symptoms of the cracked shroud plate. Shroud plates are easy to check if you are competant and careful. I also have no interest in the aftermarket tuners as it always creates more troubles than its worth. Also im a Cummins tech and they will not let me do any warranty repairs on tuned engines. That being said, check the intake and exhaust for shellacking. The boost sensors plug up with carbon due to the same problem that causes the oil filter to plug and give you low engine oil riffle pressure fault codes. Low oil pressure is not a symptom you should overlook on an ISX, it will lead to a catastophic failure. The ISX is built with tri-metal bearings and there is no room for error in the oil system, you WILL lose a bearing or oil pump without the proper oil delivery. Now, the ISX cm870 and cm871 engines suffered from retarded injector camshaft timing and unless its corrected or checked you will be plugging up filters and fouling your intake and engine internals. I am sure this also is the cause of broken rings on the cm870's. It is a fairly big job to check the cam timing but it makes a hug difference in performance, MPG and engine durability. Any time you have low oil pressure codes, verify with a mechanical guage and if its ok.......check the pressure drop across the filter. Checking for pressure drop is easy and a quick way to tell whats going on. Remember to use only Fleetguard extended service oil filters as they help to resolve some of these problems. Cheers, Ed
    Dang ! That's a lot. First , this is probably not a new problem. I had the turbo replaced ,because of low boost reading ,on a new item I installed , called a ScangaugeD. It was the first time I was able to see what the ECM way saying the boost was ,since I bought the truck , 2 1/2 years ago.
    And also , I've put 300,000 miles on it , and the turbo was on the truck for who knows how long. Only thing Cummins could tell me , was a head gasket had been replaced , by them , sometime ago, under warranty. I had the turbo replaced Because of the miles on it , and the fact that they wear out quickly, 300,000 - 400,000 miles.
    The new turbo is not acting any differently than the old turbo.
    As to aftermarket tunes , I'll take my chances. Better than ruining my engine , with the ISX EGR setup. I unplugged that EGR , as soon as I bought it. 2 1/2 years ago.
    Exhaust sensor was replaced , not due to carbon, but because Cummins didn't use a Waterproof connector , and when my truck is washed , they open the hood. Water flies around , and enough got into that electrical connection ,to FRY the hot contact ( 5 volt or 12 volt ) off.
    I checked the Intake , it's seems ok , and that's where I get the boost signal , from the ECM , right ?
    As to oil pressure . It is Not a Low oil pressure code . It is an erratic , or intermittent Warning , Not Code . I Was using Amsoil filters , or Wix , from NAPA. I switched to Fleetguard , for the secondary filter element , but , given what I've read about Fleetguard , I May switch back.
    As to camshaft timing , IDK. I've not had plugged filters , that I'm aware of. Or low oil pressure.

    My PROBLEM , and my only problem , is low boost readings , from the ECM , and poor fuel mileage. Coming from Houston , to Atlanta , with 3.55 rears , 13 speed, 24.5 Tall rubber , at 67 MPH , with a tailwind , running 78,000 lbs , was 5.8. A Cummins can do Better than That , that's why I bought a truck with a Cummins engine.
    I've been pushing these things down the road , since '78. In those days , you could invest a Dime in a Cummins , and Get Going !
    I've spent $5,000.00 on this engine , in the Last 30 days ,and Still haven't solved my Problem.
    As to Cummins mechanics , I wouldn't take my truck to Cummins At All , unless it was under warranty.its not.
    Not saying , some cummins guys aren't good , what I am saying , is given the constraints you're under , my trucks not going to your shops.
    The overhead was run , 10 months ago. Mechanic said it didn't really need it. Charge air was checked , a month later, along with an injector check. All was ok. I had the low mileage problem Then , just wasn't sure , cause I almost never was able to fill my fuel tanks . My trucks heavy , and , even with a quarter tank of fuel , I was pushing close to 80,000.
    Now , I've got smaller tanks , and lanes where I can fuel up , to full , without worrying about scales . I can SEE for sure what my mileage is , an it SUCKS. I ran 8800 miles last months , and spent 7,700, on fuel.
    Oh , and its a Cummins Reman Turbo. There had better darn well NOT be anything wrong with it !!!!
    Last edited by pawpaw1; 02.03.2013 at 08.57 PM. Reason:: Additional info

  4. #14
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    You need to check the sensors key on engine off. Boost, barometric pressure and exhaust pressure to make sure they are reading correctly when the engine is off. Have you checked the egr delta pressure tubes? If they are not the insulated type they can be prone to blockage. Sounds like you may have a skewed in range sensor fault if all the mechanical checks are ok. All these sensors are related to boost pressure. Have you used a mechanical guage to verify your readings? Good luck, Ed

  5. #15
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    Has anyone figured out what is causing this low boost/high egt issue? I have a 870 isx doing this. Replaced the barometric sensor because a actual code came up and after sensor was replaced code has become inactive. Checked the vgt and it strokes to spec when using insite, 10-12mm. Installed a fitting and monitored air psi at actuator while driving and when things are working normal truck making 35psi of boost sees 50psi of air psi at the actuator. When things aren't normal truck will only make 22psi of boost and actuator only has 30psi of air psi. Actuator and boost controller are also brand new, no change from original parts. ECM was tuned yrs ago to disable egr and this boost issue just started. Turbo actuator is a tad stiff in the bottom of it's stroke but After seeing the actual air psi fluctuations that the turbo actuator is seeing I'm not convinced it's the turbo. For some reason the ECM is telling the boost controller to only allow so much air to the turbo actuator. Has anyone solved this one?

  6. #16
    Road Train Member Heavyd's Avatar
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    The exhaust back pressure sensor can also cause all sorts of strange problems from not reading correctly. We replace these quite often for issues like this with a good chance of success!

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  8. #17
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    Quote Originally Posted by Ashman_42 View Post
    Has anyone figured out what is causing this low boost/high egt issue? I have a 870 isx doing this. Replaced the barometric sensor because a actual code came up and after sensor was replaced code has become inactive. Checked the vgt and it strokes to spec when using insite, 10-12mm. Installed a fitting and monitored air psi at actuator while driving and when things are working normal truck making 35psi of boost sees 50psi of air psi at the actuator. When things aren't normal truck will only make 22psi of boost and actuator only has 30psi of air psi. Actuator and boost controller are also brand new, no change from original parts. ECM was tuned yrs ago to disable egr and this boost issue just started. Turbo actuator is a tad stiff in the bottom of it's stroke but After seeing the actual air psi fluctuations that the turbo actuator is seeing I'm not convinced it's the turbo. For some reason the ECM is telling the boost controller to only allow so much air to the turbo actuator. Has anyone solved this one?
    Need more symptoms here. Any fault codes? Egr valve removed? You will need to split the turbo and check the shroud plate, it wasnt as bad with the cm870 but ive seen lots cracked. Even in the ism ive seen it. There are np air leaks I presume? Checked supply air pressure when out put is less? Also if the delta p sensor is bypassed you have no way to tell if the egr valve is closed other than to visibly check the plunger is not broken or partialy open. There are only a few things that cause your problem, excessive fuel or restricted air flow. Is there black smoke? Seen the sliding nozzle bind under certain circumstances such and putting the turbo on end or hot. Chances are its the turbo. Best of luck

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  10. #18
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    Quote Originally Posted by Heavyd View Post
    The exhaust back pressure sensor can also cause all sorts of strange problems from not reading correctly. We replace these quite often for issues like this with a good chance of success!
    Bang on, thank you sir! checked with insite, engine cold, and turned off and reading for exhaust gas pressure was 66.2 InHg. Checked on a 2250 engine and sure enough the reading is 27.7InHg. So replaced the sensor and now reads the same as my 2250. Test drove and I now have my boost back, 32-36psi.

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  12. #19
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    Quote Originally Posted by coastrider View Post
    Need more symptoms here. Any fault codes? Egr valve removed? You will need to split the turbo and check the shroud plate, it wasnt as bad with the cm870 but ive seen lots cracked. Even in the ism ive seen it. There are np air leaks I presume? Checked supply air pressure when out put is less? Also if the delta p sensor is bypassed you have no way to tell if the egr valve is closed other than to visibly check the plunger is not broken or partialy open. There are only a few things that cause your problem, excessive fuel or restricted air flow. Is there black smoke? Seen the sliding nozzle bind under certain circumstances such and putting the turbo on end or hot. Chances are its the turbo. Best of luck
    No charge air system leaks, egr delete tune was done prior to me owning the truck but its unplugged and steel plug is installed inside the hose prior to the engine, no exhaust leaks from egr valve onward so I wasnt convinced it was a egr issue. Also monitored air psi to the the turbo controller and after the truck built 108psi the controller would always see 108+psi. Seeing the output psi to the controller vary made me believe this wasnt a turbo issue, I can see how lots of mechs can mis-diagnose and install a turbo and it not fix the problem. Looking at a baseline of all the sensors and and there outputs has taught me lots, and will help me in the future with the many more issues i'll have to deal with.

  13. #20
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    dude,you,have,a,CAC,,leak,ibet..rubber,boots,,,,se t,your,idle,to1200,and,spay,all,the,connections,af ter,the,turbo,with,soapty,water.......se.if,theres .leaks

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