no engine light

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by slowhanddrt, Aug 6, 2020.

  1. slowhanddrt

    slowhanddrt Bobtail Member

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    Jul 20, 2017
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    I have a 1995 pete with a 5EK cat motor, i am having a problem with performance, while going down the road it will cut out like it is a throttle positioning sensor with no engine light. Does this mean a bad ecm?
     
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  3. Eddiec

    Eddiec Road Train Member

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    The TPS could loose - check connections between the throttle and the sensor
     
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  4. 062

    062 Road Train Member

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    Could be, but I would rule out all the harness’s first. I had a similar problem and it was the temp sensor harness under the alternator. It never gave a light,but logged all kinds of codes.
     
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  5. BoxCarKidd

    BoxCarKidd Road Train Member

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    I worked on a 3406E that would do stuff like that but would actually shut down about once a month. It had broke down all over the SE and a lot of money was thrown at it. Started driving it home and to work. Parts chaser, trailer spotter etc. It never logged any codes.
    Then one day it cut back like the key was turned off. It was very brief and did it several times. Pro Link showed a code and low oil pressure at the same time. Manual gauge reading was good. When stopped it had logged no active or inactive codes. Replaced the oil pressure sending unit and never had another problem.
    That is very odd and it is more likely a problem with your TPS or its wiring. However some of those type things happen. I believe there are some onboard code readers that are relatively inexpensive that could do that. Some may be able to read throttle percentage. If it is reading 20% and you have it on the floor you know there is a problem there. That will not log a code because it sees nothing wrong. ECM just adding fuel to the amount it sees requested.
     
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  6. 062

    062 Road Train Member

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    It took about 3 weeks to find it. I started driving with a scanner hooked up and the most common code was high coolant, but the gauge read normal. Finally found it about 3am, it was showing high intake air and the truck had just been started. I was wiggling the harness and it cut off showing high coolant. I went around and wiggled that harness and saw it arch behind the alternator.
     
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  7. Heavyd

    Heavyd Road Train Member

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    Get it scanned regardless. It is probably logging codes. Check engine light might not be working. Never jump to an ECM first. They are rarely bad.
     
  8. BoxCarKidd

    BoxCarKidd Road Train Member

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    I had a similar thing with a 2505 Terragator and a 3176. It had an intermittent problem. None of the truck scan tool connectors will even plug up to it. Working on it at dark 30 ( not black dark but at least 30 minutes after sundown ) the harness crossing over the hand primer pump sparked when moved. Hose wrapped around the harness and it was running. Never would have seen it in the middle of the day.
     
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