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Really rough idle— check engine light comes on— idle problem gone— and repeat🤔

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Really rough idle— check engine light comes on— idle problem gone— and repeat🤔

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  #1  
Old 10-12-2017, 08:19 PM
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Question Really rough idle— check engine light comes on— idle problem gone— and repeat🤔

Okay so this is probably the strangest thing I’ve ever seen so I’m beyong confused on where to start. 1st off I’m an ase a1 engine repair certified mechanic, on gas, but my truck is a 7.3 diesel don’t know most about em but I know what I need to know.

Anyways..

I’m having a misfire/rough idle issue at stop, kinda badly, you can feel it shake and watch the rpms rise and lower and hear it in the engine and exhaust but it goes for about a minute or two then my check engine light comes on and the idle smooths out to perfect like nothings wrong??

Then I continue driving and the engine light goes off after a moment and as I’m stopping the misfire/rough idle comes back for a few moments and then the engine light comes back on and it goes away like nothing happened and so on and so on.

I noticed my fuel mileage is getting really worse as well.

Now I’m thinking and usually a gas engine miss fire is a delayed spark in the ignition system, but in diesel there aren’t spark plugs there glow plugs that don’t give out a spark so I’m leaning towards injectors but it’s the strangest thing for it to go away completely once the check engine light comes on?

Any diesel mechanics out there that can give me any advice is majorly appreciated!

Truck: 2002 f250 7.3 turbo diesel 4x4
 

Last edited by Biggreendiesel02; 10-12-2017 at 08:21 PM. Reason: Forgot a part that might help
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Old 10-12-2017, 10:44 PM
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My 7.3 is doing the same thing... first have it scanned to find the code to make sure.. mine does that it died on the highway and started and ran fine till i stopped at a stop sign then violently idled then shut down. Mines is a bad icp plus icp pig tail this could be the Loss of mpg. Think mine lost some too. So when it starts to idle rough the check engine light comes on and may set the motor to factory setting and when it’s tunni fine (it thinks) it goes off and repeat... mess around with your icp unplug it and check for oil in the connector if there’s oil it’s bad..
 
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Old 10-13-2017, 12:02 AM
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Every scanner I put on it says there’s no codes , it won’t stall but just runs rough till the light comes on, I’ll check that though thanks
 
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Old 10-13-2017, 12:09 AM
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Keep it idling while you wiggle your icp pigtail around see if it makes an rpm difference
 
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Old 10-13-2017, 06:59 AM
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If it does then it’s the pigtail? Or icp itself, I’ve also heard about the camshaft position sensor would do it too.?
 
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Old 10-13-2017, 08:20 AM
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I suggest you "Capture" Scan Tool Data while its doing it. You need to use caution when "Wiggling" connection on the 5vRef Circuit. You could unplug the sensor and then start the truck to see if the complaint resolves itself. Otherwise, capturing data will perhaps provide the most useful information.
 
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Old 10-14-2017, 08:09 PM
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Originally Posted by Biggreendiesel02 View Post
Every scanner I put on it says there’s no codes , it won’t stall but just runs rough till the light comes on, I’ll check that though thanks
The reason for this is that your 7.3L diesel is not OBDII compliant. Most scanners will not retrieve trouble codes. If the check engine light came on, there is a code stored. You can use smart phone apps Forscan or TorquePro with WiFi adapter for Apple or Bluetooth adapter for Android. I use AutoEnginuity on my laptop. The smart phone apps are the cheapest way to go.

I suspect the problem you are having is the UVCH (Under Valve Cover Harness) has come loose. You can search the 50 cent mod.

Getting the codes will help us narrow it down.
 
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Old 10-14-2017, 10:10 PM
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Originally Posted by HD Rider View Post
The reason for this is that your 7.3L diesel is not OBDII compliant. Most scanners will not retrieve trouble codes. If the check engine light came on, there is a code stored. You can use smart phone apps Forscan or TorquePro with WiFi adapter for Apple or Bluetooth adapter for Android. I use AutoEnginuity on my laptop. The smart phone apps are the cheapest way to go.

I suspect the problem you are having is the UVCH (Under Valve Cover Harness) has come loose. You can search the 50 cent mod.

Getting the codes will help us narrow it down.
^x2
I would have suggested the exact same approach.
 
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Old 10-15-2017, 07:27 AM
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Originally Posted by HD Rider View Post
The reason for this is that your 7.3L diesel is not OBDII compliant. Most scanners will not retrieve trouble codes. If the check engine light came on, there is a code stored. You can use smart phone apps Forscan or TorquePro with WiFi adapter for Apple or Bluetooth adapter for Android. I use AutoEnginuity on my laptop. The smart phone apps are the cheapest way to go.

I suspect the problem you are having is the UVCH (Under Valve Cover Harness) has come loose. You can search the 50 cent mod.

Getting the codes will help us narrow it down.
I was just going to write the exact same post.
 
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