3.9 defender runs rough when warm. - Defender Source
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  #1  
Old September 21st, 2016, 02:45 PM
CapeRoverKid
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3.9 defender runs rough when warm.

I'm working on a 95 d90 3.9l v8. it runs rough when it warms up and stopped at a red light-
the oil light also flickers when it runs rough.
any help would be appreciated
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  #2  
Old September 21st, 2016, 03:26 PM
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Chris
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Ok so revs dropping too low when warm causing inadequate oil pressure. Could be a well worn engine or as simple as an engine needing a good tune up.
How about more information? Miles? Last Maintenace detail etc
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  #3  
Old September 21st, 2016, 03:38 PM
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I believe the fuel rail temp sender affects things when hot...
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  #4  
Old September 21st, 2016, 04:10 PM
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Try thicker oil
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  #5  
Old September 21st, 2016, 06:41 PM
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You're oil pump may need refreshing. On mine I replaced the gasket and gears but noticed that the pressure relief valve and spring would stick. So I used some fine Emory cloth to sand the valve. That solved the oil temp and pressure issue. I used rotella oil which is also good for flat tappet engines(3.9). Now idle dropping and stalling could be the vacuum to the stepper motor off of the plenum which I too experienced due to it having a crack. Now thinking about it. Oil pressure is likely flickering when the rpm's drop.


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  #6  
Old September 21st, 2016, 06:50 PM
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Check the coolant temp sensor.
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  #7  
Old September 22nd, 2016, 08:07 AM
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Kevin Keith
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By rough, do you mean low lumpy idle? Is it fine at light throttle?
Clean your stepper motor (IACV) and check both the coolant & fuel temp sensors.
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  #8  
Old September 22nd, 2016, 04:59 PM
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check the operation of your o2 sensors and coolant temp sensor at normal operating temp with rover gauge.
there is an underlying issue there...
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  #9  
Old September 23rd, 2016, 09:51 AM
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I vote clogged cat.
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  #10  
Old September 23rd, 2016, 09:58 AM
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Quote:
Originally Posted by evilfij View Post
Check the coolant temp sensor.
Also my vote. Truck takes this to judge fuel enrichment and timing.
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  #11  
Old September 23rd, 2016, 10:23 AM
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3.9 defender runs rough when warm.

I would start with the basics first, new cap and rotor button, new plugs and plug wires. (a tune up in other words)
Next step would be to clean /replace the stepper IACV, make sure the o2's are tight. Then I would test/replace the amp module.
90% of issues like this are ignition related.
Use 10/40 oil if your not already..

Ron's suggestion is also very good. And cheap to replaced anyway if not done already.

Let us know
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  #12  
Old September 23rd, 2016, 10:36 AM
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Quote:
Originally Posted by Naplm00 View Post
Also my vote. Truck takes this to judge fuel enrichment and timing.
Timing does not come from ECU, it comes from distributor or CPS. I think you mean bandwidth.
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