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3.9 defender runs rough when warm.

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2K views 11 replies 12 participants last post by  o2batsea 
#1 ·
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
 
#5 ·
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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#8 ·
check the operation of your o2 sensors and coolant temp sensor at normal operating temp with rover gauge.
there is an underlying issue there...
 
#11 ·
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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