At speed: Intermittent/brief power loss and bucking - Defender Source
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Old October 24th, 2014, 01:55 PM
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At speed: Intermittent/brief power loss and bucking

I have 94 NAS D90 with 90K on the odometer. Driving around town this week between 35-60 MPH I have had a brief but dramatic loss of power and the vehicle bucks momentarily and then resumes normally. There is no fuel smell whatsoever. This has subsequently happened a couple of dozen times.

To give you a little more background, after returning from Expo East and hitting some trails I detailed the truck including cleaning the engine (wiped by hand/no power washing). No issues with the truck.

This week, I heard loud whining and discovered the bearings in the alternator were shot. Replaced the alternator. I also filled up with fuel and 1 day/20 miles later the power loss/brief bucking started.

I've searched the Forum and found some posts that sound very similar and tried to check off the obvious stuff. This is what I've done so far:

1. I checked with the gas station. No one else complained about bad fuel (I know the owner. I believe him.)...but changed the fuel filter.

2. Added a can of Heet.

3. Sprayed carb cleaner around the plenum.

4. Cleaned the points/condenser.

Still have intermittent power loss and bucking.

I have another new alternator on order which will be swapped out for the one that was just installed. That will be done tomorrow.

Any other thoughts? Could it be the coil? I'm at the edge of my technical abilities already but any thoughts or insights would be welcomed and appreciated.

Thanks!
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  #2  
Old October 24th, 2014, 02:52 PM
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Thinking worn ignition switch needs to be on the list
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Old October 24th, 2014, 03:14 PM
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or you could have an air leak somewhere. check the fitment of all hoses and the integrity of them as well.
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Old October 24th, 2014, 03:31 PM
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Ignition module or throttle position sensor. Are there any stored fault codes?
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Old October 24th, 2014, 05:05 PM
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Re: Intermittent/brief power loss and bucking

Thanks, guys.
Let me check these things out this weekend. I'll keep you posted.
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Old October 25th, 2014, 11:20 AM
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Quote:
Originally Posted by Jedelmann View Post

4. Cleaned the points/condenser.
say what?
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Old October 25th, 2014, 05:40 PM
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Loose big plenum air hose.
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Old October 25th, 2014, 05:55 PM
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X2 on the ignition module...
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Old October 25th, 2014, 11:27 PM
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I had a similar problem but would result in a total power down of the engine (as if it couldn't go above 1000 rpms) and was less frequent. Had a tune up done (all the normal stuff) and they cleaned out the MAS (mass air sensor) which the mechanic said was pretty dirty and it now runs smooth and the problem went away. Mine is a 1994 DEF 90. So worth looking into if you haven't solved the problem yet.
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Old October 29th, 2014, 04:26 PM
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Guys,
Had to take the D90 to the mechanic and after a couple of days of investigation they identified the throttle position sensor and the ignition module as the culprits for my power loss/bucking.

Thanks to each of your for your guidance. You rock.
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Old October 29th, 2014, 04:39 PM
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Quote:
Originally Posted by Jedelmann View Post
Guys,
Had to take the D90 to the mechanic and after a couple of days of investigation they identified the throttle position sensor and the ignition module as the culprits for my power loss/bucking.

Thanks to each of your for your guidance. You rock.
How many hours labor are we talking? Glad it is fixed.
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Old October 29th, 2014, 04:41 PM
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Glad you got it licked.
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  #13  
Old October 29th, 2014, 07:30 PM
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Diagnosis Truck 2.0 hours = $229.98
Throttle Position Sensor .50 hours = 57.50
Ignition Module 1 hour = $114.99
+ Parts

Thanks guys!
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Old October 29th, 2014, 10:12 PM
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Let us know if it's actually fixed in a week ...
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