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Unread 03-11-2014, 11:08 AM   #1
spjewell
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1992 YJ Wrangler 
 
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2.5L Engine Vibrations

Does anybody know if there is a normal frequency vibration in the 2.5L engine under load at 3500 RPM? Every time I hit exactly 3500 RPM it feels like the engine is going to fall off the mounts, however 3450 is smooth as silk, and it pulls through around 4500 RPM and smooth's out . I have recently tuned up and cleaned up most of the air intake, fuel system, and ignition system. Upon a spark plug review, it looks like something is up with my #1 plug (#2-#4 look good) most likely a dirty fuel injector - quoting a cleaning job right now.

Also showing so so results on a compression check (1-4) 130psi, 130psi, 130psi, 135 psi.

Engine swap is out of the question for now, and this is not my DD so I can take my time trouble shooting problems.

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Unread 03-11-2014, 12:11 PM   #2
Xpress
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Could be something else like your harmonic balancer... Cleaning fuel injectors is easy and simple:

Step 1. Buy Fuel Injector cleaner from auto parts store.
Step 2. Pour in tank, drive, and enjoy the cleansing action.
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Unread 03-11-2014, 12:23 PM   #3
spjewell
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Quote:
Originally Posted by Xpress View Post
Could be something else like your harmonic balancer... Cleaning fuel injectors is easy and simple:

Step 1. Buy Fuel Injector cleaner from auto parts store.
Step 2. Pour in tank, drive, and enjoy the cleansing action.
I like that, however I did not get to enjoy my cleansing action . I ran a bottle of Sea foam through it, 2-4 were cleaned, but not #1. I am stepping it up a notch and taking it to a ultrasonic cleaning facility, as long as they can do it cheaper than replacing them.
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Unread 03-13-2014, 07:56 PM   #4
LJameson
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Try taking the serpentine belt off and drive it very briefly. It's best to do this when the engines completely cold, that way you can run it quick before overheating. If the vibration goes away, then it's a problem with something driven by the belt.
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Unread 03-13-2014, 10:12 PM   #5
spjewell
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Cant hurt, I will give it a try once I get the fuel injectors back from being cleaned. Are you thinking anything in particular, or just to rule out the accessories?
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Unread 03-14-2014, 12:10 AM   #6
LJameson
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Possible water pump/fan assy or alternator. While you have the belt off wiggle the pulleys and fan clutch to see if they have any excess play.
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Unread 03-14-2014, 11:46 AM   #7
StanF
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I'd check your motor mounts and transmission mount too.

Does it happen in all gears at 3500 rpm?
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Unread 03-14-2014, 01:49 PM   #8
spjewell
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Yes, it happens in all gears and it is the worst at 3500. It gradually smooth's out as I push through it and goes away as I approach 4500-5000. At 6k-7k it just sounds like a little 4 banger being pushed to its limit.
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