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post #1 of (permalink) Old 07-13-2007, 09:05 AM Thread Starter
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Engine knock/rattle question - YJ 4.0

The guy inspecting my 91 YJ 4.0 said that he couldn't get it to pass the dyno part of the emission test without tweaking something.
Well, now the engine knocks and rattles when idling. While driving it I can't hear anything.
What could he have adjusted? Is the engine damaging itself?
I also cleaned the K&N filter just before the inspection and I think I over oiled it. Could oil have gotten sucked in and damaged something?
I plan on taking it back and telling him to unfix whatever he adjusted.
Thanks

I drive over things.

Last edited by Bryan; 07-13-2007 at 09:56 AM.
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post #2 of (permalink) Old 07-15-2007, 07:26 AM
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Question

Where is the rattle coming from? The 4.0 doesn't have anything to "tweak" for emissions purposes. Could it be the cat converter? They rattle when they go out. Was it a sniffer fail? Check engine light on? They did love O2 sensors. Fuel mileage dropped? Driveability problems? More info will help diagnose problem.
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post #3 of (permalink) Old 07-15-2007, 01:08 PM
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Was 91 one of the first years for FI?
If so, I can't think of anything he could have adjusted.....there are no adjustments...

If it's not FI, then my first thought would be timing.

Take it back...he should at least tell you what he changed. But be nice about it....nice goes a long way....

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post #4 of (permalink) Old 07-15-2007, 04:33 PM Thread Starter
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The rattling seems to be coming from the front of the engine.
It is fuel injected.
The guy that inspected it is on vacation until next week. Some clueless guy is covering for him who isn't worth talking to.
He may have said that it was running rich or lean. I don't remember.
The cat is 3.5 years old and has 3500 miles on it.
Performance seems fine, I think. Perhaps a little sluggish. It's hard to tell.
The sound doesn't have a pattern to it, meaning that it isn't purely cyclic (sound, sound, no sound, sound, no sound, etc). But the frequency increases as the rpm increases. At idle it makes about 3-5 noises per second.

I drive over things.

Last edited by Bryan; 07-15-2007 at 05:19 PM. Reason: I just listened to it again.
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post #5 of (permalink) Old 07-16-2007, 01:42 PM Thread Starter
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Now I am concerned that it is the timing chain.
This is a remanufactured engine that I had installed about 8 years ago.
I put about 18K miles on it so far.
So this engine is still a baby.

I drive over things.
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post #6 of (permalink) Old 07-16-2007, 02:35 PM
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Get a mechanics stethoscope, and find out where it is. It could be your fan, pulleys, PS pump. What he "tweaked" may or may not be coincidental.

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post #7 of (permalink) Old 07-16-2007, 08:57 PM Thread Starter
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I wiggled the fan and the water pump pulley has play in it.
I am guessing that my water pump bearings are bad. Is that a correct evaluation?

It is not leaking. It is a Flow Kooler pump. It is 9 years old and has 24K miles on it.

The pump has a lifetime warranty but you have to return it and wait for a new one.

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post #8 of (permalink) Old 07-16-2007, 09:14 PM
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Very well could be the pump. Like I said get a stethascope and listen to it.

Sometimes they will ship you a new one first and charge you, then reverse the charge when the old one comes in.

but make sure it is bad first.

Scott
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post #9 of (permalink) Old 07-16-2007, 09:24 PM
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Take off the belt(s). If it still does it you'll know it's in the engine.

No? If it has several belts put them back on one at a time and try it each time.

Often just turning an alternator, water pump, idler etc by hand you can "feel" the bad one.

And - of course - look closely at the belts themselves and the pulleys they ride on. It's surprising how a tiny split or missing bit of a belt can sound soooo bad!
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post #10 of (permalink) Old 07-19-2007, 11:02 PM
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Check the timming.......
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