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Old 09-25-2009, 04:22 PM   #1
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Default Timing on a 1990 cherokee laredo

Does anyone know how to MANUALLY time a 4.0? I am stuttering at idle and have a pretty significant loss of power. Of course having 181,000 miles on it probably doesn't help. Also, steering is a bit loose. I have a 2 inch lift on it but it seems to have some extra play.....
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Old 09-25-2009, 04:51 PM   #2
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The timing on a 4.0 is set,it cannot be changed,once it is set it will not change unless the dist is removed and replaced incorrectly.
You may have other issues like fuel pump,plugged filter or restricted exhaust.
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Old 09-25-2009, 07:07 PM   #3
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You can try cleaning your idle air control and your throttle position sensor and throttle body, that can also help improve your idle. As Abovetimberline said, the timing is set and non-adjustable.
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Old 09-25-2009, 08:36 PM   #4
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Quote:
Originally Posted by Abovetimberline View Post
The timing on a 4.0 is set,it cannot be changed,once it is set it will not change unless the dist is removed and replaced incorrectly.
You may have other issues like fuel pump,plugged filter or restricted exhaust.
X2
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Old 09-26-2009, 05:09 AM   #5
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As mentioned, the idle is fixed by the computer and can't be adjusted without doing more work than you need to. Here's what I'd do:

Check adjustment on the TPS - voltage at idle. Terminals have probably been covered here, please let me know if they have not. Output voltage (Key ON) should be 17% of input voltage - whatever the input voltage happens to be.

If that's good, remove the throttle body (get a new gasket,) and disassemble and clean everything but the TPS! Do not get water on the TPS - electrical contact cleaner works neatly, you can use an old toothbrush for the really nasty bits.

Those are the two big ones. Let's see, what else would I look for (in no particular order):
- Vacuum leak.
- The MAP line often comes loose from the passenger side of the throttle body. Pop it back in.
- Check for "carbon tracking" under and along the outside of the distributor cap - it literlally looks like someone drew it on with a pencil. Replace the cap if present.
- Check resistance on your wires, make sure none are "over spec" or "under spec." (I'd have to look up the actual range of values you're looking for.)
- Check to make sure your spark plugs are clen and tight. It's rare, but I've seen spark plugs work loose (usually due to improper installation.)
- Check to make sure the terminal in teh HT lead makes good contact with the button on top of the thing.

That's most of the causes - let me know if none of them pan out for you.
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