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Unread 02-23-2013, 02:46 AM   #1
aldersonfilm
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Set Ignition Timing??

How do you check and set the timing on a 4.0 and how do you know what the timing should be?

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Unread 02-23-2013, 05:22 AM   #2
cruiser54
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With a timing light using the marks on the harmonic balancer and timing cover. Not adjustable anyway, but you can look at it. I've found most of them to be at about 12* at idle FWIW.
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Unread 02-23-2013, 04:18 PM   #3
Flyordie
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10-14* BTDC is normal. I usually adjust timing on my 4-cyl based on fuel blend. 13* BTDC is good for me during cold winter months and 12* is better for summer. (I have performed the Nutter Bypass on my 2.5L so no computer control over timing)

How to set it IF you can, there is a bolt next to the distributor that you must loosen just enough to slowly turn the distributor. Counter Clockwise does positive timing and clockwise does negative timing.
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Unread 02-23-2013, 04:36 PM   #4
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DO NOT start twisting the distributor on a 4.0.
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Unread 02-23-2013, 04:47 PM   #5
Flyordie
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DO NOT start twisting the distributor on a 4.0.
They really make it 100% computer controlled in the 4.0s?
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Unread 02-23-2013, 05:04 PM   #6
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Quote:
Originally Posted by Flyordie View Post
They really make it 100% computer controlled in the 4.0s?
Yep.
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Unread 02-23-2013, 07:49 PM   #7
aldersonfilm
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Can't you buy an after market distributor that is adjustable? I think pep boys sells them. They're red. They company is MDS or something like that.
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Unread 02-23-2013, 08:04 PM   #8
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Quote:
Originally Posted by aldersonfilm View Post
How do you check and set the timing on a 4.0 and how do you know what the timing should be?
Start at the beginning, why do you want to, or need to check the timing ? Why do you want to, or think you need to alter the timing ?

Base timing is set by the orientation of the distributor when it is installed. All further adjustments to the timing are done by the ECM. Attempting to "fool" the ECM by incorrectly installing the distributor does not work.
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Unread 02-23-2013, 08:16 PM   #9
aldersonfilm
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I have a rough, erratic idle, with all the symptoms of the timing being off. A bit of a misfire, hesitation and stumbling. Replaced spark plugs, wires, cap and rotor, air filter, fuel filter, cleaned up the grounds and ran a few additives through the system to no avail. Running out of things to check.
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Unread 02-23-2013, 08:37 PM   #10
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Timing being off does not cause rough running. It's a term that gets thrown out there, mostly by those ignorant of how engines work.

Vacuum leaks been checked? Intake manifold bolts loose? Throttle body and IAC been cleaned? CCV hoses and piping clear and clean?
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Unread 02-23-2013, 08:50 PM   #11
CJ7-Tim
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Tested the TPS ? Set the TPS voltage ? Checked the O2 sensors wires/plugs ? Tested the O2 sensor function ? Tested the MAP sensor function ?

The Jeep In-Line 6 cylinder engine has never been know for its smooth idle, and age/mileage do not make it idle any better. I wouldn't expect much from a 20+ year old Jeep.
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Unread 02-23-2013, 09:26 PM   #12
Flyordie
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Quote:
Originally Posted by aldersonfilm View Post
I have a rough, erratic idle, with all the symptoms of the timing being off. A bit of a misfire, hesitation and stumbling. Replaced spark plugs, wires, cap and rotor, air filter, fuel filter, cleaned up the grounds and ran a few additives through the system to no avail. Running out of things to check.
That sounds like transitional fuel delivery issues. However, this is from the point of a carbed setup. You got EFI/TBI. I would check Fuel Pressure.
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Unread 02-23-2013, 11:06 PM   #13
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I'll be watching this thread. I have similar problems, but mostly when it's cold. Does yours do it all of the time?
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Unread 02-23-2013, 11:31 PM   #14
aldersonfilm
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It's rougher when it's cold, for sure, but it does it always. It does surge or anything, it just idles rough and in no particular pattern. I have noticed a lot of what sounds like valve chatter, and an airy sound, but its nearly impossible to hear over the engine. One thing I did notice is a fuel leak where the fuel line connects to the fuel rail. Its always leaking and although I changed out the quick disconnect and o-rings, it still leaks. I suppose it's possible that is the entire problem right there. There is also a hissing from the fuel tank area when idling. Not sure if this is related, but it maybe part of the puzzle. Also, yes I cleaned the throttle body, but I have yet to tackle the senors. Honestly, it seems like a kind of daunting task.
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Unread 02-23-2013, 11:57 PM   #15
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Timing on 4.0 is non adjustable, period. Plus it's an hydraulic lifter engine, so it doesn't even require valve adjustment. It is made that way. The only thing that would be adjustable is the TPS on 90's and older, that's it.

Let's put it this way, if timing was off (assuming it was possible), you'd feel more than a rough idle... more like a bomb about to go off. IGNITION timing, on the other hand, is adjusted based on various sensors' readings, mainly the CPS. If sensor is bad, you replace it. But that would not cause rough idle.

There are several possible causes for rough idle, but more likely, you have a leak on the vacuum line going to the MAP sensor. Another possible cause would be a burnt out ECU, which could have been the result of disconnecting the battery while engine's running, as an attempt to test the alternator. Wonder if you're guilty of it?
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