?'s about Setting Timing on the ole' 4.2 - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 12-18-2002, 12:47 AM Thread Starter
 
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?\'s about Setting Timing on the ole\' 4.2

Just a quick question - after disconnecting/plugging the vacuum advance, what RPM do i need to be at to check the timing on the 4.2. Someone told me it was 1800RPM, which is what my Haynes manual says, someone else said to do it @ Idle, but if i set the timing @ idle it would appear to be way too advanced...

Thanks,
Pablo
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post #2 of (permalink) Old 12-18-2002, 01:36 AM
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Re: ?\'s about Setting Timing on the ole\' 4.2

I've always timed everything at idle... [img]images/graemlins/smirk.gif[/img]
post #3 of (permalink) Old 12-18-2002, 01:41 AM
 
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Re: ?\'s about Setting Timing on the ole\' 4.2

I set mine at about 8 degrees at idle, and it seems to work fine, and I believe that's what my Chilton manual says for my year (83)
I have a friend with an 88 YJ, and his under-hood sticker says 8 degrees +or- 2 at, I believe, 1500 RPM.
So, I think it varies somewhat with the year model.
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post #4 of (permalink) Old 12-18-2002, 02:57 AM Thread Starter
 
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Re: ?\'s about Setting Timing on the ole\' 4.2

btt anyone else?
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post #5 of (permalink) Old 12-18-2002, 04:41 AM
 
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Re: ?\'s about Setting Timing on the ole\' 4.2

If you've done the Nutter bypass, the timing should be set at idle (@800 RPMs). If you haven't done the bypass, the timing should be set at 1600 RPMs (or whatever the little sticker under the hood says).

Also, with the Nutter bypass, the advance line should be connnected directly to ported vacuum.
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post #6 of (permalink) Old 12-18-2002, 09:04 AM
 
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Re: ?\'s about Setting Timing on the ole\' 4.2

In the end you are trying to acheive the best performance you can get, without getting any knock or ping. Consider the factory specs as a starting point. Take it for a drive, fully warmed up. In high gear, so it's under some load, explore all throttle positions and rpms. If there is no ping, advance the distributor a couple of degrees. Repeat road test. If it pings, back it off a couple. If it doesn't, add 2 more and road test again. Repeat till you find light pinging, and back it off 2 degrees until you don't get any more ping under any condition. As your engine wears ( and fuel quality varies), so will the timing change from factory spec. If you set your timing by road testing, you will know you have the optimum total advance and possibly better performance.

One caveat, make sure you know what ping or knock sounds like. It's usually a metalic ping, like marbles or steel shot dropped in a tin can. Light hail on a tin roof? Muffled by all the road noise, etc.

The rpm issue for setting initial timing is critical, as the mechanical advance will begin at some rpm. You want to set your timing at a low enough rpm that no mechanical advance has begun. Watch the timing marks with a timing light at low rpms and see where it starts to advance. Make sure you are no setting the initial timing without any mechanical advance having already begun, or else your total advance will be less than you think and performance will suffer.
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