258 ignition timing question - JeepForum.com
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post #1 of 9 Old 06-16-2017, 06:37 PM Thread Starter
moparmagic
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258 ignition timing question

Just got my Jeep on the road(YES!!!) . I noticed when I get up to speed 50-55 mph(1900-2200 RPM) I have rattling sound. I could have sworn it was a rod bearing, but after reading a few things I decided to remove the vacuum line from my distributor. The noise went away. So I thought I had set the timing wrong. It was set it at 8 degrees with vac line removed. So I just kept playing around with it retarding it further and further until I could drive it with the vac line connected and no rattle. Then it was dead off the line with No pep, so I just set it back to 8 BTDC and plugged the vac line. Anyone else ever run into this?

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post #2 of 9 Old 06-16-2017, 07:47 PM
pedal2themetai
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HI could be a wore out advance system..(springs and such..)
good luck
tim
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post #3 of 9 Old 06-17-2017, 04:27 AM
Matt1981CJ7
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What is the timing at say 2500 RPM?

Matt


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post #4 of 9 Old 06-17-2017, 01:52 PM Thread Starter
moparmagic
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I'm not really sure?? When I check the timing without the vac line connected it appears to be around 15 btdc, but with the vac line connected it seems to go out of sight- I'm guessing 18-20 degrees btdc.
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post #5 of 9 Old 06-18-2017, 07:06 AM
pedal2themetai
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Yea it sounds like the advance is shot or the chain is bad.. Try setting total timing .. run the rpms to 2,500 to 3,000 rpms advance hooked up and set the timing to 28* (you'll need a dial back timing light) or longer timing tape on the crank pully.
good luck
tim
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post #6 of 9 Old 06-18-2017, 07:18 AM
Matt1981CJ7
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Quote:
Originally Posted by moparmagic View Post
I'm not really sure?? When I check the timing without the vac line connected it appears to be around 15 btdc, but with the vac line connected it seems to go out of sight- I'm guessing 18-20 degrees btdc.
That's perfectly normal, and desirable, when connected to manifold vac advance.

As Tim said, you need either a timing tape, or a timing light with an advance feature, to accurately check the overall timing curve.

Matt
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post #7 of 9 Old 06-18-2017, 08:19 PM Thread Starter
moparmagic
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OK, thanks for the replies. I will have to check into getting a timing light with the dial. In the mean time I had an idea(good or bad?). I remember reading that you can adjust the max timing advance by inserting a allen wrench into the vacuum port on your distributer and turning the adjustment. So I used my vac pump to change the max advance. I haven't had a chance to drive it yet and test my theory ? Will let you know.
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post #8 of 9 Old 06-19-2017, 06:15 AM
Matt1981CJ7
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Quote:
Originally Posted by moparmagic View Post
OK, thanks for the replies. I will have to check into getting a timing light with the dial. In the mean time I had an idea(good or bad?). I remember reading that you can adjust the max timing advance by inserting a allen wrench into the vacuum port on your distributer and turning the adjustment. So I used my vac pump to change the max advance. I haven't had a chance to drive it yet and test my theory ? Will let you know.
The vacuum advance adjustment only changes the point at which the vac advance comes in, it doesn't change the amount that comes in.

Also, understand that the vac advance has little to nothing to do with acceleration performance. So, if your spark knock is happening under load, it's the centrifugal advance that needs to be checked, not the vac advance.

You really need to check the centrifugal advance curve.

Matt
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post #9 of 9 Old 06-19-2017, 04:24 PM
skizriz
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Quote:
Originally Posted by Matt1981CJ7 View Post
You really need to check the centrifugal advance curve.

Matt
What matt said. A broken or missing spring can sent the advance into orbit once the rpms pick up.

At idle, and 8*, all is fine.
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