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post #1 of (permalink) Old 01-27-2001, 01:10 PM
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2.8 V6 timing

I have an 86 Jeep Cherokee with the GM 2.8 V6 (carb) in it. I have a timing problem I hope someone can help me with. It's running rich and is getting poor mileage. I noticed that on start up (with the vacuum advance disconnected) the timing is below 0. However, when it warms up, it's far past 20. Manifold pressure goes from about 5" to about 15" and back to 5" during this time. Does anyone have any ideas what might be wrong? Is it the timing chain or possibly the distributor? Any thought or suggestions would be appreciated.

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post #2 of (permalink) Old 01-27-2001, 03:38 PM
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Re: 2.8 V6 timing

<font face="Comic Sans MS">For one thing set the timing at idle when it's warm and with the vacuum advance disconnected and plugged. Lock the distributor down and test that. Are you using a ported vacuum source for the vacuum advance or the manifold vacuum? Manifold pressure goes down to 5"? Try keeping the vacuum guage hooked up to a source of manifold vacuum as you adjust the timing. You're aiming for the highest vacuum reading you can achieve, or the stock setting. Let us know what happens. </font>

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post #3 of (permalink) Old 02-02-2001, 07:34 AM
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Re: 2.8 V6 timing

Have you eliminated the possibility that the choke might be sticking closed or that the choke electric heater connection may have come loose. Also worn spark plugs could cause rich running and lousy gas mileage.

I check the manifold vacuum with the engine warm with a gauge connected directly to the manifold. On the Cherokee with a 2.8, an easy place to connect the gauge is in the supply hose at the vacuum cannisters on the passenger side of the engine bay. My 1986 2.8L Cherokee with auto trans and 4.10 axle gears gets about 15MPG city and about 20 highway. It currently has 130k miles on it. When I check vaccum at the mainfold I get about 17.5 - 18" with steady needle at operating temp idle. Good luck!![img]/wwwthreads_images/icons/smile.gif[/img]

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