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Ignition timing

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Joined: 13 Nov 2006

PostPosted: Fri Jan 19, 2007 4:37 pm    Post subject: Ignition timing Reply with quote

1990 4.0 2WD automatic 168K. My Cherokee runs well but I can only get 16.5 miles per gallon out of it(mostly highway). I have given it a complete tune up,no vacuum leaks,CCV hose unrestricted,new oxygen sensor, recently cleaned throttle body. I tried to advance the timing a bit for better milage but could not move the distributor due to the design that does not allow you to do so. I know that computer controlled engines determine timing via the computer and will try to compensate for any change in distributor position that I do. A friend of mine says grind the tang off of the distributor and advance the timing anyway and it might work as it does on some other computer controlled vehicles. Has anyone tried this? Thanks.
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Joined: 12 Aug 2006
Location: Hinesville Ga

PostPosted: Sat Jan 20, 2007 3:32 am    Post subject: ignition timing Reply with quote

The timing is not adjustable. I would not do that.
The computer will automatically dial in its preset limits.
I have a 1991 with 101,000 miles and get 21 on the highway.
About 18 in the city.
My 1988 gets 15-17 city and maybe 18 highway.
What plugs are you using? Champion or Champion truck plugs are recommended.
If you have a tach watch your RPMs to get good mileage keep the tach
around 2,000 rpms any higher and your pouring gas out the window.
Your speed maybe 55-65 depending on you.
I do believe you have a HO motor that has little more throttle response than the other engine.
1988 Wagoneer Limited XJ Tellico Tested
Rocklizards panels, Tomken rear bumper and front Tow brackets, Rocket air intake, 2 inch lift,
30x950x15, 1991 coolant system with electric fans, 8,000 mile marker winch
1991 Cherokee Limited
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