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Old 07-31-2007, 08:26 PM   #1
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Timing controled by what?

Is there a Jeep/Chrysler ECM guru in the house? My problem is my 1997 Jeep Grand Cherokee. I sucks gas like most do. The problem is that my good friend has an identical 1996 model that uses much less fuel. (mine 21 MPG hwy, his 26 mpg hwy, on the same roads, same day, same trip) We've done a coast down test with both Jeeps side by side, switched sides, double and triple checked. Mine rolls easier, and will coast further, showing less rolling resistance. On the scale, mine comes up about 150 lbs lighter than his.
I've even tried his ECU on my jeep, and still it does not get any better.
As most of you know, advanced timing will show as richer mixture on an oxygen sensor, so the ECU will lean it back down with less fuel. So my question: What controls the timing on the Jeeps engine control system? Is it only the crank position sensor, or the cam position sensor, or both, and how would i best try to advance my ignition timing?

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Old 08-11-2007, 02:02 PM   #2
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Crankshaft position sensor controls the timing. If you enlarge the mounting holes on its bracket you can adjust your timing by a few degrees.

Whats the difference between your ZJs? Drivetrain wise.

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Old 08-12-2007, 04:59 AM   #3
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not all cars are made the same, I've noticed out of 10 new cars made with the same Eng/trans/options 1-2 of them will run like a raped ape, lots more power and i guess the mpg could be different
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