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rben

Buick Reatta runing rough

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So i replaced, cam sensor, crank sensor, coil pack, ICM, and the MAF. Checked the voltage on the sensors and  the pressure of the gas line. all are good but it is still running rough and the RPMs jumping up to 6000 for a second as it runs. Also the cad converter gets red hot do to the missing and back firing. So i am believing the  the timing has jumped a tooth. anyone have another idea or is it time to tear out/repair the timing?

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i am going down that road. i pulled the oxygen sensor and started it, it ran as it usually does. then i put the sensor back in and it ran as it usually does.  One other thing i was looking and found the RPM gauge has a 0-6375 limit. 6375 is the reading it jumps to every so often. the engine does not sound like it jumps that high. it is only for a second i see that value.

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Usually a bad oxygen sensor makes the cat turn red but if you want to do the timing chain first, good for you.

 And bad wires will give you a rough idle. So does not cleaning the idle control  sensor and the casting it fits into...

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You don't give any background on how this problem started so it's hard to just guess at what might be wrong.  Part of troubleshooting is knowing the recent history of what is going on with the car.  Any chance that you have crossed the spark plug wires while swapping parts?  Are any codes showing in diagnostics?

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So i posted before about this Buick. Thus far i have changed out the Oxygen sensor, cam sensor, crank sensor, coil pack (twice), MAF sensor, and ECM.

Background, i parked it at the airport for a couple days in August when it was really hot. It started hard, which was unusual, and has been messed ever since. It starts every time and runs, the battery is a POS, so that does not help. Meanwhile, it runs and does not give off any codes other than ones induced when i unplug things.  As it runs the engine misses a little and the tac shows 6375 (the max it can display) about once every 25-30 seconds. the engine revs up and down like someone is purposely rev it up and down just a little. The tac thing sort of throws me, it shows that high rev but it does not sound like it is revving that high.

I have run it with the MAF sensor pulled, with little change but there is change. With cam sensor or crack sensor unplugged it will not start. Remove the oxygen sensor and it will run about the same as it does with it connected and mounted correctly. Removing the oil cap and nothing changes. I removed the plug wires one at a lime as it ran with little change and spark at every plug of the coil pack. It does backfire but not very often.

So i am trying to see if there is something else i missed. I am at the point of doing a motor swap but i want to be sure it is not an electrical issue, making a swap pointless. I suspect the timing jumped just enough to make it run, while it tries to correct itself. Thus the backfiring and funny revving?

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The tach. signal comes from the ICM. Sometimes it is hard to sort out which is the cause or the effect. Case in point, the rolling idle, is it trying to stabilize the engine or is the unstable idle real? Do the IAC counts ramp up and down while the idle changes and if they do, do they lead or follow the speed change? The engine should definitely be able to start and run with the cam sensor disconnected. I do not know of a reliable method of checking for timing chain issues save for opening the front cover. You could try observing the cam magnet with the sensor removed and rock the crank back and forth to see how much lag in the cam movement but the presence of the chain tensioner muddies that a bit and still doesn't answer the root question if the chain is off by a tooth. 

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