2000 Buick Misfiring - Opinions?

A friend of mine took his 2000 Regal to a hack hoping to save a few bucks on a tuneup. He had the plugs and fluids changed. Now the car has a serious misfiring problem, Check Engine light comes on when accelerating. Of course
he believes this is a coincidence.
He currently has the car at another garage (not dealer) trying to save a few more dollars. :-) The previous replacement plugs are toast, seriously scorched. The injectors were cleaned and a new fuel filter, but still no joy. The things been under diagnosis for about 10+ hours now, at $X per hour. Apparently the trouble code does not pinpoint the problem and it does not appear to be any given cylinder(s). The current best guess is an intermittent timing sensor.
I told him to take it to the dealer after the first fiasco, but he is convinced that the dealer will just keep replacing parts until his wallet is empty. I would think that experience and the right equipment would go a long way to solving this problem in short order. He will only get hosed by the dealer if he lets it happen.
So how hard are these problems to diagnose? Who's right?
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Bill, could it be something simple, like cross-wired plug wires? Anytime you have plugs changed by somebody who doesn't know what they are doing, this is a real possibility.
---Bob Gross---
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with a good scan tool, you can tell which cylinder is misfiring, not to mention that 10+ hours is freaking insane for something like that!!! geez, check spark for each cyl, then do an injector balance test, then a compression and leakdown... it's too easy to fix...... Bobo

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Bill Stock wrote:

Bad plug wires.
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Bill Stock wrote:

The question to ask is: what has changed? Maybe a sensor wire or harness was disturbed during the previous work. Maybe the plug wires are out of sequence. Maybe a vacuum line. A close mechanical inspection would help. Also, its not hard to damage plug wires. What do you want to bet you have a few intermittently arcing now? Quick test. Start the car up at night in a dark area. Open the hood. Look closely around all the spark plug cables. I did this once when i had a problem and was amazed at all the arc's i saw flying around. And the car was still running.
BOB
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Thanks for the feedback.
My original thought was plug wires too. Especially based on what I heard about the plug change. Apparently this has been ruled out though? ie. Swapping plug wires did not have any effect on the bad cylinders.
Yes, from what I heard there is some serious arcing happening. But car runs OK at idle, only has the problem under heavy acceleration. Turbocharged.
They seem to be convinced it's a sensor problem, but can't pinpoint it with the diagnostic. Oxygen and fuel sensors have been ruled out. Something about the bottom timing sensor.
I think Bob is probably right about the sensor wiring. Would these sensors be sensitive to the plugs firing, if the wiring was put back in the wrong place?

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Bill Stock wrote:

Which engine? What sensors?
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Bill, there should be ZERO wonderment about what might be correct spark plug wiring versus what might be incorrect.
(1) Get the Helm manual, follow the correct spark plug wiring order, and go from there. (2) Find out what the cam sensor is doing, too.
---Bob Gross---
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