Mechanics

INTERMITTENT MISSFIRE

2005 Renault Scenic • 150,000 miles

Dr. Cranknwrench I went to siemens renault so they said I need an O2 sensor an upstream sensor and a cam sensor, but they could'nt guarantee me that the car would be fixed. They actually replaced the O2 sensor and it didn't make a difference. So where do go from there.
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Andre jonas
October 17, 2011.




The camposition snesor has to do with timing. If they think that is an issue, they, or you can put a timing light on it and check the timing. I do not have the specification for that.
Did they run a trouble code scan to get the O2 and camshaft position failure codes?
With the mileage you have, it could also be a worn timing belt that has skipped a tooth.
In other words, even without the spec, and I am sure they have an idea as it is generally about 10 degrees before Top Dead Center, give or take a few degrees. If this is the case a simple timing light can reveal if it is a timing issue. Then you are getting into; the timng belt, possibly sprockets, the camshaft position sensor, the crankshaft position sensor, the distributor and possibly a coil driver if so equipped.
It is a game of process of elimination and some intutive experience with this type of issue as well as having experiene with that Manufacturer of car and the Model of the car.
If you ask them about putting a timing light to it as a way of double checking if it is a timing issue, see what they say and if they say it might help ask if they can set the timing. If it cannot be set by turning the distributor, or in your case you probably do not have a distributor, only coil packs, the timing signal is digital. So, then if the timing is off and non-adjustable, ask them how could the timing be off?
Also ask, if it doesn't fix it, what would be the next most likely part? Can any of the parts in question be tested? (This is back tracking a little bit), Did you get the diagnosis from the trouble codes that came up? If you have never had the timing belt/chain replaced or have not replaced it in the last 60,000 miles or 96500 Km, ask if that could contribute to the problem.
You should get a new timing belt/chain as per manufacturer suggested schedule anyway. Ask if the crankshaft position snesor could be part of the issue. If it could or any other issues, such as a coil driver, what are the chances of it not showing up on the throuble code diagnosis? When you ask him these questions, also ask if he has worked on many of these engines and if they are prone to have this issue. Then ask him what level of confidence he has in the camshaft position sensor fixing the problem. Then if his answer is not very much confidnece or even fair, ask him, "Then what are the chances of finsing the problem if this does not fix it?"
The reason I would put emphasis on the last question is that his answer should be, "We will eventually find and fix the problem, it is just that diagnsoing electrical parts is a process of elimination and educated guessing". Or something to that effect.
If he says anything else, than he is saying he might not be able to fix the car. That should give you an idea on what kind of repair facility it is.
I do beleive that checking the timing, getting a new timingbelt/chain if it is time, and replacing the camshaft position sensor is a good set of options to work with next.
Weigh the cost against how much you like the car. It probably will start to become a money pit at this point and witha car with so many miles, it is either, really prepare to do things right and rebuild the motor, transmissin, other wear and tear parts. Essentially a restoration if you want a reliable car. I say this because patching it will only buy you time to doing just that and it is better to spend the money on restoration or a new car.
So, it is up to you and your love of the car, the cost of replacing the camshaft osition snesor and the repair technicians confidence level in that fixing it and then driving it until it stops running and savng money and shopping for another car until it does so.
I hope this information helps. It is half subjective and half objective, but in the end it is just going to start costing you a lot of money to keep it going.

Take Care

Dr. C



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