poor running mystique

joe_mnApril 7, 2006

my friend called last nite. said his 98 mystique is running bad. barely runs. he got it to a shop and the codes said something about cam sensor. I did a little search. seems the sensor just unscrews from the cam cover housing. could be a real easy fix. the shop said they did not have the tools to retime the cams after replacing the sensor. huh? how complicated is this repair?

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guess i spoke to soon. seems there is timing chain/cam sprocket damage. and something about oil pan damage. hmm, i think bad things happen when your timing chain tries to chew thru the front of the motor.

    Bookmark   April 7, 2006 at 9:18PM
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The information is a little fuzzy, but I'll take a guess at it. First off, the cam position sensor may be ok. If the can chain is in so bad of shape to wear a hole in the oil pan or chain cover, its really bad. Also, if the cam chain tensioner wore out, the cam sensor found that the relationship between the cam shaft and crank was out of whack, the engine computer sets a code. Anyway, fix the mecahnical problem, then see if the cam sensor is ok.

DO NOT RUN THIS ENGINE UNTIL THIS PROBLEM HAS BEEN CORRECTED. It is in danger of valve interference with the piston. (Some engines are "free wheeling" where the pistons will clear the valves should the cam shaft stop turning, but do you know for sure? Many will hit the valves. It's best to assume the latter.)

Your chain may have jumped a tooth or two already.

I think you will need a new timing chain, crank sprocket and cam sprocket. When you get the cam chain cover off, you can better assess what needs to be done. Likely, the cam chain tensioner needs rebuiding. If there is a hole in either the chain cover or oil pan, this need repairing or replacement. (As rule, things get more expensive when a problem is ignored until its really bad.)

There's nothing special about reassembly, but you will need a repair manual to put the sprockets in sync when the chain is put on. By the way, read the manual before taking the old chain off. The crank must be positioned and not moved during chain removal and replacement to avoid valve damage. A tensioner complicates things a bit because when the tensioner is bears against the chain, parts move and you may find the chain is off by one link. Just say damn quietly, and start over. The lesson here is save the final torquing of sprocket parts to last, after checking the final position with the tensioner applied to the chain.

As final note, flush out the oil pan. There may be metal debris there.

Let us know what you find.

    Bookmark   April 8, 2006 at 4:38AM
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thanks for the input. its my friends car and he bought it last fall as a replacement for his previous car which died due to timing belt failure/overheating. he is not having good luck. its at the dealer now. their diagnosis is timing chain/cam sprocket. its a 98 mystique. 4cyl.125k miles. payed about $3k last fall. dealer is at $1500 for repair.

    Bookmark   April 8, 2006 at 9:00AM
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