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Has Anyone Had a Chrysler/Volvo Ignition Knock Sensor Fail? Sudden Low Power Diagnosis... 200

posted by  Caliban on  Mon Oct 5 08:22 CST 2009
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last visit: Sat Aug 11 14:05 CST 2012
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I am trying to diagnose a lack of power concern on my '84 245 with the B23, auto trans and C/V ignition system. I replaced the head gasket about 1000 miles ago and everything has been running great up until the last week or so. The first day I noticed the problem, it was intermittant, but by the second day, there was a loss of power at all times, leading me to believe it is something electronic/electrical. The car idles fine and feels ok in first gear, but as soon as it shifts into second and I try to accelerate, it bogs down like I have fouled plugs (I pulled the plugs on Friday and all are OK, consistent light grayish-tan deposits on all four). If I press it hard and force a late shift, it seems to clear up around 35 mph, but as soon as it upshifts again, it bogs down again. It has also affected top speed; two weeks ago, I had it on the interstate and it did 70 mph just fine. Now it is a struggle to do 65 mph with the gas pedal floored. In addition, the weather here has cooled into the low Fourties to high Thirties degrees F. The car will start and idle just fine, but when I try to pull away from a stop, there is a massive flat spot just off idle. It will hesitate for a second and then take off. Last, but not least, my fuel mileage has dropped to 17 in town, where I was getting 20-22 mpg before the summer. So, here are my thoughts:

1) Coolant temp sensor failure. I replaced this 9 months ago with a new engine harness, but it could have been hit during the head gasket job.

2) Knock Sensor Failure. I had the center spade terminal of the knock sensor fall off over the summer and the symptoms were much the same as the current ones. I was able to solder the terminal back on, but I have since wondered about the quality of the repair. I also read the knock sensor section on the FAQ, and the symptoms seem to fit.

3) Throttle Switch Sticking. This is the least likely possibility in my opinion, but it is still possible given the symptoms, esp given the flat spot off idle when cold.

Can anyone point my in the right direction? I am in the middle of college and don't have much time for car work right now. I do intend to test the coolant temp sensor and knock sensor, but if anyone has some experience with failure modes of these two, guidance would be appriciated!

Thanks,
Nick






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