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Discussion Starter #1
Here is the deal. My engine keeps jumping out of time. When I realign everything the car will run correctly for about 10 minutes and then it will slip out of time. Can someone please tell me why this is happening. The timing belt is less than a year old so I dont think that is the culprit.
 

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The ECU will take readings from the knock sensor and advance or retard timing accordingly. Primitive knock sensors will only retard timing when knock is sensed, I believe the Celica Supra ECU is programmed like this. Some current day OBD systems will advance or retard timing depending upon engine speed and whether or not knock is occuring.

If your knock sensor may not be working properly, then the ECU may be retarding timing automatically. Since I haven't heard or read much about the Celica Supra OBD system and sensors then I am only making an assumption based on what I know about some early systems.
 

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I can't say, some knock sensor will send a constant output to the ecu. Then, when knock is detected, the voltage will drop; so the ECU will retard timing then. Others will send a voltage to the sensor, but the output will be nil until knock is detected.

Just try unplugging the knock sensor, spray some contact cleaner on the plugs, then plug it back in. Reset the ECU, then see if anything happens. It might take all of 20 minutes to find out.
 

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Are you talking ignition timing or valve timing? the knock sensor would affect ignition timing but not valve timing.


setting the ignition timing on a supra requires jumping the test connector and checking with a timing light. Is that what you did? I would presume that would negate the knock sensor.

If you're losing valve timing, that's another story.
 

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Discussion Starter #8
Sorry I guess I should have been more clear. I am losing valve timing. No matter what everytime I set the timing it runs fine for a little bit then it slips out of time. Basically what happens is the crank gets ahead or behind the cams.
 

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As Flyin' Hawaiian says, check the keyway on the crank first.

When you changed the timing belt, did you change the belt tensioner too? If not, check it to be sure it spins freely, no resistance. Just loosen the bolt that holds it in place, pull it back away from the belt and see if it spins freely. If not, replace it.
To be safe, many people say you should change the tensioner and its spring when you change the timing belt.
 

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I found you had to have the belt tight and tensioner tightened down to even turn the engine by hand to check the timing. If not, the belt would not seat completely in the belt and walk up the sprocket on the exhaust side, eventually moving a tooth on the sprocket. The spring tension on the tensioner was not enough, I had to lever the tensioner a little into the belt to get it tight enough that didn't happen.
 

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i had the same problem on my supra. the keyway in the crank broke out and the timing wouldnt stay where it was supposed to. it can be fixed, you just have to pull the crank out and take it to a machine shop and they can weld it. it cost me $75 to weld it and $45 for a new timing sproket
 
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