Mechanics

HOW TO DIAGNOSE ENGINE PROBLEM?

2006 Lexus SC 430 • V8 2WD Automatic • 26,000 miles

My SC430 was running perfectly, then began to misfire. A scan showed a misfire on cyl 5. Checked plug, wire, coil, could find no problem. Couple days later running rougher, scan showed misfire cyls 1, 3, 5, 7. Couple days later, refused to start. Acts like it would if engine immobilizer had been activated: runs about 1 sec, then shuts off. Scan showed problems with both cam position sensor and crankshaft position sensor circuits. Replaced cam position sensor: no change. Reluctant to believe crankshaft position sensor is bad due to progressive nature of faults. Any suggestions would be greatly appreciated.
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Dwafford
October 18, 2011.



Have the timing belt checked. Though mileage might be low, there is a possiblity of one of the cam skipping a tooth.

The other possible cause would be a sticking VVT solenoid.

KHLow2008
Oct 18, 2011.
Can you tell me how to determine if the timing belt has skipped a tooth? I'm a reasonably competent mechanic and I have a service manual. Or is this something that only a dealer can do? Thanks again!

Tiny
Dwafford
Oct 19, 2011.
Remove the both upper timing belt cover and turn the crankshaft until the timing marks lines up for the pulley and the camshaft pullies and check if any is out of position.

Testing the engine compression might show some differences between the two banks.

KHLow2008
Oct 26, 2011.