Stories from the Road, Safari with Faulty Pick-Up Line

Automotive Robo Tech was called in for a 1999 GMC Safari, with a 4.3 liter engine. This was the first time this shop had called me. The complaint was a bad misfire on cylinder number 2, with some other random misses on the other cylinders. This vehicle had a poor maintenance record, so the shop did a basic tuneminus up to get the ball rolling. The Safari still had the miss when hot and was also setting a code P1345 or cam crank correlation error, along with the basic P0300 and P0302. After they tried a cam and crank sensor with no change, and ran out of ideas, they gave me a call. I came to their shop and took a look at the GMC. I also pulled the same codes they had, and the tech also showed me that when it starts to misfire, you can hear the spark snapping inside the distributor cap. The first step was to perform a scanner exploration of the coast, to get a preliminary survey of the issue, While watching the cam retard on my scan tool, I saw it jumping all over the place from minus 8 to minus 21 degrees. But, what could cause this? The cam retard should be holding steady at around minus 10 degrees at 1000 rpm. A bad cam sensor, timing chain, distributor gear, crank sensor, excess crankshaft end play could all cause this GMC to behave this way. GM's trouble tree for code P1345 pretty much states that at 1000 rpm, you should have between minus 5 and minus 15 degegrees, and if you revv the engine to 2000 rpm, there should be no more than a 2 degrees change. If there is more ...

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