Expert: Mike Evans - 8/1/2009

Question
QUESTION: suburban starts hard , went through 5 starters, i have checked flex plate and replace crank sensor. still it seems that there is alot of compression when trying to start. if i unplug the CPS it turns over fine. not sure what to check now

ANSWER:      Are you saying that it cranks slowly?  And that unplugging the crankshaft position sensor lets it crank fast?  Or are we talking about the camshaft position sensor?  Most GM engines will run without the camshaft position sensor, just not in closed loop sequential mode.  Slow cranking can be caused by a bad timing chain, even though that doesn't seem to make sense, I have seen it many times.  Hard starting(not slow cranking) can be caused by a bad fuel injection spider.  I wish I had a little more information about the problem.

---------- FOLLOW-UP ----------

QUESTION: when starting i notice the flex plate will kick back like the timing is advanced. thus causing a grinding of the bendix and the flex plate. could this be due to the reluctor coming loose or breaking woodruff key???


Answer
    I have a real feeling that it's the timing chain.  If there are over 100K miles on the engine, it's the most likely candidate.  Although, again, it could be the fuel injection spider causing a backfire.  The crankshaft position sensor really can't get out of time, although the wheel that triggers it could be damaged.  There's no way that the key broke, it just doesn't happen.