GMC Yukon 2001 does not always pulse injectors first start attempt

[jeff massoglia]

My truck (6.0L) does not start consistently the first time.  Always does the second time and always runs great when starts.  About 30% of the time it will only start on second attempt.  I never need a third attempt start.   This began happening around the time I had fuel pump changed but do not think related.   I actually had two fuel pumps installed (long story) and this was happening with both.   A mechanic spent a few hours on it,  there is fuel pressure and spark but noid light reveals fuel injectors not getting pulsed when it does not start on that occasional first attempt when fails.  There are no codes.  He thought might be ECM but I changed that and it is same problem.  He says crank sensor / cam sensor ok,  fuel regulator ok. 

Help !  Please !

[riverbanks]

Try to isolate a little more,do the injectors have 12v with key on and crank when no start?

[Doug_Scott]

How long are you holding the key in the start position?  Do you turn the key to the run position, stop for a second or 2, then continue turning the key to the start position and hold it there for 5 seconds while it cranks?  You may think you do that, but, if you try watching how you start the truck you may be surprised at how short of a time the key is in the start position. 

[davester]

You might consider cleaning the power and grounds between the battery and the ecm...

[jeff massoglia]

Yes we have checked connections and the key being held in run for extended period and then moving to start and cranking longer etc has no effect.   It is not a fuel prime issue.  Again,  great fuel pressure that does not drop,  there is a spark,  just injectors do not pulse initially.  I have never had it fail on second start attempt

 

[davester]

Find the wiring diagram for the injectors, and trace back, to see where there's a power and/or ground problem.

 

The full-service manual may also have some diagnostic stuff about the injectors not firing, you can subscribe to it at a site like alldatadiy.com

Edited March 4, 2020 by davester

[jeff massoglia]

I had another mechanic take a look and he suspects,  and I do as well,  this is a security issue.  Here is some info I found below.  Looks like the injectors are disabled when security enabled.  This would explain the intermittent nature of the no start / no injector pulse condition.  You can change out the whole ignition lock assembly,  the part is about $100,  and this gives you a new hall effect sensor but the job looks very challenging as steering wheel and airbag need to come out.  I read that the magnet weakens over time and signal is iffy.

 

The PassLock system works when the lock cylinder moves a magnet past a Hall effect sensor. The sensor then sends a signal to the control, which GM has moved several times over the model years. The control then sends the code to the PCM. If the code is correct, the PCM will allow the car to start and run. However, if the thief yanks the lock cylinder, it removes the magnet as well, so the sensor can’t detect the magnet movement.

This system proved VERY unreliable as the Hall effect sensors had an extremely high failure rate. To repair the system, the shop would have to replace the lock cylinder housing because the Hall effect sensor can’t be replaced separately.  So GM moved to PassKey III