Problem: The truck was towed to the shop
because, while holding the key in the Start position, the starter
would begin cranking the engine over, then stop cranking before
the engine started.
When the technician called Tech-Assist, the consultant asked him
to check the fuel rail pressure while cranking (NOTE:
Specification is 6000 psi). The fuel pressure was correct.
Next, he asked the technician to check the cranking speed. The
technician connected a scan tool to check RPM. The cranking speed
was 900 RPM. That was way too high. The consultant explained to
the technician that Powertrain Control Module shuts the starter
off when it sees an RPM that is fast enough to indicate the
engine should be running. Because the cranking RPM read high on
the scan tool, and the engine didn’t seem to be cranking that
fast, the consultant asked the technician to scope crankshaft
position (CKP) sensor signal.
When he scoped CKP, he found the signal was full of glitches.
Upon further inspection, the technician found the CKP terminals
were loose in the connector.
Confirmed Repair: The technician replaced
the CKP connector and made sure that the two connector halves
locked together tightly. After that repair, the engine cranked
over and started normally. Fixed!