Crank, no start - RPM; on tach or not?

[macleanflood]

Ok...out at Moab with folks today we had a crank no start situation. I noticed no rpm on the tach and suggested we change the crank position sensor. It's also possible it was vapor locked...or something else. While the CPS was being changed I pulled my fuel pump relay and induced a crank no start...but also no RPM on the tach.

It's been common forum wisdom that no rpm on crank is the CPS...but is this a myth?

Or is this a quirk of the 97s?

Is it possible you'll see RPM with a scanner looking at the PCM's PID?

-Mac

 

[Painfultruth]

If the ASD relay, fuel pump relay etc remain engaged during cranking the PCM is seeing a CPS signal.

If the PCM doesn’t see a CPS signal within 2-3 seconds of the ignition switch being turned on it will time out and drop the ASD relay ground shutting the relay off and subsequently the fuel pump.

 

[hear]

I've always silently questioned the RPM test. Now I want to know.

 

[gasiorv]

Mac,
Back home and getting caught up on work, messages, etc... Plan on going wheeling this weekend with the Down Home Zukin crew (bunch of Suzuki Samurai based buggies and even stock sami's which is a blast) and wanted to see if you ever figured this out.

Note: I changed the CPS while in Moab after running Metal Masher and it shut down on me again when working it on an obstacle for a while at Pritchett and then again at Coyote Canyon. At Coyote Canyon when I cranked it over, the RPMs were showing?
Since I have been home I did hook up a code reader and there was two codes. P0340 which is related to Cam Position Sensor and P1391 which could be CMP or CKP, so I ran out an grabbed a CMS from Napa (Echlin brand, can't find a MOPAR anywhere). I am also planning on reinstalling the Mopar CPS and wrapping the wire loom with some additional heat insulation.

It was great meeting you and thanks for your help.