Hello All,
Ok, I last drove my beast several weeks ago. She has been running good with no indications something is a-miss. Went out today and got the dreaded crank and no start. My batteries are old and I have to keep them on a tender all the time. But it was a warm day today in the upper 70's. I tried multiple times to get her to start and she would just crank. I can hear the fuel pump running. The injectors are clattering away like they should. So I started pulling some numbers;

FICM 48.5 key on and cranking
Fuel pressure 58psi key on and cranking
HPOP 1500psi during cranking

And then she started. Seemed to run good. Checked for DTC's. Found a P0336. Crank shaft position sensor. That darn sensor has less than 5k miles on it. What the hell. So, I know what I'm doing tomorrow, checking the wiring and making sure the sensor connector is tight and plugged in.

Anything else I should check before replacing the sensor again? Thanks, B.

 

You need to be checking more PIDs when you crank.
Cam/Crank Sync
FICM Sync
cranking rpms
FICMLPower
FICM VPower
Fuel Pulse Width
ICP volts

It is uncommon for a new(ish) OEM CKP to fail.

 

Thanks Mark,
I guess I need to break out my laptop and fire up AE and dial in some stuff. I went out last night and got the crank and no start issue again.
This morning I went out to get some data and she fired up right away. Cold at idle this are the numbers she showed right now;
FICM Sync 1.0
EBP Volts 1.4
ICP Volts 1.2
ICP Regulator 29.7%
Logic Power Volta 13.5-14.0
FICM 48.5v
Intake 14.8PSI

So, I need to keep trying her until she messes up again to get those numbers. I sure don't feel like changing that sensor again. The cam and crank sensor synch modes on my cell phone app don't show anything. It's the OBD Link app. Which has been usefull, but it is limited. B.

 

It is a pain when things are intermittent!! Hate to see anyone have to deal with that! The data you posted above looks good to me.

If codes aren't specific enough, then the only other option we have is to catch it when it won't start (unless you have the IDS system, and then a few more options exist).

 

Tell me about it Mark. She has been flawless since I changed the crank sensor like 2 years ago in the middle of my driveway on a hill. I don't drive her that much, mainly because of fuel costs. She has about 8k since I did a full rebuild. I will just keep plugging away and get the laptop hook up and running all the time to grab that stuff when she fails again. B.

 

In the middle of Mark's PID list was Cranking RPM. If your batts are old and likely weak, they may look ok voltage wise, but don't have the amps to spin the motor over fast enough. 150 rpm or so minimum or no injectors will fire... Besides yanking the batteries and having them load tested, you could try jumping another truck to your passenger battery and rev the donor truck while cranking. It's caught me once...

Good luck!

 

Update,

I have had it on a regular charger for the past few days. Several times a day I will go out and she fires right up and runs normally. I disconnected the batteries and load tested each one independently of each other. The passenger side battery load tested good and held 800 amps at 11.2 volts with my Snap On load tester for 15 seconds. Bear in mind when I rebuilt my engine two years ago I switched the batteries from side to side. So this battery HAD been on the driver's side until two years ago.

I did the same with the driver's side battery, which had been on the passenger side until two years ago. It FAILED MISERABLY!!! When load tested, it went right to negative amps and the voltage dropped to 7.5 volts after about 5 seconds under load. I looked at the tag and it appears as though the battery was made in September 2016? See attached pic. So, my problem is most likely battery related. Thank God, Because I was not looking forward to changing that darn crank sensor again. What a bear it can be.

So I will get two new batteries and see how it goes. B.

 

Thanks for the update, now let hope that's all it is

 

I installed two brand new Costco AC Delco 850cca batteries today. So far she is starting right up like she used too. Took her for a 20+ mile drive and all parameters appear to be normal. I guess that one dead battery really threw a monkey wrench into her. If I have any further issues related to this I will post up. Thanks guy. B.

 

Went out today to fire up the old girl after sitting for several days. Got the dreaded crank but no start. Plugged in my OBD2 bluetooth adapter and fired up the app on my cell phone. During cranking the RPM's are registering very low. The engine is cranking normally, but the crank sensor data is fluctuating. I don't have a mechanical tach to give you the actual RPM's of the engine during cranking, but it IS cranking normally. So I guess it is a crank sensor issue? I'm going to have to check the harness and plugs to make sure everything is tight and solid. SMH B.

Cranking RPM's fluctuate between 30 and 58 than after about five seconds of cranking it settles on 41rpms.

 

Got some more numbers here,

ICP Voltage KOEO .2v. Cranking 1.5V
ICP PSI KOEO 0.0 Cranking 1280PSI
ICP % KOEO 14.8 Cranking 51%
FICM Sync 0.0 Cranking 0.0
FICM Volt KOEO 48-49 Cranking 48-49
SYSTEM Volt 12.7 Cranking 11.3
Logic Volt 12.7 Cranking 11.0
EBP Volt .9 Cranking .9
MAP PSI 14.5 Cranking 14.5
Cam Sync 0.0 Cranking 0.0
Crank Sync 0.0 Cranking 0.0

And while doing this she started and runs great. Cam, Crank and FICM Sync are all 1.0 running. System voltage is in the 14.3 range. I don't get it. It's NOT an HPOP issue, because my pressure jumps up to 1500PSI within like 2 seconds when I first start cranking and settles in around 1280PSI after a few seconds of cranking. It's not a fuel pump issue either because as soon as I turn on the ignition I have 58PSI of fuel pressure within 2 or 3 seconds.

Could it be a PCM issue? Something going bad in the PCM? I'm NOT getting any trouble codes right now like I did when I first posted this thread. Which was prolly contributed to by the bad battery. It's just odd that everything is circling around a bad crank position sensor or harness/connection issue. When she won't start, I get that odd low RPM number. But as soon as the RPM's start to register it starts. What am I missing? Thanks, B.

 

Just went to go start it again and nothing. Spins over like it should, but wont fire. Good HPOP and fuel pressure. RPM's are listing right around 66 and I'm not getting a FICM or cam/crank sync. I'm going to change the crank sensor, unless I see some harness damage in the process. Then we'll see. B.

 

Sounds like what needs to be done. Keep us informed!

 

That would be an interesting one to see a scope signal on

 

Please don't forget: you are dealing with a Fix-Or-Repair-Daily brand vehicle. hahaha

Don't be offended as I have too many F O R D's.

I drove a GMC 6.5L turbo diesel for 15-years. The 'pmd' and 'oil pressure sensor's" were notorious for failing causing your grief.
What I learned over those 15-years is that most codes are a "default" and only a starting point for diagnosis.
A for-instance is if the 6.5 diesel had a vacuum leak, the code thrown would be Injector Pump, so default codes can be very mis-leading.

Good luck on finding the Gremlin.