Hello all! New member, but have been surfing the site for awhile.... I have a new to me 2006 F250 with the 6.0L. The engine was rebuilt a few thousand miles ago and within the last couple months has developed a random crank/ no start... I have been through 100s of forum posts about similar crank/ no start and have been chasing this problem along with my diesel mechanic, we think we have it narrowed down to the wiring harness, but before dropping big bucks on that, I was wondering if I could compile a checklist of possible things that could cause this.

 

Well first off you need to post readings.
With a quified mechanic involved, you should have access to readings while cranking. Post them.
If you have a log on no start verses start, that would really be helpful.

 

Welcome Heres a good checklist Mark made just for you

Troubleshooting a No-Start condition - Ford Truck Enthusiasts Forums

 

Yes, thank you. That's the type of list I'm looking for.
So, this months long hunt of random no start actually started with a random die. I was sitting waiting for a light to change, and the truck just shuts off... no warning... everything else like the radio stayed on.... I tried cranking a few times... didnt fire. Called the tow truck, and while waiting figured I'd try again.... started up! So I took off towards home and while driving it died two more times.... had my mechanic come over the next day with his SnapOn scan tool, started up no problem! Only code was camshaft sensor, probably from long, multiple cranks.... we ended up putting a data logger on it and it finally no started. We caught a FICM no sync, all other values were good, besides CMP fault again..... also caught on my SCT logger that the RPMs while cranking were erratic and mostly below 100 even though batteries were charged and it was audibly cranking fast. Swapped FICM for known, good 'Bulletproof', changed out the CMP sensor, even though it was new from when he rebuilt the engine. A few days later, no start again.... replaced the pigtail to the CMP, a few days later, no start... so next we are going to put a loaner PCM..... and this has been a condensed version of my 3 month long random no start nightmare.....

 

Issues w/ bad rpm values usually indicates a crank sensor problem. It is discussed in the no-start thread.

 

Right. Because the PCM picks up its RPM signal from only the crank correct? ....that sensor is also new from rebuild...

 

Yes, rpm is from the CKP. Not sure why you focused so much on the cam shaft sensor (CMP) and wiring.

I hate to assume that the cranking was sufficient (150 rpm required) when you are basing that on the sound of the crank. Maybe it is just me, but my hearing isn't calibrated very well. Have to take your word for that one.

Well then maybe there is an issue w/ the CKP harness (wiring) or maybe even a bent/damaged crankshaft trigger wheel.

Are you getting a consistent injector pulse width (or also called fuel pulse width) signal when cranking?

 

Another thing I was curious about... what commands the buzz test to happen? Should it happen every time the key is turned to on?

 

I would check the connections to the pcm to make sure all plugs are clicked in and don't have broke clips.
6.0's vibrate a lot while operating.
Next question. What is a bulletproofed Ficm? Surprised Mark didn't catch that.

 

I assumed it was one from BulletProofDiesel. They sell a very reliable one (for some big bucks)!

I know I shouldn't assume though!

Good suggestion on the PCM plugs!

 

-Well, I am an aircraft mechanic, with plenty of experience in gasser cars, trucks, and motorcycles. So I'm leaning on the knowledge of my diesel mechanic for specifics in this engine.... that being said, im not sure why he focused on that... maybe because that was the only code it would throw, or maybe he mixed up where he thought the rpm signal comes from...

-I say it sounded like it was spinning fast enough because it had the same crank sound that it does when it does start.... and because I can hear that its slowing down after a few long cranks.

-I doubt the crankshaft trigger wheel is bent or damaged because it will start and run fine for days or weeks at a time, but then one day not start.

-If the FICM never syncs because it is getting a bad rpm signal, then would I still be getting injector pulse in my no start?

 

I took the PCM out yesterday. All of the connections were tight and nothing was broken.

Yes, the loaner was a bulletproof FICM, But that has gotten switched back to mine after mine came back from FICM repair for preemptive repairs/ upgrades.

 

A question that you guys may have missed a couple of posts ago... what commands the buzz test to happen? Should it happen every time the key is turned to on?

 

In the old days it was a LONG debate over where the rpm signal came from. Also, lots of folks look at cam and crank sensor codes as an indication of a problem w/ those sensors when some of those codes simply come from a stall or excessive crank situation. A lot depends on the exact code number - which is always a good thing to post.

I wouldn't expect an injector pulse width value if there are sync issues.

Good point on the trigger wheel. Often times if that wheel has an issue, then there might be cylinder contribution codes on "opposing cylinders" in the firing order.

 

Well on that reply I would say do the old BYM trick. If you really are down to electrical issue.

When the crank no start happens, get under the hood and wiggle the harness. See what happens.
Next alternative would be just buy a harness or do some serious electrical diagnostics. I guess I would have pcm checked also. Probably do that first.

The shutting down at the light while running still has me thinking loose connection somewhere. Maybe a ground. You have two write there close to pcm.