Hey guys, hopeing that someone might be able to give me some insight into whats going on with this truck I am working on.


I work for the transportation department at a school and we have a bunch of 6.0 f350/450 busses and this bus I am working on has a no crank condition. Bus in question is a 2006 F450 6.0.

Currently if you turn the key to start the engine the solenoid just clicks but the engine wont crank. The person working on it before me assumed that the batteries and or starter were bad so they were replaced(0 miles on them right now) but the problem still persists.

First thing I did when I started working on this bus was jumping the starter relay and the starter engages and starts the engine perfectly. That being said I know the starter wiring is fine.

Secondly I looked through the wiring diagrams and saw that the PCM grounds the 85 terminal on the starter relay so I tried grounding the 85 and I was able to crank the engine with the key so that was telling me that the actual starter relay is fine. Next I went and swapped the PCM with another 2006 f450 thinking maybe the grounding switch in the PCM was bad and I have the same no crank condition. The PCM from the bus in question was swapped to the doner bus and it cranked perfectly(PCM in question is fine).

Next thing I did was look up all of the ground locations for the PCM or anything to do with the starter and they were all cleaned and still have the same no crank.

Looking around on the internet I see that the viscous fan can cause a problem if it shorts out so I unplugged that and no change in the no crank. I also saw that the trans range sensor could cause a no crank condition but I am getting back up lights/beeper and the bus "wants" to crank so I am thinking that the TRS is not the problem.

Lastly I tried hooking my Modis scanner up to this bus and was NOT able to communicate with either of the PCM's I tried. Not sure if this is related to my no crank condition. I checked all of the wiring that I could but could not find any chafing or breaks in any of the OBDII wiring.

Anyone have any suggestions? My planned next step is to replace the TRS but I am hopeing that someone here can point me in a direction.



Thanks in advance

 

Do you have a wiring diagram? Have you checked ALL of the powers and grounds to the PCM at the PCM connector?

 

Yes, I have the full service manual + wiring diagrams and yes, I cleaned all of the grounds that have anything to do with the PCM. I even ran a new wire from the 85 on the ignition relay to the plug for the PCM after sounding out the correct pin.

I also went through the plugs and checked my resistances for the ground pins and nothing was out of the ordinary.

As my problem seems to be on the ground side I never checked my power supply to the ECU. Have to assume its fine because when jumping the 85 on the ignition relay to ground I am able to start and drive the bus and everything operates normally(other than the neutral safety which is needed for DOT inspection).

 

With a wiring diagram, I would verify circuit integrity of all of the TRS wires before replacing it. I had a similar problem about 4 years ago. I removed the TRS and cleaned the contacts with spray contact cleaner. No problems since. Might be worth a try.

 

click and no start...but starts with jumper cables....I would get an ohm meter and check the resistance from the negative terminal of battery to the one of the starter mounting bolts. if you do not get zero......clamp a jumper cable from negative battery terminal to a bolt near the starter....if the starter spins....its either a ground cable....or improperly torqued starter retaining bolts.

 

Will definitely try that, going to have to drop the pan either way.




This is not the issue.

 

Since you have the complete service manual, have you gone through pinpoint Test B in the Starting section for the Diesel?

Edit:

Well, I was scratching my head and trying to figure out how the 6.0L engine starting logic works when I came to the conclusion that, other than noticing that diesel fuel stinks differently from gasoline, I've never learned much about how the start-up process works. In Googling the subject, I came across this magazine article which describes how to diagnose your concern (from a slightly different perspective, admittedly): www.motor.com/magazine/pdfs/112011_09.pdf The article also directs the technician to Section 4 of the PCED which does have the diagnostic information.

In a nutshell, the PCM only permits the starter relay to energize (to crank the engine) when all its preconditions are met.

I don't have time today to look through the following, but a Google search of 'ford 6.0 diesel "no crank" -cranks' will return a number of hits that might be good leads.

After all that, all I know is that diesel still stinks different from gas....

 

I have not completed the pinpoint tests because I know my starter and ignition relay are good. Like I said, I can trigger and start the engine if I jump my 15 and 30 on my starter relay as well as if i ground my 85 and use the key. The problem has to be on the ground side but I have cleaned all of the grounds for the PCM and ignition system that I can find in the wiring diagrams.

I will check my wiring from the PCM to the TRS and drop the pan and visually check the TRS today.

As far as I can tell the way the starting system works on the 6.0 ford is....

The PCM sees a duty cycle or voltage(not sure which) from the TRS depending on the gear it is in and that acts as your neutral safety. When the PCM sees the correct gear it allows the ignition relay(85) to ground and this completes your coil circuit and allows you to start the engine with the key. Now this is JUST the starter engagement we are talking about, actually starting the engine is more complicated but my problem is not with the actual engine starting, its just starter engagement.

 

Okay, go back and read the EDIT section above. You have a condition where the PCM is not being satisfied so it will not activate the starter relay. You have to determine which PCM input is missing or out of spec. There is more than just the TRS (which can be read using your scan tool, there is no need to drop the pan to check its operation) that can cause this. Have you even hooked up your scanner to check for related codes?

 

Would the starter relay/solenoid click even if the PCM wasnt being satisfied?

All PCM fail safes like this that I have delt with would never send any current to the starter solenoid if it was in safe mode.


And yes, after the first post I found the OBD fuse and replaced it and pulled codes. Only code was for #8 glow plug.

 

Are you positive WHICH relay is "clicking"? The starter relay cannot energize (click) unless the PCM grounds pin 85 and the starter solenoid (mounted on the starter motor) cannot engage unless the starter relay first energizes. Therefore, there's something either your observations or your reporting of them that is inconsistent with how the circuit is *supposed* to operate if either the starter relay or the solenoid is energizing and you've reported that pin 85 is not being grounded.

If you checked for codes AFTER pulling the fuse that supplies the PCM's keep-alive memory, any stored codes would have been erased and that information is now lost.

Also, if you are not able to communicate with the scan tool and it properly powers up when connected to the DLC, check the +5Vref supply (generated inside the PCM). If one of your three-wire sensors or that circuit is shorted to ground, it will inhibit the PCM's proper operation and keep it from activating the starter.