Cranks but no start and no wait to start or tuner power - strange

[AlaskanEngineer]

Ok... just went out to fire up the 7.3 and it started to crank right up, but then died after having caught (just about 1/2 second after I let go of the key.) I thought that very odd and went to start it up again... but this time the Wait to Start Light won't light up, My DP tuner switch does nothing (nothing on the display at all -- no power) and when I turn the key, it just turns the engine... oh and no RPMS show on the dash.

That last bit about no RPMs makes me want to say CPS, but I just had the recall done 6 months ago and the lack of power to the other items has me wondering... grabbing a different CPS right now to try out, but looking for ideas as I am very doubtful

Note -- nothing leading up to this... just happened without warning... only thing out of the ordinary is I have been driving on bumpy dirt roads more than normal lately...

Thanks in advance...

[sldghamr]

check the fuses under the hood, specifically the #22 spot. a no wait to start light a on 7.3L usually means that fuse was blown.

[AlaskanEngineer]

Interestingly enough... #22 fuse was fine but # 4 was burned out... (yes looking at ones under hood and not in cab)

replaced #4, still nothing -- shouldn't matter anyhow though since I believe that #4 has to do with my towing lights (it blew out once before while launching a boat if I recall correctly)

I think step 1 is new CPS since I am not seeing any RPMS when cranking... but the no power to my DP tuner, nor a wait to start light have me concerned that I am barking up either the wrong tree or at the very least one that has more than one branch...

[AlaskanEngineer]

Ok, I have 2 hours of daylight or so remaining, replaced the CPS, no dice. Also tried removing the fuel bowl heater plug, still no dice...

I am not still not getting power to my DP tuner, nor getting a Wait to start light... batteries are strong and cranking well, but still no hint of starting...

Tried swapping relays 30 & 31 as I was wondering if my PCM relay was dead...still no dice

All fuses including in cab and under hood are checked with multimeter for continuity...

Running short on time, advice welcomed!!!

[AlaskanEngineer]

Ok, I removed the fuel bowl heater plug... then swapped relay #30 out with a known good relay... still no wait to start light...

Now I am trying disconnecting the batteries for 5 minutes then reattaching... hoping to clear some memory... (EDIT this did not work)

Also downloaded the operators guide and checked EVERY SINGLE FUSE that had anything to do with the PCM...contacts and all (not just continuity test as done earlier)

I need to know how to check for voltage getting to this relay and to the PCM... where are my check points?

[AlaskanEngineer]

Ok... I tore my PCM out and checked the connection of my DP tuner... put it all back together... still nothing....

Thus I now have 2 conclusions:

A. Relay is not getting proper exciter voltage to kick on

or

B. My PCM is Fried!! (and I want to know WHY)

So how can I check for voltage getting to my PCM? (Essentially how do I check the output of that relay #30??)

Thanks

[cliford]

Originally Posted by AlaskanEngineer

Ok... I tore my PCM out and checked the connection of my DP tuner... put it all back together... still nothing....

Thus I now have 2 conclusions:

A. Relay is not getting proper exciter voltage to kick on

or

B. My PCM is Fried!! (and I want to know WHY)

So how can I check for voltage getting to my PCM? (Essentially how do I check the output of that relay #30??)

Thanks

im guessing this. . . have you checked the codes?

[AlaskanEngineer]

cliford,

I was under the impression that if there were any codes, I would get an SES light... I don't... am I mistaken on that one?

Next, I was pretty sure that when the PCM fries, you cannot connect to pull codes... Correct?

If it is fried, could it have taken my DP tuner with it, or perhaps vise versa?

Again, how can I be sure its getting power? has to be something I can check for power to the PCM...

[AlaskanEngineer]

Ok... so tonight I decided to step through the system one contact at a time.

Started with the relay #30... looking for B+ (battery) voltage against ground... check

Trigger voltage (KeyPWR) approximately 1.8 VDC... way below needed threshold voltage for tripping the relay.

KeyPWR voltage on the relay for the blower motor however was fine at 11.8VDC ... thus I was pretty certain it wasn't in my key/tumbler system.

Looked over the fuse block again, both under hood and in cab... pulled all fuses related to the PCM... when I pulled Fuse 30 from in the cab I noticed some black oxidation on the contacts (not heavy -- just a dusting)... so I cleaned it off and put it back in -- still nothing... but that got me thinking about how the contacts in the fuse block must look... just for kicks I checked the resistance across the contacts on the fuse block itself... noticed that I had HIGH resistance... then I checked voltage drop with key on... had about 10VDC drop across the fuse... 10V + 1.8 V = 11.8V which is what I had on the trigger voltage for the other relay... so I cleaned the crap out of the contacts for the fuse... presto it works!! guessing someone prior to me blew the fuse pretty bad and the resultant mess caused poor contact in the block itself... little bit of time, little bit of oxidation, little less voltage until one day there just wasn't enough to trip the relay... thus no power to the PCM or DP tuner

Thus closes my issue... hope it helps the other folks out there with similar problems...

[m-chan68]

Originally Posted by AlaskanEngineer

Looked over the fuse block again, both under hood and in cab... pulled all fuses related to the PCM... when I pulled Fuse 30 from in the cab I noticed some black oxidation on the contacts (not heavy -- just a dusting)... so I cleaned it off and put it back in -- still nothing... but that got me thinking about how the contacts in the fuse block must look... just for kicks I checked the resistance across the contacts on the fuse block itself... noticed that I had HIGH resistance... then I checked voltage drop with key on... had about 10VDC drop across the fuse... 10V + 1.8 V = 11.8V which is what I had on the trigger voltage for the other relay... so I cleaned the crap out of the contacts for the fuse... presto it works!! guessing someone prior to me blew the fuse pretty bad and the resultant mess caused poor contact in the block itself... little bit of time, little bit of oxidation, little less voltage until one day there just wasn't enough to trip the relay... thus no power to the PCM or DP tuner

As a Ford dealer tech I would like to say KUDOS to you for solving your own problem.

As one of my instructors used to say, "VOLTAGE DROPS, VOLTAGE DROPS, VOLTAGE DROPS" and "CHECK THE BASICS, CHECK THE BASICS, CHECK THE BASICS".