My 08 F-150 4.2 coil doesn't have power to it. Truck just died and wouldn't start. Checked the relays, fuses and swapped out the ignition switch. My question is does the power to the coil come on with key on or is it a combination of things like key on and crank? Tried it both ways nothing...What am I missing... I need someone with a big brain.

 

Still trying to find that person with the big brain , but maybe somebody might be able to offer a suggestion or two.
Power to injectors is controlled by PCM (Computer).
Normally,,, key on, PCM power relay ( In computer) is closed, power sent to all injectors.
Did you look in your owner's manual for what the fuses in the vehicle (in engine compartment and in driver's side dash) control ?
Don't know how you are checking the fuses,but you can't always tell just by pulling a fuse and looking at it.
Need test lamp or meter to verify power is getting to the fuse and through it.
How about some help here and tell us just where we are equip wise and checks done? Thanks.

 

I have fuel, No spark, not getting power to coil, checked fuses with a test light jumped relay power swapped out ignition switch. Not sure when and how the coil is powered up. should I get power with key on or is it more than that.

 

You should have power with the key on.?

Because we changed ign sw , are we sure it is adjusted correctly ?

Unfortunately, them more things we change the more opportunity for things to go wrong.

 

I have both switches the new switch was $34. I don't usually change parts to fix stuff, but I've been all over this thing and it was cheap, so I tried. I changed the switch about 6 mo.'s ago and thought maybe it failed, hard to get good parts. I don't know if I can run a acc..power wire to the coil and run it that way.

 

I don't believe that will work.
If you have power to other things with the key in the on position, that could mean either there is no power to the PCM or a problem with the PCM.. PCM=computer

 

No coil power regardless you have no start issue first thing test the starter relay, remove it and test it, basically you test the continuity and resistance, shouldn't take you more than 5 minutes.


Now let's look at the electrical diagram flow below:


Now let's go over each component one at a time.
1) Ignition switch - C250:


Look at circuit 32, use a voltmemter and test the present of 12v voltage while turning the key to START position. If your steering column shrouds are already removed, you can get ground on the metal of the column.
Follow circuit 32 leads you to CJB's C270 and then it gets complicated so let's go backward and start from starter relay terminal 85 and 86, you can tell 86 is a positive trigger to the starter relay. Therefore terminal 85 should get ground signal from the SMJ. Let see the range sensor diagram as shown below to confirm it's a positive trigger to terminal 86:


Pin 9 (Circuit 295) and Pin 10 (Circuit 325) are getting incoming voltage in START position. Pin 9 is beyond the scope since it's not mentioned in the diagram so if you look at just Pin 10 (circuit 325) you can see it goes back to CJB thru C270A to energize the starter relay.
The SMJ sends ground signal to terminal 85 at rest or key in RUN position is not important and it's for you to find out if you are getting ground signal there.
Remove the starter relay again, locate where terminal 85 goes to, test and see if you get continuity to chassis ground, also test and see if the resistance btw.
Do the same thing on terminal 86 BUT with a voltmeter to see if you are getting 12v there while key in START position. If you don't, you have a problem between ignition switch and the DTR and test the DTR first. Unplug the electrical connector and test pin 10 (circuit 325). Plug the connector back in and test pin 12 (TEST WITH CARE) so this time you need to remove the starter relay in case your truck starts and run you over. If you do and still no start, then you need to check the battery wiring and maybe bad terminal at starter motor.
As far as ignition coil here's the diagram:


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