2008 GT - No Crank, No Start - will start if pushed

[Jello_08GT]

Hey there I have an '08 GT/CS with 120K miles.I've been dealing with this issue for the past couple of years and I'm at loss at this point, it's an intermittent electrical issue and very hard to troubleshoot...from my findings so far

I've checked everything:

• Alternator is good
• Battery is good
• Starter is good
• Brand new ignition switch
• Clutch safety switch is good (even tried bypassing it)
• Fuses are good
• Relay is good
• SJB by the passenger side is clean, not a speck of dust
• ECU has no corrosion, all pins are solid
• Grounds are all good (added extra ones for a beefy audio system previously)
• Keys are good, and I even have a spare, and when issue happens key don't matter.

Despite this issue of no crank, my car runs fine if I jump it on second gear down a hill. I've even resorted to installing a push switch inside to jump the positive to the starter relay pin, so I don't have to mess around under the hood with a wire every time (jump 2 pins, which is what turning the key would do)

From my troubleshooting, it seems like there's a fault between the clutch safety switch and the starter relay pin that's supposed to be energized. Trying to find it in the mess of cables is a nightmare. The ground from the computer is good, indicating the car is ready to turn on, but the positive pin just isn't getting the power it needs.

**UPDATE -
ok new development, I think...

I measured voltage on the clutch safety switch and I'm getting 4~ volts ? shoudn't I be getting 12?

This test was done while the issue is happening , I want to get a reading while the car starts and see if I get 12v if is that at least I would narrow down the specific problem and maybe run a new wire?

can someone confirm the voltage on the safety switch ? please ! I'm chasing this for 2 years and would really love some closure

Thanks a bunch.

 

[MrBhp]

Your clutch safety switch can test good and still not work when installed. If you take the switch out of its bracket, but leave it plugged in and push the button, will the car crank? If you try this, make sure trans is in neutral.

 

[Juice]

You could monitor PCM live data w/Forscan and see if the pcm is getting the start request signal.
Or have a code for something like a PATS issue.
Thats where I would start to narrow it down.
Forscan does not need to be licensed to read data, but you do need an adapter. The VS Linker I think its called, is hands down the best for Forscan, costs around $30 bucks.

 

[Jello_08GT]

Your clutch safety switch can test good and still not work when installed. If you take the switch out of its bracket, but leave it plugged in and push the button, will the car crank? If you try this, make sure trans is in neutral.

same behaviour, if I jump it will start and then not start so the clutch switch is good.

 

[Jello_08GT]

You could monitor PCM live data w/Forscan and see if the pcm is getting the start request signal.
Or have a code for something like a PATS issue.
Thats where I would start to narrow it down.
Forscan does not need to be licensed to read data, but you do need an adapter. The VS Linker I think its called, is hands down the best for Forscan, costs around $30 bucks.

Can you send me a link on what I need to buy ? Thank you

 

[crjackson]

https://www.amazon.com/Vgate-vLinker-Adapter-FORScan-MS-CAN/dp/B094Z7PBLS

 

[Juice]

Thats it.
Software at forscan.org

 

[DieHarder]

Review the starting system diagrams. Make sure you understand how the circuit is supposed to operate (See Starting System Description). Troubleshoot using the Pin-point tests. Check out Utube/other sites for troubleshooting ideas/solutions. Try to narrow down the problem area. Once you find something that doesn't work right check further into why.

Starting System Description: https://iihs.net/fsm/?d=204
Starting System Testing: https://iihs.net/fsm/?d=206&f=Starting System.pdf
Pin-point testing: https://iihs.net/fsm/?d=206&f=Starting System.pdf&p=3
Starting System Wiring Diagrams: https://iihs.net/fsm/?d=40&f=Starting System.pdf&p=2

From your description I would check/verify continuity of the clutch switch operation & cabling to the BEC/starter relay (see wiring diagrams) . Pin-point tests should help you narrow down what the issue is. There are also relay testing kits you can buy to test the operation of the relay. You need the green one for the starter relay.

Checking for a bad clutch switch:

FYSA, On the outside chance:

 

[Jello_08GT]

Review the starting system diagrams. Make sure you understand how the circuit is supposed to operate (See Starting System Description). Troubleshoot using the Pin-point tests. Check out Utube/other sites for troubleshooting ideas/solutions. Try to narrow down the problem area. Once you find something that doesn't work right check further into why.

Starting System Description: https://iihs.net/fsm/?d=204
Starting System Testing: https://iihs.net/fsm/?d=206&f=Starting System.pdf
Pin-point testing: https://iihs.net/fsm/?d=206&f=Starting System.pdf&p=3
Starting System Wiring Diagrams: https://iihs.net/fsm/?d=40&f=Starting System.pdf&p=2

From your description I would check/verify continuity of the clutch switch cabling to the BEC/starter relay (see wiring diagrams) . Pin-point tests should help you narrow down what the issue is. There are also relay testing kits you can buy to test the operation of the relay. You need the green one for the starter relay.

FYSA, On the outside chance:

I did some testing and found weird results.

with key out ? (light blue/yellow wire) <<< this is the weird part

With Key in start stationary wire(light blue/yellow wire)this means it's not sending 12v to the PCM right ?

Clutch safety switch black wire (ground G204 is good) I just cleaned it as well

why am I getting 7~ volts and why am I getting 12 with key off, should I be getting 0 ? or turning key in start causes a load and that's why it drops ?

 

[JC SSP]

All this info should be a sticky for future quick reference.

 

[DieHarder]

The clutch switch provides continuity only (review wiring diagrams). You need to determine if 12v is getting to the starter relay and the relay is energizing. If not, why not? Go thru the Pin Point tests and tell us the results. You might have 7v due to bad grounds. Do yourself a favor and watch all of the videos thru their entirety and then re-read the description of how the circuit works and do the pin-point tests. Then, let us know what you find out.

Ford Workshop Service & Repair Manuals - fordrepair.info - 2005 Mustang Starting System Starting system

Ford Workshop Service and Repair Manuals, 2005 Mustang Workshop Manuals Powertrain Engine Starting System DIAGNOSIS AND TESTING Starting System

iihs.net

 

[Juice]

Going from memory here, but, the key sends signal to pcm start request. (This is what you will look for wirh Forscan). If the pcm sees a valid key (PATS), it grounds the stater relay in the BEC. That in turn powers up that single wire going to the starter.
So, if forscan confirms start request is seen, the issue is after the pcm. If start request is not seen or an immobilizer code is present, pcm will not crank the starter.