2005 Mustang GT Ground Tracing Help

[50mBz]

Hi my first post and its a long one. Even though I have read hundreds and hundreds of threads on many websites I cannot find the possible fix to my particular issue.

First let me explain I am a victim of the famous BEC burn out connections. After 2 fans, 2 radiators, 3 thermostats, 2 water pumps, High and Low pressure AC switches. None of these were the issue causing the burn of these BEC connections to the High Fan. Low fan works fine but its starting to heat up but still healthy so for now its parked until I figure this out.

So let me state after all this I was attempting to run external relays to run the fans. This is where we find the issue in discussion.

Once I ran the relays the fan worked but was constantly on.

Here is the connections I ran which is based off the cars wiring diagram default to the PCM. This works fine but "Constant" only.

Pin 86: 12v only when key is in the start/run position.
Pin 87: 12v constant (directly from the positive side of battery)
Pin 85: PCM signal (attach to lt grn/vio wire coming from pcm to fuse box)
Pin 30: Fan power (attach to lt grn/vio wire on cooling fan motor)

This is where the stuff shows up after head scratching why the relay was grounded constantly even with the PCM wired in as factory.

============================
Here is the results from probing (Multi-Meter) fuses inside the engine bay for ground problems

Fuse 40, 42 47 read 12.2 on the meter when ground testing fuse

fuse 40 is 15amp Engine #2
fuse 42 is 15amp Engine #3
Fuse 47 is 15amp Engine #1

Fuse 54 reads 10.1 when ground testing.
Fuse 54 is 10amp PCM Delay

Test of all the other smaller fuses do not show any power at all including the jcases.

IMPORTANT: I do not get any blown fuses whatsoever. Just grounds out my High Fan relay. Factory and External but they both still work

NOTE: All relays are brand new even inside the fuse box.
============================

Since that is out of the way here is some more basic probing tests I did.

KEY OFF

I tested several on top grounds like around the radiator, all the ones I can see on the firewall and several other spots.. All show powered as they should. did not find any ground that didn't show up on the meter.

Tested the plugins for the Throttle body. Some showed reading (key off) not sure if this normal. But its worth mentioning in case it isn't.

============================

Here is the HELP question.

Where would you if this was your car start looking for the problem? I am picky and rather keep it factory rather than run external relays. If I know there is a problem my OCD will batter me to death.

Any ideas or advice where to search is appreciated for the bad ground!

Only electrical additions to the car was the Touch Screen Radio/DVD never had any problems and been in since day 1

Sirens and Lights for Fire Department at one time but nothing that would come close to the fans for connections. All toggle switched system. Since then the light and siren system has been removed from this vehicle.

============================

The good stuff: Mods and Build

Bought Brand new 16 years ago
Tuned by Paul Automotive Engineering out of Cincinnati Ohio

Still good ole 4.6
80,000 Miles

AirRaid Intake (Tuned Required Model)

Ford Racing Cams
Forged Internals

MSD StreetFire Ignition Coils
Not sure about plugs just know they were expensive
Ford Racing 62mm Throttle Body
Upgraded fuel injectors not sure size. Cant remember but was matched with my build

Champion / 2 row radiator
Edelbrock High Flow Performance Victor Series Water Pump
SVT Performance Cooling Fan

All Steeda Pulleys

Cat Delete with Custom Exhaust with Flowmaster Resonators work done by Pro Muffler (local shop sponsor)

3.73 Gears
Ford Racing Single Piece Aluminum Drive Shaft
20 Inch Wheels
Power Stop Big Brakes complete swap
Lowered cant remember how much

I am sure I am missing some things but this is close to all of it.
Pictures of actual car attached.

============================

Again any ideas or advice where to start a search is appreciated!!

 

[86GT351]

Possibly something got corrupted in the tune from back feeding? Your tune should have the fans controlled to turn on at a certain temperature.

 

[DieHarder]

First, I'd put it all back to stock. Next, troubleshoot the cooling fan circuit. https://iihs.net/fsm/?d=40&f=Cooling Fan.pdf

If you do a search on "cooling fans" you're going to find a good deal of info on this forum. The simplest youtube video that explains the basics and pin assignments/function for the relays is here:

To determine what's happening with the relays (while the car is running and my recommendation to troubleshoot effectively) you're going to need a relay tester. Lisle 56850 (Green). Plug the relay into the top of the relay tester and the relay tester into the BEC. Then you can monitor exactly what's happening on the each of the pins with a VOM. You can also use a ground to turn on the relays by applying an external ground to pin 86 of the low speed relay or pin 85 of the high speed relay. This test will immediately tell you if the circuit is working (sans the PCM signals).

The PCM sends a ground when the reference signals from the CHT/Oil Temp (2005/06) sensors reach a certain value. I had difficulty monitoring that signal and never saw a true ground reference. With the car on (fan off) B+ will be present on the three lines of each relay and zero volts on the PCM feed. What you will see on that line is B+ when the fan activates.



I finally figured out that my fan was drawing too much current due to an old fan motor and corrosion in the wiring so I replaced it with a newer GT500 unit.

The primary ground to check is the fan ground (C-148 black line to G100 body ground). See manual pg 10-2 https://iihs.net/fsm/?d=40&f=Grounds.pdf&p=2 and physical location pg 151-1. https://iihs.net/fsm/?d=40&f=Component Location Views.pdf
An ohm reading for that ground should be less than a 10th of an ohm.

If you've eliminated all other issues I'd suspect the PCM/possible tune issue. Troubleshooting the PCM signals will likely take a much more sophisticated tester like you would find at a dealer however you can narrow down likely culprits fairly quickly with a relay tester and ground checks.

Good luck.

 

[DieHarder]

Two more pics.... cat walked across my keyboard before I was able to upload.

Voltage on the PCM signal pin when fan is active. Lisle 56850 relay tester

 

[DieHarder]

First, I'd put it all back to stock. Next, troubleshoot the cooling fan circuit. https://iihs.net/fsm/?d=40&f=Cooling Fan.pdf

If you do a search on "cooling fans" you're going to find a good deal of info on this forum. The simplest youtube video that explains the basics and pin assignments/function for the relays is here:

To determine what's happening with the relays (while the car is running and my recommendation to troubleshoot effectively) you're going to need a relay tester. Lisle 56850 (Green). Plug the relay into the top of the relay tester and the relay tester into the BEC. Then you can monitor exactly what's happening on the each of the pins with a VOM. You can also use a ground to turn on the relays by applying an external ground to pin 86 of the low speed relay or pin 85 of the high speed relay. This test will immediately tell you if the circuit is working (sans the PCM signals).

The PCM sends a ground when the reference signals from the CHT/Oil Temp (2005/06) sensors reach a certain value. I had difficulty monitoring that signal and never saw a true ground reference. With the car on (fan off) B+ will be present on the three lines of each relay and zero volts on the PCM feed. What you will see on that line is B+ when the fan activates.

View attachment 79595

I finally figured out that my fan was drawing too much current due to an old fan motor and corrosion in the wiring so I replaced it with a newer GT500 unit.

The primary ground to check is the fan ground (C-148 black line to G100 body ground). See manual pg 10-2 https://iihs.net/fsm/?d=40&f=Grounds.pdf&p=2 and physical location pg 151-1. https://iihs.net/fsm/?d=40&f=Component Location Views.pdf
An ohm reading for that ground should be less than a 10th of an ohm.

If you've eliminated all other issues I'd suspect the PCM/possible tune issue. Troubleshooting the PCM signals will likely take a much more sophisticated tester like you would find at a dealer however you can narrow down likely culprits fairly quickly with a relay tester and ground checks.

Good luck.

C148 should have read C1048 (typo, sorry).

 

[DieHarder]

Of note: Wiring is most of these cars is now ~20 years old and corrosion can be a major/minor issue depending on where you live and the condition of the car.

Q: What's your running alternator voltage? B+ across the battery?

If troubleshooting/continuity and resistance checks don't reveal anything (and the PCM works as it should) I'd consider replacing the main battery and major/fan ground cables. You'll notice that my B+ is only 13.3v when I know it should be at least a volt higher. I have one of the best alternators available and I'm still having issues... In my case to get it that high I had to add an additional (04 gauge) motor ground from the strut tower ground to a bolt on the alternator to ground it properly because my engine ground cable had corrosion in it which was creating a high resistance/ floating ground condition. Unfortunately, they salt the roads where I live and it's a constant battle to fight corrosion issues. If you're experiencing low alternator voltage you might want to think about adding another ground. If that changes your readings it'll be readily apparent. If your alternator voltage is above 14v consider yourself lucky and look elsewhere (provided the fan ground is also good).

 

[50mBz]

Of note: Wiring is most of these cars is now ~20 years old and corrosion can be a major/minor issue depending on where you live and the condition of the car.

Q: What's your running alternator voltage? B+ across the battery?

If troubleshooting/continuity and resistance checks don't reveal anything (and the PCM works as it should) I'd consider replacing the main battery and major/fan ground cables. You'll notice that my B+ is only 13.3v when I know it should be at least a volt higher. I have one of the best alternators available and I'm still having issues... In my case to get it that high I had to add an additional (04 gauge) motor ground from the strut tower ground to a bolt on the alternator to ground it properly because my engine ground cable had corrosion in it which was creating a high resistance/ floating ground condition. Unfortunately, they salt the roads where I live and it's a constant battle to fight corrosion issues. If you're experiencing low alternator voltage you might want to think about adding another ground. If that changes your readings it'll be readily apparent. If your alternator voltage is above 14v consider yourself lucky and look elsewhere (provided the fan ground is also good).

I will run some of these you mentioned see what happens. I did forget to mention I did switch out the alternator but do not know the brand "Orielly's" I think is where it came from..

Come to think of it the alternator used to whine when running. Now it does not. May be a sign. Since you pointed it out "Picture" memory kicked in. If not mistaken all this happened after the alternator install. But after and about 2 years after install not immediate.

"Tuner" guy checked everything except the Turn on and Turn off test. Since I will not drive it he forgot his MaxiCOM scanner. (Mine Quit) reason for all the external tests for the time being. That's coming in a couple days, he is 3 hrs away. So have to wait.

That said here is some more tests I ran. Both checked out and fans came on low and high.

Condition of car absolute like new. garage kept no snow, no ice, no rain, no salt. Even if it is cloudy outside it stays wrapped up in the cover and garage. Only 5 to 8K miles per year dry weather only.

After the com test see if they turn on then I will put back on the rack in the garage and make a field day out of it. I know there is one main ground to the passenger motor mount this could be the issue even though its reading, does not mean it is fully connected without corrosion.

Ill post back later.

 

[50mBz]

Possibly something got corrupted in the tune from back feeding? Your tune should have the fans controlled to turn on at a certain temperature.

The MaxiCom test is coming in a couple days this will least say if its PCM shorted not functioning or not. I hope it functions. I replaced this one in 2013.. Damn things are expensive.

 

[50mBz]

Of note: Wiring is most of these cars is now ~20 years old and corrosion can be a major/minor issue depending on where you live and the condition of the car.

Q: What's your running alternator voltage? B+ across the battery?

If troubleshooting/continuity and resistance checks don't reveal anything (and the PCM works as it should) I'd consider replacing the main battery and major/fan ground cables.

Where is the "major/fan ground cables" you mentioned run from and to? I may go ahead switch it out anyway. Everything is else is pretty much new might as well do wiring as well.

 

[DieHarder]

You can buy an OEM replacement WC95954 (use only Motorcraft). This is the complete assy (Pos & Neg) battery cables. Price varies depending on where you get it. Since your car is kept inside and never sees weather I'd recommend disconnecting/cleaning all major battery (B+) lines and major grounds for continuity and check for any major signs of corrosion vs buying anything at this point. The Fan ground is G100 by the passenger headlight. To check continuity for that one disconnect C1048 (at the fan connector) and the ground end where the bolt is and do an end-to-end continuity (Ohms) check from the connector to the end of the cable. If that measures 0 ohms and appears in good condition bolt it down and check again. The other major ground that gives people fits is the engine ground. It's a thin braided cable (rubber covered) that runs from the body at the back of the engine bay (under the cowl cover) down to somewhere on the transmission (I believe; though never chased that one down completely).

You can find all of the primary grounds in the engine bay by referencing this: https://iihs.net/fsm/?d=40&f=Grounds.pdf&p=1 and this: https://iihs.net/fsm/?d=40&f=Component Location Views.pdf

Wire brush the metal under the bolts (and clean the bolts/washers) where the grounds connect until you have clean metal and reconnect/bolt down. If you notice green corrosion at the cable ends or the ground connections that's a sign the copper has oxidized and also a sign of increased resistance. That does not mean the cable is no longer any good but something you should check on a regular (yearly) basis. In your case from the sounds of it it's unlikely that's your problem. However, if your continuity/resistance checks read higher than a 10th of an ohm end-to-end or to ground you'll want to know why.

It goes without saying disconnect the battery before you start disconnecting/cleaning/reconnecting things and double-check your work. Do one/a few at a time and move to the next. Loss of grounds will show up as all sorts of crazy symptoms if you forget to reconnect them.

 

[DieHarder]

I will run some of these you mentioned see what happens. I did forget to mention I did switch out the alternator but do not know the brand "Orielly's" I think is where it came from..

Come to think of it the alternator used to whine when running. Now it does not. May be a sign. Since you pointed it out "Picture" memory kicked in. If not mistaken all this happened after the alternator install. But after and about 2 years after install not immediate.

"Tuner" guy checked everything except the Turn on and Turn off test. Since I will not drive it he forgot his MaxiCOM scanner. (Mine Quit) reason for all the external tests for the time being. That's coming in a couple days, he is 3 hrs away. So have to wait.

That said here is some more tests I ran. Both checked out and fans came on low and high.

Condition of car absolute like new. garage kept no snow, no ice, no rain, no salt. Even if it is cloudy outside it stays wrapped up in the cover and garage. Only 5 to 8K miles per year dry weather only.

After the com test see if they turn on then I will put back on the rack in the garage and make a field day out of it. I know there is one main ground to the passenger motor mount this could be the issue even though its reading, does not mean it is fully connected without corrosion.

Ill post back later.

View attachment 79607 View attachment 79608

Regarding the information in yellow... yes, both pins read B+ with the car running. In fact with the car on (fan off) B+ will be present on all three lines of the relay and zero volts on the PCM feeds. When the PCM activates a ground (fan on) then all four lines of the relay will read B+ which then sends B+ (if low the fan resistor reduces voltage slightly to run the fan at a lower speed) to the fan low or high circuit as the case may be. When the PCM is not activated the PCM line reads zero volts. The ground line for the fan is the black cable in the connector (C1048) and the other end that connects to the body is G100.

There are several grounds on the engine and in the bay. I would check/clean the major B+ and motor grounds to ensure good connectivity and look for any signs of corrosion.

If you want to test the ground for the alternator check across the battery +/- terminals. If it reads above 14.5v it's about as good as anyone can expect. If it reads less than 13v you may have a bad ground. To see if that's the case if you have a set of jumper cables connect one end to a mounting bolt (ground) on the alternator and the other to the ground on the passenger strut tower. If your voltage increases there is a bad/poor body ground somewhere.

 

[50mBz]

Regarding the information in yellow... yes, both pins read B+ with the car running. In fact with the car on (fan off) B+ will be present on all three lines of the relay and zero volts on the PCM feeds. When the PCM activates a ground (fan on) then all four lines of the relay will read B+ which then sends B+ (if low the fan resistor reduces voltage slightly to run the fan at a lower speed) to the fan low or high circuit as the case may be. When the PCM is not activated the PCM line reads zero volts. The ground line for the fan is the black cable in the connector (C1048) and the other end that connects to the body is G100.

There are several grounds on the engine and in the bay. I would check/clean the major B+ and motor grounds to ensure good connectivity and look for any signs of corrosion.

If you want to test the ground for the alternator check across the battery +/- terminals. If it reads above 14.5v it's about as good as anyone can expect. If it reads less than 13v you may have a bad ground. To see if that's the case if you have a set of jumper cables connect one end to a mounting bolt (ground) on the alternator and the other to the ground on the passenger strut tower. If your voltage increases there is a bad/poor body ground somewhere.

Battery test with car running 14.2 solid. 12.1 non running. Firewall ground (Top Only so far) taken off brushed, and added back with resistance grease (Terminal Grease) had a small discoloration under the terminal.

On to the next one in your list.

 

[50mBz]

Whatever from 3 days ago until today the fan magically worked. I didn't want to wait three days for the scan test. Pulled out some of my 1990 electrical books from college years.

So I ran a 14 gauge wire to the PCM in the BEC and then waited for the car to get up to temp turned A/C on and waited with the multimeter.

Walked around the garage waiting for the meter to beep for indicating power from the PCM connected wire WALA BEEP the fan kicked on reading 13.9 to 14.1 power to the fan

Steps taken. Cleaned and brushed and greased all but two grounds. For now the fan is blowing high and low normally no toggle switches turned on

Extra Steps taken.
Ran 2 separate 10 gauged wires to a 50amp toggle with a 40amp maxi fuse in the relay (Pin 30) for manual turn on for precautions on the road.

More steps.
Ran a 30amp circuit breaker with the power to toggle in case of back feed with a warning light to indicate a problem.

As of now we are in business. Hope this post can help someone in the future.

Thanks for all the replies and tips.

 

[gbstang]

When it comes to the the fan, voltage is the least important, I would have checked the current vice the voltage, if your current is high to the fan, chances are you have a bad ground somewhere..
A simple clamp ammeter would have sufficed..
When you said resistance grease, did you mean Dielectric grease?

 

[50mBz]

Yes Dieeletric Grease. Phone types what it wants at times I guess.

I did use a Clamp ammeter. Note this problem only exists with the A/C on (I see I forgot to mention that in the original post) otherwise the car never raises over 202, except going up hill but never over 206 depending the steepness of the hill.

With A/C sometimes it get to 210 and higher w but with A/C on. I changed all relays in the fuse box even ones not related to the fan just to say I did it.

A/C clutch kicks in all that blows cold car. A/C High Pressure switch was changed prior to the testing. What I did was to see if the high fan circuit was working. If it powered then the PCM was telling to the fan to kick on which was my goal. I am still going to do the fan on and off but didn't want to wait around until then for self conscience.

Yesterday the car was blowing hot air (A/C) on after a while ran 216. Once that went down it blow cold air again. So whatever this case its in the A/C. The grounds underneath will be checked soon just haven't had any extra time since doing all the other stuff.

But I agree definitely a ground somewhere or the A/C is being stubborn one of the two. A/C. R134 is perfect not low at all. Still need to change out Low Pressure switch (To match all other new stuff) other then that all is new.

 

[gbstang]

Good job thus far thinking it out.. I agree with what you said about the phone, I think mine is possessed!

I think it would be a good idea to go ahead and recover the the oil and Freon from the system, I would be curious to see just how much oil is in there.. When I got my tractor (Deutz) the A/C hardly worked, found out they routinely overfill the oil at the factory, so it had to be drained and recharged correctly..

Cheers!