Got it. Now you need to electrically check the harness. Just looking at it is almost useless.

 

Yeah I hear that, just gotta do some research on correct way to follow wires back as I have not done that with multimeter and not sure how to test connections correctly

 

Just start at one side of the wires and ohm test it to the next connection point. Can be a bit tedious but it will narrow it down to exactly where the issue is. That was how I tracked down my drain on the battery, I just wish I would have known to check the alternator 2 days sooner. 8 would rather waste a few hours for a couple days finding the exact cause then throwing parts at something.

It is most likely a short over the PCM, just have to be patient and find the source. I let my first tow rig sit for 8 months until I found the bad connector in the harness, that was just messing with it when I had a weekend off and nothing better to do.

 

I am having same issue with my truck. "COPs???"
have replaced turbine speed sensors front & back. No change. Does on idle when in gear only. Don't smother and choke down, motor just quits. Mechanic said back sensor showed 6000 revolution at times so it shut motor off. But replaced with motorcraft sensor and no change. What do I do now? What is COP? Codes PO720 and PO722

 

The rear one is the Output Speed Sensor.

Someone needs some in depth diagnostics. It could be a failed diode in the alternator. This will put an A/C ripple in the wiring harness. It takes an oscilloscope to see this, and most shops don't have one.

The PCM reads this as speed signals from the speed sensors. It can read some really high RPMs that way.

COP is Coil On Plug. These are the ignition coils on top of the spark plugs on the gas engine trucks.

 

Hey there Shelbyhooten,

As you have probably read on here I ran into the same crap on my Excursion, changed ALL the sensors shift solenoid etc..... after dumping a ton of money at guesswork I FINALLY nailed the problem. If you can believe it, the alternator was the culprit for all the dumb crap the truck was doing, towhaul light flashing, engine shutting down when put into gear, etc.... Do yourself a HUGE FAVOR , change the alternator even if it appears that it’s working fine. I LITERALLY went through the same crap saying it can’t be the alternator because it’s still putting out voltage. I was wrong, the SMALLEST voltage changes coming from that alternator WILL cause this issue for you and it will go undetected through regular voltage tests. At least it did for me. I had what appeared to be a normally functional alternator charging the battery but in actuality the voltage regulator is a finicky bitch and it threw the PCM into a tailspin if the SMALLEST deviation in voltage is picked up. I think your gonna be a happy camper if you swap that out for a NEW not re built alternator. I found that remanufactured alternators SUCK because they don’t get rebuilt under same voltage tolerances as NEW OEM parts. Give it a try, you’ll save yourself A LOT of stress and hair pulling out moments! I hope it helps you in your endeavors

QUOTE=Shelbyhooten;19754699]I am having same issue with my truck. "COPs???"
have replaced turbine speed sensors front & back. No change. Does on idle when in gear only. Don't smother and choke down, motor just quits. Mechanic said back sensor showed 6000 revolution at times so it shut motor off. But replaced with motorcraft sensor and no change. What do I do now? What is COP? Codes PO720 and PO722[/QUOTE]

 

Where do I find a NEW (not rebuilt) alternator? My 2000 PSD 2wd Ex still has the same alternator it had when I bought it 18 years ago. It's never thrown a code until the engine shut off while in D sitting at a light last week. Showed code P0720. Truck runs great until warmed up, then starts dying at lights unless I shift into N while coming to a stop. OD light flashes. Doesn't want to pull away from a stop, etc., as described above. I R&R'd the OSS, but the engine still dies.

PS - My local Autozone has "100% NEW" alternators for my truck in stock for $235

PS2 - My batteries where at 11.7 volts this morning before starting the engine, and went up to 13.45 volts after the engine had run for a couple of minutes. Is there a better (more direct) way to check alternator output? Batteries were replaced 10/18.

 

PS3 - Did some more googling and found that to check the alternator directly touch the multimeter's positive probe to the positive post on the back of the alternator (where the heavy red or red/black striped lead attaches), then the negative probe on the alternator case. It read 14.0 - 14.4, mostly at about 14.1 at idle with no load. Going to put the charger on it in the morning for a few hours to see if a fully charge set of batteries makes a difference. The article said high-idle output should be 14.2 - 14.6. I didn't have anyone to hold the revs up, but I figure 14.1 sounds about right.

 

Put your multimeter leads across the two positives - one on the B+ (battery positive) post on the back of the alternator, and the other on the positive post for the driver side battery - let us know what reading you get in DC volts. That number is referred to as a "voltage drop". It indicates how much resistance is in your cables and connections between the alternator (where the voltage is generated) and the battery that is furthest down the line/cable (driver side).

 

Thanks! I'll check it first thing in the morning.

 

The drama continues. Yesterday I put my new 'smart charger' on the batteries for about 6 hours after reading them at 11.7 volts in the morning. After disconnected they both read right at 13 volts. This morning they were both at 12.4 volts, and would not start the engine. I could hear and feel the starter engage, but it could not turn over the engine. My plan is to put the charger back on them for an hour or so to get the engine started and perform the "voltage drop" test suggested above by Nicmike. Then I'll remove the batteries and take them to get load tested (and replaced if needed).

In any case it appears my batteries are worn out, which makes me wonder if their condition might explain the stalling issues and P0720 codes I've been getting.

 

Okay, after charging up the batteries and selecting the 80 Amp start assist, the engine fired right off. I disconnected the charger and let the engine run for about 5 minutes then performed the voltage drop test suggested above by Nicmike. After bouncing around for a few seconds below 1 volt, the meter settled on 0.00 vdc. I moved the negative probe between the driver side battery's positive terminal to the alternator case, where each time it read about 14.2 volts, then near zero on the battery terminal.

Bad batteries?

 

Sounds like batteries need to be checked/load tested as you mentioned. Very rare to see 0VDC on the voltage drop...there is usually a .1 to .2 VDC drop...more if bad connections or corrosion in the cables.

 

I finally took the Ex to Autozone to have the batteries checked. The passenger side was dead, but the driver side battery checked good. Took me a week or so to arrange to drive to Costco an hour away, but there I was able to swap out the bad battery under warranty. Since the alternator seems to be working well I was hoping this would resolve the issue, but the engine started dying again after just 5 minutes or so of driving. Which reminds me, why does the truck need to warm up a bit before the issue manifests itself?

I'm limping it along by shifting into Neutral while waiting at lights and then gently revving the engine a bit before shifting into D to pull away. Otherwise the engine will die as soon as I come to a stop while in D. Any other suggestions? I swapped out the output speed sensor...is there an input speed sensor in the same loop?

Thanks again. I appreciate the help.