2.9 misfires while alternator is working.

[dirtracer11591]

Alright guys, I need some fellow mechanics to bounce ideas around with because I'm running out of them. Im working on a 87 2.9 ranger with ammeter for a buddy of mine. The ignition skips at idle and cuts out so bad under load it doesn't want to rev past 2000 rpm. It COMPLETELY clears up when the voltage regulator is unplugged or when the alternator belt is so loose it basically isn't putting any load on the engine. This is how I received the truck but from my understanding the truck wouldn't start one day, PIP ended up being the culprit. The ignition cutting out started once it started running again. My buddy and the shop he had look at it before me has basically replaced the entire ignition system, some pieces multiple times and even tested with another ECU. With my spark tester inline with the coil wire I can clearly see the ignition cutting out. Before I discovered the alternator behavior I tested the fuel system and verified nothing was amiss there.

The only thing I have done aside from diagnostic is replaced the alternator and internal regulator which didnt help. From there I assumed it was a wiring issue and I'm a little at a loss here as the new alternator didnt have exactly the same plugs so I had to crimp some wires to adapt but that left some unhooked wires and the regulator plug seems pinned differently than the wiring diagrams I have found so far.

His truck has the yellow wire on the A terminal, the green wire on the S terminal, no wire pinned to the I terminal. There doesn't seem to be a wire too hook the new alternators S terminal too off the stator connector. If im not misunderstanding the green key on wire should be on the regulators I terminal, the stator S wire should be looped too the regulators S terminal, rigged that up to test but didn't seem too help. Anyone have any bright ideas?

I appreciate any help, this truck has been down for months and now that I've got my hands on it I see why. I did see a couple threads where people had a similar issue but go figure, the resolution was never posted if it was found.

 

[franklin2]

With idiot lights in the dash, you are correct, the red/lightgreen goes to the I terminal. If you have a ammeter, the red/lightgreen goes to the stator terminal with no connection to the I terminal.

Just make sure the ECU ground is good. There is a special small wire coming off the large negative battery terminal that runs down to a small single connector. From there it disappears into the harness. This is the ECU ground. There is a lot of possible corrosion over near the battery for that connector, and a lot of reasons for this wire to have a bad connection with it being at the battery. If you lose this connection completely, the engine will not run at all.

 

[RonD]

Set Volt Meter to AC Volts
With alternator hooked up and engine idling
Ground meter to alternator's metal case, other probe on the B+ alternator terminal, should see no more than 0.5vAC, 0.3vAC is normal, its called AC ripple test

And alternator generates "alternating current"(AC), diodes convert that to DC
If AC voltage is leaking out it will cause all sorts of issues in the electrical system including spark system

 

[dirtracer11591]

With idiot lights in the dash, you are correct, the red/lightgreen goes to the I terminal. If you have a ammeter, the red/lightgreen goes to the stator terminal with no connection to the I terminal.

Just make sure the ECU ground is good. There is a special small wire coming off the large negative battery terminal that runs down to a small single connector. From there it disappears into the harness. This is the ECU ground. There is a lot of possible corrosion over near the battery for that connector, and a lot of reasons for this wire to have a bad connection with it being at the battery. If you lose this connection completely, the engine will not run at all.

Ok so the wiring is correct for the in dash Ammeter. I was told the shop that had it before me "fixed some of the old wiring" so I was weary blindly trusting the relatively clean connector when it didn't match the wiring diagrams that were supposedly for a truck with an ammeter. So the "S" terminal coming out of the stator just needs to be wrapped and left unplugged or does it need to be spliced into the red/light green wire with the ammeter?

I will check that ground in particular when I mess with it tomorrow but I have already verified the ground are all in decent shape considering there 36 years old and the engine and chassis is showing battery voltage.

 

[dirtracer11591]

Set Volt Meter to AC Volts
With alternator hooked up and engine idling
Ground meter to alternator's metal case, other probe on the B+ alternator terminal, should see no more than 0.5vAC, 0.3vAC is normal, its called AC ripple test

And alternator generates "alternating current"(AC), diodes convert that to DC
If AC voltage is leaking out it will cause all sorts of issues in the electrical system including spark system

I had read that the most common cause would likely be the alternator leaking AC voltage but I didnt know what the proper location to test for it would be so I will check that. I did check the diodes on the Motorcraft i removed with my fluke just because it was laying out and easy to get at and they seemed to be working as intended. Considering it has now had two alternators in it that are both showing the same symptoms it is unlikely the old Motorcraft I pulled out and the reman i just put it in would fail the exact same way but ill spend the 3 minutes to verify regardless.

 

[RonD]

And also read the DC Voltage, I don't see that mentioned
Measure at battery terminals
Key off, Battery volts, 12.3vDC to 12.9vDC is expected
Engine running, at idle, 13.5vDC to 14.6vDC
At 2,000rpm or so it should be no more than 14.6vDC

If engine running voltage goes up and down with RPMs then voltage regulator is bad

 

[dirtracer11591]

And also read the DC Voltage, I don't see that mentioned
Measure at battery terminals
Key off, Battery volts, 12.3vDC to 12.9vDC is expected
Engine running, at idle, 13.5vDC to 14.6vDC
At 2,000rpm or so it should be no more than 14.6vDC

If engine running voltage goes up and down with RPMs then voltage regulator is bad

I did verify the alternator was charging properly however after realizing the alternator could be left powered on but the belt could be left to slip and it didn't seem to misfire I should probably examine what it does when it is trying to rev up a little closer.

 

[dirtracer11591]

Another odd symptom i noticed is when I disconnected the battery while the truck is running the truck ran even worse, nearly stalling out at idle, than it does running off pure battery power. At this point im convinced there has got to be something amiss in the truck wiring causing two different functioning alternators to not be able to sustain the engines electrical system.

Im thinking it might be a good idea to start pulling fuses while its running to see if I can find a system that clears the ignition system up once it Is shut off from the rest of the electrical system. Perhaps something is seizing or has a dead short that is putting fffaarrr too much load on the alternator but the battery can sustain it with its reserve capacity for the short 5-10 minute test drive I've done so far. Just brainstorming out loud lol

 

[Uncle Gump]

Not a dead short... you would blow fuses or certainly smell some magic smoke.

So if you render the alternator inoperative... the engine will run fine until the battery gets low?

Disconnecting the battery... while running is never a diagnostic on an electronically controlled engine management system.

 

[RonD]

Test alternator wiring, assuming 2G or 3G alternator

Key OFF
Test battery voltage, remember it
Use alternator's metal case for the ground in testing
3 wires to test
Black/orange wire to B+, larger wire or wires, should read battery voltage, exactly

Yellow/white wire, should read battery voltage, exactly
If either is lower than battery voltage then you have a corroded connection

Green/red wire, 0volts, or very close, depends on your meter
Turn key on
This wire should now read Battery volts, but 0.2v less is OK since vehicle's electrics are now powered up
This is the ON/OFF switch for the alternator, so it doesn't drain the battery with key off
This wire was used for Battery Light circuit in later models


Ammeter is connected to the Black/orange B+ wire at 2 places, the wire between these 2 places is called a Shunt, so the dash gauge only "sees" a small % of the AMPs travelling thru this larger B+ wire
These 2 connections can corrode
A "+" or "C" on dash gauge means amps/volts are travelling from alternator to battery positive, charging battery
A "-" or "D" on dash gauge means amps/volts are travelling from battery positive to alternator, discharging battery

 

[dirtracer11591]

Not a dead short... you would blow fuses or certainly smell some magic smoke.

So if you render the alternator inoperative... the engine will run fine until the battery gets low?

Disconnecting the battery... while running is never a diagnostic on an electronically controlled engine management system.

Yes, best way i can describe it is the engine misfires at idle and as soon as throttle is applied it starts cutting out so frequently its almost like it has a 2000 rpm rev limiter but you can let it stumble its way up. The second you disconnect the regulator it clears right up. Doesn't misfire at all and revs all the way out with no problem. I drove it for about 5-10 minutes like this with no issue but I didn't go farther than that because obviously its just a matter of time before the battery begins to die.

At idle with no additional electrical loads like lights and what not the alternator should easily be able to sustain the engine's FI and ignition system. This was basically me just poking and prodding to see what happens but told me whatever the issue is, the charging system has an issue when working and the battery is helping it limp along better than it does by itself.

 

[dirtracer11591]

Test alternator wiring, assuming 2G or 3G alternator

Key OFF
Test battery voltage, remember it
Use alternator's metal case for the ground in testing
3 wires to test
Black/orange wire to B+, larger wire or wires, should read battery voltage, exactly

Yellow/white wire, should read battery voltage, exactly
If either is lower than battery voltage then you have a corroded connection

Green/red wire, 0volts, or very close, depends on your meter
Turn key on
This wire should now read Battery volts, but 0.2v less is OK since vehicle's electrics are now powered up
This is the ON/OFF switch for the alternator, so it doesn't drain the battery with key off
This wire was used for Battery Light circuit in later models


Ammeter is connected to the Black/orange B+ wire at 2 places, the wire between these 2 places is called a Shunt, so the dash gauge only "sees" a small % of the AMPs travelling thru this larger B+ wire
These 2 connections can corrode
A "+" or "C" on dash gauge means amps/volts are travelling from alternator to battery positive, charging battery
A "-" or "D" on dash gauge means amps/volts are travelling from battery positive to alternator, discharging battery

All of these wires check out. The only thing I seen off is his Ammeter doesn't seem to be moving. Sits just off center toward the C and doesn't seem to move with engine on or off. But I've tested the voltage at the battery and confirmed the alternator is charging. Would a malfunction in the Ammeter effect the function of the alternator?

 

[dirtracer11591]

And also read the DC Voltage, I don't see that mentioned
Measure at battery terminals
Key off, Battery volts, 12.3vDC to 12.9vDC is expected
Engine running, at idle, 13.5vDC to 14.6vDC
At 2,000rpm or so it should be no more than 14.6vDC

If engine running voltage goes up and down with RPMs then voltage regulator is bad

Charging voltage looks good. 13.5 at idle and gets up to about 13.8 while it's spitting and sputter and doesn't seem to be fluctuating even tho the engine is bucking all over the place.

No AC voltage at the alternator either. My meter flashes like it may have just barely picked something up every couple seconds but never displays an actual voltage.

 

[RonD]

Long shot
Try grounding alternator to battery negative, if you have jumper cables use it from alternator adjuster bolt to battery negative terminal
See if that allows engine to run smoother


No, ammeter working or not shouldn't effect anything, but would be good to have it working

 

[franklin2]

I have never seen one of those factory ammeters ever give any good movement or indication of charge. I would not worry about that gauge. Not sure why Ford kept wasting money on them.