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Mine seems to cut out around 5600-6000 rpms and doesn't come back on until I let off the throttle. This can't be good for this to happen at WOT and its possible that this is why I lost an engine at the track. So far 4 alternator have done this: 2 reman 105 amp, 1 OE 145 amp with some mile, and a 145 amp reman. I'm thinking about installing a heavy-duty diode setup to see if I'm killing them maybe. After that I need to drop $$$ to see if that solves it. Hope it does b/c I just can't have a loss of voltage at WOT.
You didn't loose a motor because of this because you have a battery in the system that acts as a reservoir. So even if the alternator stops working, the battery picks up the slack, and it can handle all the draw you throw at it.
I wouldn't be surprised if all alternators have a built in shut off function when they reach a certain speed. That's why road race cars use larger alternator pulleys to slow them down so they stay alive.
Mine seems to cut out around 5600-6000 rpms and doesn't come back on until I let off the throttle. This can't be good for this to happen at WOT and its possible that this is why I lost an engine at the track. So far 4 alternator have done this: 2 reman 105 amp, 1 OE 145 amp with some mile, and a 145 amp reman. I'm thinking about installing a heavy-duty diode setup to see if I'm killing them maybe. After that I need to drop $$$ to see if that solves it. Hope it does b/c I just can't have a loss of voltage at WOT.
How is your field wire setup? You may have 2 issues. Once you shoot too much voltage through the exciter wire I've read the alt is toast and will never work right. Putting 5v only to this wire with the light in series definitely helped in my case. But I still think I have too many amps.
Losing voltage could cause you a motor. In my case it not only throws off the deadtimes/injector timing, but it also dropped my fuel pump output a ton. Fuel pump will flow a lot less at 12.2v than it does at 13.6 where mine use to charge steadily at. I didn't notice my voltage was dropping initially. I noticed the fuel pressure was dropping and inj DC was way up.
IN order to get the output up most performance alternators use a smaller pulley and spin the alternator faster. I'd look into some of the $150-250 high RPM/output units and be done with it. Hopefully my cheapie 160a unit will cut it.
I happened to have a new self exciting 105a deal I picked up for my mustang project. I installed it before I went to the track last night. I'd see 14v pretty much constantly. WOT it would drop to 13.8 or so on low boost. Turned the boost up to 17 and it started doing the same thing. I believe I'm just overloading it.
[QUOTE=Project GatTagO;19379428]You didn't loose a motor because of this because you have a battery in the system that acts as a reservoir. So even if the alternator stops working, the battery picks up the slack, and it can handle all the draw you throw at it.
I wouldn't be surprised if all alternators have a built in shut off function when they reach a certain speed. That's why road race cars use larger alternator pulleys to slow them down so they stay alive.
When I lost that engine, battery voltage was down to 11.xx and fuel pressure was beginning to drop, but closed-loop did keep the AFR inline. I also know that the ECU will handle some of the necessary corrections for voltage fluctuations. But at WOT with a boosted motor things are happening fast...I dont know how the injectors, coil packs, timing etc are being affected with the much lower voltage. I do run a larger pulley to slow things down. It helped a bit by raising the threshold before it cut out.
Originally Posted by Forcefed86
How is your field wire setup? You may have 2 issues. Once you shoot too much voltage through the exciter wire I've read the alt is toast and will never work right. Putting 5v only to this wire with the light in series definitely helped in my case. But I still think I have too many amps.
Losing voltage could cause you a motor. In my case it not only throws off the deadtimes/injector timing, but it also dropped my fuel pump output a ton. Fuel pump will flow a lot less at 12.2v than it does at 13.6 where mine use to charge steadily at. I didn't notice my voltage was dropping initially. I noticed the fuel pressure was dropping and inj DC was way up.
IN order to get the output up most performance alternators use a smaller pulley and spin the alternator faster. I'd look into some of the $150-250 high RPM/output units and be done with it. Hopefully my cheapie 160a unit will cut it.
I happened to have a new self exciting 105a deal I picked up for my mustang project. I installed it before I went to the track last night. I'd see 14v pretty much constantly. WOT it would drop to 13.8 or so on low boost. Turned the boost up to 17 and it started doing the same thing. I believe I'm just overloading it.
Just a wire to the "L" term which I think is for light, another wire goes to a hot terminal block to measure system voltage. Other than the wot cut-out, I start out with about 14.6 volts and it dips to about 14-14.1 running for a while. Its just that wot crap that is the issue. Next is a Powermaster to see what happens. I would think if I damaged the alt or wired it wrong somehow I wouldnt get the nice voltage output I get the 99% of the time I'm not in wot.
Pretty sure you can't run straight voltage to the L term. It needs to have a resistor or lamp inline to work properly. Using a 5v source did make it slightly better.
Pretty sure you can't run straight voltage to the L term. It needs to have a resistor or lamp inline to work properly. Using a 5v source did make it slightly better.
Yes the Mustang factory wiring has some kind of resistance to it as the voltage is significantly lower than 12v, just cant remember. I then ran a 12v wire to that term with a bulb inline to rule out the factory wiring...same result.
I am also wondering if what Andrew said is correct...perhaps these alternators have some kind of high-rpm cut-off to prevent alt. damage. Who knows...
The other thing that I am wondering about is why this "problem" is not more common. There have probably been 10's of thousands LS swaps done over the years and I don't see many posts (if any) with this problem.
Also consider the millions of stock cars that have gen 3 and gen 4 engines many of those are modified with all kinds of upgrades, and few (if any) complain about the alternator not working at high RPM....
All that leads me to believe that something is wrong with how the people with issues have their alternator wired. I am not being critical, just using some logic to arrive at some sort of solution.
Here is how I have my alternator hooked up. The L terminal is wired to my Dominator ECU through a pigtail that Holley sells that has the proper built in resistor. My alternator is a 130 amp truck alternator. Once the Dominator senses that the engine is running, it energies the L terminal through a resistor. I also added a wire to the S terminal. This wire goes to my main power distribution point, which on my Cougar is the hot side of the starter relay.
This configuration gives me a steady 14.2-14.4 volts, even when everything is turned on (fan, headlights, fuel pump, etc...). I haven't done any data logging to see if the voltage drops at high RMP, but I do have the volt gauge on my Holley digital dash configured that it will change color if it drops below 13 volts, and I have never seen that happen during WOT pulls...
If you have a light bulb tied to a 12V source on one end, and the light bulb is off; that means the light bulb is behaving as an 'infinite resistance' i.e. there is only a voltage drop when the light bulb turns on (working as a load). The reason the bulb stays OFF when the alternator is working, is because the 'diode trio' prevents the A/C current from acting as a ground to the 12V DC power supply to the other end of the bulb. IF one of the diodes goes bad, the light will illuminate because the A/C acts like a ground and current leaks past the diode.
next, you can run an engine without an alternator. Heck I just tuned on with 10volts off the battery last week. The ECU compensates in the injector with around half a millisecond of fuel, which is significant around idle speed if you have a large injector (80lb/hour~) but insignificant at WOT where injector on-times are typically 6-12ms, so losing or gaining 0.5ms of fuel is not going to ruin an engine (you can't "lose a motor" from low voltage if the ecu is tuned correctly). ECU typically shut down the alternator at high RPM; it isn't something I would consider a problem. Actually, its more of a problem if they keep working at high RPM IMO, what with the additional load on the engine (same with the A/C compressor: it shuts off at WOT)
The other thing that I am wondering about is why this "problem" is not more common. There have probably been 10's of thousands LS swaps done over the years and I don't see many posts (if any) with this problem.
Also consider the millions of stock cars that have gen 3 and gen 4 engines many of those are modified with all kinds of upgrades, and few (if any) complain about the alternator not working at high RPM....
All that leads me to believe that something is wrong with how the people with issues have their alternator wired. I am not being critical, just using some logic to arrive at some sort of solution.
Here is how I have my alternator hooked up. The L terminal is wired to my Dominator ECU through a pigtail that Holley sells that has the proper built in resistor. My alternator is a 130 amp truck alternator. Once the Dominator senses that the engine is running, it energies the L terminal through a resistor. I also added a wire to the S terminal. This wire goes to my main power distribution point, which on my Cougar is the hot side of the starter relay.
This configuration gives me a steady 14.2-14.4 volts, even when everything is turned on (fan, headlights, fuel pump, etc...). I haven't done any data logging to see if the voltage drops at high RMP, but I do have the volt gauge on my Holley digital dash configured that it will change color if it drops below 13 volts, and I have never seen that happen during WOT pulls...
Just food for thought.
Andrew
I realize Andrew there's a lot of folks that don't seem to have an issue, but I also wonder how many are really checking/data logging voltage??? Bottom line is that I may be using **** reman alternators. I need to step-up and drop $300+ for a Powermaster or similar to see if it continues.
I need to step-up and drop $300+ for a Powermaster or similar to see if it continues.
With as much money as you must have in the car seems like a wise investment.
If nothing else good thread.
Not sure if this affects the OP but one wire alternators simply do not regulate voltage as well as multiwire units. And you can't convert a one wire to multi wire just by hooking up the added wires.
Obviously the rest of the electrical system needs to be up to par as well. The link above goes on to talk about how important it is to not wire the alternator "straight to the battery". A battery can suck up way more than 100 amps of draw if it is wired wrong.
$140, 160A one wire showed up yesterday. I’ll have it installed and tested this weekend. I’ll let you know how it goes. Also found a slightly larger alum pulley for $28 on ebay.
I actually liked the idea of a 1-wire alternators for street/strip cars that don’t see super long drives. They put out a pretty steady voltage that usually a tad higher than it should be. The one I just installed sits pretty rock solid at 14.2-14.3v helps with fuel pumps, coils, fans etc. Also helps keep the tune in check if the voltage isn’t all over the board. My 160lb injectors are pretty sensitive to voltage swings. There’s a voltage offset table on the MS for this, but I had no luck trying to tune with it.
Last edited by Forcefed86; 09-07-2016 at 08:27 PM.
There’s a voltage offset table on the MS for this, but I had no luck trying to tune with it.
What you do is, disable the alternator (so the system goes to 10v or similar) then adjust the battery comp until the a/f returns to 'normal' (whatever it was when you are at 14v that you desire) usually 14.3:1 a/f for a dead alt. and 14.7-15 a/f ratio for good voltage idle
with such large injectors you probably cant find such a lean a/f at low speed idle (Depends on rpm) so you just decrease battery comp until the engine starts to misfire from injectors that do not open, add back a tiny of comp and done.
For what it's worth, I was driving the Cougar today and I was paying special attention to the voltage on my dash. Granted, this isn't as good as data logging, the the dash response time is very fast, so it's close. I made several WOT pulls paying very close attention to the voltage. I zinged it up to 6750 RPM and bounced it off the rev limiter several times and the voltage never dropped below 13.8 volts. It was really hot today, which I am pretty sure effects alternator performance. Normal driving it was around 14.0 and normally I see 14.2-14.4v...
My alternator is nothing special that I know of. It is the 130 amp truck alternator that Holley sells.
Hey ForceFed86, That look's a lot like the 105 housing........I would seriously be interested in knowing where you got that bad boy, i have to run the 105amp in my car due to clearance issues, as the 130 truck amp is much bigger than the 105. IF i could get a 160amp alt in a 105 housing, mannnnn id pay that damn near $200 for it!
There's a link back on post 37 I think. It is the fbody housing.No idea if it's any good at this point. I took the back off and the rectifier and diode set look to be different than the auto zone unit at least.
98 ls1 in a 91 c1500 and I had the same issue today. Noticed my fuel pressure would drop below 50 @75% TP up to WOT. EFI live quit logging on 2 WOT runs 55-5700 rpm. One of my fans quit, looks like a relay went out. Searching the board as I thought it was my fuel pump, but now having second thoughts after reading. First time in 15 years its acted up like this.
98 ls1 in a 91 c1500 and I had the same issue today. Noticed my fuel pressure would drop below 50 @75% TP up to WOT. EFI live quit logging on 2 WOT runs 55-5700 rpm. One of my fans quit, looks like a relay went out. Searching the board as I thought it was my fuel pump, but now having second thoughts after reading. First time in 15 years its acted up like this.
If this is the first time it acted up like this in 15 years, then it isn't a systematic issue. Your alternator may just be going bad or it is another problem all together.
09-03-2016, 07:38 AM
