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Halogen lamps draw way more than stock ones. I'd say that's your issue.
Electrical Gurus - Idle gets worse with Headlights on (1 Viewer)
- Thread starter RWBeringer4x4
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- Thread starter
- #22
Right, but even with 80W halogen, if rudimentary physics serves me that would be an amp draw of ~6.7A per bulb...so based on that, plus what @bikersmurf said previously I'm looking at a total amp draw of 33-35A probably, which should be getting produced easily by a 94A 12SI alternator spinning in the realm of 1800rpm - per the original chart I put up...then again if it's really spinning closer to 1500 I might be on the cusp...
I'd say you're overthinking all of this . Check the battery voltage at idle . Compare voltage drops around the system - at the fuse box , alternator main battery post and headlight voltage at idle . It can be the way the alternator is tied into the system - without a centralized point for the alternator to read amperage loads the main system voltage can drop too far and give the coil pack system a negative effect on Chevy engines - see this all the time . I just re-wired half the engine bay of a '62 Belair Wagon and gave it a central connection point for the alternator , battery and fuse box system . It never deviates from 14.5v , idle or otherwise . It's basically the same system setup that is outlined on Mad's tutorial pages - just with my input to tie it into an old Chevy system that originally used the horn relay as the central point of detection .
Sarge
Sarge
- Thread starter
- #24
Thanks Sarge,
I'm traveling on business this week but that's the next step. If i recall, I tied the voltage sensing line back to the battery...
Coolerman
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The GM HEI ignition system is power hungry and does not like to have low voltage. My first question is where is the HEI getting it's power from? If you used the stock ignition wiring you may have a large voltage drop to the HEI when the lights are on. I personally would install a 30-40 amp +12V relay triggered by the stock ignition line and feed the HEI with 12ga wire straight from the battery through the relay contacts and an ATC fuse. Same concept as the IPF relay harness... reduce the voltage drop for brighter lights.
Dead on Mark , that was my whole point about checking voltage drops across the system in various points - one of the bigger drawbacks of the HEI system is voltage levels must be steady...
Sarge
Sarge
- Thread starter
- #27
@Weber Sarge or @Coolerman - where do I check voltage on an HEI?
Just touched back down in Philly - hopefully I'll get a chance to look at this this weekend.
Just touched back down in Philly - hopefully I'll get a chance to look at this this weekend.
I'd check it at the 12v power line that connects to it.
BTW, I'm running a points type distributor with a Crane Cams points replacement electronic module.
BTW, I'm running a points type distributor with a Crane Cams points replacement electronic module.
bj40green
Tssss, tssss
FYI: The voltage regulator regulates the voltage output of the alternator and thus regulates the (available) Amps.
More rpm = more Volts = more Amps. When the voltage goes up, the VR controls the voltage output to max set point.
Should be between 14 and 14.8V
If the rpm is too low and the demand too high, the voltage will drop. The alternator can not do its job at low (idle) rpm.
It's just enough to keep the ignition going.
As said before; it's pretty normal behavior. Add another set of fog lights and the engine will die at idle.
There is simply not enough energy available at idle.
If you want the bright light at idle..... pull the throttle a bit.
Rudi
More rpm = more Volts = more Amps. When the voltage goes up, the VR controls the voltage output to max set point.
Should be between 14 and 14.8V
If the rpm is too low and the demand too high, the voltage will drop. The alternator can not do its job at low (idle) rpm.
It's just enough to keep the ignition going.
As said before; it's pretty normal behavior. Add another set of fog lights and the engine will die at idle.
There is simply not enough energy available at idle.
If you want the bright light at idle..... pull the throttle a bit.
Rudi
- Thread starter
- #30
But this brings me back to my original question about pulleys. If I reduce the size of the alternator pulley, wouldn't this keep the alternator RPM's higher, thereby spinning FASTER at idle, thereby more amps?
I'm home and was going to run a couple of voltage tests, but now it's pouring rain! So stay tuned for that
- Thread starter
- #31
Ok so I did a quick series of voltage tests at the battery:
At idle, no load (headlights off):
Looks ok to me...
Then I turn on the headlights:
It drops a full volt. The engine drops a corresponding 75-100 rpm, from a steady 750 to a rougher 650-ish (bounces between 625 and 675)
Under a LARGE electrical load (wipers, headlights, hazards, fan) the voltage drops further:
But it doesn't drop below 12V. The idle doesn't seem to get any "worse" or lower. Obviously upping the idle to about 900-100rpm brings the voltage back up as well.
So is the charging system functioning normally or is that too significant a voltage drop?
At idle, no load (headlights off):
Looks ok to me...
Then I turn on the headlights:
It drops a full volt. The engine drops a corresponding 75-100 rpm, from a steady 750 to a rougher 650-ish (bounces between 625 and 675)
Under a LARGE electrical load (wipers, headlights, hazards, fan) the voltage drops further:
But it doesn't drop below 12V. The idle doesn't seem to get any "worse" or lower. Obviously upping the idle to about 900-100rpm brings the voltage back up as well.
So is the charging system functioning normally or is that too significant a voltage drop?
bj40green
Tssss, tssss
This normal behavior. The battery voltage is still more than 12V so your still running on the alternator.
It seems that the HEI is acting up a bit as @Coolerman said. Follow his advice.
Rudi
It seems that the HEI is acting up a bit as @Coolerman said. Follow his advice.
Rudi
- Thread starter
- #34
Will do, but the alternator belt is also the fan/water pump belt so it's going to be a pretty quick test!
A bit of a different take on this issue - just my opinion so don't read into me trying to bash anyone's expertise .
The hotrod builds I helped work on never drop below 14.2 when I'm done with them . We are usually only using the go-to stupid Delco 12si alternators and whatever the owner comes up with for pulleys . This last '62 Chevy Belair Wagon was a pain in the arse due to an aftermarket set of pulleys (read-'90's era billet junk) that weren't even cut on center and ate the water pump on a brand new race shop-built engine . Fast forward to a whole new set of pulleys , relatively decent brackets (March - but still needed washers , really?) and finally got everything to run straight and true . Heater on high , headlights on and such it never drops off the 750rpm idle and voltage sits steady at no less than 13.8v with everything electrical drawing hard . Now , part of that is a relatively new , expensive 9.5:1 engine with 3500 miles on it , brand new Delco alternator and I ditched the previous owner's mods that were done to tie in a 1-wire alternator from a previous restore . The new alternator is a 3-wire unit with remote sensing set up at a second point in the system just off the firewall where the main harness feeds the car's interior fuse box . Down near the starter is the main tie-in for the starter's power , battery feed and alternator's charging wire . Car retains the stock generator lamp in the dash and it works correctly . There is a fuse link in the alternator's feed wire to prevent cooking the system or the alt itself - the whole thing works perfectly .
I think a lot of the issue with GM alts is how they are tied into the electrical system and how the sensing wire is picked up - if it cannot properly detect a voltage drop you will have a problem . The other thing is the condition of the engine , if it's got decent compression and holds correct vacuum at idle it helps a lot - very weak engines will show even the slightest load changes . Speeding up your pulley size may help , but also might make it worse . I'd look into the stock pulley size of what that Delco came from/fits and go accordingly .
Sarge
The hotrod builds I helped work on never drop below 14.2 when I'm done with them . We are usually only using the go-to stupid Delco 12si alternators and whatever the owner comes up with for pulleys . This last '62 Chevy Belair Wagon was a pain in the arse due to an aftermarket set of pulleys (read-'90's era billet junk) that weren't even cut on center and ate the water pump on a brand new race shop-built engine . Fast forward to a whole new set of pulleys , relatively decent brackets (March - but still needed washers , really?) and finally got everything to run straight and true . Heater on high , headlights on and such it never drops off the 750rpm idle and voltage sits steady at no less than 13.8v with everything electrical drawing hard . Now , part of that is a relatively new , expensive 9.5:1 engine with 3500 miles on it , brand new Delco alternator and I ditched the previous owner's mods that were done to tie in a 1-wire alternator from a previous restore . The new alternator is a 3-wire unit with remote sensing set up at a second point in the system just off the firewall where the main harness feeds the car's interior fuse box . Down near the starter is the main tie-in for the starter's power , battery feed and alternator's charging wire . Car retains the stock generator lamp in the dash and it works correctly . There is a fuse link in the alternator's feed wire to prevent cooking the system or the alt itself - the whole thing works perfectly .
I think a lot of the issue with GM alts is how they are tied into the electrical system and how the sensing wire is picked up - if it cannot properly detect a voltage drop you will have a problem . The other thing is the condition of the engine , if it's got decent compression and holds correct vacuum at idle it helps a lot - very weak engines will show even the slightest load changes . Speeding up your pulley size may help , but also might make it worse . I'd look into the stock pulley size of what that Delco came from/fits and go accordingly .
Sarge
- Thread starter
- #36
@Weber Sarge - you bring up a lot of valid points, that echo what @Pin_Head is saying - that really it's my engine responding to the drop in horsepower required to increase the electrical current to keep up with load. A pulley alignment issue could be part of it for sure - I'm still dealing with the "hand I was dealt" on the pulley front - a Long water pump big block double pulley mounted on a short pump on a small block, and a very jerry-rigged alternator bracket to compensate and "sort of" align things. I know there's an issue because it tries to squeal/throw the belt if I wind it up over about 3000 RPM. No apparent squealing below that, but that doesn't mean there's no slippage.
The engine itself is pretty strong, compression wise, and doesn't smoke at all, but far from perfect. It reads in the high 140's across all cylinders, but only pulls about 14 lbs of vacuum, and the vacuum is not perfect at idle (random, intermittent surging, which drops vacuum to about 13.5). My understanding is vacuum should be higher (17-18 range), but I have a sneaking suspicion based on previous owner's receipts that this 283 has a mild cam in it, which could be part of the low vacuum and surging. It also wants about 14 degrees of initial advance in timing which also seems to point to cam (or just tired).
Voltage sensing wire is tied directly back to the battery, which seems like it should work, since measuring at the battery is showing the voltage drop I posted above. If the voltage is dropping at the battery, and the sensing wire is tied to the battery, the alternator should be sensing the drop, right?
In short, you may all be, at least partially, right, and I guess I'll just run it as is until I can get the engine out, and the incorrect pulleys off and alignment issues resolved. If I can ever get my butt in gear and finish my shop renovation, this engine is coming out for an overhaul or replacement soon. (It was supposed to come out in May).
The engine itself is pretty strong, compression wise, and doesn't smoke at all, but far from perfect. It reads in the high 140's across all cylinders, but only pulls about 14 lbs of vacuum, and the vacuum is not perfect at idle (random, intermittent surging, which drops vacuum to about 13.5). My understanding is vacuum should be higher (17-18 range), but I have a sneaking suspicion based on previous owner's receipts that this 283 has a mild cam in it, which could be part of the low vacuum and surging. It also wants about 14 degrees of initial advance in timing which also seems to point to cam (or just tired).
Voltage sensing wire is tied directly back to the battery, which seems like it should work, since measuring at the battery is showing the voltage drop I posted above. If the voltage is dropping at the battery, and the sensing wire is tied to the battery, the alternator should be sensing the drop, right?
In short, you may all be, at least partially, right, and I guess I'll just run it as is until I can get the engine out, and the incorrect pulleys off and alignment issues resolved. If I can ever get my butt in gear and finish my shop renovation, this engine is coming out for an overhaul or replacement soon. (It was supposed to come out in May).
Try moving the voltage sensing wire into the main fusebox lead close to the firewall - that should change how it reads the system .
Sarge
Sarge
Another angle on pulley size... Since output doesn't seem to be big issue.
A smaller pulley will = more mechanical advantage =
Less load on engine
Low idle vacuum could be related to being a bit lean. I'd think it would be about 16.5 at idle (but it has been years since I last read up on it... So I could be wrong).
Totally different direction... What intake do you have? I switched to a somewhat disliked Edelbrock Sp-2p-1 (or something like that). They kill output above 4K rpm, but idle vac is way up, idle torque is way up, motor is quieter, economy is supposed to be better (haven't done math yet, but seems better). It was free to me, and I've got no regrets. It is a 4x4 not a hot rod, and the rev limiter was already set at 4K so there seems to be no downside. BTW, the points conversion has the limiter built in so it made sence to use it... With the new manifold, it also seems to reach the 4K way quicker.
A smaller pulley will = more mechanical advantage =
Less load on engine
Low idle vacuum could be related to being a bit lean. I'd think it would be about 16.5 at idle (but it has been years since I last read up on it... So I could be wrong).
Totally different direction... What intake do you have? I switched to a somewhat disliked Edelbrock Sp-2p-1 (or something like that). They kill output above 4K rpm, but idle vac is way up, idle torque is way up, motor is quieter, economy is supposed to be better (haven't done math yet, but seems better). It was free to me, and I've got no regrets. It is a 4x4 not a hot rod, and the rev limiter was already set at 4K so there seems to be no downside. BTW, the points conversion has the limiter built in so it made sence to use it... With the new manifold, it also seems to reach the 4K way quicker.
Last edited:
bj40green
Tssss, tssss
FYI:
Rudi
Rudi
