'85 Vette SI17 to CS-144 Alternator Upgrade
08-20-2007, 04:11 AM
#1
Melting Slicks
Thread Starter
'85 Vette SI17 to CS-144 Alternator Upgrade, Low Voltage Problem
It's been a long time since I posted anything here, it's good to be back.
I sold my '85 a couple of years ago and as often occurs the buyer, a friend of mine, was having trouble with a low voltage problem and asked me to try and fix it. This thread ulitmately performs a CS-144 swap but the previous problem that leads to the upgrade is interesting. It seems the voltmeter was always showing low voltage at idle. The gauge would default to the red indicator and a low voltage reading of less than 11 volts. He replaced the alternator and battery once and the problem continued. At upper rpms the voltage would increase but never above 12.3 or so volts. At idle it would quickly drop below 11 volts and the red light would go on. I spent at least a week trying to find the source of the problem but couldn't figure it out. I tried cleaning the battery leads, swapping with good leads, cleaned the grounds, the starter connections, tested the fusible links, bypassed all the leads with wire, but couldn't figure it out. I decided to try the CS-144 upgrade. I didn't want to buy another SI17 alternator and battery since it might not fix the problem and throwing money at it isn't always a good idea. After removing the old alternator I could hear a loose part inside so I figured the alternator was a goner. A friend had a couple of extra CS-144 alternators from his two late '90s Impala SSs. This is a popular swap with many other vehicles and is nearly a bolt in for an '85.. This upgrade is also in the C4 tech tips. Since this alternator was out of an Impala SS I had to reclock the alternator so the connector and battery leads were rotated further counter-clockwise otherwise the connector was inaccessable. Re-clocking is simple to do. Remove the pully and fan, remove the four small screws and rotate the end that is toward the front of the car. I used a little persuasion, a rubber mallet, to aid in the rotation. After that was done I needed to make up an SI17 to CS-144 adapter from instructions on the internet. An adapter can be purchased but I didn't want to wait to order one so I built one myself. An adapter with and inline resistor or one without is available from GM but a test needs to be performed to determine which one is needed. The test is to measure the resistance from the old exciter lead to the battery terminal with the key in the on position and the battery disconnected. If the resistance is more than 35 ohms then a resistor isn't needed. While performing this test I noticed that the ohm reading started out high and slowly dropped. I found this interesting because it should have been a solid reading. I found that by moving the key cylinder the resistance kept changing and starting out high again. This particular lead is what provides voltage to the alternator field and is a key circuit in the charging system. The ignition switch was the last place I would have ever thought would have contributed to a charging problem. I removed the old switch and bench tested it and lo and behold the swinging high resistance was still there. There should have been zero ohms between the terminals in the switch but there wasn't. I began to realize this may be where all of the charging problems could be. There was also a nagging flicker in the cluster at night, and a little surging too. This particular terminal is what feeds the charging system, fuel injection system, the dash, the ac fan and other circuits. I replaced the ignition switch with a new one from NAPA. About $15. What a real pain. I won't go into it but anyone who has performed this swap can testify that it is such a PITA and so tight to get to the fasteners and to move the other stuff out of the way. Anyway, I replaced the switch and performed the resistance test again and I had a solid 10 ohms of resistance which is exactly what it should be on an '85. I was also thinking that replacing the switch would fix some of the other problems the car was having. After determining I had only 10 ohms of resistance I needed to splice an additional resistor inline with the exciter lead. As I previously mentioned a GM 8078 adapter is available but I built one from a 330 ohm 1/4 watt resistor from Radio Shack and the connectors from NAPA. A little solder and heat shrink was all that was need to assemble it. Once built, I installed the CS-144 and installed the adapter. The rear of the CS-144 can't use the rear brackets the old Si17 used, just the top and bottom bolts to the mounting ears are used. Unless someone knows something I don't, I couldn't figure out any way the existing hardware would attach to the back of the CS-144. After startup the voltage at the alternator was a solid 14+ volts. Road testing proved the new alternator was operating in the 13.7 to 14.0 range even the the ac on, the power amp on, the fan on, and the headlights on. The voltage fluctated down to 13.4 when the cooling fan kicked in but recovered quickly. I know this is a long story but had I not checked the resistance in the charging circuit while performing the upgrade, I would have never found the problem in the ignition switch. The dash lights no longer flicker and the engine is running smoother, and the charging systems seems to be working much better. I read that these CS-144 alternators put out 110 amps at idle and peak out at about 140 amps. This is much better that the 97 amps that the old alternator was rated at.
Save the wave,
Art
I sold my '85 a couple of years ago and as often occurs the buyer, a friend of mine, was having trouble with a low voltage problem and asked me to try and fix it. This thread ulitmately performs a CS-144 swap but the previous problem that leads to the upgrade is interesting. It seems the voltmeter was always showing low voltage at idle. The gauge would default to the red indicator and a low voltage reading of less than 11 volts. He replaced the alternator and battery once and the problem continued. At upper rpms the voltage would increase but never above 12.3 or so volts. At idle it would quickly drop below 11 volts and the red light would go on. I spent at least a week trying to find the source of the problem but couldn't figure it out. I tried cleaning the battery leads, swapping with good leads, cleaned the grounds, the starter connections, tested the fusible links, bypassed all the leads with wire, but couldn't figure it out. I decided to try the CS-144 upgrade. I didn't want to buy another SI17 alternator and battery since it might not fix the problem and throwing money at it isn't always a good idea. After removing the old alternator I could hear a loose part inside so I figured the alternator was a goner. A friend had a couple of extra CS-144 alternators from his two late '90s Impala SSs. This is a popular swap with many other vehicles and is nearly a bolt in for an '85.. This upgrade is also in the C4 tech tips. Since this alternator was out of an Impala SS I had to reclock the alternator so the connector and battery leads were rotated further counter-clockwise otherwise the connector was inaccessable. Re-clocking is simple to do. Remove the pully and fan, remove the four small screws and rotate the end that is toward the front of the car. I used a little persuasion, a rubber mallet, to aid in the rotation. After that was done I needed to make up an SI17 to CS-144 adapter from instructions on the internet. An adapter can be purchased but I didn't want to wait to order one so I built one myself. An adapter with and inline resistor or one without is available from GM but a test needs to be performed to determine which one is needed. The test is to measure the resistance from the old exciter lead to the battery terminal with the key in the on position and the battery disconnected. If the resistance is more than 35 ohms then a resistor isn't needed. While performing this test I noticed that the ohm reading started out high and slowly dropped. I found this interesting because it should have been a solid reading. I found that by moving the key cylinder the resistance kept changing and starting out high again. This particular lead is what provides voltage to the alternator field and is a key circuit in the charging system. The ignition switch was the last place I would have ever thought would have contributed to a charging problem. I removed the old switch and bench tested it and lo and behold the swinging high resistance was still there. There should have been zero ohms between the terminals in the switch but there wasn't. I began to realize this may be where all of the charging problems could be. There was also a nagging flicker in the cluster at night, and a little surging too. This particular terminal is what feeds the charging system, fuel injection system, the dash, the ac fan and other circuits. I replaced the ignition switch with a new one from NAPA. About $15. What a real pain. I won't go into it but anyone who has performed this swap can testify that it is such a PITA and so tight to get to the fasteners and to move the other stuff out of the way. Anyway, I replaced the switch and performed the resistance test again and I had a solid 10 ohms of resistance which is exactly what it should be on an '85. I was also thinking that replacing the switch would fix some of the other problems the car was having. After determining I had only 10 ohms of resistance I needed to splice an additional resistor inline with the exciter lead. As I previously mentioned a GM 8078 adapter is available but I built one from a 330 ohm 1/4 watt resistor from Radio Shack and the connectors from NAPA. A little solder and heat shrink was all that was need to assemble it. Once built, I installed the CS-144 and installed the adapter. The rear of the CS-144 can't use the rear brackets the old Si17 used, just the top and bottom bolts to the mounting ears are used. Unless someone knows something I don't, I couldn't figure out any way the existing hardware would attach to the back of the CS-144. After startup the voltage at the alternator was a solid 14+ volts. Road testing proved the new alternator was operating in the 13.7 to 14.0 range even the the ac on, the power amp on, the fan on, and the headlights on. The voltage fluctated down to 13.4 when the cooling fan kicked in but recovered quickly. I know this is a long story but had I not checked the resistance in the charging circuit while performing the upgrade, I would have never found the problem in the ignition switch. The dash lights no longer flicker and the engine is running smoother, and the charging systems seems to be working much better. I read that these CS-144 alternators put out 110 amps at idle and peak out at about 140 amps. This is much better that the 97 amps that the old alternator was rated at.
Save the wave,
Art
Last edited by MrRenoman; 08-20-2007 at 04:18 AM. Reason: Corrections
08-20-2007, 11:48 AM
#3
Race Director
Member Since: Sep 2000
Location: The Top of Utah
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VERY interesting. Did you happen to check the exciter voltage as a follow up before replacing the ignition switch? In other words is there any confirmation or back up test? That is a great write up and very informative. Who'd a thunk?
RACE ON!!!
PS. Great diagnostic work. No throwing money at it, here.
RACE ON!!!
PS. Great diagnostic work. No throwing money at it, here.
08-20-2007, 06:59 PM
#4
Drifting
I just completed this mod a month ago. The shop I went to had a reman and a brand new one for me to choose from. They looked the same to me, but measuring distances on each alternator in regard to mounting, the brand new one would've required some minor grinding to get it to fit, and the reman was smaller in the same spot. My idle used to noticeably drop when I would come to a stop in rush hour traffic, and now it is way more stable. It's got the juice it needs now.
08-23-2007, 10:52 PM
#5
Melting Slicks
Thread Starter
Sorry I haven't replied. My computer is having problems.
I didn't check the voltage before replacing the switch. When I tried to follow the factory manual to test the circuit I wasn't seeing what the manual was telling me. Maybe the problem with the switch was the reason. Anyway I committed to installing the new alternator so I didn't check the voltage. Per the manual I was supposed to see about a 2 volt difference which I never saw. I think that the 10 ohm resistance is what would have lowered the voltage. Without having an original working alternator I don't think I can measure the voltage with out.
Cya,
Art
I didn't check the voltage before replacing the switch. When I tried to follow the factory manual to test the circuit I wasn't seeing what the manual was telling me. Maybe the problem with the switch was the reason. Anyway I committed to installing the new alternator so I didn't check the voltage. Per the manual I was supposed to see about a 2 volt difference which I never saw. I think that the 10 ohm resistance is what would have lowered the voltage. Without having an original working alternator I don't think I can measure the voltage with out.
Cya,
Art
VERY interesting. Did you happen to check the exciter voltage as a follow up before replacing the ignition switch? In other words is there any confirmation or back up test? That is a great write up and very informative. Who'd a thunk?
RACE ON!!!
PS. Great diagnostic work. No throwing money at it, here.
RACE ON!!!
PS. Great diagnostic work. No throwing money at it, here.
