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alternator - new thread

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JPSmit

JPSmit

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Ms Triss still isn't starting right - hope to disconnect the alternator and try again today. If it runs without alternator hopefully that isolates the problem.

To recap

I installed a GM-Delco alternator and now she won't start right.

I've checked the connections - all seem good

here's my questions

1. What would happen if I have reversed the leads on the plug? The voltage (thick brown) wire is correct but what about the two others? The dash light does go on and off as it should but could these be backwards? and how would I know? If I reversed them to test would I let any smoke out?

2. Someone suggested a diode in the regulator could be at fault. This seems to send an AC signal through the system. If I put my meter across the battery with the car running and the meter on VAC - what would I expect to see if the diode were the problem.

thanks all
 
When you say it's not starting right--what exactly is it doing or not doing? Not cranking OK? or just not starting when you crank it? Or starting and running rough? Or...?

I suspct the alternator is a red herring; probably you bumped or moved something inadvertently when you were working on it.

The wiring is really pretty simple. See https://teglerizer.com/alternator/wiring.htm, but I suspect you have already. There are only three connections: the output, which is a screw connection, and two others. They are the idiot light and "sense" connection. I'm not sure exactly what that is in this case, but usually this is just a connection to the electrical system to sense the voltage at some point, since the voltage is not constant throughout the system. In many cars, this is sensed at the alternator, but for a lot of reasons that's not always the best place. So, this provides the option of sensing the voltage at a more appropriate locations. Now if these get reversed, my guess is that it won't make much difference--probably just get the voltage a little off from what it should be. MIGHT damage the unit but my guess is probably not.

In any case, I have a hard time seeing how this would affect starting.

If you connect an AC meter to a DC circuit you might get a reading. Depends on how the meter works. Also, there is a lot of noise in the electrical system, so even if the meter is insensitive to DC, you'll still get some kind of reading.

If you can get to the diodes in the alternator, it's easy to check them with an ohmmeter. Measure the resistance of each diode, reverse the leads. One way should be a low resistance, the other, high.
 
It is unfortunately rather difficult to come into the alternator to measure the diodes individually. An oscilliscope is best for measuring for alternator AC output, which should not be there. A reversal of the smaller wires would cause the ignition light to remain on when the ignition switch is turned off. It would not hurt the alternator, as both the smaller terminals receive +voltage when the ignition is turned on. When the alternator starts charging, one of these terminals (the one closest to the large bolt-on terminal) receives charge-voltage and therefore turns off the ignition light. The small terminal furthest from the bolt-on terminal is quite often connected directly to the bolt-on terminal with a short wire.

Disconnecting the alternator and rechecking the starting of the car sounds reasonable right now. There could be something else wrong with the car.
 
Sarastro said:
When you say it's not starting right--what exactly is it doing or not doing? Not cranking OK? or just not starting when you crank it? Or starting and running rough? Or...?
Click to expand...

It was starting instantly (and I mean instantly) - now it turns over and over and over and then when it starts - it chugs and dies when you give it gas, idle is erratic, felt like tree cylinders - then all four. After it is running takes about 5 minutes to smooth out
 
Well, there is no harm in simply removing the wires from the alternator, insulating them to prevent shorting and starting the engine. See if it starts OK. Check the voltage at the coil. It should be full voltage during starting and then reduced voltage (around 6 volts) when running. If it still starts hard, check your points for starters and your timing.
 
well doesn't seem to be the alternator. disconnected - no difference. pulled the plugs. so, tell me about very black carbon covered plugs - what does this indicate? all four are black - two had light (proper) coloured patches on the top.
 
JPSmit said:
well doesn't seem to be the alternator. disconnected - no difference. pulled the plugs. so, tell me about very black carbon covered plugs - what does this indicate? all four are black - two had light (proper) coloured patches on the top.
Click to expand...

Extremely rich? Maybe a needle valve is stuck open in one of your carbs allowing raw fuel to flood the engine. Which cylinders were black?
 
Black plugs mean it is rich for some reason.
 
JP
Blacken plugs are generally indicative of a rich mixture. They can also be a sign of ignition system trouble. Now for the big question. The last place you were working on was, the carb, or the electrical system ?

Either way i would venture taking a good look at the ignition first, then the carbs.


mark
 
Agree with steve. Check first.
 
You're right - only one carb - IT'S A 1500!!!
grin.gif


haven't done anything carb wise - only alternator and relays therefore electrical - I replaced the rotor. checked connections. is there a way to test the coil? or is there a generic coil I can buy? (and if so, how much?)
 
JP,
please check the voltage at the coil hot side to ground , with the key on and also check the voltage on the coil hot side when the engine is cranking. What is you ignition set up? points? or electronic?

mark
 
electronic ignition.

which is the hot side? negative?

Oh, and how do you set the carb for mixture (Zenith Stromberg - I know)

thanks
 
The hot side is the wire coming from the ignition switch(sometimes you will find a resistor in line) the other side is the wire that goes to the distributor. The hot side will have voltage when you turn the key on.
 
JPSmit said:
You're right - only one carb - IT'S A 1500!!!
grin.gif
Click to expand...

<span style="font-weight: bold">D'oh!</span>

Seriously...big problems don't have subtle causes. From what you describe, something is seriously messed up. Check all the possible parts in the appropriate way, and you'll find it.

Might have nothing to do with the work you just did. Coincidences happen.
 
It's very likely the carb membrane (diafram) is cracked. That would cause running rich and poor starting. Pull the dome off (4 screws) and pull the piston up. Check carefully around where the rubber mounts to the piston. A crack there will cause exactly the problems you describe.
 
Golden_Swan said:
It's very likely the carb membrane (diafram) is cracked. That would cause running rich and poor starting. Pull the dome off (4 screws) and pull the piston up. Check carefully around where the rubber mounts to the piston. A crack there will cause exactly the problems you describe.
Click to expand...

ordinarily I would agree but it is new. - see next post
 
well I spent some time on the interweb today and took a look at the coil.

went here

https://tinyurl.com/66yx3b

and then tested with my multimeter at ohm setting left side picture (primary) mine read 1.6 (at 20 ohm setting) and centre to side (secondary) read 4.39 (at 2000 ohm setting) - what does this mean?

also saw this

https://www.clarks-garage.com/shop-manual/ign-04.htm

the ignition coil test seems like it could help but there is no ground wire on my coil - help!

thanks
 
Aye no ground wire on a coil. Only input, hot lead, output, hot lead, to stud on the side of the Dizzy and the high tension wire out the center of the coil to the center of the dizzy cap.
 
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