Testing the coil

[Alpine 1789]

I have had a number of "fuel system" problems of late, primarily difficulty starting the car when warm, less power than before and a relatively uneven idle. Someone here recently said something to the effect that "most fuel problems are electrical" (I looked for the exact quote so I could credit the author, but didn't find it) and based on comments about some others' problems, decided to test my coil.

I don't know much about doing this, but started with the Pertronix site, since I have a Pertronix-modified distributor and am using their Flame-thrower coil. http://www.pertronix.com/support/tips/default.aspx#a2 The site recommends checking amperage by dividing the voltage between the coil and the ground by the resistance of the coil. With the ignition on, the coil grounded and the car not running, I show 10.4 volts. Resistance across the positive and negative terminals of the coil is 3.2, which seems about right for a 3 ohm coil. Dividing the two gives me 3.1 Amps. The Pert site only says it should be below 4 for a 4 cylinder car.

Before I go any further, I wanted to see what this initial test is telling me. Is my coil ok, should I test further, and what about only showing 10.4 volts? Is that normal?

Thanks.

 

[Bill Blue]

Jim, what is your voltage at the battery?

Bill

 

[Alpine 1789]

Good question. 12.4 at the battery; 12.2 at the solenoid, which is now just a remote starter switch since I switched to a gear reduction starter. If I test just the white wire that goes to the coil I get 11.7. That reduces to 10.4 when I connect that wire to the coil, along with the red wire from the Pertronix unit in the distributor.

 

[Bill Blue]

Jim, you know very well I'm not an expert in electrical matters, but it sounds to me like you have a series of iffy connections that result in very iffy ignition.

I don't have enough understanding of the circuit to comment on the 11.7 to 10.4 drop, but there should be no drop to 11.7.

Bill

 

[Alpine 1789]

Thanks Bill. It will be the weekend before I can do any work on the car, but I have an idea on where to start and will report back.

 

[LarryN]

Looking at the wiring diagram, the white wire to the coil comes from the ignition switch off Terminal 2. Terminal 2 is common with another white wire which goes to the Ignition Warning Light. The Ignition Warning Light also has a yellow wire which goes back to the voltage regulator and then on to the windings of the generator and eventually to ground (Sorry, don't know enough about generators to tell you which windings). It looks as though your coil test includes that side of the circuit in parallel with the coil side.

With the engine running and the generator making adequate voltage, the yellow and white wires are roughly the same voltage and the Ignition lamp doesn't light. In your tests, checking the white wire when removed from the coil should show some voltage drop due to the current flowing through the warning lamp and the windings. Connecting the white wire to the coil adds in the additional path to ground through the coil.

 

[LarryN]

You might want to also take a look at the green wires coming off the fuse block on the opposite side from the white wires - horns, stop lights, flasher can plus the gas gauge and temp gauge. These circuits are also in parallel with the coil circuit and have the possibility of putting some significant loads on that leg of the circuit. They're not supposed to be energized without being switched on, but stuff happens.

I agree with Bill - the voltage drop doesn't sound right.

 

[LarryN]

Sorry this is so disjointed, but it occurred to me that there might be a simple test: remove the fuse and check the voltage on the white wire again (on and off the coil). This will take the gas gauge, temp gauge, horns, stop lights, and flasher can out of the circuit. If the voltage drop looks more reasonable (like zero with the wire off and not huge with coil connected), it could indicate that the electrical problem is in one of the green wire legs.

You could then disconnect the green wires from the fuse block and check resistance to ground. The one to the gauges will probably show a high impedance, but not necessarily infinite. The others should all show infiinte resistance since they pass through switches to get to ground.

Although you would be without all of the things on the green wires, you could drive the car and see if the performance problem is still there.

 

[Alpine 1789]

It has been a challenging summer and today is the first chance I had to work on the SV in months. I am multi-tasking today and in addition to thinking through the electric fuel pump I have finally gotten back to working through this issue. I have now confirmed that I have 12.7 volts through to terminal 1 on the ignition switch. However, with the switch in the accessory position, there only 10.4 volts coming out on terminal 2 where the white wires connect. I tried replacing the switch with an NOS one I had been saving for the S3 and got the same result.

I am wondering if I could have somehow brought the voltage regulator in to play too early when I switched to an Datsun alternator several years ago. I am not sure how to test for this, as I can't see the regulator in the wiring diagram.

 

[Tom H]

Jim, Not enough info.

You say 12.7 at Term 1 of Switch . Then you say with sw in ACC position you get 10.7 at Term 2 . Please provide voltages at both points at same switch setting. And is te car running or not?

Note that Terminal 1 should have NO voltage when the sw is in the accessory position. When in the RUN position the voltage at Term 1 should NOW be the same volatge as at Term 2

Term 1, the brown wires , should always be at Battery voltage plus or minus a fraction of a Volt depending on if charging or if some load is on, like lights, motor, wipers,


Term 2 , The white wires are the power to the coil to run the notor. Should not be powered when in accessory position. That's just for the radio, etc.

Tom

 

[Alpine 1789]

Jim, Not enough info.

You say 12.7 at Term 1 of Switch . Then you say with sw in ACC position you get 10.7 at Term 2 . Please provide voltages at both points at same switch setting. And is te car running or not?

Note that Terminal 1 should have NO voltage when the sw is in the accessory position. When in the RUN position the voltage at Term 1 should NOW be the same volatge as at Term 2

Term 1, the brown wires , should always be at Battery voltage plus or minus a fraction of a Volt depending on if charging or if some load is on, like lights, motor, wipers,


Term 2 , The white wires are the power to the coil to run the notor. Should not be powered when in accessory position. That's just for the radio, etc.

Tom

Sorry. I mistyped. I should have said in the Run position. To clarify, here are the voltages:

Off: T1=12.7; T2=0; T3=0; T4=0; Coil=0

Accessory: T1=12.5; T2=0; T3=0; T4=12.5; Coil=0

Run: T1=10.5; T2=10.7, T3=0; T4=10.7; Coil=10.7

Running: T1=14.3; T2=14.2, T3=0; T4=14.2; Coil=13.9

I just realized I probably should have tested T3 while cranking, but didn't. I can do that this evening if it is important.

Thanks.

 

[Tom H]

Jim, OK, most of that makes sense. just 2 puzzlers there:

1) In Run position, the voltage on Term 1, the brown wires, drops down to 10.7 volts or so. At this switch position, only the coil is powered, (assuming you don't have lights, wipers or anything else running). This is quite low and would indicate the battery is in poor shape, or the connections are bad somewhere - at the battery posts, at the solenoid, or at the ground end of the grnd cable of the battery. Or in the connections of the brown wires at the solenoid or at the fuseholder. With just coil current - about 3 A- flowing, you should still have pretty close to 12 V at the switch term 1. With the switch in the ON position measure the voltage at different positions along the string from Battery to switch and see how far back you go before you find 12 V. Probably a good idea is to start at the battery. With the switch in the ON position measure the battery AT the posts. Put the black test lead on the top of the lead NEG post and the red lead on the top of the Pos post. If less than 11.5 V,(or so) the battery seems very weak to me. Assuming you have 12.7V, next measure at the cable connectors, if more than 0.1 V lower than at the posts, you have a bad cable connection. If OK, next put the black test lead on a good chassis ground and measure the voltage at the Pos cable clamp. If it now is more than 0.1 V lower than step earlier, you have a bad ground cable connection where it attaches to chassis. My guess is that you will measure about 12.0 volts or more at all the places noted to this point. Next measure the voltage at terminal 1 of the fuseholder. That should be where the brown wires connect. If it reads near the 10.7 you have a bad connection either at the fuseholder or at the solenoid where the brown wire connects to the solenoid. If it read 12 V or so at term 1 of the fsueholder, next measure at term 1 of the switch. If it's 12 V at the fuseholder and 10.7 at the switch you have a bad connection at one of the ends of that wire - from fuseholder to switch.

2) some small issue about 10.5 at term 1 and 10.7 at term 2 of the switch. Can't be! Must have read the meter wrong or made a bad connnection with your test probes. Terminal 1 is the supply or INPUT to the switch. No way can the output (terminal 2) be higher than the input (term 1).

Tom

 

[Tom H]

Jim, one more thing - going back to your earlier post. You say you may have "brought the regulator into play too soon..."

Do you mean you still have the original 4TR regulator wired into the circuit? And you are using an Alt from a Datusn 14231 alt? That would be a no no. The Datsun Alt already has a built in regulator.

Tom

 

[Ken Ellis]

Might be good to remove the radio memory/clock circuit from the equation by removing its fuse. Unless you've already done so, of course.

And just an anecdote: I had some low voltage trouble, traced to a bad connection on the fuse block. (Measured fine unloaded, but voltage sagged under load.) There's a screw by one of the fuseholders, that was not 'tight', and slightly corroded. Not sure of its intended function, but things improved when I tightened it. It's not a mounting screw --- but rather right by one of the fuse clips.

 

[Alpine 1789]

Thanks guys. It will probably be the weekend before I can trace the voltage along the path as Tom recommends and check connections per Ken's recommendation, but I will do so and report back. As for "the regulator" I should have been more specific and said the "voltage regulator". I removed all of the extraneous components when I changed to the internally regulated alternator. Isn't 10.4 volts about what comes out of the voltage regulator?

And, Ken: good memory on the clock/radio memory circuit. Both were connected during the tests I reported yesterday.

 

[Tom H]

Jim, Do you mean the "voltage stabilizer"? That is the little gizmo behind the dash that stabilizes or regulates the voltage for the Temp and Fuel Gauge. Yes, the output of that is about 10.8 V (RMS) if you are using an original switching On/OFF type, or 10.0 Volts DC if you are using a modern solid state one.

But no need to be concerned about that. I doubt very much that is anywhere close to being involved in your coil current. The fact that the switch and coil volatge get up to about 14 V when the car is running seems to rule that out. But if things are still mysterious after you get the readings I and Ken suggest, THEN we can look to see if you managed to wire it up very strangely!

But I'm bettin' you have a similar bad connection as described by Ken.

I'd like to know how the Alt is wired. mainly the heavy B+ wire from the Alt. Where does it go? Do you have an ammeter? How is it wired?

If you have an ammeter there should be just one (brown) wire on the small terminal on the solenoid, where the battery is connected. BIG battery cable and a small terminal on same post. Just one wire (other than Battery Cable) should be there. That one wire should go to the ammeter. Then from the other term of the ammeter, there shoud be another heavy brown wire that goes to the Term 1 of the fuse box. At term 1 of the fuse box you should have 3 more connections besides the one heavy cable from the ammeter. a) a heavy brown wire from the B+ of the Alt, b) a brown wire to the Light switch, and c) the brown wire to the Ignition switch.

My bet on a bad connection is at one of these points:
a) at the brown wire at the solenoid,
b) at the ammeter input term
c)at the other ammeter terminal
d) at the connection where the wire from the ammeter connects to the fuseblock.

This would explain why you lose a lot of voltage when coil is powered by the battery only (car not running), but you do not lose much volatge when the coil is powered (mostly)by the Alt - when the car is running. Two slightly different paths!

Tom

 

[Alpine 1789]

Thanks Tom. I will trace everything as soon as I can and report back. As for the ammeter, I can tell you how that is wired, which is basically the way it was done when I bought the car in 1977, although I did have to make one small adjustment when I put the gear reduction starter on, since the solenoid just became a remote starter switch at that point.

• The battery cable connects to both the starter and the ammeter. As I recall, the three cables used to be connected together at the solenoid; I just used a small bolt and nut to replace the solenoid connection and wrapped the whole thing well with electrical tape. I also cleaned all of the terminals at this time.
• The other ammeter connection goes to the heavy brown wire from the alternator, along with two brown wires and one brown/black wire. I can't tell where these go, as they disappear into the harness just past the connection point. As I recall, I also cleaned up this connection point when I put the new starter.

I recall a discussion a few years ago on how to connect the ammeter and know this wasn't the recommended way, but I figured it had worked well since before I bought the car and left well enough alone. At least, I think it was well enough.

Oh and, yes, I did mean voltage stabilizer.

Jim

 

[Tom H]

OK, we'll wait for the measurements. I remember the thread about the "remote starter" and the gear reduction starter. I'll see if I can understand what's connected where!

Re the ammeter. After starting , the ammeter should show initially a very high positive "Charging current" as the alternator replenishes the charge on the battery, and it will decrease as the battery gets charged. And with the car not running , if you turn on the lights, the ammeter should show negative about 10 Amps as the lights draw current FROM the battery. If the ammeter is wired in the most common incorrect manner I have seen, it will only show the neg "draining" current and never show the positive charging current. Des your ammeter ever show the high positive charging current after starting. Or does it always read in the same direction ?

Tom

 

[Alpine 1789]

Des your ammeter ever show the high positive charging current after starting. Or does it always read in the same direction ?

Tom

The ammeter works exactly as it should. That is the reason I decided to leave well enough alone. If fact, because it is a standard Lucas 35 amp gauge and I have a 45 or 50 amp alternator (I forgot which; it might even be 60), the needle will peg if the battery is low when I start the car. I recently purchased a Lucas 50 amp gauge, but won't put that in until everything else is checked out.

While tracing the current is still a few days away, I do have a question about the process. I know it is not good to leave the car in the ignition position for long when you have a Pertronix unit. How long do I have before I should shut it off and let everything cool down?

 

[Tom H]

Jim, good on the ammeter wiring,

Good idea to be concerned about leaving the Pertronix turned on too long.. One solution would be to disconnect the black wire from the coil to the dizzy. Then simply connect that coil terminal to ground. You still won't want to keep the switch in the ON position too long, as the coil will get pretty warm, but at least this keeps the Pertronix safe.

And remember, when you are making these measurements be careful to note where you are touching the test probe to. The problem is most lkely at a Connection. So when you get to the problem connection you will likely see a different voltage depending on which side of the "connection" you are contacting. for example, at term 1 of the fuseholder, test the voltage by touching the stamped metal piece that includes the male blades. Next touch the female terminal part of each wire connected to that terminal. You are looking for a place where there is a different voltage depending on which side of the connection you are measuring. Normally there would be no significant voltage difference, but with a bad connection there is voltage drop across the connection. You might also find the problem connection by temperature feel. The coil is drawing about 3 amps and you are "losing" about 2 volts somewhere (12.7-10.7) in connections. That is 6 watts (3 A x 2 V = 6 W) that will be going into heating the terminals and the area around that connection. That's about the same wattage as an old type (pre LED) Christmas tree bulb). Should be warm to the touch. Note also that as you probe around, you may very well move / wiggle that bad connection and thus fix it. Then you will see 12.7 V everywhere and you willl not know where the problem had been!

Maybe a simpler solution will be simply connect your meter and measure the voltage at the point where you see the 10.7 . Then while watching it or checking it frequently, wiggle one connection after another. at each connection, see if it's warm, wiggle it, see if the 10.7 goes up to 12.7.

Tom