Starter circuit

[psalt]

I've seen many 911s with hesitant starters. Usually this is blamed on the long wires to the back, ign switch, sticky solenoids, the design of the ground circuit inside the BOSCH starter, aliens, Algore, etc. I have seen the problem even with a full 12 volts at the yellow wire. I have replaced starters with factory BOSCH rebuilds that act up only after a few months. I have torn down solenoids right to the "Made in Mexico" stamp and polished and lubed the internals. I have fitted remote switches in the engine compartment to jump the big cable to the solenoid, but even this sometimes fails. My usual suggestion to this symptom before part swapping is using a battery charger immediately before attempting to start the car and this seems to work almost 100% of the time, the extra juice makes the difference. Even so, I had to push a few to start. My experience with this is always at a cold start. If you have CIS and a lazy starter, be aware that the CSV is spraying away while nothing is happening.

Today I was replacing a burned out A/C blower relay and looked at the wiring diagram. The wiring is designed to turn off the A/C and Heater blowers (High amp draw) while the starter is engaged to keep the voltage up. The wiring is different for the circuits. The A/C blower relay gets its ground from the starter 50 terminal when the ignition is ON, but in the Start position, terminal 50 is powered by the yellow wire from the ign switch, so the ground on the A/C relay coil is broken and the blower stops. Oddly the heater blower puts the switch before the relay in its circuit on the way to the starter terminal, perhaps because the A/C blower is three speeds and need the resistor pack.

Does anyone have any insight on these circuits and can a failure of either relay cause a starter problem ? Is it true that anytime these blowers are running there is current running though the starter 50 terminal to ground ?

[T77911S]

if you are still seeing starting problems after replacing all that you said above, check and clean grounds, especially the body to engine. in fact, clean ALL major electrical connections pos and neg. not to argue, but most i have seen have been hot start issues.
if you suspect battery problems, have it load tested, you should not have to charge a good battery just to start a car.
another problem with no starts are car alarms, mainly aftermarket ones.

[RoninLB]

from key switch to solenoid is an electric fault waiting to happen.


some guys install an extra relay for the solenoid trigger. ie: the key activates the relay which closes the relay to pass 12v directly to solenoid.

I've run a 8ga wire directly from switch to solenoid.

AC on 911s work lousy. I deleated the whole worthless mess.

[psalt]

from key switch to solenoid is an electric fault waiting to happen.

This seems to be the issue, but I think it involves the amount of current needed to throw the solenoid switch, not voltage which can measure 12v at the yellow terminal, while this problem occurs. Engine grounds are not the issue and I have seen it with multiple, new, fully charged, batteries. There was a post about the ground circuit in the Bosch starter that goes untouched during a rebuild causing the same problem after replacement.

Take a look at the wiring diagram, the solenoid yellow terminal appears to be the ground for the low draw relay coil for the heater and A/C blowers until the key is turned to the Start position. The question is, does this choice of wiring cause of "the dead click starter" issue because the relays can be wired differently quite easily.

[T77911S]

yes, the available current is important. you can have 12v at the SOL, but if the ground from the tranny to the body is bad, there may not be enough current available to turn the motor, even though the SOL is pulled in, which is where the bad ground (or bad battery terminal connections) come into play.
i am not sure if i am understanding what you are trying to say. you said the yellow terminal appears to be ground? are you referring to the yellow wire to the SOL? or something on a diagram. also, what year/s are you talking about, i only have the book for a 77.
the short time i did electrical work on cars, bad grounds/connections were a big problem for no starts. i have only seen the start signal go straight to the starter, except through car alarms, so that max current is available. if this is different on porsche, i would like to know.
perhaps ronin will chime back in.

a hi power battery can overcome a partial bad ground/connection, but sooner or later that bad connection will catch up and nothing will start it.

[RoninLB]

The greater the amp draw the greater the wiring is stressed and the lower the voltage measured. A cold solenoid should draw around 4-5 amps. A hot or old solenoid may draw around 10 amps.

Every wire connector and switch has a voltage drop. From switch, to under dash bulkhead connector, to a Y connector for AC in trunk, to the 14 pin, to the solenoid. A 30-40 year old wire is no prize either. It's a perfect storm imo.

Many ways to attack this issue. Different strokes for different folks.




an engine compartment solenoid jump momentary switch or attaching a push button wire jumper to the solenoid should be able to tell you if the non-active solenoid is due to a wire connection fault between ignition switch and solenoid or a bad solenoid.

after crawling around under the car with a screwdriver to jump the solenoid directly from the large battery lug i installed a 20 amp marine silver plated contact momentary switch... about $20

[911pcars]

The starter solenoid is a relay that depends on 12 volts to energize. The current-carrying capacity of the solenoid windings isn't that much of an issue. The key is, less voltage = less current. The copper disk that connects the battery circuit with the starter motor armature circuit carries the bulk of the starting current. The solenoid cannot operate efficiently if excessive resistance in the starting circuit results in <12 volts.

Sherwood

[RWebb]

Originally Posted by RoninLB

Every wire connector and switch has a voltage drop. From switch, to under dash bulkhead connector, to a Y connector for AC in trunk, to the 14 pin, to the solenoid.

true if they have significant corrosion buildup - but only then

first thing to do is to ensure the ground strap from trans. nose to the body has no appreciable contact resistance

- clean; and soak the ends and "landing spot" on the body in strong vinegar until shiny

get acetic acid from a old-timey photo shop and dilute to ___ (was it 10%?) if you cannot find strong vinegar in your town

search on "Warren" for additional details

[RoninLB]

Originally Posted by RWebb

true if they have significant corrosion buildup - but only then

True even when brand new in perfect condition.

[T77911S]

i may not have helped paul. i read his first paragraph that i think was there to set up his question/issue about some other wiring that may or may not be part of the starting circuit. i just did not want him to undervalue the importance of clean good grounds. they are so overlooked as a resolution to starting problems and other mystery electrical problems. bad grounds can even cause poor engine performance.

i went back and read his question again, i caught the al gore thing this time.
it does seem weird.
in my book, the heater relay, pin 85 is tied to the yellow wire, start. pin 86 goes to T14, the big connector on the relay panel, and to the fuse on the same panel.
when the key is turned to start, 12v is applied to pin 85. if pin 86 already has 12v on it from the relay panel, then BOTH sides have 12v but no place to go, thus no current flow and the relay opens.


no wasted current thru the yellow wire. all current thru big yeller is aplied to the SOL.

the wife just got home, time to get busy maybe, ill get back to this later.
see ya

[RWebb]

Originally Posted by RoninLB

True even when brand new in perfect condition.

well, NO.

a properly operating switch will not introduce enough resistance to measure and that is what causes the voltage drop


- someone asked a question b/c they need help - so let's help them -- the very 1st thing to do is to clean the tranny ground strap

[RoninLB]

Originally Posted by RWebb

well, NO.

a properly operating switch will not introduce enough resistance to measure and that is what causes the voltage drop

There is even voltage drop along the length of a wire although amp flow will remain the same.

excessive resistance is another story.



Please keep your routine wrong info away from my posts.

[911pcars]

b]"when the key is turned to start, 12v is applied to pin 85. if pin 86 already has 12v on it from the relay panel, then BOTH sides have 12v but no place to go, thus no current flow and the relay opens."[/b]

Are you saying source voltage is constantly applied to the yellow wire? If so, the starter solenoid will be constantly energized (starter motor ON). Obviously, that's not the normal case.

"There is even voltage drop along the length of a wire although amp flow will remain the same.

excessive resistance is another story. "

Can you expand on this? I'm not sure I follow.

If the load is otherwise working normally but there is excessive resistance in the circuit path then voltage will drop. And if voltage (pressure) is reduced, so does current flow. If the load is a headlamp bulb, then the bulb will be dimmer. If a motor, then it will rotate slower.

i = e/r (current = voltage/resistance)

Example 1:
i = 12/2 ohms
i = 6 amps

Example 2:
i = 12/3 ohms
i = 4 amps

In order for current flow to be the same with increased circuit resistance (3 ohms), the applied voltage must be 18 volts
i = 18/3 ohms
i= 6 amps

Sherwood

[RoninLB]

Originally Posted by 911pcars

b]

"excessive resistance is another story. "

Can you expand on this? I'm not sure I follow.

If the load is otherwise working normally but there is excessive resistance.......

better wording than mine

[RWebb]

Originally Posted by RoninLB

There is even voltage drop along the length of a wire although amp flow will remain the same.

excessive resistance is another story.



Please keep your routine wrong info away from my posts.

you are just confusing this poor guy who wants help

there is no _significant_ voltage drop in the stock wire

re "routine wrong info" - please try to comport yourself in a more adult fashion; save this stuff for OT

[psalt]

"it does seem weird.
in my book, the heater relay, pin 85 is tied to the yellow wire, start. pin 86 goes to T14, the big connector on the relay panel, and to the fuse on the same panel.
when the key is turned to start, 12v is applied to pin 85. if pin 86 already has 12v on it from the relay panel, then BOTH sides have 12v but no place to go, thus no current flow and the relay opens. "


Getting closer to my question. When the heater blower and or A/C blower are on, the starter solenoid terminal appears to be the ground source for the relay circuit. I have seen many 911 heater blower motors with shot bushings and brushes from constant running, all it takes is leaving the levers up a bit or a misadjusted switch. I know what they are trying to do, turn of the high draw blowers to save power when cranking, but the question is does this choice of circuit lead to an increase in current needed to trigger the solenoid over time. The relays could be rewired to stay out of the starter circuit.

There can be a full 12 voltage at the yellow wire at the solenoid when this problem occurs. The trick is to measure the voltage drop with the wire connected when the intermittent problem occurs, which is not easy. Mulitple attempts introduce a residual charge in the windings.

I am just looking at all the suspects in the case of the random "dead click solenoid" which seems to reappear, even with new BOSCH rebuilds, after all connections and ground have been cleaned and tested.

[911pcars]

Can you post an image of that relay in question?

In general, all relays have two source voltage terminals; one for the control circuit; one for the power circuit. The control circuit contains the low current windings that, when connected to source voltage, cause the contact points to either close (make) or open (break). The control circuit is always grounded via a separate terminal. The power circuit contains the contact points; one to source voltage, the other to the circuit load.

It could be a break-type relay. That is, during engine cranking, the relay momentarily disconnects the loads connected to it (A/C blower, heater blower, etc), to ensure all battery voltage is used for starting.

Hope this helps,
Sherwood

[burgermeister]

I think Kirchoff's law is the thing relating resistance and voltage throughout a circuit. I believe it states the sum of all voltage drops in a circuit is the same as the applied voltage.
Current is the same everywhere along the circuit. Power used for a given circuit component is proportional to the voltage drop across the component. A wire is a component, just like everything else in the circuit. Total power for the circuit is current * voltage.
So, if the wires, switches, and relays add up to 15% of the total resistance in the circuit, they will use up 15% of the power. If crappy connections add another 15%, not only will the wires et al now use 30% of the available power, the available power will go down by 15% as total resistance increased, and available voltage did not increase.

All wire has resistance. Here's a chart from one of my favorite books, "Pocket Ref" by Thomas Glover.

[Jim Williams]

Paul.

I'm skipping over all the responses so far and going straight to your question. It's true that the odd wiring here is to keep the A/C and the heater blower off while the starter is engaged. The scheme uses the principle that the relays controlling both of these units pick up a ground through the starter solenoid. The current required to operate the relay coils are milliamps compared to the amps required to operate the starter solenoid, so the starter solenoid essentially can't tell the milliamps from no amps, and is not affected in the least.

For the A/C and heater relays, they get 12 volts on one side of the coil and essentially ground on the other when the starter is not operated. When it is operated, 12 volts one side as normal, and 12 volts on the other from the starter. 12 volts minus 12 volts = 0 volts across the relay coils and no current flow. The power relay for the A/C is energized the entire time the ignition switch is on, except during start.

[psalt]

http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911M&section=ELchrg&page=3&bookmark=19&part_number=911-615-103-01-M206

You need to look at the wiring diagrams if you are interested in understanding the question