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Re: The '87 5k-S without spark

> Mr. Bentley's subject: Ignition coil (with power stage), checking.
> 1.  Voltage at the battery ----------------------- 12.39 volts.
> 2.  Voltage between terminals 1 and 2 on the
>     ignition coil power stage -------------------- 12.13 volts.
>         Note: These results are said to be ok.

That's good.

> 3.  Voltage between terminals 2 and 3 (with engine cranking - I smell gas
>     when I do this) changed randomly from 1.66 to 1.99. Mr Bentley says
>     2.0 volts is minimal and a range of 2.34 to 2.44 volts is average.
I can't remember the details exactly, just got rid of my Bently that covers your

You have 12 volts going in to a power resistor, and a gate (the signal that
fires the resistor, which is in series with the coil, supplying a 12 VDC to it,
causing the high voltage secondary side of the coil to fire the plug) signal
that comes from the hall sensor. The hall sensor provides a very small input
(from the distributor rotation) to the power transitor which in turn fires the
coil.  I believe the 2 volt signal is from the hall sensor.

Your voltage was about 1.6-19 volts, but remember, your car was being cranked
over, and your battery is probably lower than normal due to it not
starting/cranking the engine over. As long as you have a changing signal to the
power transitor (ignition coil power stage) I would say that it is acceptable.
> What do you think of this?
> The Bently book says that I should check the wiring between terminal 2 of
> the connector and terminal 16 of the "electronic ignition control unit,"
> according to the wiring diagram.
> If there isn't a break in the wiring between these treminals I am to
> check the ignition coil.
> MY PROBLEM: I don't know where to find the ELECTRONIC IGNITION CONTROL
>             UNIT. Where is the wiring diagram in the manual?

If you want to check the primary side (12 VDC side ) of the coil, remove the two
small wires that are attached to it. Select Ohms on your multimeter and check
for continuity between terminals. If it is open (bad) you'll get infinity. If it
is good, you'll get some relatively small value like 1-10 ohms (the bently tells
you what you should get).

Check the continuity of the wire runs from the hall sensor to the coil, check
the coil is grounded on one side, and if everything else passes, the power
transitor is TOAST. It happened on my 87 5KSQ. The part wasn't cheap, about $185
from the local dealer.

Check everything at least twice until you understand how the system works!

Good luck.


91 200 q

P.S. - the coil is one of the last things I would suspect, never had one go bad
on me. I would suspect the power transitor.

Paul Waterloo                    TEL: (860) 267-7714
HydroAire Incorporated           FAX: (860) 267-7387
875 Old Hartford Rd
Colchester, CT  06415          EMAIL: 74543.407@compuserve.com