HELP: Porsche 944 no spark

Technical aspects of automobiles, et. al., post #18,974
Author:
Date:
Subject:
 jonb55198@yahoo.com
 2008-05-12 20:29:44
 HELP: Porsche 944 no spark
Hi Group,

The other day my car would not start. The battery is fully charged
and the starter cranks well. My friend and I did some preliminary
diagnosis with which we discovered:

1. There is 12V at the ignition coil (both wires to ground).
2. The resistance/impedance numbers of the coil are within spec.
3. There is no water in the coil, we displaced it with lubricant and
the protective boot looked ok anyway.
4. We hooked up a 2 different spark plugs to the output wire of the
coil (the wire that goes from the coil to the cap) and then grounded
it and turned the key into the ON position (but not the start
position) and did not get any spark.
5. There is fuel in the rail.

My question is, if there is 12V at the ignition coil, and the
resistance numbers are ok, could it still be a bad coil, or does this
point to something else like a bad DME/ECU, a bad DME Relay, a bad
crank position sensor or speed sensor?

I've read in other posts that when these sensors go bad, there is no
spark... but did the authors of these posts mean to write that when
these sensors go bad, there will NOT be 12V at the coil? Please
help. Thanks.
Author:
Date:
Subject:
 Steve Austin
 2008-05-13 07:50:16
 Re: HELP: Porsche 944 no spark
[email protected] wrote:
> Hi Group,
>
> The other day my car would not start. The battery is fully charged
> and the starter cranks well. My friend and I did some preliminary
> diagnosis with which we discovered:
>
> 1. There is 12V at the ignition coil (both wires to ground).
> 2. The resistance/impedance numbers of the coil are within spec.
> 3. There is no water in the coil, we displaced it with lubricant and
> the protective boot looked ok anyway.
> 4. We hooked up a 2 different spark plugs to the output wire of the
> coil (the wire that goes from the coil to the cap) and then grounded
> it and turned the key into the ON position (but not the start
> position) and did not get any spark.
> 5. There is fuel in the rail.
>
> My question is, if there is 12V at the ignition coil, and the
> resistance numbers are ok, could it still be a bad coil, or does this
> point to something else like a bad DME/ECU, a bad DME Relay, a bad
> crank position sensor or speed sensor?
>
> I've read in other posts that when these sensors go bad, there is no
> spark... but did the authors of these posts mean to write that when
> these sensors go bad, there will NOT be 12V at the coil? Please
> help. Thanks.

Is there a pulse at the injectors?
Author:
Date:
Subject:
 jonb55198@yahoo.com
 2008-05-13 06:42:59
 Re: HELP: Porsche 944 no spark
On May 13, 8:50 am, Steve Austin <[email protected]> wrote:
> Is there a pulse at the injectors?

There is plenty of fuel in the rail. We haven't' checked the
injectors yet because we were unable to get spark. So we wanted to
solve that problem first. They are unrelated, right?

-Jon
Author:
Date:
Subject:
 Scott Dorsey
 2008-05-13 10:17:25
 Re: HELP: Porsche 944 no spark
<[email protected]> wrote:
>On May 13, 8:50 am, Steve Austin <[email protected]> wrote:
>> Is there a pulse at the injectors?
>
>There is plenty of fuel in the rail. We haven't' checked the
>injectors yet because we were unable to get spark. So we wanted to
>solve that problem first. They are unrelated, right?

No. Both the spark and the injectors are commanded by the ECU. If the
ECU doesn't know that the crankshaft is turning, it won't fire either one.

If your coil were gone, you would not have spark, but you would still have
plenty of fuel coming out of the injectors. But you'd have noticed this
if it were the case because the exhaust would have smelled strongly of
unburned fuel.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Author:
Date:
Subject:
 N8N
 2008-05-13 06:50:53
 Re: HELP: Porsche 944 no spark
On May 12, 11:29 pm, [email protected] wrote:
> Hi Group,
>
> The other day my car would not start.  The battery is fully charged
> and the starter cranks well.  My friend and I did some preliminary
> diagnosis with which we discovered:
>
> 1. There is 12V at the ignition coil (both wires to ground).
> 2. The resistance/impedance numbers of the coil are within spec.
> 3. There is no water in the coil, we displaced it with lubricant and
> the protective boot looked ok anyway.
> 4. We hooked up a 2 different spark plugs to the output wire of the
> coil (the wire that goes from the coil to the cap) and then grounded
> it and turned the key into the ON position (but not the start
> position) and did not get any spark.
> 5. There is fuel in the rail.
>
> My question is, if there is 12V at the ignition coil, and the
> resistance numbers are ok, could it still be a bad coil, or does this
> point to something else like a bad DME/ECU, a bad DME Relay, a bad
> crank position sensor or speed sensor?
>
> I've read in other posts that when these sensors go bad, there is no
> spark... but did the authors of these posts mean to write that when
> these sensors go bad, there will NOT be 12V at the coil?  Please
> help.  Thanks.

Could be any of these, but I would try the DME relay first, this is
the classic failure of these vehicles. I had a similar failure on my
'88 and it ended up being a combination of bad coil and poor solder
joints in the DME (likely caused by the bad coil overheating the coil
driver) but if you are confident in your diagnosis of the coil as
being good try the DME relay. You can bypass it temporarily, look for
a procedure on Clark's Garage.

nate
Author:
Date:
Subject:
 jonb55198@yahoo.com
 2008-05-13 06:58:57
 Re: HELP: Porsche 944 no spark
On May 13, 9:50 am, N8N <[email protected]> wrote:
> Could be any of these, but I would try the DME relay first, this is
> the classic failure of these vehicles. I had a similar failure on my
> '88 and it ended up being a combination of bad coil and poor solder
> joints in the DME (likely caused by the bad coil overheating the coil
> driver) but if you are confident in your diagnosis of the coil as
> being good try the DME relay. You can bypass it temporarily, look for
> a procedure on Clark's Garage.


Yes, but if there is 12V at the coil, should it be sparking? there is
12V at the terminals on the coil, the impedances are correct, but we
aren't getting any spark.
Author:
Date:
Subject:
 HLS
 2008-05-13 08:59:55
 Re: HELP: Porsche 944 no spark
<[email protected]> wrote in message news:559d5410-1976-4120-a908-
> Yes, but if there is 12V at the coil, should it be sparking? there is
> 12V at the terminals on the coil, the impedances are correct, but we
> aren't getting any spark.

Simple presence of 12 V at the coil does not guarantee a spark, if that
helps any.

There are a number of different types of ignition circuits around, and I
dont know what that Porsche uses...
Author:
Date:
Subject:
 jonb55198@yahoo.com
 2008-05-13 07:10:55
 Re: HELP: Porsche 944 no spark
On May 13, 9:59 am, "HLS" <[email protected]> wrote:
> Simple presence of 12 V at the coil does not guarantee a spark, if that
> helps any.


So, if there is 12V there, can we rule out a bad DME or bad speed and
reference sensors? asked another way: would a fault in the DME, or
these 2 sensors cause no voltage at the coil?
Author:
Date:
Subject:
 Andre
 2008-05-13 09:13:45
 Re: HELP: Porsche 944 no spark
The spark is actually produced by taking away the 12v. The DMA will ground
the coil for every time it needs to spark. You can try testing the coil by
using Clark's website suggestion. I tried this and I thought I would see
more of a spark. I actually had a hard time seeing the spark so I had to
move the coil and battery into a dark room like a walk in closet to see it.

My guess is if your coil measures good it probably is good. Do you know
about Clark's web site. Here is a link to the troubleshooting section on
"No Spark": http://www.clarks-garage.com/ go to "Garage Shop Manual" click
on "T" for Troubleshooting and then on "TS-01"

BTW my problem was a bad ignition switch.



<[email protected]> wrote in message
news:559d5410-1976-4120-a908-c339a741ef38@w7g2000hsa.googlegroups.com...
> On May 13, 9:50 am, N8N <[email protected]> wrote:
>> Could be any of these, but I would try the DME relay first, this is
>> the classic failure of these vehicles. I had a similar failure on my
>> '88 and it ended up being a combination of bad coil and poor solder
>> joints in the DME (likely caused by the bad coil overheating the coil
>> driver) but if you are confident in your diagnosis of the coil as
>> being good try the DME relay. You can bypass it temporarily, look for
>> a procedure on Clark's Garage.
>
>
> Yes, but if there is 12V at the coil, should it be sparking? there is
> 12V at the terminals on the coil, the impedances are correct, but we
> aren't getting any spark.
Author:
Date:
Subject:
 Scott Dorsey
 2008-05-13 10:18:43
 Re: HELP: Porsche 944 no spark
<[email protected]> wrote:
>
>Yes, but if there is 12V at the coil, should it be sparking? there is
>12V at the terminals on the coil, the impedances are correct, but we
>aren't getting any spark.

Voltage does not cause the coil to spark. The CHANGE in voltage causes the
coil to spark.

If there is 12V on BOTH sides of the coil, there is no voltage across the
coil anyway.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Author:
Date:
Subject:
 darthpup
 2008-05-13 15:57:39
 Re: HELP: Porsche 944 no spark
The ignition coil works by rapid collapse of the voltage in the
primary coil. If the primary and secondary show propter resistance
then the coil is probably OK. The sensors can only be tested with an
oscilloscope. They may have slipped in position. You need to check
this. Go to http://www.clarks-garage.com for more specific data.
Have two 944's and have been through this drill a few times. If you
have an older model that has been stored outside your problem is
probably a bad connection on the blade connectors on the relay
panel. Try wiggling the wire mass when starting to see if it fires.