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Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

Ok guys, I've been fighting with my ignition system for a couple days now. So basically here is what's going down: (It's a 1981 turbo btw)

1. Dizzy is new and checks out
2. Cap, rotor, and wires are all new and good
3. Ignition coil checked out good, but I replaced it with a new one anyway

On the ignition coil, 12v come out of the coil to dizzy cap wire. However, when the engine cranks, no spark comes out of the other plug wires.

I crawled under the dash to pull out the ignition control unit, which looked good and new(er). However when I was pulling the ICU I noticed a smaller black box behind it.. The stock alarm brain, complete with German writing on it and everything! I noticed the brand of the alarm was Hella, I found this interested because there are two connectors under the hood hanging behind the intake manifold but against the fender which also read "Hella".

I was not aware that this car came with an alarm system. Double checking the Haynes revealed that the 81 and 82 models indeed came with a (extremely poorly documented) alarm system (page 298 in the book). No information is given about this system other than the wiring diagram. And according to this diagram, terminal K1 on the alarm system connects to the ignition coil and possibly the Fuel Pump Relay.

So all this fun information aside, does anyone have any more information about this alarm system and how to bypass it?
_________________
Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped

924RACR · Posted: Thu Mar 01, 2012 11:12 pm Post subject:

The lock right behind the driver's door will turn the alarm on or off. I think it might very well be possible to jump the two wires together and thereby bypass the lock; accessible through the vent grill on the B pillar.

Mine is still fully functional.

Does the tach bounce when you crank? Most likely problem with those cars is actually the crank position sensor failing...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

924RACR · Posted: Fri Mar 02, 2012 4:09 am Post subject:

Mmmm, so your grounds sound to be boogered, for one.

I can't look at my DITC connectors right now, but that sounds really funky. Gonna have to find that tach wire, it should drive both the tach and the fuel pump IIRC...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

ptheskil · Joined: 03 Aug 2004 Posts: 128 Location: Essex, UK

Don't forget the ignition amplifier on the front lhs wheel arch. This switches the primary coil current under control of the ditc. If this is ng then there will be no spark. I would eliminate the alarm as a source of problems by temporarily running a 12V feed to the ditc and amplfier. If you are not switching the coil current then the fuel pump relay will.not power the fuel pumps of course.
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1981 931 series2 Euro spec

Cedric · Joined: 27 Aug 2004 Posts: 2815 Location: Sweden

My ignition module broke, the rev counter were bouncing around and suddenly the car stopped working from time to time. Changed it to one on the shelf from a volvo 740 (a std component) and it worked flawless ever since

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1980 924 Turbo
www.instagram.com/garagecedric/

Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

Ok, so lets forget about the fuel thing all together. I'm in the process of converting to EFI. We have the fuel stuff all worked out, we're just not getting spark from the coil. When the engine is cranking, the coil wire is only producing 12 volts.

Aside from that, what is a good way to bypass it? The DITC appears to be getting 12v but it does not appear to have a ground or a tach signal. I haven't messed with the ICU at all. The flywheel sensor appears to be working just fine as well.
_________________
Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I know you said not to worry about fuel, but have you eliminated the boost cut-off switch as a possible culprit? If it's disconnected or inoperable you get no power to the FPR. You can bypass it by disconnecting the lead and running it to ground. I attach mine to the alternator housing.
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erstwhile owner of just about every 924 variant ever made

Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

FPR = Fuel Pump Relay. As far as I know, the boost cutoff switch lifts ground to the fuel pump relay when boost is exceeded, or when the switch fails or is disconnected. I don't believe it cuts ground to ignition...but I could be wrong about that, because it might be different on DITC equipped cars. It's worth checking out, particularly since it appears you have no ground...
_________________
erstwhile owner of just about every 924 variant ever made

Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

Ok guys, lets talk grounds here for a moment. I think we may have isolated the problem.

We reanalyzed the book and wiring diagrams and noticed that all grounds and brown (brown/ground, it rhymes. Silly Germans!). Whilst removing the yucky CIS components, I also removed the nasty wiring harness, the huge one that snakes around from along the fire wall, it has two main connectors and dozens of little connectors that attach to all the anciliery equipment. Coincidentally, there are also a ton ground connections that, since the harness isn't connected, the grounds are not connected.

So the question: Does the main wiring harness have grounds that also apply to the ignition system?
_________________
Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

924RACR · Posted: Fri Mar 02, 2012 11:06 pm Post subject:

Definitely, and don't forget also the stack of grounds inside the cabin, behind the fusebox and next to the firewall...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Bockscar · Joined: 16 Nov 2010 Posts: 392 Location: Sandy, Oregon

how are you gentlement. all your ground issues are belong to me.

Turns out that big'ol wiring harness does indeed have grounds for most systems in the car. By disconnecting it, I effectively disabled pretty much everything electronically in the car. There does appear to be two sets of main grounds though, the nest of grounds under the dash as 924RACR pointed out, but also the grounds from the engine wiring harness. To make a long story short, we attached the grounds and now the ignition works.

Lessons Learned:

1. All grounds in the car appear to be solid brown wires
2. Don't write off grounding issues as problem sources!!
3. Don't unplug random wires without knowing what they go to!!
_________________
Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped