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Mclaren924
Joined: 13 Oct 2021
Posts: 222
Location: California
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 Posted: Tue May 13, 2025 3:38 am Post subject: Difference between 80 and 81 924 ignition system. |
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Hey guys need somebody with experience to chime in here, trying to help a buddy get his 81 weissach back to running again and just realizing now that his car has a completely different ignition module and a 3 pin distributor compared to the 77-80 cars I'm used to seeing. Tried going thru the PET to sort out what's what but there's little to be found if it truly belongs in 1981 NA. The ignition module has a part number starting 477 905, which leads me to believe somebody may have grafted in a later model turbo ignition module and potentially more. I am just going off photos from my buddy so I will try and get the full part number off it. I may be completely off track and this just may be the way 81 924's were setup but that's the point of this post is for hopefully somebody with experience in the later cars can set me straight. Thanks if you read my incoherent rambling this far.
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
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924RACR
Joined: 29 Jul 2001
Posts: 8942
Location: Royal Oak, MI, USA
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| Posted: Tue May 13, 2025 9:33 pm Post subject: |
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Well, the late Turbo distributor has NO leads, so not sure that's entirely right...
I'd wonder if maybe it has a Euro NA setup?
Is the ignition module maybe really small, barely bigger than a matchbook, on an aluminum heat sink?
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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
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Mclaren924
Joined: 13 Oct 2021
Posts: 222
Location: California
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| Posted: Wed May 14, 2025 2:37 am Post subject: |
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| 924RACR wrote: | Well, the late Turbo distributor has NO leads, so not sure that's entirely right...
I'd wonder if maybe it has a Euro NA setup?
Is the ignition module maybe really small, barely bigger than a matchbook, on an aluminum heat sink? |
It's a little black box mounted in the same location as the standard 77-80 ones but its roughly half the size, it does appear to be mounted on some solid block of metal as well. Would assume it's a heatsink but photo isn't great. It could be a eruo setup, It wouldn't be the most impossible thing to believe. The connector for his wiring harness to the Ignition module doesn't come back in the 80-85 PET so I'm wondering if it is EURO stuff. Would the euro parts not be in my version of the PET, I'm assuming there's different versions for ROW cars hmmmm.
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon |
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Raize
Joined: 18 Sep 2013
Posts: 337
Location: Scotland
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| Posted: Wed May 14, 2025 2:52 am Post subject: |
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My Haynes Manual has a bit about this at the end, it's a TCI-H Hall Effect ignition system. As well as that control unit there should be an idle stabiliser unit somewhere.
Anyway the main question is, does it spark? All of these things are basically black boxes anyway. |
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Mclaren924
Joined: 13 Oct 2021
Posts: 222
Location: California
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| Posted: Wed May 14, 2025 3:04 am Post subject: |
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| Raize wrote: | My Haynes Manual has a bit about this at the end, it's a TCI-H Hall Effect ignition system. As well as that control unit there should be an idle stabiliser unit somewhere.
Anyway the main question is, does it spark? All of these things are basically black boxes anyway. |
No spark to the coil at all is the main problem, cars 4000 miles away from me so I'm trying my best to put this guy on the right path. He's done a lot of parts shotgunning and un-surprisingly it hasn't fixed it. I told him to check his coil negative and positive leads as they are resistor wires and will mess the whole system up if not working correctly. Then trace all the wires back to the ignition module and make sure it's getting power. That leads us to here, he's telling me that he's tested the ignition module and says it's dead. My problem here is I'm doubting if he correctly tested it and if it is actually dead, finding a replacement because the actual PN on it is telling me its off a turbo which I also have my doubts about. If the systems all factory as should be then im not too worried about him testing it incorrectly, was mainly worried somebody Frankenstein it and now he's using the wrong test or wiring diagram or pinout to ascertain ignition modules health.
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon |
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Mclaren924
Joined: 13 Oct 2021
Posts: 222
Location: California
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| Posted: Wed May 14, 2025 3:06 am Post subject: |
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https://imgur.com/a/PQpHSLy
Posting photos has always been the bane of my existence lol.
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1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon |
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Raize
Joined: 18 Sep 2013
Posts: 337
Location: Scotland
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| Posted: Wed May 14, 2025 3:14 am Post subject: |
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https://imgur.com/a/yWfu2Z2
I think it’s this. The wire colours match. Looks like this type doesn't use resistor wires.
It's really not a hard circuit to check. Is there any voltage at coil terminal 15? Plug A12 burned out on my car at the fuse box and I had to bypass it. |
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924RACR
Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA
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924RACR
Joined: 29 Jul 2001
Posts: 8942
Location: Royal Oak, MI, USA
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| Posted: Wed May 14, 2025 4:05 am Post subject: |
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More into the details... from the '81 924/924 Turbo Service Information booklet.
On the NA, the new style transistorized ignition unit is fired by the Hall effect sensor in the distributor (and the unobtanium flywheel sensor on the Turbo).
The additional black box stacked on the smaller ignition unit is the idle stabilizer.
From the manual - Checking Operation:
Connect a voltmeter or a test lamp between ignition coil terminal 15 and ground. Start engine and observe volt meter or test lamp.
If volt meter needle pulsates or test lamp flickers, the Hall sender and control unit are probably OK.
Also, the idle stabilizer can be switched off (to adjust mixture/CO level and idle speed adjustments) by disconnecting the connector between the throttle switch and the ignition control unit. This plug is accessible in the engine compartment on the left wheel housing (in the harness right by and leading to the ignition unit on the fender).
Much better detail in the full manual, starting on page 28-33:
The ignition stabilizer can be completely bypassed for diagnostic purposes by disconnecting its two leads and plugging them together.
Beyond that... really should step through the manual, with voltmeter in hand, step by step.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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Mclaren924
Joined: 13 Oct 2021
Posts: 222
Location: California
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| Posted: Wed May 14, 2025 5:19 am Post subject: |
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Thank you Raize and 924Racr, you guys saved me a lot of time with this. I have the FSM so I will dig through and check out the sections you mentioned. Had a feeling I was just overthinking this. Have already forwarded your message to my friend in PA and he will start trying that while I read up more on how the system actually works. Will post back here when we get to the bottom of the issue. Cheers lads
_________________
1980 931 "Salt" Bucket wannabe racer (not started)
1979 924 Sebring "Pepper" -Sold
1980 924 "Donnie" (Parts car)-DEAD
1977 924 Slicktop "Pennie" Bucket turned Silver Spoon |
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