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chuck21401
Joined: 20 Feb 2005
Posts: 526
Location: Annapolis, MD
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 Posted: Fri Aug 20, 2021 3:23 am Post subject: |
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Have you replaced the starter/alternator/battery harness? I'm going through that now.
A company called Kroon makes them for 79/80 924 turbos.
https://www.kroonwireharnesses.com/porsche-924/porsche-924-1980?product_id=897
I believe they will recreate other harnesses if you send them the original to replicate.
Have you checked voltages at the battery, alternator, fuel pump etc. Is the battery fully charged? Is the alternator charging the battery when the engine is running with accessories running (lights, A/C, engine fan, etc)?
Yes, do check the connections/grounds at the starter/alternator/battery but also consider that the wiring has been cooking for 40 years now.
I'm not sure if replacing the harness in my car will fix my problem (which sounds a lot like yours) but I am hopeful I've found the gremlin.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler |
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bear924
Joined: 26 Jul 2005
Posts: 95
Location: South West Queensland, Australia
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| Posted: Mon Oct 25, 2021 9:59 pm Post subject: |
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| Eliza wrote: | Hi Bear,
According to my wiring diagram, terminal 3 if the DITC plug (green-white wire) connects to terminal 6 on the transistor ignition box on the front fender, and from terminal 1 on the same box to the coil, from there to pin1 on the FPR.
So apparently, the DITC pulses the coil via the transistor ignition unit. Maybe an idea to check that for correct operation, if you haven't yet.
I have the DITC manual, including wiring diagram, if you think that might help. Let me know if you want it.
Good luck!
Eliza |
Hi Eliza,
I didn't make the connection between the DITC and the transistor ignition unit. I'll have a look around that area as it's possible I have something silly like a loose connection. I might take you up on your offer of the DITC manual as my fault finding as been put on ice for the last little while while we move house. |
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bear924
Joined: 26 Jul 2005
Posts: 95
Location: South West Queensland, Australia
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| Posted: Mon Oct 25, 2021 10:04 pm Post subject: |
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| chuck21401 wrote: | Have you replaced the starter/alternator/battery harness? I'm going through that now.
A company called Kroon makes them for 79/80 924 turbos.
https://www.kroonwireharnesses.com/porsche-924/porsche-924-1980?product_id=897
I believe they will recreate other harnesses if you send them the original to replicate.
Have you checked voltages at the battery, alternator, fuel pump etc. Is the battery fully charged? Is the alternator charging the battery when the engine is running with accessories running (lights, A/C, engine fan, etc)?
Yes, do check the connections/grounds at the starter/alternator/battery but also consider that the wiring has been cooking for 40 years now.
I'm not sure if replacing the harness in my car will fix my problem (which sounds a lot like yours) but I am hopeful I've found the gremlin. |
Hi Chuck,
All good points. Essentially everything is working fine apart from the erratic stops. I did replace the battery and a few other items associated with the ignition system however still having same probs.
Did your wiring replacement solve your problem. Connection for future wiring harness options is a good option and could potentially be my problem as problem started after I removed the engine which did cause lots of wiring harness movement. |
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chuck21401
Joined: 20 Feb 2005
Posts: 526
Location: Annapolis, MD
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| Posted: Wed Oct 27, 2021 11:43 am Post subject: |
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| bear924 wrote: |
Hi Chuck,
All good points. Essentially everything is working fine apart from the erratic stops. I did replace the battery and a few other items associated with the ignition system however still having same probs.
Did your wiring replacement solve your problem. Connection for future wiring harness options is a good option and could potentially be my problem as problem started after I removed the engine which did cause lots of wiring harness movement. |
I think my car has multiple problems that may or may not be related.
Going back many months, I would have a random problem where the car would run very rough and barely idle. The A/F meter would read extremely lean and the car would die as if it was running out of fuel.
Mysteriously the problem seemed to go away. A couple more weeks went by. I went for a ride and the car worked fine. Went to drive it again and it would not start. I found that the fuel pump fuse was melted. I replaced the fuse and car worked fine again (and I know that fuses rarely just burn out, there is probably something else going on). I was running a 16A fuse for the fuel pump; the 1980 924 turbo current flow diagram, indicates it should be 25A, so I have a 25A fuse there now.
More time passed...same problem. Again seemed the the car was running out of fuel. I changed the filter. I drained the tank and checked the in tank screen. I checked the connections at the fuel pump and the ground for the fuel pump. The car seemed to run fine after I did all of that.
Several week later the problem came back. I checked voltage at different places...checked for voltage drop. There appeared to be a significant voltage drop from the fuel pump fuse to the fuel pump. I checked the grounds. I ran a new ground line from the engine to the rear ground point. I checked the ground at the battery. I cleaned the connections at the ignition box. I replaced the ground wire from the alternator to the engine.
Charged up the battery (replaced 2 months before that point). Car seemed to work fine.
I drove the car for a couple more weeks. As I was getting off a highway ramp at speed I lost all power. Had the car towed home. Checked the fuel pump relay, the solder at one of the pins broke loose. Resoldered that pin, car worked again, ordered another relay.
The problem re-emerged. Checking voltage in different places, it seemed like there was a significant voltage drop between the battery and the fuel pump fuse. The alternator wasn't putting out the voltage that it should be, especially with accessories and the headlights running. Decided to replace the wiring harness mentioned above. Everything seemed to work better until the problem re-emerged.....would barely idle, low voltage all around. I also have noticed that the fuel pump relay and fuse would heat up.
At that point I decided to replace the alternator. Since I am running fog lights and a separate water pump for the intercooler, I bought the 90A version. The voltages increased all around at idle and under load. Voltage at the fuel pump fuse was 12v or better. I figured that this was an improvement.
As I drove the car around I kept an eye on things. The fuel pump relay and fuel pump fuse still get hot. So I dropped down the relay panel and replaced each of the connectors that plug into the fuel pump relay. The overboost ground seemed a bit flakey. I'm not running the overboost switch so I ran a fresh wire to the ground tree. I didn't cut the old wire, I labeled it an tucked it back with the other wires.
I reconnected everything and it seemed to work fine. I've gone driving several times...the fuel pump fuse and the relay continue to heat up. So I'm wondering if the fuel pump fuse contacts are building up resistance. I've ordered new copper contacts but I think they might be coming from Germany.
Here's where the story takes a turn. I've noticed that I seem to have a boost leak at the higher end. The car was making close to 15 psi wide open but now it's been between 13-14psi and I haven't touched the boost controller. I also noticed some oil film between the intercooler and the throttle body. There are two gaskets there. A black outer gasket and an orange O-ring. As I looked closely I could see the orange O ring pushing out at the bottom. I pulled apart the intake and found that the O ring was broken. I removed it and ordered a new one.
I needed to pull the car back in the garage so I put everything back together (without the o ring) thinking I could limp it back into it's parking spot. I turned the car on....and it ran poorly....just like it has been doing on and off for the past several months. So now I'm thinking that the O ring would move around slightly from vibration or contract/expand with heat just enough to cause a problem...but then disappear.
That's just a theory but it will be interesting to see if the problem goes away after changing that O-ring. I think the problem with the fuel pump fuse/relay heating up is a different problem happening at the same time.
I should also mention that I connected the CIS fuel pressure tester at one point. Edit - Now that I look at the pictures and the specs in the book, it looks like my warm control pressure is a bit high @ 59 psi. The air temp was 78 degrees. The spec book indicates 3.45...3.85 bar @ 68 degrees (20C)....50 - 55 psi.
Some pictures
Wiring behind fuel pump relay, notice the corrosion and discolored wire
New connection for red/black wire
New connection for red/blue wire
New ground for Fuel pump relay
Left the original overboost wire in place and labeled it
Bad O-ring at intake and pressure pipe (in my case, the intercooler)
CIS pressure tester connected, engine not running
Closer view of how things are connected
Control pressure warm - about 59 psi
System pressure - about 90 psi
_________________
1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler
Last edited by chuck21401 on Fri Oct 29, 2021 12:33 am; edited 3 times in total |
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chuck21401
Joined: 20 Feb 2005
Posts: 526
Location: Annapolis, MD
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| Posted: Wed Oct 27, 2021 11:49 am Post subject: |
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I also wrote up a chart to help document what I've checked. Of course I'm no expert but it might be helpful.
_________________
1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler |
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bear924
Joined: 26 Jul 2005
Posts: 95
Location: South West Queensland, Australia
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| Posted: Thu Dec 23, 2021 10:06 pm Post subject: Intermittent problem solved |
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Hi all,
So for the last few years I've had an issue where my car would run really well ... then just stop. Initially it would restart after this occurred however over time it was taking longer and longer for the car to start working again.
I presumed it was an intermittent electrical problem and replaced the coil, fuel relay and went looking for loose wires (which I did find ... check that the wires connecting your relay's are secure as some of mine were not.
Anyhow, after each littel find I'd get excited thinking I'd fixed the car and then it would stop again. I was beginning to think it was my crank sensor or the DITC box.
As the period of the car not restarting increased, I was able to start actually taking some voltage measurements. What I discovered was that the pulse to the fuel relay wasn't working. Instead of a pulse I was getting a constant 12V on the trigger or 'base'. This led me to believe that I had an ignition problem and made me start thinking about the crank sensor etc.
What I did find however was that I was getting tach bounce while cranking. I was able to confirm that the needle movement was indeed tach bounce as when I removed plug from the DITC, I had no needle movement. This didn't make sense to me as I presumed that the bounce indicated I was getting ignition.
This had me confused, however @Eliza (thanks again Eliza) stepped up and provided some advice and wiring diagrams which had more details than the ones I had. This information helped me realise that there are two components to the DITC .. one the silver box under the HVAC in the cabin, and the second was the ignition unit on the fender in the engine bay (it sits on a heat sink and has a warning sticker underneath it). In short, the silver box triggers the ignition unit, which then drives the coil.. and the coil sends the pulse to the fuel relay.
So I purchased a new ignition unit (it was cheap and easy to obtain) and replaced it and since then I've driven 1200km without a hint of a problem.
Also of interest is that when I removed the old ignition unit, it no longer had any thermal paste between the ignition unit and the heat sink. Probably something worth checking regardless of whether you suspect you have a problem or not.
So nice not to have to been constantly looking for a run off area now that I have some confidence back in the reliability of my car. Appreciate everyone's ideas with this. |
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924RACR
Joined: 29 Jul 2001
Posts: 8803
Location: Royal Oak, MI, USA
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| Posted: Fri Dec 24, 2021 10:13 pm Post subject: |
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Yes, those can indeed cause problems; found some improvement with my car on replacing that.
I assume you got new thermal paste to install? Easy enough to find in electronics sources; once upon a time Radio Shack was the easiest option, now it's online mostly... or any local PC outlet (MicroCenter anyone?).
That said, even after replacing mine (with new), and then converting to Microsquirt and still using it, I still had some misfiring/running problems, which weren't completely eradicated until I changed the ignition setup entirely. Which makes me think the wiring to the unit itself was still a problem, and I mean simply power and ground - because those weren't reused when I changed to the VW 4-tower coil setup.
So I recommend getting ahead of the problem and thoroughly going through those as well, to that ignition box on the fender, as they maybe also suffer with age...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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bear924
Joined: 26 Jul 2005
Posts: 95
Location: South West Queensland, Australia
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| Posted: Sun Jan 02, 2022 8:28 am Post subject: |
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Yes, I did install the thermal paste. I was actually organised and purchased the paste in preparation for when the unit arrived.
To my surprise, the unit arrived with a little tube of paste so my forward planning ended up being for naught.
What I did notice ... and was going to mention in my last post ... was that when I removed my original unit there was no thermal paste obvious between the unit and the heat sink. I believe it had simply disappeared over time ... therefore if you are still running your original ignition unit it may be worth refreshing the paste (personally I'd refresh the control unit while going).
Hopeful I don't have a wiring integrity issue ... as part of my fault finding I wiggled lots of wires while connected to a multimeter. I understand wiring loom failure is a big issue on Cayenne .. imagine how much wiring they'd have! |
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gord
Joined: 08 Feb 2022
Posts: 6
Location: Toronto, Ontario
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| Posted: Wed Feb 23, 2022 11:52 pm Post subject: |
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I'm also chasing a fuel pump relay problem with my 1980 Turbo, only in my case pin #31 on the relay is not attached to anything (there's a broken connector at the socket), and I have no loose wires under the dash.
@chuck21401's notes say #31 goes to the manifold pressure limiting switch.
Can anyone tell me what this wire is supposed to be (colour and gauge), and how it gets to the switch? Is it a straight path with a single wire, or does it go via a connector and/or get routed by the fuse panel?
Where is the manifold pressure limiting switch physically located in the car?
Any help is much appreciated!
Gord
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chuck21401
Joined: 20 Feb 2005
Posts: 526
Location: Annapolis, MD
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| Posted: Fri Feb 25, 2022 12:37 pm Post subject: |
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| gord wrote: | I'm also chasing a fuel pump relay problem with my 1980 Turbo, only in my case pin #31 on the relay is not attached to anything (there's a broken connector at the socket), and I have no loose wires under the dash.
@chuck21401's notes say #31 goes to the manifold pressure limiting switch.
Can anyone tell me what this wire is supposed to be (colour and gauge), and how it gets to the switch? Is it a straight path with a single wire, or does it go via a connector and/or get routed by the fuse panel?
Where is the manifold pressure limiting switch physically located in the car?
Any help is much appreciated!
Gord
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The manifold pressure limiting switch aka overboost switch is located on the boost pipe.
On my car, the boost switch wire was grounded to a bolt on the intake manifold when I bought it.
I thought maybe there was a flaky ground from the fuel pump relay to where the wire is grounded in the engine bay. So I ran a new ground wire-- no difference.
If the boost switch is bad or the wire is not grounded, the car will not run...since the fuel pump relay is not grounded.
From the wiring diagram, I believe the wire is brown with a white stripe. From what I recall, the wire disappears into the wiring harness before it goes through the firewall.
_________________
1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler |
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