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Eric's Troubleshooting Thread

 
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Eric P  



Joined: 21 Jun 2017
Posts: 94
Location: NY, USA

PostPosted: Tue Jul 18, 2017 2:22 am    Post subject: Eric's Troubleshooting Thread Reply with quote

It seems like something is constantly letting me down, so I figured I would just make one thread so I can stop cluttering up the board (sorry).

This past weekend, I took the 924 out for the first long trip that I've made. Hopefully the first of many. She made it over 800 miles total and even climbed to the top of Whiteface Mountain - the 5th tallest mountain in NY. Obligatory photo:



I'm fairly proud of the car for making it. This is the most miles that I've put on the car without a major failure. That being said, I had two that I need to fix. Any pointers on where to start looking would be helpful.

The first problem was a blown fuel pump relay. When I bought the car, the relay was burned out and the previous owner had wired in a toggle switch. I cleaned all the grounds, soldered a jumper across the burned out part of the fuel pump relay, and away I went. I made it about 1600 miles on that repair. Unfortunately, the relay burned out again, so I bought a new one thinking my repair went bad. The second FPR failed, so I'm back to a toggle switch again. At least it gets me home.

I'm wondering if I have a failing fuel pump. Does anyone know the correct resistance value across the in line fuel pump? How about the in tank pump? Why would I be blowing the relays but not the fuse? It has the correct 16A fuse in slot #2.

The other issue I ran into was constantly blowing radiator fan fuses (fuse #3). 300 miles or so into my trip, I started having problems. As soon as the fan would kick on, the 16A fuse would blow. I replaced it with a 25A fuse just hoping to make it until I could get home. That held for about 200 miles then blew. I replaced it with another 25A fuse, which blew immediately. Luckily, I was able to drive the entire way home without stopping or slowing down too much.

Is there a correct operating procedure for testing the radiator fan? One item that I noted: The fan does not kick in at low speed but doesn't blow the fuse either. Then I insert the key, the fan fuse blows. I checked the relay. It appears to be functioning. I tried jumping the thermo switch. The fuse still blew when I turned the key on. What is the correct resistance across the driver side fan? I'm thinking I may have a wire shorting out to ground but I'd like to check that the fan is ok during my troubleshooting. It appears to spin smoothly when spun by hand. Assuming that all the components in the system check out (thermo switch, relay, resistor, fan, fuse block), I may just run new wires and see if that resolves my issue.

As always, any suggestions are appreciated. Even with all of the issues I've had, this is by far my favorite vehicle that I've owned so I'd like to get it back up and functional soon!
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brian19600  



Joined: 28 Oct 2013
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PostPosted: Tue Jul 18, 2017 3:40 am    Post subject: Reply with quote

Do you have a repair manual? Haynes?
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Eric P  



Joined: 21 Jun 2017
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PostPosted: Tue Jul 18, 2017 4:00 am    Post subject: Reply with quote

I have a Haynes manual, but it isn't overly detailed in the troubleshooting department and assumes that all your wires and connections are in perfect shape.
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morghen  



Joined: 21 Jan 2005
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PostPosted: Tue Jul 18, 2017 7:13 pm    Post subject: Reply with quote

Check how many amps the pump is drawing, maybe its the wrong pump or maybe there is something making it draw more power to do its job...clogged internal fuel pump? clogged fuel filter?

regarding the fuse blowing...you may have the wrong relay in that socket.
NEVER use a stronger fuse instead of the factory one...you will do more damage to the wiring and even risk setting the car on fire.
My car has AC and two fans, and one of the fans was never working..i looked and it had a blown fuse, replaced it and instantly blew as the fan started. It turned out I had the wrong relay and as soon as the fan started there would be a short in the system because of the wrong relay feeding power to the wrong terminals.

Do a proper check...it really paid off in my case, now my car has fully functional AC, cooling and all electricals.
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Eric P  



Joined: 21 Jun 2017
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Location: NY, USA

PostPosted: Wed Jul 19, 2017 3:47 am    Post subject: Reply with quote

morghen wrote:
Check how many amps the pump is drawing, maybe its the wrong pump or maybe there is something making it draw more power to do its job...clogged internal fuel pump? clogged fuel filter?

regarding the fuse blowing...you may have the wrong relay in that socket.
NEVER use a stronger fuse instead of the factory one...you will do more damage to the wiring and even risk setting the car on fire.
My car has AC and two fans, and one of the fans was never working..i looked and it had a blown fuse, replaced it and instantly blew as the fan started. It turned out I had the wrong relay and as soon as the fan started there would be a short in the system because of the wrong relay feeding power to the wrong terminals.

Do a proper check...it really paid off in my case, now my car has fully functional AC, cooling and all electricals.


I cleaned the tank and the screen on the in tank pump when I bought the car and I also installed a new fuel filter. That's a good point on the fuel pump possibly not being original. Is there a resistance value that I should be able to measure across each pump? It isn't listed in the Haynes manual.

As far as the fan goes, there is nothing listed for troubleshooting the fan circuit in the Haynes manual. It just shows the procedure for removal/re-installation of the fan. As for the fuse, it was more of a "try to limp it home" kind of fix. I assumed (I believe correctly as nothing appeared to be hot) that the wiring for the fan could handle 25A for the split second before the fan fuse blew. I agree that I still shouldn't have done this, but I was 300 miles from home and needed to do something about my engine overheating.

According to what I could find online, the relay is correct for the radiator fan. I cleaned all the grounds I could find when I bought the car so that shouldn't be the issue.

I'm assuming that my issue is cracked wire insulation somewhere in the system grounding out to the frame. I would like to verify the correct fan resistance before I go too far though. Again, the Haynes manual simply glosses over the fan circuit. If I can verify that the radiator fan is still good, I'm just going to re-wire the entire fan circuit.

On a side note, what is the coolant capacity of a 1980 924 NA? I want to replace the thermo switch and I'm going to flush the coolant while I'm at it.
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Eric P  



Joined: 21 Jun 2017
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PostPosted: Fri Jul 21, 2017 3:41 am    Post subject: Reply with quote

A new thermoswitch didn't solve the fan problem - not that I expected it to, but it would have been nice. I still don't know how much coolant I need to buy, so I just topped off what's in there and bled the system after replacing the switch. At $36/gallon from porsche, I'm hesitant to buy too much.

Since one of my friends is getting married this weekend, I'll be driving out of state to go to the wedding. I need the fan to be functioning reliably so I'm going to wire in a new circuit tonight and leave the old one in place but disconnected (and without fuses).

I have 4 questions about the radiator fan system:

1) When the car is hot, the key is on, and the A/C switch is OFF, should the passenger fan kick on when the driver's fan does? I assume yes based on the Haynes diagram, but I want to double check correct operation.

2) What is the correct resistance of the driver side radiator fan? Since I have 12V and a 16A fuse, I know it has to be higher than .75 Ohms, but I'm looking for a range to see if my fan is within spec.

3) What is the resistance value of the low speed resistor? I've seen a few online that have different ratings stamped on them. I believe the correct rating is 1.8 Ohms, but I wanted to verify as this isn't in the Haynes manual.

4) Is it ok for me to wire the fan without a low speed resistor for now? I would add it later, but the resistors don't appear to be available locally. I would wire the car so that the fan runs at high speed whenever the thermoswitch tells it to kick on. Will this work, or is there enough draw there to drain my battery?

The plan is to re-wire everything so the car operates as close to stock as possible and repair the original circuit at a later date.
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morghen  



Joined: 21 Jan 2005
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PostPosted: Fri Jul 21, 2017 6:30 am    Post subject: Reply with quote

Dont start rewiring stuff when its not needed..please...these systems can still work flawlessly.

If your car has AC then you need to have two fan relays, each 16amps.
If one of the fans is blowing the fuse but the other is working i'm 90% sure you have the same problem as me.

You should have two identical relays, one that runs the AC compressor, internal fan(blower) and the passager side cooling fan.
The other relay just runs the driver side fan.

This is how the AC relay and the other fan relay must look like. If yours dont look like this then thats the problem.
My car had a non AC fan relay insted of the correct relay and no relay for the AC.
This drained my battery slowly and always blew the passager side fan fuse.


this is how the relay socket connections must look like if you have AC:





this is the wiring connection (i think this is the right one..but regardless this will help)


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Eric P  



Joined: 21 Jun 2017
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PostPosted: Fri Jul 21, 2017 7:42 am    Post subject: Reply with quote

The relay appears to be completely operational. I've taken it apart, cleaned the contacts, and tested it with a battery and multimeter. It has two contacts inside so it appears to be the correct relay. I even installed it in the car and watched it click closed. If it were the wrong relay, wouldn't it have been blowing the fuse immediately? I put over 1800 miles on it before I blew a fuse and everything appeared to be operating correctly until recently.
By the way, my battery isn't draining and the driver's side fan fuse is the only fuse blowing.

There isn't much here to fail:

-Temperature switch: Brand new
-Fan: Spins freely. I'm still trying to find a resistance spec, so I can't test it to be sure. When the fuse isn't blown, it runs without making excessive noise.
-Resistor: Appears to be working as the fan spins at low speed when the car is hot and the key is off - provided that the fuse hasn't blown yet.
-The relay is correct and functional -see above

The only unknowns are the fan and the wiring. I don't want to hack up my stock shroud for an aftermarket fan until I confirm that the fan is indeed the culprit. If I re-wire it and it blows a fuse, that will point towards a bad fan. To me, that sounds unlikely given that the fan spins freely without excess noise. If I do need a new fan, the old wiring will still be there to plug back into. No harm done.

I'm not looking to cut corners here. I just need to be able to get to work and my friend's wedding this weekend. If I re-wire it, I'll do it all with relays, resistors, and fuses. I just can't afford to not have a car because something so simple doesn't work. It isn't like I'm wiring it up to a toggle switch in the dash to turn the fan on like I've seen people posting all over the internet
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morghen  



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PostPosted: Fri Jul 21, 2017 6:17 pm    Post subject: Reply with quote

ok its clear, look at the schematic I posted above.
You should have two relays, one for AC and one for the cooling fans.
They are connected in such a way that the AC relay will start both cooling fans regardless of the coolant temperature switch.

After the engine is started there is power coming to terminal 30 and A of the cooling fan relay.
The coolant temp switch will offer ground to both fans when the coolant temp reaches a certain value.

Separately the AC relay will offer ground to both fans when the AC is turned on.

Do both of your fans work when AC is on and a fresh 16A fuse is on?
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Eric P  



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PostPosted: Sat Jul 22, 2017 1:40 am    Post subject: Reply with quote

For anyone having this problem in the future, make sure your A/C pulley isn't rubbing on your fan wires. After dropping the skid plate on the bottom of the car and going to unhook the fan, it was clear where my problem was. The 37 year old zip tie that holds the wires to the fan shroud had gotten brittle and let loose. The wires started rubbing on the spinning A/C pulley, which explains why the fuse was blowing intermittently and not all the time.



I Had an old VW wiring harness kicking around, so I cut out a section of the appropriate colored wires, soldered in a new length of wire, heat shrunk it all, and zip tied the wires in place with two new zip ties. I took it for a nice long drive last night. No more blown fuses. Success.
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agfisher  



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PostPosted: Sat Jul 22, 2017 3:44 am    Post subject: Reply with quote

Awesome! Love that feeling!
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brian19600  



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PostPosted: Sat Jul 22, 2017 3:54 am    Post subject: Reply with quote

Nice! Especially when the repair doesn't cost anything other than time.
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Defender405  



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PostPosted: Sun Jul 23, 2017 1:03 pm    Post subject: Reply with quote

You are fortunate, I had to change the fan on mine last year. That job is a PITA, everything is in the way. Did give me an excuse to flush the system and put in new coolant. While I was in there I also changed the thermostat and temp switch following Ideola's recommendations. The car runs pretty cool now unless I'm stuck in traffic with the AC on but never really overheats anymore.
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Eric P  



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PostPosted: Tue Oct 17, 2017 2:28 am    Post subject: Reply with quote

So I'm back to troubleshooting my fuel system.

In the past few weeks, I've had the following problems:
- Cold start problem
- Leaking gasket at in tank pump
- Hot start problem
- Burned out fuel pump relay

I've hashed out a plan to address most of these issues, but not all.

The cold start issue has been a problem since I bought the car but has been getting progressively worse. From the beginning, it wouldn't start unless I held my foot down while cranking then would misfire for a few seconds and smooth out. The last time I was at the salvage yard, I bought a used AAV off a 1978 924. I cleaned the new AAV and tested its function in the freezer. Last week, I finally swapped in the new one. My car now starts right up without the foot to the floor trick, but it still misfires a few seconds until it clears its throat.

When I bought the car, I also had an issue with a leak at the in tank pump where it threads into the tank. Tightening the pump helped for a bit, but the gasket finally gave out this past week after I had just filled the tank. I proceeded to drain out 12 gallons of gas so I could pull the in tank pump.I was a bit surprised that the inside of my gas tank and my in tank pump's filter were both spotless After replacing the old crumbling gasket, my leak has completely disappeared.

Since I had all the gas out of the car, I decided to tackle (or at least diagnose) my hot start problem at the same time. My first step was to pull the screw on my fuel accumulator. No dice. It was bone dry. Then I went to pull the check valve off my fuel pump. I was a bit surprised to find an aftermarket "NUPRO" stainless check valve in the line. Apparently it's supposed to be rebuildable. I used a pick to gently pull the o-ring out of it. I'm not sure if it was torn before or during removal, but it was definitely torn once I had it out. I replaced the o-ring with one out of my Harbor Freight Viton o-ring kit for now. It seems like it only holds pressure sometimes, so I ordered a new factory check valve and put it all back together for the night. After refilling the gas tank and checking for leaks (none found), I checked the injectors for leaks and didn't locate any. Since I knew I would have to drain the gas yet again, I decided to order a new Walbro fuel pump. My old Bosch one has been making a bit of noise and I don't want it to leave me stranded on my drive to Iowa next month... which leads me to my next question.

How do I tell which pump is causing the excessive draw that keeps burning out my fuel pump relay? The in tank pump looks to be in good shape visually but both pumps can be heard easily from the driver's seat with the relay jumpered and the car not running. I disconnected one and then the other to test them both. I'd like to leave the in tank pump in there if it's in good shape, but I have now idea how much noise is normal for these things?

So I've narrowed my list down to a hot start issue which should hopefully be solved when my check valve arrives in the mail tonight and an excessive draw on my fuel pump circuit... which will hopefully be remedied by a new pump.

I've driven over 5000 miles this summer and hopefully worked most of the bugs out. I need this car to be reliable for my 1500 mile round trip drive to Iowa next month. I intend to change all the fluids (oil, transaxle, brake, coolant), filters (fuel, oil, air), and spark plugs before the trip. I'm also planning on bringing a few spare FP relays, a few jumper wires, and basic hand tools with me. Is there anything else I should be looking over before I leave? My longest drive so far has been 800 miles round trip. I'm really looking forward to almost doubling that.

VW or not, the 924 is still a beautiful piece of engineering.
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