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Overheating 928s4, Cooling fans not kicking on

 
Old 07-09-2019, 08:34 PM
  #31  
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removing the connector from the switch at the front of the radiator, then turning on the key to run will trigger the fans to run.

Touching the two wires together at the top of the intake manifold sensor will cause the fans to run without regard to the key being on.
Report what you see please
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Old 07-09-2019, 08:48 PM
  #32  
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Make sure the battery is charged.

Yes, the intake temp switch is top rear of the intake. Brown wire, brown/green wire IIRC. Brown is ground, brown/green is switched ground to primary controller.

The primary controller lives under the cover next to the passenger seat. Silver box with two multi-pin connectors. This controller signal the "final stages" module on the front right apron near the hood latch. "Right" is the right side of the car while sitting in the driver's seat. Black finned module, round connector with a screw-secured arm retainer. The final stages module has two independent power feeds, one for each fan. Those route from the battery positive via a couple smaller red wires that attach to the battery positive cable clamp at the battery. They must be kept clean (shiny clean), tight, and be protected from corrosion (Vaseline). From the battery, those wires pass through the fuse panel and two separate fuses. From the fuses they route to the final stages module. Each fan has its own connector on the fan console harness. The legs on the harness are long enough to allow swapping the connectors for testing. Handy when you want to find a faulty fan motor or an electrical/control problem.
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Old 07-10-2019, 05:47 PM
  #33  
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Have you tried applying 12v directly to each fan. If one of the fans does continue turning once you spin it by hand it kinda sounds like its a problem with the fan motor itself. I had almost exactly the same issue with my sons 88. We bought a couple of used fans and now everything works perfectly.
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Old 07-11-2019, 09:21 PM
  #34  
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Originally Posted by Mrmerlin View Post
removing the connector from the switch at the front of the radiator, then turning on the key to run will trigger the fans to run.

Touching the two wires together at the top of the intake manifold sensor will cause the fans to run without regard to the key being on.
Report what you see please
So if I touch the two wires together at the top of the manifold, key off and manually pressing the hood ďclosedĒ switch, but nothing happens with the fans, what does that mean?
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Old 07-12-2019, 12:37 AM
  #35  
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the fan system is not being powered.....
at this point please get the WSM and trace out the fan power system,
this will get you back to running.
And you will have a better understanding of how things work on your car,
NOTE simply jumping to guesses will not teach you how to fix your car.
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Old 07-12-2019, 01:04 PM
  #36  
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Originally Posted by Mrmerlin View Post
the fan system is not being powered.....
at this point please get the WSM and trace out the fan power system,
this will get you back to running.
And you will have a better understanding of how things work on your car,
NOTE simply jumping to guesses will not teach you how to fix your car.
I donít have a wsm. And unfortunately even if I did I would need to spend days reading through it and seeking clarification trying to figure it all out.

Surely this is a simple issue, but I havenít found a thread where it was discussed and resolved.
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Old 07-12-2019, 03:24 PM
  #37  
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Originally Posted by Shark2626 View Post
I donít have a wsm. And unfortunately even if I did I would need to spend days reading through it and seeking clarification trying to figure it all out.

Surely this is a simple issue, but I havenít found a thread where it was discussed and resolved.

No time like now to get one..books or on CD.

Dont have to read much, its a few pages of simple steps.

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Old 07-12-2019, 05:11 PM
  #38  
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IF the fans run when temporarily powered with a jumper from the jump post on the fenderwall, you'll want to start at the battery and a couple of the smaller wires that connect to the battery positive cable clamp there. The two fans, the fuel pump and the injectors have dedicated smaller feeders there. Connections need to be shiny and tight. I used a brass "detailer's toothbrush" to burnish the ring terminals and the clamp bolt faces.

Power passes through two dedicated fuses in the CE panel. Usually 28 and 29. There's some voltage-drop testing you can do at the fuses if you suspect they aren't getting or passing current. A needle probe on your voltmeter pokes into the small test holes in the back of each fuse.

From the fuses in the CE panel, power continues to the fan "final stages" module on the front apron. That unit switches power to the fan, according to signals that come from a logic controller in the cabin, under a cover next to the passenger's seat. Diagnosis of controller functions really requires that you have the workshop manual and wiring diagrams so you can isolate the controller itself and test all the inputs.

Things that fail:

-- battery terminal connections are dirty, corroded, or loose. Often we find that the connections come loose while servicing the battery terminals. They tend to corrode too thanks to acid fumes generated when the battery is charged by the alternator or with a separate charger.

-- The fuse holders in the CE panel will melt and distort, making for poor connections at the fuses. Diagnosis is with the DMM and the needle probes described above.

-- The final stages modules fail They use FET switches to pass power to the fans. The FETs have heat sinks and the heat sink paste where they mount dries out. The FETs overheat and fail. Used controllers you might find have the same old paste inside, so the best solution is to find a rbuilt one, where the failed FETs and the paste have been renewed.

-- The controller modules seldom fail, but once in a while we hear of one. Clean conections at the controller elp a lot with function.

-- Clean The Grounds In the Engine Bay and throughout the car. The same clean-shiny-tight requirement exists for the grounds as for any other electrical connection. Your WSM wiring diagrams include a drawing that shows the locations of all of the ground points in 3D space. Disconnect the battery before you start down this path. Ground cleanings have solved a boatload of interesting symptoms in our cars over the years. It's part of a good annual electrical maintenance protocol needed to keep the car happy. A 10mm wrench and socket, that little brass brush, and some patience will get it all taken care of. I paint mine with a coating of Vaseline (petroleum jelly) after they are clean and tight. so they are protected from any corrosive fumes that may waft by.
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Old 07-12-2019, 09:07 PM
  #39  
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The grounds have been properly cleaned and the battery terminal wires are all clean and tight.

The control module on the passenger front bumper has super clean connector, cleaned it anyway and added Deoxit.

I canít seem to see a way to remove the cover to the module next to the passenger seat. It has three empty holes on either end... Under the hatch release **** is a plastic piece thatís also a mystery to me.

The cooling flap relay seemed to not be working so I replaced it with a new one, with the key on the flaps went wild and wouldnít stop cycling so I pulled the fuse.

Ive read that the fog lights being out can be linked to the fans, mine were out. I had a spare scavenged relay, but itís an xxxxxx01 not the xxxxx02 that is supposed to be in the car. Installed that relay anyway and now the fog lights work.

The drivers side fan will work on low speed if I give it a spin. The connector in front of the radiator is currently unplugged.

I just had the AC serviced with fresh freon and itís blowing ice cold air.

The fans were coming on with just turning the key on a week ago, I donít understand what could have changed.
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Old 07-12-2019, 11:01 PM
  #40  
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Fans come on with key on and cold engine only when AC button is depressed. Then the speed is dependent on the pressure in the high side of the AC system. That's the little cylinder transducer on top of the receiver/drier with the ring terminals.

Check the fans final stages module connector to make sure you have batter voltage at the correct terminals 1 and 4 in the connector. You can use a needle probe to test for voltage on both sides of each fan fuse (28 & 29 in my '89 car). With everything connected and the intake temp switch jumpered, you need to see full battery voltage on both sides of both installed fuses for the fans to run. They should be on low speed with key off and intake switch jumpered.

---

I spent the best part of a Sharktoberfest day working on someone's fans that wouldn't run. Everything pointed to a power problem and I was tool-cramped with just a voltmeter. he didn't want to go into the battery well since it was just prep'd for display, but assured me that the battery connections were secured. His controllers worked fine in my car, and I was running out of possibilities. Finally forced him to go into the battery well, where the fan wire connections and battery he'd detailed so carefully were very pretty but were loose. Re-did those and the fans ran. So pardon my jaundiced yellow eye when someone says those are fine. Please double-check.
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Old 07-14-2019, 06:14 PM
  #41  
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Originally Posted by dr bob View Post
Fans come on with key on and cold engine only when AC button is depressed. Then the speed is dependent on the pressure in the high side of the AC system. That's the little cylinder transducer on top of the receiver/drier with the ring terminals.

Check the fans final stages module connector to make sure you have batter voltage at the correct terminals 1 and 4 in the connector. You can use a needle probe to test for voltage on both sides of each fan fuse (28 & 29 in my '89 car). With everything connected and the intake temp switch jumpered, you need to see full battery voltage on both sides of both installed fuses for the fans to run. They should be on low speed with key off and intake switch jumpered.

---

I spent the best part of a Sharktoberfest day working on someone's fans that wouldn't run. Everything pointed to a power problem and I was tool-cramped with just a voltmeter. he didn't want to go into the battery well since it was just prep'd for display, but assured me that the battery connections were secured. His controllers worked fine in my car, and I was running out of possibilities. Finally forced him to go into the battery well, where the fan wire connections and battery he'd detailed so carefully were very pretty but were loose. Re-did those and the fans ran. So pardon my jaundiced yellow eye when someone says those are fine. Please double-check.
I have not been able to do very much today as far as using my multimeter. But I did sand (320 grit), clean, and Deoxit my battery terminal red wire connectors again, and securely retightened to be sure. They cannot get any shinier than they are! 🤣

I hooked up a 12v battery to both fans, the right side came on slow speed for just a second and then wouldnít again, tried it an hour later and it ran perhaps 2-3 seconds and then nothing. The left side would run at slow speed if I gave it a push before I started to notice that I have a cooling fan issue (the connector in front of the radiator lower left side is unplugged), but with the 12v directly attached it runs at full speed.

I have no experience with these systems, and the fans are definitely original to the car. Is it safe to believe that the right fan is completely shot and the left is perhaps fine but very near itís end? And just replace the both, or is there likely something else going on in addition?

Last edited by Shark2626; 07-14-2019 at 06:37 PM.
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Old 07-14-2019, 07:21 PM
  #42  
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smart to replace the fans
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Old 07-14-2019, 07:28 PM
  #43  
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IIRC, Roger has identified some non-Porsche replacement fan motors you can use to replace yours in your existing fan console.

The fan motors themselves suffer when shaft bearings wear, when motor brushes wear, and when the commutator wears to the point that brush contact isn't good. You can buy the bearings (Rollerblade wheel bearings...) and hack the case to install them. You can find "universal" brushes at better industrial hardware places. If the commutator wear is deep there's not much you can do.

Perhaps someone who's been through this will jump in with more details. Search may be your Good Friend.
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Old 07-14-2019, 07:45 PM
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Originally Posted by dr bob View Post
IIRC, Roger has identified some non-Porsche replacement fan motors you can use to replace yours in your existing fan console.

The fan motors themselves suffer when shaft bearings wear, when motor brushes wear, and when the commutator wears to the point that brush contact isn't good. You can buy the bearings (Rollerblade wheel bearings...) and hack the case to install them. You can find "universal" brushes at better industrial hardware places. If the commutator wear is deep there's not much you can do.

Perhaps someone who's been through this will jump in with more details. Search may be your Good Friend.
Phew, Iíve read about the rebuilding on both the 928 and 944 forums. Itís probably easier than it looks. The 944 writeup priced out the parts at $60 per fan, and there are some tools that I donít have that I would need to buy. The 928 writeup was more of a cleaning or tune up without replacing any parts.

The Bosch fan new is available at Partsgeek or eBay for about $142 - $155 and Carid for about $185 (but they guarantee to price match any deal on the Internet). Checked 928srus, 928 specialists, and 928 International but I didnít see any good options. I have no problem using a different brand thatís a direct fit or bolt in piece.

The Bosch part number is W0133-1647404 for reference.

ETA: I searched for a substitute brand that would be a direct (or very close) fit but I didnít find references to any. There are a lot of people putting in new systems of different types but I didnít find any less invasive options other than the Bosch or OEM Porsche, or used.

Last edited by Shark2626; 07-16-2019 at 05:03 PM.
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Old 07-14-2019, 08:29 PM
  #45  
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If I could buy new Bosch fans they would already be ordered.
Get the best parts put them on and forget about your cooling fans.
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