Adrian

Dear Randall,
Now you ask a difficult question. Depends a lot on what model you have. 1991 models technically require no mods to install the 993 unit because they should have the updated 964 unit already. However I have found this not to be the case in al parts of the world and with RHD 964s found in Singapore, Australia, Hong Kong etc. For 1989 and 1990 models one has to modify the connector and install a jumper lead. All I can recommend you do is plug the new unit in and make sure everything works. If it doesn't we will have to work things out from there. Wish I could be more certain but I worked for some weeks helping a few people out of this confusion,
Ciao,
Adrian
911C4

Randall G.

Hi Adrian,

>1991 models technically require no mods to install the 993 unit because they should have the updated 964 unit already.

>For 1989 and 1990 models one has to modify the connector and install a jumper lead.

This is consistent with what Kenn at Hendricks Porsche told me, so I should be fine. Also, the CCU I've bought is sold by the factory as the update for my model, so it should either be exact or close. Anyway, as you suggest, I'll just plug it in and see what happens. At worst, it will take a little tweaking. I'll post on whether or not it turns out to be "plug and play."

Thanks!

964Cab

Adrian and Randall:

I have a '94 Service Technik Porsche manual that descibes the 993 CCU as working fine in a 964 no matter what year 964. However, that "Max" A/C mode doesn't provide any more A/C like it does in a 993. Also, the cabin air vents are not turned off when the car is in reverse like a 993 does with it's on board 993 CCU. Other than those changes my Porcshe lit doesn't state any other issues.

Adrian (a question):

I have a sudden loss of high voltage to all the plugs at once. Can happen at idle or while driving. No misfiring, just a sudden loss of high volatge to all the plugs at once. At idle when the problems occurs the car just dies and all the lights stay normal, no flicker in the lights. Car can always be restarted, can start in no in cold and warm situations. Idles perfect and runs perfect until the high volatge to the plugs cuts out (but why ?). When the high voltage dies at hiway speeds the car always re-starts itself with a sudden "jerk" motion that resembles a "push-shove" start.

Here is a list of what I have done to no avail:

Replaced twin dist with a factory rebuild from Hendricks ($253 with exchange). New caps and rotors. Made sure no spark plug wires were aching.

Took off the Mass Air Sensor 4 pin connector to force the DME in "emergency limp home" mode and the problem still exists. Checked the flapper in the air sensor and it moves as normal with no hang ups.

I'm on my 3rd DME relay.

I took an old working DME relay and wired it to force the fuel pump on all the time and the problem still continues even with the fuel pump forced ON.

Don't know what else to do, any ideas ?

Curious if you have any knowledge of the after market stand alone ignition systems for the 964 that bypass the whole 964 stock DME ?

Many thanks,

Patrick

Randall G.

Okay, just to add to the confusion, I called Hendricks to get more info on the CCU vs. model year:

-A "plug and play" CCU is no longer sold for the '89-90 model. There's a note in the part's catalog (PET) specifying that such-and-such jumper/modifications are to be used in conjunction with the updated part #.

-The part # for the '91-94 CCU is 993-659-047-00. No note about having to install a jumper, etc., so appears to be plug & play (at least in the US).

-The part # changes for the '95-98 model years. Actually, only the suffix changes, from 00 to 01 = 993-659-047-01.

So, Porsche is currently selling two CCU types for the 964/993, both with 993 prefixes. One for 964s (which must be modified to fit 89/90 models), and another for 993s.

Now, perhaps there is a way to modify a 993 unit to work on a 964, if one was to find a used unit at an attractive price. However, Kenn at Hendricks didn't know what would need to be done (if anything), and neither do I.

MikeF

Randall,

There is a note in my manual that refers to adding a jumper from G1 to G19 when adding a new CCU on models prior to 1991. Specifically it reads:

"On vehicles prior to 1991, the heater/
ac unit wiring loom must be modified if a new heating/ AC regulator with index 01 is fitted. A jumper that connects pin 19 of connector G to pin 1 must be fitted."

There is a "note" following these instructions that reads:

"If the jumper is missing, a fault (Fault Code 46 and 47) on the missing left-hand rear blower is detected and the left-hand heater blower will therefore ooperate at reduced speed while the heater is on."

Hope this helps.

Good luck,

Adrian

Dear Patrick,
The information you have I am afraid is completely false. Mike posts the data. It is clearly identified in the Carrera 4 Maintenance Manual and seeing I have helped a number of people directly with this problem, I know it exists and in some cases cannot easily be solved. The 1989 and 1990 964s have a different wiring set up to the 1991 models. This is also different between some RHD models.
Loss of high voltage is obviously related to the coils. The voltage to the coils is controlled by the DME. I would suggest you look at your DME connector. It is possible that both coils are damaged. Maybe a bad earth connection on the ignition coil assy.
The only other item I know which could cause this is the knock sensors retarding the spark. I would check that your knock sensors are working.
Ciao,
Adrian
911C4

Randall G.

Following up on what Mike and Adrian has written, I took a look at the wiring diagrams for the '90/'91 models:

-G19--from the CCU--terminates at the rear-blower relay fast-speed power output. It appears to be some sort of voltage feedback? It's not the main power supply, and it isn't the control signal.

-On the '91 wiring diagram, G1 also terminates at the relay fast-speed power output.

-On the '90 wiring diagram, only G19 terminates at the relay fast-speed power output.

-By shorting together G1 & G19 on a pre-91 model, you've made it (electrically) equivalent to a '91+ model.

So, I understand this part. But why the distinction about the 01 index (which I assume refers to the suffix)? If I understood Kenn at Hendricks correctly, 00 suffix is for a '91-94 964, same part number with 01 is for the 993. So, why not simply buy a 964 CCU and install it in your pre-91 964? It appears to me that a 00 suffix CCU for a '91-94 CCU would need the G1-G19 jumper to work properly on a pre-91 964, not just a 993 (01) unit.

I think I need to take a harder look at my PET this afternoon. It sure would be educational to have a '90, '91 and '95 CCU in hand for a physical comparison of the pin connectors, as well.

Randall G.

Hello,

Well, after staring at the PET long enough, as well as the section in the manual Mike speaks of above, I think I've finally got this straight. I'll do my best to explain:

-The original part number for an '89-90 964 CCU has a 964 prefix, and a 00 suffix.

-In '91, the part number still had a 964 prefix, but the suffix changed to 01.

-The old 964 CCU part numbers have all been superseded by a 993 part number, with a 00 suffix.

-The 993 models use the same part number as a 964, but with a 01 suffix. Just as Kenn at Hendricks explained to me.

Here's where I think the confusion lies. When the manual speaks of the 01 suffix, it's with respect to the old 964 part number. I believe it needs to be updated to also refer to the new 993 prefix part, which does not have a 01 suffix.

Bottom line, if you own an '89-90 964, and you buy a new CCU--or install a used unit from a newer 964--you'll need to install the jumper.

Make sense?

BTW, having just read the manual, I can say that the jumper that must be installed is about as simple as can be. Just like it sounds, a wire from G1 to G19.

Finally, I don't know for certain what will happen if you install a 993 unit in an earlier (not necessarily '89/90) model car.

Bill L Seifert

I just had a major service on my 1991 CII Cab, and the fault thingie said the same thing on mine, and all of the fans were working. My tech says this happens all the time, but he had not idea why. He is not at a dealer, but he is very trustworthy. He said about 80% of the 964's do this. So, I didn't worry about it, but you never know. This is why I hate computers.

Bill Seifert

1991 CII Cab
1983 944 race car

Adrian

Dear Bill,
I would ask your mechanic which software he is using. As the systems were modified, so was the Bosch Hammer software. I believe there were six software updates issued by Bosch. If your mechanic is not using the correct software package for your 964 then this fault can happen.
For the 1991 model year the aircon system was redesigned. Using pre 1991 model year software will produce these faults.
Ciao,
Adrian
911C4

JOHNPAUL

I own a 90 C4 cab and have been following this thread ... The thing that caught my attention was when the A.C. is on the condensor fan cycles ...About 3 months ago I had a blown fuse and the AC stoped working replaced the fuse and I thought all was fine ,I think that the resistor for the condenser blower shorted and now has opened .. Also
I changed the oil last week and thought I should check the operation of the oil cooler fan , Being winter in Utah (with no lower cover) The car never reaches 8'Oclock and I can't remenber the last time I heard the cooler fan kick in , ....Low speed never works The fan will only turn on after the temp sensor reaches 10 o'clock then it blows like a mother ...
I'm Planning on picking up the parts (resistors for AC and oil cooler) from the dealer next week , unless there is another source ? Thanks for the help

Randall G.

Hi John,

You might want to verify your oil cooler fan resistor is bad before buying a new one. Have you performed the jumper test yet? Or, checked the resistance? While you're at it, you might as well check the A/C condenser fan resistor (although it sounds like it's definitely bad).

The oil cooler fan kicking in at 10:00 and "blowing like a mother" sounds like fast-speed operation. The oil cooler fan is supposed to start in fast-speed at 239F. The fact that the fan starts in fast-speed means your temperature sensor is probably okay.

Best of luck!