GP964

Hi folks,

Is there a proper procedure that is suppose to be done before i can disconnect my DME?
If so how?

I have a LWF,ring gear, waiting in my garage, how many teeth are suppose to be on a LWF (german made), and how many on the ring gear.

I have a 90 C2 US version.

Thanks

Adrian

Guys, lots of questions here to answer. First to the DME part number question. It is not until the 1992 model series of the 964 that the DME had just one part number (except the 964RS and the Taiwanese model). Up until then it is almost impossible to say what you should have. There were eight DME part number changes between 1989 and 1991. The 911-XXX-XXX-04 was the last of the modified 911 DME units. Then the part number switched to a 964 number. Unfortunately it appears that Porsche used up one stock and then moved to the new part number. USA versions appear to have got the new numbers before the rest. California models first.
Now to the condenser fan "high speed". This is controlled by the pressure switch. When the pressure in the system gets to high, it means the freon vapour is of too high pressure (too hot) and the fan cranks up to cool it down more.
As far as teeth on timing rings, I believe there are the same number. It is the pitch of the teeth that is changed and the pickup gap and number of teeth used as pick ups that are changed. No more data is available I am afraid because this is "internal data for Porsche and Bosch only". Maybe one of the tuner companies may know this data.
Now to the DME and XMAS tree problem. This is a toughie. I will need to think more about this. The XMAS tree effect is normally tied up with arcing ignition leads. Especially the low set of leads inducing an emf into the 964 cable system.
The warnings are all controlled by the central informer, except the airbag and seat belt warns (which are supposed to come on together). Worse case scenario is that the whole system has been zapped. I would certainly be checking out the electrical systems. I would also be checking out the alternator condensor (radio filter) as well to see if this is disconnected. This type of problem is very hard to work on in cyberspace. Maybe Patrick you could record the actual warning lights that come on. This may help identify something else that is in common with them.
How can you check the ignition coils. Well the only way really is to check by pulling off a top and bottom spark plug and check that they are working and creating a spark. The DME controls the voltage supply to the coils.
Now slant, with your problem. It may well be a failed knock sensor. Your timing may be retarded by 6 degrees and you have no advance movement in your timing. However I would have your airconditioning system checked out as well. It may be running at over pressure due to a dirty condenser. This is not uncommon.
The LH Blower fan is the 1-4 speed controlled fan. The RH Blower fan is the defrost fan.
Troubleshooting and confirming the correct operation of each and every component will have to be carried out. Assuming without proving can be costly in time and expense.
I do not want you to get into shot gunning and replacing components. Does the system work correctly in fan positions 1 to 3 and only problems occur at position 4. This may indicate a failing LH Blower motor. Excessive current draw.
The battery powers the 964 not the alternator. The Alt has to supply the charge current. The Alternator is a 115VA (AC rated) unit. I would certainly be checking the capacity of your battery. Something we haven't mentioned yet. We found a couple of 964 owners in England recently who had 45AmpHr batteries installed and ran into severe problems.
I think for now that this reply is long enough. I am concerned that the PO replaced all these items 8 months ago. Maybe the problem was already there.
Hooking up the Bosch Hammer and doing a full DME diagnostic maybe helpful. Somehow though I think it will not tell you much. Have you checked out the O2 sensor. Remote chance but at least check out the wiring,
Ciao,
Adrian
911C4

phil@tech9

The teeth on the LWF and the standard versions are the same.

The sensor sends back the signal to the ECU that it has counted 58 teeth with 'two missing' as the reference point.

964Cab

Adrian and Slant, et al:

Slant, I don't know how but I seem to have a DME brain that didn't come with the car new. I'm the 3rd owner and the "brain" digit ends in -04 (911-618-124-04). Adrian noted that that's the last of the 911# DMEs. My car is a 1990 C4 Cab USA model and never been in Calif. (the car that is).

Adrian: The airbag and seat belt always on problem is recent as of 3 days ago and caused by me somehow when I was trying to solve the XMAS tree effect and audio alarm (a 4 month intermittent problem).

Today I removed both coil protective plastic caps off and tested each coil's primary and secondary resistance in ohms. The primary and secondary resistance are in the coil itself. I think they (Porsche) mean primary winding resistance and secondary winding resistance (not sure). Anyway, the main dist coil had good primary and secondary ohms at 0.5 and 5.5kilo-Ohms respectively. However, the "wiper" dist (driven by rubber belt) had only rock steady secondary resistance but intermittent primary resistance. I'll order a new coil for the "wiper" dist and see what happens regarding the sudden loss of high volatge to the 12 plugs at once problem (intermittent).

XMAS tree effect: None of the spark plugs are arching. The alt and battery are fine, no lights dimming, etc. Always bright lights. The radio however is non-Porsche and has no place for that radio alarm wire(s) which are now just janging free; could that be the problem ? Where is that "alt condensor" you mentioned ? (radio filter), is that in the engine bay ?

Adrian: What's the proper way to remove the DME brain and to "teach it" new sensor parameters ?

Many thanks,

Patrick

964Cab

Me again:

Adrian:

Here is the intermittent alarms fault XMAS Tree problem:

High pitched audio alarm, traction light, ABS light, brake light and Park Brake light, washer fluid, fuel level warning, Pad Sensor fault, spoiler fault, Oil Level warning, and lastlky Alt Belt fault. All these are on or off but as a group intermittently. Less so at idle than while driving. Once the audio alarm joins the above noted group of faults the alarms stay on until the car is restarted anew.

Always on faults: Achtung lamp, seat belt lamp, and air bag lamp.

I think, but not sure, but doesn't only the 964 Turbo have the radio suppression part in the engine fuse box area ? I can't find same on my '90 C4 Cab (non-Turbo).

Take care,

Patrick

slant911

Did not get a chance today even though it was part of my new year's resolution to check out the controls part number. When I get to it this coming weekend I'm planning on checking that, the O2 sensor, and cylinder head temp sensor. I'll try and verify that I'm getting correct voltage/resistance/etc... and report back.

Patrick,

Seems weird that we have virtually the same model other than that yours is NOT a CA version. According to sources I've seen, my DME part number is correct for the year. It appears you have something other than stock unit.

Randall G.

Hi Slant, Patrick,

Please find below PET DME Illustrations.

The way I read this, Patrick has an updated (most current) DME, and Slant still has his original unit.

Adrian

Dear Randall,
You want to be really careful posting PET data into the public domain like this. You may incur the wrath of the owner.
The 964 series of DMEs are the latest "NOT" the 911 series.
Patrick,
Your Christmas tree effect looks like an ignition problem to me. I suggest that you carry out a visual inspection of the looms in the engine, especially around clamps. Check that none of these clamps have chaffed through the wiring. The warn horn and master warn light will go off when any major warn is activated. Something is activating all these warns. They are all exclusively earth seeking so it suggest a chaffed set of wires and or ignition arcing from damaged ignition leads. Could well be a combination.
For the airbag you may well have disconnected part of the circuit with power "ON". This will activate the warning. The only way to clear this is, is a Hammer Reset. No other possibility I am afraid. I suggest this will fix your airbag problem.
To reset the DME you do not need to disconnect it. You just disconnect the battery, leave it off for 20 minutes. Then reconnect and go for a drive. You are not teaching the DME any new parameters. You are telling the DME which MAPS you like to use and the DME transfers these maps into a volatile memory.
Every auto has a condensor or radio filter. Some have additional suppressors. Mine is bolted to the alternator.
We have almost three threads going here. May I suggest that they be split up. Please email me privately with these descriptions.
I am afraid that both of you, Slant and Patrick have some troublesome problems here which are going to be tough to fix over cyberspace,
Ciao,
Adrian
911C4

964Cab

Thanks Randall for posting that DME data. Looks like my DMe brain is for a 964 with the following factory techs: X64.03, X64.01, and X114. Now if I only knew what they mean ? I assume one is for the 5spd trans versus a Tip ? My car is a 5spd.

I have a new ignition coil on it's way from Porsche and hopefully that will cure my ignition problem. I know it has two coils of course but one of yhem is showing intermittent primary coil resistance from open to normal (500 ohms).

Adrian: My XMAS Tree effect has to be related to something common to all those faults. It might be a faulty "central informer" as when I unplug the latter the XMAS Tree effect goes away of course.

Patrick

Randall G.

Hi Patrick,

Considering all the poking, prodding, disconnecting and reconnecting your DME and clock have undergone, it seems to me that you won't be able to say what's bad until you've given a tech. with a hammer a chance to clear all the errors.

As you know from my own recent experience--and as Adrian has indicated--the airbag light won't be going anywhere until it's reset with a hammer. Perhaps you'll have luck resetting the XMas tree lights using Adrian's suggestion?

Best of luck!

964Cab

Hi Randall:

I tried Adrians' suggestion regarding disconnecting the negative battery terminal, waiting 20 minutes, then disconnecting the DME brain and checking the contacts. Then I reconnected the DME brain and drove but the problem still continues.

Today, eager to drive to the Porsche tech to try another donor car's same year C4 DME brain in my problematic C4 '90 I found that I couldn't even be driven out of the parking lot. It seems the problem has progressed to the point that it's not driveable ! The idle now is terrible, lots of dramatic hunting and it just dies. I can't even get it into 1st gear with it cutting off. So the Porsche Tech said to just take the DME brain out and bring it to him and he is willing to try it in a working same year car he has in his shop (tomorrow afternoon). If that test proves my '90 C4 DME brain is functioning OK then I guess my alt could be the problem as now the lights do dim when the car is hunting. I thought one of the two ignition coil primary windings was intermittently open but now I find that the coil is good but my ability to keep the ohm meter terminals on the coil stud-nuts was erratic and thus I had a false positive reading.

At least now the problem has gotten so bad it's no longer "intermittent" but rather "chronic" and thus hopefully that will hasten it's diagnosis ? I'll know more tomorrow. I just hope the engine itself is OK and I don't have a bent valve or something worse !!!

I priced a factory rebuilt alt and it was $492 (rebuilt and my old core exchange) with a two year Porsche factory warranty. FYI: A new DME brain from Porsche is $1,400 !!!

Patrick

964Cab

I forgot to add that last week I took the alt belt off and the problem continued so I assumed that the alt must not be involved. But now I think maybe it is somehow.

Patrick

Adrian

Dear Patrick,
This is certainly starting to get serious. I wish I could help more but it is very tough over cyberspace.
I somehow think your DME will check out fine. I would suggest a fuel supply problem. Fuel pump, maybe even a fuel filter. I do not think this is related to the alternator because the DME will work off a nominally charged battery for a while.
I would also check the knock sensor circuits. I do not think they will kill your C4 like this though.
I wish you luck,
Ciao,
Adrian
911C4

964Cab

Hi everyone,

Well I'm happy as I just got back from the
Porsche Tech where I had taken my problematic 1990 C4 Cab (USA) 5spd DME "brain" (#911---04) and plugged it into a known working donor car that he had just worked on (Donar car: 1990 C2 Cab 5 spd with a #964----02 "brain"). Thus, my "brain" is fine and so my car has another problem. That's a relief as a new "brain" is $1,400.

The car can at times idle perfect but only for maybe 10 seconds. And then the idle gets lumpy for a few secondas and then the engine dies. I can always restart the car but can't drive it as the problem has worsened and the car would die every 20 feet. In the engine area I hear a clicking song from the throttle body area. Sounds like a relay click but I don't think there are any relays in the engine are there ? The Porsche Tech said maybe my Mass Air Flow Sensor if bad even though it yields satisfactory ohms values at the DME brain connector.

As as test I took the bottom dist hi voltage feed off and the car won't run but will try to start. I then tried to run the car on only the bottom dist but again the car would try to start but wouldn't run. So the proble, whatever it is, is common to both distribitors.

Thanks,

Patrick

Adrian

Dear Patrick,
Time Zones are going to play havoc hear but I would clearly check the fuel delivery system pressure. Fuel filter.
Is this when the engine is stone cold or just when the engine is hot, or all the time.
The Mass Aurflow Sensor may be jammed shut. Oil contaminated. I would certainly be checking this. I would also be checking the connector to the airflow sensor. Make sure the wiring is intact.
I am sure it is an input to the DME or the fuel.
I guess you have already checked the secondary distributor belt. The O2 sensor would be suspect if the problem was after around 90 seconds of running.
I am afraid you are going to have to isolate the problem. Did you happen to use any additives in your fuel to clean the injectors,
Ciao,
Adrian
911C4