Switch to MSD

[MTURO]

Can I switch to MSD if I have 1991 964 Turbo? I don't know much about the issues if I do. I am trying to simplify the ignition system to increase reliability. I don't trust the turbo control unit have already had some issues regarding loss of power to fuel pumps because of this control unit. I ended up direct wiring the fuel pump relay to ground and using a different + to activate the relay. Any help is appreciated.

[964Cab]

Hi,

I too have that same problem with my 1990 C4 Cab.
I suspect that the DME relay circuit is the problem as the fuel pump
just dies suddenly. In that DME relay are two coils and one coil
goes to the ignition key switch and the other coil goes to the fuel pump.
Somehow the DME gets involved in the mess as well as well as the anti-theft alarm system.

Which terminals did you jumper to get your fuel pump
to behave ? I assume when you turn the car off the fuel pump stops running ?

Many thanks,

Patrick

PS: I too have tried to find a stand-alone ignition system that would bypas the onboard stock DME system.
I believe Motronic makes one but it's for racing ($$$).

[Britwrench]

The first thing to do is to diagnose the actual problem you have.
You can replace all the parts in the world, but if the fault is in the wiring or some other part not changed...you will still have the same problem. There are thousands of 964s and many 965s running around with stock set-ups.. The DME relay should be changed every 5 years anyway. On the turbo, sounds like you need to have some more diagnosis done before condeming any particular part.

[964Cab]

I just spoke with a Porsch Tech who has a '90 C2 customer car
in his shop and he got permission from it's owner to plug his DME brain in my '90 C4 to see if that cures my sudden loss of high volatge to all the plugs at once problem.

Hopefully that test will done today around 5pm or at the latest tomorrow.

The Porsche Tech also noted that high voltage coils and their companion high volatge controllers either work or they don't and don't usually enter into an "intermittent" phase of operation.

All eyes now are looking at the DME brain as the problem ($$$$).

Here is what I've done so far to no avail:

Rebuild factory twin dist installed ($253 from Hendricks Porsche with core)

Took the Masss Air Flow Sensor 4 pin connector off to force the DME brain into "emergency
limp home" mode and the problem still ocurrs.

Made sure the Mass Air Flow Sensor flapper moves freely with no hang ups.

New Caps and Rotor (time two)

On my 3rd DME relay.

Rewired an old working DME relay so the fuel pump was forced ON and still the high volatge dies (intermittently).

Ck'd all the ground points except the hard to see and reach starter to trans ground strap.


Thanks,

Patrick

PS: When the car is running it's running beautiful and that DME "brain" does a great job of monitoring the fuel/air ratio wonderfully. At cold starts it's beautiful and yields a rock steady idle. At hot starts it wonderful, instant starts. Never floods, never misfires, no pinging ever (94 Sunoco). At 4k rpm in 4th gear the sounds are music. But when the high voltage dies to the plugs it's very frustrating to say the least.

[Britwrench]

I would not plug another ECU into your car. If there is a wiring or other fault in your 911, which has damaged the control unit, then there will be two damaged units. Always plug the suspect one into a known good car and then run the Bosch hammer test.

If you have a lack of voltage to the fuel pump, it is entirely possible the alarm system is causing it. Do you have the factory alarm or an aftermarket one?

The coils and amplifiers can be faulty and still work; last week we chanegd the coils on a 91 C4 that had a running fault. The coil was causing the engine to cut out at idle and run rough.

BTW on all early C4s you should change the brake pump relay and ABS relay as preventative maintenance. The pump relay can stick and burn out the motor ($2000)

[964Cab]

Thanks BritWrench:

Hopefully in an hr I'll make the trek to see what the "brain" swap yields
and I'll suggest what you noted as I'd hate to deep-6 the other owner's
"brain" !

I have the factory stock alram systems. I didn't know I had
such a system until a few days ago I accidently set the
alarm off and the horn kept beeping until I re-opened the door
with the key.

Even if I force the fuel pump to stay ON (via a wiring mod to an old DME relay)
I still intermittenly loose high voltage to all the plugs at once. But when that DME
relay shuts off, even with the fuel pump still getting + volts and humming,
the car still dies from high voltage to the plugs.

I called the Porsche dealer and they noted that the ABS system has numerous
relays and couldn't tell me which one I should change. They noted one relay called the
"ABS Relay" at $75 part number: 928-615-124-01 and another called the "Terminal X"
relay at $23 part umber 928-615-111-01 Do you have the part numbers of the required ABS
relays that should be changed ?

I neglected to say that I also have the intermittent "XMAS Tree"
effect where all the warning lamps light up on the dash in an intermittent fashion.
Plus, that audio alarm goes off (intermittently) ! No wonder my "friend" was so keen
on selling me the car although I did pay a great price.
I should also mention that this whole mess started when I took off the DME brain connector
to measure some resistance values while scoping out a problem with lack of warm
heater air from the rear blower motor. I now have heater operation (bad ballast resistor)
but upon reconnecting the DME brain connector the DME has never been the same since
and yes, I did disconnect the DME brain connector with the ignition OFF but I left the
battery still grounded.

Take care,

Patrick

PS: I've read that the 993 4 wheel system can be adapted to fit in the 964 although one
must retain the rear suspension and just use the 993 1/2 shafts.

[Britwrench]

The pump relay is 946 615 135 00
The ABS relay is 928 615 124 01

If all of you warning lights are coming on; this indicates a voltage or interference problem.

If you have a faulty ignition wire, this can and will set off the warnign lights. With the engine running, remove one of the amplifier unit plugs (this makes the engine run on one set of plugs) and check the running.. should be smooth, if not you have a problem.

Check the alternator and charging system, there has been a problem with the wiring harness to the alternator melting, this could cause you warning light and running fault.
Remove the alternator to access the wires and carefully inspect for burnt or melted parts.

The audio alarm is for low brake pressure. This can be caused by the switch on the boost pump. Your Porsche shop can check this.

[964Cab]

Thanks Britwrench: Do both of those relays you noted go on the
fuse panel relay panel (where the DMe relay is) ?

Regarding the possibility of a bad alt wiring. I took the alternator belt off
and so thus the alt was out of the circuit (?) and the problem still persist.

I ck'd the ground under the driver seat and it's fine. I ck'd all
the grounds points with the exception of that ground strap that go from
the starter to the trans housing (can't get to it). All the grounds points I
could access were perfect.

I ck'd the + volts status from the DMe relay (with a jumper)
to the DMe brain and the brain is always getting that required
+ volts from the DME relay (with the ignition on of course).
So the DMe relay circuit isn't the problem.

I took the "central informer" out of the dash to kill that
annoying LOUD audio alarm and all those XMAS tree effects. I'll deal with that
problem after I get this loss of high volatage to the 12 plugs condition
sorted out.

That "brain" swap should take place in an hr.

What mystery "bolt" where you referring too ?

Thanks,

Patrick

[Britwrench]

Both of the relays are in the relay board.

I would remove the cowling and inspect the wiring to the alternator, removing the belt does not disconnect the wiring.

Voltage and amperage are different animals, you may have 12v but not enough current to power the particular unit.

The central informer is not setting off your lights, if ALL of the lights come on there is a another problem.

When the car was checked with the Bosch tester, what fault codes were listed?

[964Cab]

Thanks Britwrench,

I went to the Porsche Tech and he plqced my DME "brain" into
another client's 964; it ran perfect with no problems.

But when I put my DMe "brain" back into my car my problems still
exists.

I got my car to start and run but it's very difficult as the car often looses
high voltage to all the plugs at once.

Today I'll try and see if the Porsche Tech will let me try his client's 964 in my
car.

Thanks

Patrick

[Britwrench]

If installing your ECU in another car and carrying out the system adaptiona nd fault memory check revealed no problems then your ECU is probably ok. You still need to diagnose the fault.. How did you actually determine that voltage was lost to the plugs?

If you are certain that it is an ignition fault then I would suggest that either the coils or the amplifiers are faulty. This needs further careful diagnosis to locate the actual fault.

[964Cab]

Hi Britwrench:


Actually when the tech did my DMe "brain" test in another clients car he
didn't run the Hammer to see if any faults were present. He and I just heard the
engine run at idle and he rev'd it up while in the shop and it sounded perfect so
my DMe brain was deemed by the tech as "fine".

I actually don't know for fact that the 12 plugs are losing a spark but the way the car
acts its asi if all the plugs all lose juice suddenly at once in an intermittent fashion. Does it sometimes at idle and also while driving and if driving the car always restartes itself with a sudden jerking motion.

When the engine dies it's to late to see if there is a spark. Would there be a spark
at the plugs after the problem happened ? For example, is the DMe "brain" still pulsing the ignition
coils even after the car dies ?

I have ordered and will get in the mail this Friday two news ignition coils and
2 ignition ignitors. Hopefully that will solve the problem.

If it doesn't I'll consider a new alt even though when I take the alt belt off the problem
still exists.

I even shorted via jumpers the DMe relay and the problem still continues.

I even ran a wire directly from the battery to each igntion coil (through a "kill switch")
and the problem continues.

I have already installed a rebuilt twin dist, new O2 sensor. I have disconnected the
air flow sensor to see what happens (forces "limp home mode") and the problem still continues.

I ck'd all the ground points except the started to trans ground point but my car
starts fine so I assume the ground point at the starter to trans is good.

Thanks for trying to help,

Patrick

[beetos]

964Cab
Whats the latest? did you get it fixed, if so was it the coils / ams.
Thanks