Volla

Ok, Here is my problem:

Randomly my 928 (88 s4 auto) will work like a dream, then suddenly wont start, or while driving it will cut out. When it wont start it cranks good and fast, but no spark

I have done the following basic stuff:

Cleaned all ground points
Cleaned all fuses
Replaced all relays
Cleaned connectors in CE
Checked battery earth strap

Further, I have determined that the car dies because there is no spark. The output from the EZK to my LH stops giving the crank pulses. When the EZK is giving pulses to the LH then the car works 100%.

I have opened the EZK and probed directly on the pins of the EZK connector (to eliminate wiring harnass problems) and there is no output pulses.

Further:

The EZK gets power
The EZK is grounded
The Alarm is bridged out (connected black/red wire (B23) to yellow wire (F25) at CE)
The CPS is giving the correct signal to the EZK when cranking when it doesnt want to start (confirmed with scope).
Engine temp sender to EZK and LH is giving correct readings
Have a "new" confirmed to work EZK unit that i replaced mine with and still it gives the exact same problems
Has happened when car is cold and hot (happened while driving for about 60km as well as fresh start on cold morning)
The rest of my electronics on the car still works 100% when car dies: the gauges, my LH unit the radio everything keeps on going except the engine stops or wont start.

I will be more than happy if anyone here can give me a suggestion as to what I can check or anything else that I can do to figure out what is causing this!



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19?? VW Baja Bug (Completely custom, Golf 1.8 motor, and many, many mods) - Currently my daily drive
1988 Porsche 928 S4 Euro/ROW (Black with Ivory interior) - Under ECU surgery
1982 Porsche 924 Euro (Silver with cream interior)- Gone
1982 Porsche 928 S (Manual) Euro (Petrol Blue with Blue with black and white chequered interior) - Gone
1983 Porsche 928 S (Auto, NA spec, Red, black interior) - Gone
1994 BMW 530i Manual (Maroon, grey interior) - Gone

Landseer

I guess you looked hard for twisted/damaged wires at bosch connectors for MAF, CPS and the injectors? (We've seen that bring S4 sharks down in a random way as the wires (presumeably) change orientation slightly with heat during driving. Personally have limited experience beyond that to help.)

Volla

Thanks for the info, must also add that the MAF is a reconditioned unit and that it's signal gets to the LH perfectly.

When I had the scope on the EZK connector pin coming from the CPS (with the EZK open measuring at the actual pin) the signal was perfect, but still wont start.

What other sensor (or lack thereof) will cause an EZK not to send spark?

==================================================
19?? VW Baja Bug (Completely custom, Golf 1.8 motor, and many, many mods) - Currently my daily drive
1988 Porsche 928 S4 Euro/ROW (Black with Ivory interior) - Under ECU surgery
1982 Porsche 924 Euro (Silver with cream interior)- Gone
1982 Porsche 928 S (Manual) Euro (Petrol Blue with Blue with black and white chequered interior) - Gone
1983 Porsche 928 S (Auto, NA spec, Red, black interior) - Gone
1994 BMW 530i Manual (Maroon, grey interior) - Gone

UKKid35

Perhaps the EZK is failing, it is unusual but it has been known.

Volla

Thought of that, and got a second EZK that is tested on another 928 and works. But that did not make a difference. That is what is leading me to suspect some sensor input that will make the EZK think that the engine is not turning or putting it into a safety shut down mode killing both banks.

==================================================
19?? VW Baja Bug (Completely custom, Golf 1.8 motor, and many, many mods) - Currently my daily drive
1988 Porsche 928 S4 Euro/ROW (Black with Ivory interior) - Under ECU surgery
1982 Porsche 924 Euro (Silver with cream interior)- Gone
1982 Porsche 928 S (Manual) Euro (Petrol Blue with Blue with black and white chequered interior) - Gone
1983 Porsche 928 S (Auto, NA spec, Red, black interior) - Gone
1994 BMW 530i Manual (Maroon, grey interior) - Gone

AO

Sounds like a relay. 3 or 4 relays to look at: Fuel pump, EZK, and LH. Ignition relay could also come into play, but it's usually one of the first three.

Volla

Will swop out the relays and test, but all of those relays are brand new. The error happened before and after relay change.

Will double check them all tonight and verify that power is going to the EZK. The Fuel pump, LH and Ignition relays all work 100%

==================================================
19?? VW Baja Bug (Completely custom, Golf 1.8 motor, and many, many mods) - Currently my daily drive
1988 Porsche 928 S4 Euro/ROW (Black with Ivory interior) - Under ECU surgery
1982 Porsche 924 Euro (Silver with cream interior)- Gone
1982 Porsche 928 S (Manual) Euro (Petrol Blue with Blue with black and white chequered interior) - Gone
1983 Porsche 928 S (Auto, NA spec, Red, black interior) - Gone
1994 BMW 530i Manual (Maroon, grey interior) - Gone
Volla is online now Report Post Edit/Delete Message

AO

Okay then, how about the Ignition switch?

LVPAVING

Had a similar problem on MY 89 A/T, replacing the CPS cured the problem.

fraggle

How long does the condition last? Mine seems to cut for no reason but it starts right back up. I also get a surgining idle on mine that comes and goes. I'm not sure if they are related.

Lizard928

Your troubleshooting has been fairly thorough.

I have seen a number of these failures you are experiencing. They have all been caused by old and bad CPS or Reference sensors. You do not list that this part has been changed either. So I would recommend without further hesitation that you replace the CPS.

The MAF, and injector wires will take out fuel not spark, so ignore those for now.
As well, I know you say that you have scoped the output signal, but from my experience, I can tell you that could still be the problem.

BPG_Austin

CPS stands for (blank blank) sensor?
Colin which reference sensor are you speaking of? Can't find CPS or reference sensor on 928 international website.

BPG_Austin

crank positioning sensor.

Landseer

Check back of CE panel for subtle melts that can drop the voltage to the relays andrew mentioned. Seen this happen twice now. When separated, the intersected wires each showed a tiny bit of copper at their inappropriate junction.

When you say all grounds, did you include the ones buried in the very back of the S4 block valley, under the fuel regulator & damper (hidden)? There, and not the visible grounds on the firewall above the CE panel, is where the electronics are grounded.

Stromius

Volla - Are you able to see if the connector from the CPS pigtail to harness is not broken or fractured? Might be why you get intermittent issues.