Brett Jenkins

I'm back on the widebody now, trying to get it to start after removing the VEMS/CoP setup and going back to LH/EZK. Car is an 85, engine and harness are 89, LH/EZK is from an 87. My issues are these: fuel pump doesn't prime when ignition is turned on and no spark to ignition wires. If I jumper the fuel pump relay, the pump will run, but still no spark. 2 separate issues, perhaps?
Going back to stock, all new coils, rotors, caps, new plugs and plug wires, new ignition amps, All sensors on the engine were replaced during the VEMS installation.
I have done the following to troubleshoot:
New, fully charged battery.
All new #53 relays, all bench tested before replacing. New, good fuses in all the relevant spots.
Tried 2 different LH and EZK.
Tach jumps past max when cranking, doesn't bounce. CPS is new. I verified resistance between +/- and +/shield. I scoped pins 23 and 6 on the EZK to verify the CPS and got a solid reading.
I have 12v on the coils with key on and the meter ground to body. If I ground meter to the other side of the coil, I never get 12v, key on or cranking. Am I right in thinking the ignition amps ground the coil?
I verified 12v with key on for relay slot 30 on the ignition, EZK, FP, and LH relays, as well as 12v with key off on the LH relay. Not sure how else to test that the relays are doing what they are supposed to be doing, though.
I do think I smell some fuel after cranking a bit, but that could be my imagination. I will pull a plug and see if it's wet. Since it's probably 2 issues, I'll pull the fuel pump fuse to try to figure out the spark issue, if that makes sense.
I think what I need is a bit of an education on the sequence of events that occurs between turning the key and the car starting. Could someone explain to me in simple terms what happens? IE, a certain relay is triggered, which triggers another, etc, or perhaps step one is something from the LH/EZK, or?

It has been pointed out that S4's don't prime the fuel pump, so even though it did with VEMS setup, this might be normal for the stock setup.

Kevin in Atlanta

89 Harness

Have you jumpered the ignition protection relay at the computers?

No relay - no start.

FredR

This depends on whether this "mongrol build" has cats or not as the case may be. If no cats are fitted then the indexing plug needs to be configured correctly to tell the brains what is going on. Whether this is the problem [or not] remains to be seen but given the original car is an 85....?

Kevin in Atlanta

No, he mentioned the engine and harnesses are from an 89. 89 has a harness end for the ignition protection relay.

FredR

My late 90S4 and current 92 GTS have the harness but nothing hooked up to them as I have no cats. The potential issue is not about the 89 harness- all S4 and later models can be kitted with or without cats depending on the market- all 89 US models were probably cat equipped or so I would think albeit I understand some grey imports did not.

The concern is whether this 85 model had cats and whether they have the sensors to flip the relay not to mention the coding plug needed to tell the brains what is going on and what to look for. If the OP intends to fit CATS if they are not present all well and good.

davek9

The protection relay only cuts the Fuel, not the spark and yes the CAT protection wasn't a thing in the 1985 MY, so no sensors or such wiring existed.
As far as I recall, the Crank Position Sensor signal tells the EZK that the engine is turning and then EZK turns on the spark, the EZK then tells the LH that spark is active then the LH turns on the Fuel Pump.

How are you addressing the lack of Knock and Hall sensors feeding the EZK?

FredR

Dave,

It is an 89 motor

Brett Jenkins

When I bought the car, it had a hybrid engine built with 944 turbo pistons for low compression, high boost. It was an S3 lower half and S4 top half. It used LH/EZF. It did have cats. When that motor went south after 928 Rendevouz in SD, I bought an S4 engine from Harvey C and refreshed all sensors , including new knock sensors and Hall sensor. Instead of getting S4 LH/EZK, I thought I'd try a standalone setup to try to optimize the performance. I went with VEMS with coil on plug, but I could never get it right, despite a ton of help from Colin and Hans and others. Instead of sending it to a tuner, I decided to go with a stock setup and sharktune it since it has much larger injectors and a supercharger. I added an x-pipe with high-flow cats during that installation. I bought the ignition monitor bypass/jumper from Roger. The car would start and run with this setup, it was just pig rich. Before deciding to go back to stock management, I smoke tested the vacuum system again and found a leak under the intake, so I pulled it and made sure everything was correct under there. Before re-assembling, I decided to go back to stock and installed a new, stock TPS in place of the one that came with VEMS. I sourced a used set of LH/EZK and rebuiit MAF and replaced the CoP with all new ignition components.

What I would like to do is test everything from point A, being key on, to point Z, being the car starts and runs. So, I'm hoping I can piece together the sequence of events in between. Here's what my limited understanding is in my mind. I am sure I am missing steps and have most out of order, but this is a starting point for me. Please add/subtract, re-order.
A. Key on
B. Ignition relay activates
C. Key turned to start
D. CPS sends RPM signal to EZK
E. EZK propagates RPM signal to LH
F. LH relay activates, providing 12v to fuel injectors
G. EZK Relay
H. Fuel Pump Relay
I-Y. Other stuff with knock, hall sensors, temp sensors, etc
Z. Car starts

I did just find this fantastic document, but further clarification above will help me tremendously.

This overview provides insight into Porsche 928 S4 and newer models engine control systems (928oc.org)

FredR

Brett,
My interpretation of what you wrote that is more or less correct:

Step A-key turned to ignition on position
Step B- EZK relay activates but only if the alarm system is disengaged
Step C- key turned to start
Step D CPS generates constant trigger signal to EZK unit per rpm pulse
Step E- the EZK simultaneously generates rpm ignition pulsed signal as per ignition maps and fires up the LH unit.
Step F - LH unit now functioning generates a signal within the secondary tile that causes the fuel pump relay to energise and also produces injector rpm dependent modulated impulse signals as programmed to fire up the injectors. If the fuel rail is pressurised it will start within a second or two, if the fuel rail has lost pressure it may take a few seconds to prime.

Kevin in Atlanta

That answers my question, thanks.

Brett Jenkins

Where in there does spark get generated on each cylinder? I see the coils have 12v at key on, but aren't grounded. What grounds them and when? Is it the ignition amplifier?


I verified that the TPS and CPS connectors/wiring are in good shape and are not reversed.

FredR

Brett,

Logic says the sparks are generated the moment the crank starts spinning. Ignition pulses are generated in the EZK unit 4 times a revolution via the ignition amplifier that is triggered by the EZK. The high tension pulse is generated simultaneously and transmitted to both the coils and then sent to both distributors but only one of them has a leak path to earth via the spark leads wherein the rotor arm passes the HT pulse to the one pot of the distributor cap that is open- the spark plug then fires on the cylinder that is in the firing stroke or so I understand.

Brett Jenkins

Ok, making more sense to me now. It is my understanding that the ignition amp modules are just high power switches that ground the coils at intervals based on a signal from the EZK, which previously received a signal from the CPS. Since I have 12v at the coils, key on (with negative side of multimeter grounded to body), but I don't get ground at the negative side of the coil while cranking, then I think my problem is that the amps aren't doing their job. Since they are new and the system previously worked, I believe the issue is that EZK isn't telling them to do their job. Is there a relay or fuse anywhere dealing specifically with the ignition amps?

Brett Jenkins

Going through the troubleshooting list This overview provides insight into Porsche 928 S4 and newer models engine control systems (928oc.org), I have found the following:

CPS resistance 1100 Ohms, should be 600-1600
CPS output via scope, https://photos.app.goo.gl/nNNKsaSiNbeq773t9

EZK continuity from pin 13 to LH pin 1 confirmed

Fuel pump relay continuity from relay pin 85 to LH pin 20 confirmed
Bridging fuel pump relay points 30 and 87, fuel pump runs
Fuel pump runs when cranking

12v voltage on pin 30 at all times for LH, EZK, and fuel pump relays confirmed
LH pin 4 12v voltage (same circuit as above relays), no voltage at pin 4 <<<<<<<Issue?
Continuity between LH relay pin 85 and LH connector pin 21 confirmed

Fuel injection circuit, LH relay jumpered, no voltage at LH connector pin 18 <<<<<Issue?

Ignition amps

Connect scope to pins 2 and 5 on each ignition amp connector, no signal on either while cranking
Continuity from EZK pins 15 and 32 to pin 5 on respective ignition amp connector<<<<<<<<If continuity exists but no signal, then EZK isn't telling amps to do their job?

Temp II sensor is suspect. Not sure if that would affect spark, but ordered a new one anyway.

Next step is to check all ground spots.

hans14914

I would take a close look at the CE panel connectors. On the S4 harness, it's the W and V. I am pretty sure that some of the pins between the S3 and S4 on those connectors need to be swapped.

Print out the engine control schematics for both years, as well as the CE panel pages at the end of the manual and trace it all back.

I am reasonably confident you need to change the pinout on those connectors for the relay triggers.