928GT8108

My 928GT have an igntion problem issue, the cylinders 2, 4, 6 , 8 seems doesn't work at all, only cylinders 1, 3, 5, 7 is running. I already replaced rotors, full set spark plug wires, distributor caps, ignition switch unit, ignition coil and hall sender.

Please help!

Thanks!

Stromius

Coil ground? Coil? Coil wire corrosion? Believe injector ground would affect all vs one side. Welcome btw!

Rob Edwards

Coil wires?

Not sure how its possible for none of the even cylinders to work, unless you've moved some plug wires around. One distributor cap runs to cylinders 5,2,3, and 8, and the other to 4,6,7, and 1.

Is it always running on 4 cylinders or is it ok for a few seconds after startup and then goes to 4-cylinder mode? There's an ignition control monitor (ICM) relay that is mounted on the bottom of the LH/EZK brain bracket, to the right of the CE panel. There are exhaust temp sensors that trip the relay if one coil's cylinders are not firing, which lights up either a red or green LED inside the clear plastic ICM relay.

Check to see if this relay is 'lit up'.

Lizard928

Bypass the ICM relay and test first.

Rob Edwards

3 0.25" male spade lugs, 2 short stretches of wire. 2 wires to the 'center' spade, running to the red/yellow and red/green wires.

James Bailey

You counting 1-4 on the passenger bank, 5-8 on the drivers left bank ?

928GT8108

Thanks for your help. I will try to test later.

The doesn't work cylinders is on the passenger side like below photos:

Mrmerlin

what was the last thing you fixed before this happened?

Since you have RHD car all of the notes posted here are for LHD cars

From the photos you may have miswired the ignition wires.


So with you standing facing the engine the left bank or passenger side head is counted as 1 to 4 then the driverside head is 5 to 8.
each distributor cap will have 2 wires from each cylinder head plugged into it

Passenger's side cap: from left to right as you stand there, 4,6,7,1
Driver's cap as viewed from the front, left to right: 5, 2,3,8

As long as your standing there, Passenger's side, from front to back: 1,2,3,4 (clyinders)
Driver's side, front to back: 5,6,7,8

Mrmerlin

The 928 S4 and newer engines have two separate ignition circuits. Ignition circuit 1 is comprised of cylinders 1,4,6,7, the right side coil and distributor. Ignition circuit 2 is comprised of cylinders 2,3,5,8, the left side coil and distributor. If there is a failure in one of the ignition circuits, raw fuel is pumped out of the cylinders and into the exhaust system. When the raw fuel hits the hot catalytic converters a fire may occur – OUCH!

From model year 1989 onwards, Porsche added the Ignition Circuit Monitoring Relay as a safety feature. This circuit is completely independent of the LH injection system. It is identified in the workshop manual wiring diagram as the Ignition Control Circuit. The function of the system is to turn off the fuel injection to the failing ignition circuit. The inputs to the relay are two exhaust temperature sensors that provide input to the relay. If one of the ignition circuits fails, the “Ignition Circuit Monitoring Relay” shuts off the pulse signal to all of the fuel injectors of the affected circuit.

As you might imagine, the symptoms of a shut down ignition circuit are a significant reduction in power and a rough running engine. For trouble shooting, you need to determine if the shut-down is due to a failed ignition circuit or a failure of the Ignition Circuit Monitoring Relay itself.

The first step is to quickly identify which circuit is affected. Look at the clear relay module that is fitted next to the EZK spark control unit in the passenger compartment.

When ignition circuit 1 (cylinders 1,4,6,7) is shut-down, a red LED is illuminated.

When ignition circuit 2 (cylinders 2,3,5,8) is shut-down, a green LED is illuminated.

Check the ignition circuits and repair as necessary. If no problem is found with the ignition circuit, there may be a failure of the Ignition Circuit Monitoring Relay circuit, the signals to test are:

1. Terminal 31: ground
2. Ground must be present at terminal AL when the ignition switch is in the off position.
3. Battery voltage must be present at terminals A1, A2, 15 and 87 when the ignition is in the on position.
4. Battery voltage must be present at terminals AL and 61 when the engine is running.
5. A Voltage value of approximately 2.7 V must be present at both terminals E1 and E2 when the ignition is in the on position.
6. The resistance between E1 and E2 is approximately 5 – 10 Ohms (measured at the disconnected relay socket).

The temperature sensors that fit in the exhaust system should also be inspected.

A more detailed explanation is provided in the factory workshop manuals.


9203
Subject: Diagnosing Ignition Monitoring System
ATTENTION: Service Manager/Service Technician
Models Affected: 928 S4/GT/GTS From 1989 Models –

Concern: Checking of components after activation of the ignition monitoring system (injection circuit switched off fault codes 1131 of 1231). Activation may be caused by the following:
- Damaged or defective exhaust gas temperature sensors.
- Possible damage to the ignition coil wire left side (in driving direction) between the ignition coil and distributor cap.
- Poor grounding of the mounting plate for the ignition final stages.
- Poor physical connection of the electrical plugs on the ignition final stages.

Parts Information:
New version temperature sensor Part Number 928 606 155 02 New coil wire with
hose covering Part Number 928 602 040 01 (for left side)
Repair Information: 1. Check the left side ignition coil wire. Be certain the coil wire is routed freely and not under tension. If damaged, replace with new version (see parts information).

2. Check all ignition components and connectors for corrosion, tightness, correct connection and damage. Repair or replace as necessary. If an ignition circuit has malfunctioned, an LED indication will be given by the ignition monitor relay located on the L-H control unit mounting plate.
Ignition circuit I (cyl. 1-7-6-4) Red diode
Ignition circuit II (cyl. 3-2-5-8) Green diode

3. Before replacing temperature sensors, check the voltage difference of both temperature sensors as per step 4 of this bulletin. Sensors are located in the exhaust ports:
Model '89-'90, cyl. 4 and 8
Model '91 cyl. 3 and 7
The function of the ignition circuits and light diodes located in the ignition monitor relay remains unchanged. It is not possible to determine from the LED display of the ignition monitor relay if one or both temperature sensors are defective or which temperature sensor has failed. When installing temperature sensors, coat the sensor adapter threads with molykote paste HTP (white) and torque sensors to 10 N-m.

4. The voltage difference of the temperature sensors must be checked in order to ensure proper operation of the ignition monitor system.

Checking sensor voltage difference:
- Start engine and bring to operating temperature.
- Loosen the mounting bolt for the ignition monitor relay and pivot the relay up to gain access to the plug terminals Do not disconnect the relay plug.

- Set volt meter to the millivolt range and connect leads between E1 and E2 of ignition monitor relay (Figure 3, white wires). A digital volt meter must be used. Polarity is not important.
- Measure voltage with the engine idling and again at approximately 2000 RPM. A maximum difference of +2.5 mV or -2.5 mV (depending on polarity) is permitted. If the voltage difference is above 2.5 mV, stop the engine, loosen and rotate one temperature sensor. Retighten sensor and check voltage difference. If the difference is above 2.5 mV, stop the engine and rotate the other sensor. If after rotating the sensors to different positions, the voltage difference is too high (above 2.5 mV) the temperature sensors are defective and must be replaced.

James Bailey

I think he is saying the passenger bank cys 1-4 are not firing......so has me thinking the fuel rail. That or camtiming to take out one bank....

928GT8108

Thank you for your useful info. Is the below marking on the photos correct? Thanks!

worf928

First thing I see is the injector retaining clips have been ripped out of the injectors and are busy doing nothing on the radiator. So, my first bet is that the injectors are not well-connected.

Next, can timing and indexing (intake to exhaust relationship) can cause problems like this. Have the cams been out?

Last, a failing speed sensor can cause a problem _exactly_ like this. It's a very rare mode of failure, though.

928GT8108

Found that the exhaust temp sensor wire got damaged, the car seems back to normal now after replacing the wire. Thank you for your help!

James Bailey

That would kill 2 cylinders on each bank.....not one whole side....But glad you got it fixed !