Scotty1

Hi all,

Just got my car back 1990s4 auto after a full valet including some detailing on the engine bay and it is not running good with poor idle down on power seems to be only firing on 4 cylinders .I drove home the short distance and today started some trouble shooting . I have spark at all spark plugs using a spare plug I tested this however the ignition monitor relay has lit up with a red led which I believe is picking up an issue in one of the signals within the ignition system . I jumpered this relay to see if it would make a difference but no change. I also checked the two ignition modules at the front of the engine bay and what is strange is that if I disconnect the one on the left there is no difference however if I disconnect the right the engine stalls .? I also swapped the connectors around and the opposites happens so it seems that the final ignition output is not coming through the connector on the left could this be a short ,loose wire somewhere or could this be fuel injector related since I have spark on all cylinders or possible LH issue.? car ran great before this and i don’t want to start throwing new parts and hope for the best. If someone has any tips to try and narrow this down further that would be much appreciated. Thanks

FredR

Try squirting some WD40 into the left hand LT coil connections - take off the plastic cover first.

GregBBRD

Generally, you will find "green" corrosion in one/both of the coils.
And a little bit of water makes the spark jump to one of the posts on the coil.
This is the result of improperly seating the coil wire rubber boot around the plastic cover.
The rubber boot on the coil wire end must go over the plastic cap about 1.5mm.

GregBBRD

Generally, you will find "green" corrosion in one/both of the coils.
And a little bit of water makes the spark jump to one of the posts on the coil.
This is the result of improperly seating the coil wire rubber boot around the plastic cover.
The rubber boot on the coil wire end must go over the plastic cap about 1.5mm.

There are also two distinctly different coils and coil wires used on these cars.
Using the wrong coil wire on a coil will result in the spark jumping and the same "green" corrosion..

The Forgotten On

You just narrowed down your issue. Try swapping the plugs on the amps to see if the engine starts and runs and then unplug the right ignition module again to see if the engine still stalls.

You may as well replace both ignition amps as they are a fairly common failure item (why Porsche installed the ignition monitoring relay) as proactive maintenance if they are original. They're less than $100 for the pair.

Scotty1

Hi All,

thanks for all of the suggestions so far but unfortunately no joy yet with fixing it I took the coil off on the LH side and checked the contacts under the plastic cover and they looked very good no sign of corrosion .I did clean them and also the earth strap and it made no difference also I had already swapped the ignition amp connector from the right sidewhich is working to left side and the car still starts with no difference if I unplug this connector that is working engine will stall. I m thinking that there is something in the wiring of this left amp connector that is not right or disconnected somewhere ?

Mrmerlin

try swapping the coil wires side to side
NOTE usual failure is a bad coil wire,
make sure that the coil wires do not touch anything in their run,
If they were touching metal then the wire could be damaged.

Scotty1

Hi Folks ,

I still have not resolved my issue with the s4 not firing on all cylinders , I brought it to my local indie shop who advised that the leads were bad so a full set was replaced but with no difference. He has confirmed there is good fuel pressure , good spark plugs distrubtor and compression on the two cylinders not firing 3 and 6 . I am thinking it could be something to do with the ignition ECU as there is no spark at these two cylinders and just wanted to get some thoughts on this and if this might be the issue as we are running out of ideas at this stage . Any help as always much appreciated

thanks
Scotty

FredR

The ECU initiates a firing pulse every 90 crank degrees of rotation and this causes the coils to fire ignition HT pulses that the distributor routes to specific cylinders as needed. These pulses fire as the rotor arm passes the specific cylinder electrode. Thus if your assessment that only 3 and 6 are missing logic suggests the problem cannot be down to the ECU and must be somewhere between the distributor and the plug.

Perhaps you can try swapping over the distirbutor caps and see if the same cylinders have the same issue or whether the issue migrates to two other cylinders.

daveo90s4

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.

daveo90s4

Broken Central Tube Shaft Vehicles With A/T



9228porsche01

July 7, 1992

Model 928 S4

Group 3

Part Identifier 3903

Number 9206



Subject: Broken Central Tube Shaft Vehicles with Automatic Transmission



ATTENTION: Service Manager/Service Technician



Models Affected: 928 S4 Model Year 1989 to 1991



Concern: Activation of the ignition monitoring system (injection circuit switched off fault codes 1131 or 1231) can lead to breakage of the central tube drive shaft.



General Information: Oscillations in the central tube system that occur when the ignition monitoring system has switched (flywheel effect) can lead to breakage of the central tube drive shaft. This can occur only in vehicles with automatic transmission where the vehicle is operated at an engine speed of approximately 1000 RPM. Possible causes are:



- 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: A new version temperature sensor, central tube and coil wire are installed in production.

Temperature senso, Part Number 928 606 155 02

Central tube with changed material for drive shaft, Part Number 960 421 012 07

New coil wire with hose covering (for left side), Part Number 928 602 040 01



Repair Information:

1. If the central tube drive shaft is broken, replace the central tube with the new version part (see parts information). Refer to Technical Bulletin Group 3, Number 9203, dated May 5, 1992 for hints on central tube installation.



2. Replace the left side ignition coil wire with the part number listed in this bulletin. Be certain the coil wire is routed freely and not under tension.



3. 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



4. Replace both temperature sensors located in the exhaust ports:

Model '89-'90, cyl. 4 and 8

Model '91 cyl. 3 and 7

Use the new version temperature sensors listed in this bulletin.



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.



5. After the temperature sensors are installed, the voltage difference of the 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.

mj1pate

…and only use factory Bosch amps. There are non-OEM bolt-in units that are problematic In our cars.

GregBBRD

A month later and your shop has not figured out what is wrong?
.....You need to find a shop that knows a bit more about 928's.

This is a 2 hour...maximum....problem to trace.
(Until someone screws things up and there is more than one problem...that can be a nightmare.)