worf928

Ok.... not going back through the whole thread to review...

A single consistently misfiring cylinder can cause the IMS relay to trigger. A good place to start, diagnostic wise, is to determine if you have a misfire issue with one or more cylinders but not all controlled by a single half of the ignition system. So, bypass the IMS relay, and then determine which cylinders are misfiring. A straight forward way to do that is, with the car idling, one at a time, pull out a plug wire (don't fry yourself) and then determine if the engine is running rougher or if there's no difference with the wire pulled. Then put it back and go to the next cylinder.

If you find that all of 1,4,6,7 or 2,3,5,8 are misfiring then you've got an ignition problem that is effecting an entire circuit (e.g. coil, coil amp, coil ground, coil wire, rotor, cap, etc.) If you find that not all cylinders on a circuit are misfiring then you've got a problem that isn't a 'whole bank' failure mode.

If you find that 1 to 4 or 5 to 8 are misfiring then ... I'd suspect a fuel or timing problem.

If you have one or two misfiring then narrow the search to potential issues down-stream of the caps.

Stan.Shaw@Excell.Net

Progress report:

Per Dave Roberts of 928 Specialists suggestion, I removed both exhaust temperature sensors, cleaned them, and installed them in opposite sides. His guidance is that if the problem switches sides, then it is a sensor issue, if it the issue stays on the same side, it is a real temperature issue or perhaps a wiring issue, or if the IMS issue does not re-occur it was a dirty sensor…..

A few drives later and no faults yet. Wouldn’t it be too ironic if this could have resolved this so quickly by cleaning the sensors, perhaps a couple of hours for them….

I found that my bypass relay is no longer around, the shop lost at least one other part, provided no diagnosis information, so I guess I should not be surprised. I now have 3 IMS relays…

Thanks to David Roberts, regardless of the outcome on this.

jej3

Is the above statement correct for 1990 vehicles????

If so, shouldn't I move mine to 3 and 7, if I am going to trouble of getting down there to swap around to determine why IMS triggering? Still getting IMS trigger of GREEN LED. Swapped ignition amplifiers and MAFs with known good. Next step is going under the car to figure out why this triggers the Green LED about 20 seconds in. I think that is ALSO the interval until it does the first 02 Sensor sampling. This car is driving me crazy.

Mrmerlin

Did you swap distributor caps for new ones
if so swap the old cap back in
We have seen some new caps with shorted internals

jej3

No. The caps were changed a few years ago. any ideas on the placement of the IMS EGT sensors on the 1990 vehicles?

jej3

Removed sensors and cleaned them on both sides. I did not swap them side to side, yet. Also, on my 1990, they are in the 4 and 8 position. If I move the sensors from 4 to 3 and 8 to 7, won't I also have to plug it into the opposite sides as the IMS won't know about the move of the sensor and if the sensor at 7 triggers, it will stil think it is sampling cylinder 8 and then shut off 2-3-5-8?

Very confused but also thinking I have a miss so will be doing what Dave C suggests on figuring out miss. I suppose it could be plug wires OR a not great injector. I have tested the iginition amplifiers, the MAF and don't think I have a full ignition circuit failure with one coil, coil wire or dist. cap.

Thoughts appreciated!

milrad

Sorry to drag this up, but I have a similar issue except that I'm getting the red light. Did cleaning the sensors make a difference?

Kevin in Atlanta

This is what I followed to resolve my running on 4 cylinder issue. Lucky for me all I had to do is pull the coil wire and reseat it as suggested below:

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.

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 voltmeter to the millivolt range and connect leads between E1 and E2 of ignition monitor relay. A digital voltmeter 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.

jej3

I never got it fixed on mine. It's going to Howard at European Classics in Atlanta early next month. Good Luck!