Running on 4
11-08-2009, 02:30 PM
#1
Rennlist Member
Thread Starter
Running on 4
The other night, after work went to the garage to start up the road warrior and go home. Only started up on 4 cylinders. Since home was a short distance and no hyway, got her home, but had to goose her to keep running at stop lights. Pulling into the drive way she stalled. When I re-started her she came up on all 8. Had her out for a run this morning for an hr with no problem.
What do you think the issue is? bad solenoid?
'94 GTS
What do you think the issue is? bad solenoid?
'94 GTS
11-08-2009, 05:46 PM
#2
Rennlist Member
Plenty of info here! See the most recent "limp home mode" thread down the front page.
Please start with this, though - there are two kinds of "disabled" modes... limp-home mode is an LH program the ECU uses when it is not getting MAF or O2 sensor data (or so I think - no doubt I will be corrected if I'm wrong!). I don't know much about it beyond that.
The other "disabled" mode is a true 4-cylinder mode that is triggered when the ignition circuit monitor (p/n 928 618 175 00) thinks you are not firing on all cylinders. This mode is positively identifiable by checking for a green or red LED on the ignition circuit monitor, which is located on the right side of the passenger foot well, just below the LH & EZK controllers. The ignition circuit monitor reads two exhaust manifold temperature probes, one on each bank. If it senses a significant discrepancy between these two probes, it assumes you are not firing a cylinder on that side and puts you in 4-cylinder mode to keep unburned fuel from hitting the cats and catching fire.
If the temp difference is real (check with IR gun), then you have an ignition problem. Check every single ignition part and wire, from the coils to the plugs. Do the "firefly test" as well (run engine at night in the dark and look for sparks).
If the temp difference is not real (see the thread I mentioned), then a failure of one of the temp sensors or a problem at the connector (behind each valve cover, just in front of the firewall) or where the sensors plug into the ignition circuit monitor. It is also possible that the ignition circuit monitor is faulty, although our suppliers say that doesn't seem to happen much.
There is a relay available from the suppliers that replaces the ignition circuit monitor altogether if you cannot find or correct the fault that is putting you into 4-cylinder mode.
I battled this problem for over a year on my car. I futzed with the temp probe wires and cleaned the connectors to make mine go away. I keep the bypass relay in my glove-box, though.
Good luck!
Please start with this, though - there are two kinds of "disabled" modes... limp-home mode is an LH program the ECU uses when it is not getting MAF or O2 sensor data (or so I think - no doubt I will be corrected if I'm wrong!). I don't know much about it beyond that.
The other "disabled" mode is a true 4-cylinder mode that is triggered when the ignition circuit monitor (p/n 928 618 175 00) thinks you are not firing on all cylinders. This mode is positively identifiable by checking for a green or red LED on the ignition circuit monitor, which is located on the right side of the passenger foot well, just below the LH & EZK controllers. The ignition circuit monitor reads two exhaust manifold temperature probes, one on each bank. If it senses a significant discrepancy between these two probes, it assumes you are not firing a cylinder on that side and puts you in 4-cylinder mode to keep unburned fuel from hitting the cats and catching fire.
If the temp difference is real (check with IR gun), then you have an ignition problem. Check every single ignition part and wire, from the coils to the plugs. Do the "firefly test" as well (run engine at night in the dark and look for sparks).
If the temp difference is not real (see the thread I mentioned), then a failure of one of the temp sensors or a problem at the connector (behind each valve cover, just in front of the firewall) or where the sensors plug into the ignition circuit monitor. It is also possible that the ignition circuit monitor is faulty, although our suppliers say that doesn't seem to happen much.
There is a relay available from the suppliers that replaces the ignition circuit monitor altogether if you cannot find or correct the fault that is putting you into 4-cylinder mode.
I battled this problem for over a year on my car. I futzed with the temp probe wires and cleaned the connectors to make mine go away. I keep the bypass relay in my glove-box, though.
Good luck!
11-08-2009, 06:31 PM
#3
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Two most likely problems appear to be:
- Bad connection on a coil wire, often the driver's side. Mostly due to rain and wash water running off the fender lip onto the coil. Clean the coil tower connections.
- False Ignition Monitoring System operation. As Gaz says, one cylinder on each ignition system is monitored, and if there is a difference in exhaust temps, the monitoring system determines the cylinder with the cooler exhaust, then kills the injection on the four cylinders hooked to that ignition system. This is done to prevent the cat from overheating as it oxidizes the unburned fuel from the four misfiring cylinders.
If you drive the car with four non-firing, but injecting, cylinders, you can set the car on fire.
Two comments:
- This four-cylinder operating is NOT "limp mode"!
- The four cylinders are not on one bank, but two on the left and two on the right.
- Bad connection on a coil wire, often the driver's side. Mostly due to rain and wash water running off the fender lip onto the coil. Clean the coil tower connections.
- False Ignition Monitoring System operation. As Gaz says, one cylinder on each ignition system is monitored, and if there is a difference in exhaust temps, the monitoring system determines the cylinder with the cooler exhaust, then kills the injection on the four cylinders hooked to that ignition system. This is done to prevent the cat from overheating as it oxidizes the unburned fuel from the four misfiring cylinders.
If you drive the car with four non-firing, but injecting, cylinders, you can set the car on fire.
Two comments:
- This four-cylinder operating is NOT "limp mode"!
- The four cylinders are not on one bank, but two on the left and two on the right.
11-08-2009, 07:25 PM
#4
Rennlist Member
...- False Ignition Monitoring System operation. As Gaz says, one cylinder on each ignition system is monitored, and if there is a difference in exhaust temps, the monitoring system determines the cylinder with the cooler exhaust, then kills the injection on the four cylinders hooked to that ignition system. This is done to prevent the cat from overheating as it oxidizes the unburned fuel from the four misfiring cylinders...
Just to be clear, this only applies to later models. What years have this system?
11-08-2009, 08:27 PM
#5
Addict
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The ignition monitoring system is on Porsche 928s from MY 1989 and newer.
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.
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.
11-09-2009, 09:37 AM
#6
Rennlist Member
Thread Starter
VehiGAZ, Wally, Jadz, Rich... many thanks the above information. I took the car out yesterday and ran for over an hr and she ran fine. I have printed out the above and will start with the basics (as suggested) and work my way along. As I'm just a week-end warior when it comes to mechanical work, once we get to the more complicated I might take to a shop.
Am I right that if I was in 'limp mode', there would be some idiot light on the dash telling me so ('94 GTS).
Interestingly, running on 4 cylinders was not really rough, but just a lack of power, although, as mentioned, prone to stalling when foot off the gas. No gas smell, so appears exhaust gas temp probes probably working.
In any case, thanks again and will revert with findings
Am I right that if I was in 'limp mode', there would be some idiot light on the dash telling me so ('94 GTS).
Interestingly, running on 4 cylinders was not really rough, but just a lack of power, although, as mentioned, prone to stalling when foot off the gas. No gas smell, so appears exhaust gas temp probes probably working.
In any case, thanks again and will revert with findings
11-09-2009, 12:02 PM
#7
Rennlist Member
Nice post, Rich!! Alan, if you are reading this, that procedure should definitely go into the good book you are working on...
The first diagnostic step is entirely straight-forward and doesn't require any special skills - just check for the LED lights next time it goes into the fault mode to see if you are in ignition-protection mode or limp-home mode. If in ignition-protection mode, the next steps are just measuring voltages with a multimeter, but if you are not familiar with their use, then I would suggest to get familiar with it rather than dump the project on a mechanic, as a multimeter is a phenomenal diagnostic tool for LOTS of things besides cars. One way or another, you can do the diagnosis yourself rather than pay a mechanic $90 - $150 per hour to do learn how to do it for you.
I have never heard that the LH's limp-home mode is indicated to the driver by a warning of any kind, but I am not familiar with it.
Good luck!!
I have never heard that the LH's limp-home mode is indicated to the driver by a warning of any kind, but I am not familiar with it.
Good luck!!
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11-09-2009, 12:10 PM
#8
Shameful Thread Killer
Rennlist Member
Rennlist Member
Yes except:
"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."
Should read:
When injection circuit 1 (cylinders 1,4,6,7) is shut-down, a red LED is illuminated.
When injection circuit 2 (cylinders 2,3,5,8) is shut-down, a green LED is illuminated.
"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."
Should read:
When injection circuit 1 (cylinders 1,4,6,7) is shut-down, a red LED is illuminated.
When injection circuit 2 (cylinders 2,3,5,8) is shut-down, a green LED is illuminated.
