Rlucas

1989 Porsche 928 S4
Rennlist 928 Forum

5/5/18

The Ignition Control Relay is switching off ignition circuit 2 (Green Diode) approximately 30 seconds after starting the car. I purchased a new Ignition Control Relay from Porsche, and the new relay switches off circuit 2 immediately after starting the car. It appears that the new relay does not have a time delay.
I replaced the ignition wires, coils, distributor rotors and caps, plugs, and almost all of the relays and sensors on the car. I rotated the exhaust temperature sensors for cylinders 4 and 8. The problem still exists, therefore I just purchased 2 new exhaust temperature sensors from Porsche. Do the new exhaust temperature sensors need to be calibrated with the ignition control relay?

I have the workshop manual. Does anyone have any bulletins published by Porsche or technical information on resolving this issue that can be shared with me? I will appreciate it very much.

thanks

Richard

davek9

No calibration that I know of, are you sure that both coils are working, did you swap the Ignition AMPs located up front to the left of the hood latch?
Simple check is to use a timing light and see if all 8 are getting spark.
The coils fire Ignition bank (1,5,6,4) or (4,2,3,8) and if one bank is cold that relay kills the fuel to those cylinders so you don't flood the CAT's with fuel and cause a CAT fire.

Dave

ROG100

Bypass it - too many issues once it goes bad.

dr bob

Fix the problem. Too many issues when things go bad. Like fires. There are good reasons why the "ignition protection relay" is there.

Use a good inductive timing light to test for good spark to every cylinder. Easy to do even if the relay has shut off fuel to the cylinders. After that, you can jumper the contacts in the relay socket to fool the system into running both injector banks. Use your IR temp gun up close to find the cold exhaust manifold at a not-firing cylinder. The relay is intended to protect against one ignition system failing, but in fact anything that causes either of the two sampled cylinders to not fire will trigger the relay. I'm separated from my WSM's by a country, so can't tell you exactly which cylinder is the Most Likely Suspect.

The system works by comparing readings from two thermocouples. They each generate tiny voltages that the relay amplifies then compares. In the most simple iteration, the TC's would be wired opposite each other in a small bridge, and the voltage compared with a zero reference to find which sensor is colder.

Mrmerlin

GregBBRD

There is a technical bulletin that tells exactly how to diagnosis the system.

Rob Edwards? Paging Dr. Edwards.%\5
​​​​

Rob Edwards

Did someone page?

Here's the 1st TSB on ICM diagnosis:

https://webfiles.uci.edu/redwards/pu...nformation.pdf

and installation details for the thermo sensors:

https://webfiles.uci.edu/redwards/pu...0for%20ICM.pdf

Rlucas

5/9/18
Greetings

My car has been in my garage for the last 20 years. I purchased it with 14,000 miles and now and has less than 20,000 miles on it.
I bought the car from a collector in Hollywood Hills 20 years ago, drove it to Las Vegas and then to SF. It has been in my garage since.
The car had unbelievable power.

I replaced the following:

Water pump, timing belt
idle control valve'
Throttle position switch
vacuum hoses
cam shaft position sensors
crankshaft position sensors.
ignition wires, spark plugs
distributor caps and rotors
final stages
Mass Ari Flow sensor
Temperature sensor !!
LH computer
ignition computer
Ignition control relay

After replacing all of this, the ignition control relay with the green light still comes on after 30 seconds.

I purchased the exhaust temperature sensors and ignition coils and just received them

I appreciate the information that I received from all of you especially, the Porsche bulletin on the specifications for relay and temperature sensors.

I will check this this week

Thanks so much

rlucas













I repplased the ignitionnswitch

Adamant1971

I'm going through the same on an 89. In my case it would appear that one of the temp sensors is out of whack. The car has no cats so I'm likely just going to bypass it with the bypass plug.

I was reading through the WSM and it talks about rotating the sensors to find the optimal position that will secure the voltage difference at or below 2.5v when measured on the back pins of the relay. I may try this before bypassing or spending $$$ on sensors.

Mrmerlin

Since it appears that the issue was not an issue until you replaced the Ignition parts.
(Hopefully you used all Bosch components,if not you should replace all of the non Bosch parts, The wires should be Beru)
Their have been a few issues with bogus Bosch distributor caps causing misfires,
and when installed into a car with the ignition monitoring relay cause this unit to activate.


Don't do anything else until you put the old distributor caps and rotors back in place,
do one at a time and see if the condition changes,
disconnect the battery after each try to reset the computers

If none of these things change from swapping the caps, and rotors.
Then look into the thermocouple sensors on the manifolds.

NOTE simply disconnecting the sensor and spraying with Deoxit 100 will usually restore performance .

Rlucas

928 Forum
5/13/2018

Greetings Again

I replaced the exhaust temperature sensors, purchased new from Porsche, and the car is not switching off circuit 2 anymore. I ran the car several times over the weekend and it is back to normal.

FYI: , I tried switching the sensors in exhaust ports 4 and 8, but the switching off circuit 2 still existed. Therefore, this effort proved to be non-useful in my case.
Initially, 3 months ago, I thought the car was running on "limp mode". But later I determined the car was switching off ignition circuit number 2. A test light was plugged into each of the fuel injectors and the test light showed injectors 2,3, 5, and 8 were not working. The car was running on 4 cylinders.

Luckily, I found an article on Rennlist 928 forum that gave me the possible solutions and joined the forum. . Before that time, I did not know the car had exhaust temperature sensors.
.

Thanks for all of the information. All of the suggestions were helpful.

Sincerely

Rlucas, MS PE




.

Mrmerlin

Thanks for the followup

Philip Bond

Hi new on here just been give a 928 it's been in a garage since it's little bump 6yr ago its got a Clifford alarm on I've now got key fob alarm Sean's to go off and on but got no power to dash cluster etc check all fuses now we're or wat to do next not sure can any 1 help

Rob Edwards

Hi Philip, welcome. First thing would be to find the control box for the Clifford alarm, trace every wire that connects to it, and disconnect each wire from where it interfaces with the factory wiring harness, repairing any installed-induced damage along the way. Second is to throw it and the key fob in the trash. Third is to tell us more about the year and condition of the car- it if has been sitting for 6 years there are a bunch of things that need to be checked before you try starting it.

Philip Bond

Hi Yeh so this has had a load of mods it's got a 1off body kit apparently an old man did it all some stuff cool and old the alarm opens doors no hands on out side and boot opens from a switch that unlocks and power opens boot. Well it had a front little bump well bumper missing and old lady who husband made this Carr lost key fob I've had this give me so I've had key fob done that all wks check ING switch got power out but no power to dash clocks and no start no radio She say it all wkt wen it was part up 6yrs ago now its a mess but if I can get it started etc I will do all repairs and turn it back to red. The reg is HES 8 . The wipers Wk and jazz lights and side lights here's some pic I hope