Peter F

In my hunt for an intemittent cut out and rough running on my 90GT I have started to test the monitoring relay.
There is no visible light from the green and red LED when the problems show.
Since the relay could be faulty in itself I started to tear into all the test ponts.
One is: The resistance between E1 and E1 is approximately 5 - 10 Ohms (measured at the disconnected relay socket)
Mine measures only 2,6 Ohms, would this indikate a problem with one of the sensors?
I also put a timing light on the engine running at idle and it shows 15-16 deg.
Would this be right at idle?

Thanks/Peter

Peter F

Has anyone experiense how the temperature sensors at each head measure out when in good shape?
WSM says 5-10 Ohm and mine measured 2,6 Ohm.
Does that mean one is bad?

/Peter

Vilhuer

No idea but can do some measurements in few days if it helps.

AO

I wanted to respond to this yesterday, but I knew I couldn't help without tearing into mine...but now that I've had some time to think about this, let me tell what I came up with.

As I understand it, these sensors monitor EGT (exhaust gas temperatures) and continuously compares right bank to left bank. If the two sides differ to much (e.g. cat fire), it shuts down the injectors on the higher temp side. The relay only trips if it sees a significant difference between the two sides. This is not a gradual cutoff. You either have fuel or not to that entire bank of injectors. So just because one seems to be out of spec, doesn't mean much by itself - and certainly would not explain a rough idle.

It sounds like maybe your issue is more spark related than fuel. I had an issue for a while when I would wash my car, it would only run on 4-cyl. I, too, thought it was one of these relays, but it turned out to be a bad coil wire that was getting wet. I would check your coils and coil wires. Make sure everything is grounded and that the wires and boots are in good shape.

Hope this helps.

WallyP

Check the coil wires, especially the one on the driver's side (on LHD cars). Make sure that the connections are clean and tight, and that the wire is routed well away from any other harnesses or metal.

Peter F

Thanks Andrew and Erkka,

at this point any advice helps since I'm stuck with solving this problem.
The rough idling shows as a complete cut out sometimes and only for short moments when driving.
The thing is that the monitoring relay does not light up the green/red LED when this happens.
I'm just grasping for loose ends that I have not tried before.
Andrew, both coils have been replaced and all ignition wires except the coilwire on the driverside.(which looked ok when checking)
I have now ordered a new and will replace that as well.
The greatest mystery part is that i do not get any error codes when testing the car with Johns spanner.
Well, when doing the activator test it sometimes says the WOT switch does not work.

/Peter

Peter F

Thanks Wally,

left coil wire is suspect and on order to be replaced.

/Peter

AO

My other thought was (for the rough idle) the TPS in the idle position, but that would not account for the cutout, but a bad coil/coil wire would.

You know... now that I think about it even more... if a coil went out, each side of the engine would be firing on 2 cyl, so the EGT should remain roughly the same and not trigger the ignition monitoring relay, although you'd be dumping some serious fuel down the pipes.

Vilhuer

Aren't distributors and monitoring relay sides taking case for same cylinders? Thats why four plug wires go to other bank of cylinders at front of the engine. If relay determines one set of four is not working properly EZK will shut down that coil and LH those four incjectors?

AO

Errka-
You're probably right. Sorry, if I threw out some erroneous thoughts.

John Speake

On LHD car, driver's side distributor fires cylinders 5,8,3 & 2 (actual firing order)

Passenger side distributor fires cylinders 1,7 6 & 4.

Igntion protection relay will switch off injectors only (not igntion) of either bank if temp of cylinder group in lower than the other.

You can buy a relay type device which bypsses the relay with the LEDs or just link pins 87 to A1 and A2 on the relay socket. Don't confuse pin A1 with the similar looking pin AL.

The diagnostic tester won't tell you if there is an igntion problem.

John

Peter F

I actually bought this relay bypass device some time ago and have it laying somewhere in the garage.
Will take a tesdrive with it tonight if found, if the problem still exists with this I guess the relay and tempsensors can be ruled out.
I have ordered the coil to distributor wire from Porsche here in Sweden and it will take a week for them to get it here from Germany .
I will post later today how the testdrive went.

/Peter

docmirror

I had a similar problem with my car. It would cut out and sputter intermittantly. When I use bad gas, it got worse. I haven't found the problem completely, but suspect the ignition drivers up near the front of the car too. The ignition drivers take the signal from the EZK and amplify and shape it, then send the signal to the coil. Two flatish black boxes mounted in front of the radiator on the deck behind the hood latch. Check the connections and then try swapping.

The resistance measurement from your EGT probes is likely 5-10 ohms at full temp. If it reads 2.6 ohms when cold, try checking when hot. Although I haven't looked it up, I think that's correct.

Peter F

Hi Doc,

well the amplifiers will be the next suspect if the new coilwire doesn't cure the issue.
I testdrove tonight with the relay replacement and the fault was showing it's ugly face just as with the original red/green LED relay.
Well I guess the only good thing is that I can rule that relay and temp sensors out from the list of potential reasons for this very annoying fault.
One good thing with all the fixes done so far is that the car runs very strong compared to before with the exception of when it stutters and losses power every now and then.
Anyway to test the amplifiers for being OK?

/Peter

TheoJ

Hi all,
just a bit about the EGT sensors: they are not temperature sensors comparing to Temp2. The temp2 is typically a NTC sensor, of which resistance decreases when temperature increases. These EGT sensors are thermo elements. The produce a voltage when hot. A higher temperature gives a higher voltage. The two sensors are fixed in a opposing polarization (?) serial connection +- to -+ Therefore the same voltage of both sensors ends up at zero output. Any difference appears like a positive or negative voltage in the mV range, triggering the relay, and thus shutting down some injectors. It actually disconnects the injectors as one set (1,4,6,7 or 2,3,5,8) from their common power feed (12v). It does not affect the sparks !
The engine feels very rough when it happens.

I know: it doesn't explain your problems, Peter, as bypassing the relay did not solve the problem. Please let us know your findings....