I have GEMS on my rally car and had a similar fault, the Water temp sensor went short circuit for no apparent reason. Could this be the problem? Check it's resistance with the plug disconnected from it. Also had a MAP sensor fail resulting in similar symptons. Check the output voltage from the MAP sensor.

:(

I'll need to go buy a volt meter!! Will do it this afternoon :)

Still have the JECS fitted and got it in diagnostic mode just now and it's showing a fualty sensor I think :confused:

I get 4 1.3 second flashes, then 5 0.2 second flashes. (45?)
It repeats this over and over
Am I correct in saying that is the pressure sensor that is faulty?
(Pressure exchange solenoid valve)MAP sensor?

[Edited by Scoty - 1/11/2004 1:03:11 PM]

Running speed density from a dodgy pressure sensor would certainly screw things up big time.

Why were the fans on though?

Guessing to say much more, needs laptop connected for proper diagnosis.

Dont know John, they dont run with the JECS though :confused:

Should I try a new MAP sensor, what about upgraded ones or ones from 99-00 cars, are they not a bit more reliable up to about 24psi?

Measure the voltage with the ignition on position II engine off - so it is measuring atmospheric. On a 99 this is about 2.3V +- about 0.1 depending on atmo pressure. Someone will be able to confirm what it should be on the 98.

OK John, off to get a meter and try it.

Mef what MAP sensor are you using with the GEMS?
(Weber Marelli APS/05 3 bar sensor?)

The map sensor is the same for MY97/98 and MY99/00. So the voltage should be as per John's... 2.3 volts at atmos.

Tony.

Wild stab in the dark here about the fans as I don't know the GEMS ECU, but could it just simply be 'panic mode' switches the fans on, just in case? Hence a red herring?
Dodgy MAP sounds a likely offender as seeming this setup isn't using the MAF or lambda, about the only thing left for it to go on is MAP & rpm :)

Took mesurements from the MAP with the ignition on, engine off.
Bottom two wires first..............

Red/green stripe 12V
Light Blue 12v

Top 3 wires, all read zero

Are those readings what would be expected if the MAP sensor was faulty?

[Edited by Scoty - 1/11/2004 4:25:55 PM]

Marelli sensor is 0-5v and 0-3bar absolute.

So atmospheric is about 1.66 volts.

Don't know the pin out though.

Paul

My MAP sensor is whatever the standard Sti4 uses, when mine went wrong the fans came on too, as John said it must be a default to switch on the fans if the MAP signal is wrong. The GEMS ecu is a bit funny like that, I have noticed that the fans do come on under certain configs, just cant remember exacly what circumstances it was though. My MAP sensor was accidently blown up by me when an uninsulated live wire touched the ecu case during some troubleshooting earlier this year! The symptoms where exactly what you've described,

Martin Fox

Cheers Paul/Mef :)

Would you say mines in knackers considering the readings I just took from it then?

Anyone got one the could send me in the morning please :( ?

I wouldn't expect to see 12V on a MAP sensor, they are normally fed from the regulated 5V supply from within the ECU. Disconnect the plug from the sensor and check the supply voltage, if it's 12V then the ECU regulated 5V supply must be up the shoot. If you fit a replacement MAP sensor you will damage it if the supply is 12V. You should also see the +5v supply on the throttle pot so check it there too.

Martin

Wheres the throttle pot?

It's on the end of the butterfly spindle of the throttle body, it's on the oppposite end to where your throttle cable pulls from.

Big learning curve for me here.

Which sensor is the MAP sensor:confused:

There is a small black sensor roughly 1 inch cubed in size and there is a bigger flater dark grey box below it.

The small black sensor has 3 wires, the bigger flater dark grey box has 5 wires




[Edited by Scoty - 1/12/2004 1:18:56 PM]

The MAP sensor has 3 wires, +5v, earth and output, it's normally black and only attached by hanging on one bolt and it has a piece of rubber tube on it. The larger plastic thing fixed on with 2 screws is probably the igntion module. There is also the solenoid valve for the turbo wastegate but this has only a 2 pin plug.


Hope this helps,

Martin

It does indeed Martin!!!! :)

I've took readings from the "MAP" sensor today and not the ignition module :rolleyes:

With plug connected

Red : 3.78v
Yellow : 3.56v
Black : - 0.14v

Plug disconnected, reading direct from plug

Red : 5.15v
Yellow : 1.85v
Black : -0.14

Should I replace the MAP sensor now?

Top

Hi Scoty, sorry for the delay, have been out. Yes the readings are up the shoot! The MAP sensor is faulty and is dragging the 5V rail down under load (as you can see it's 5V when you disconnect the map sensor)

Replace the MAP sensor and re-check the readings.

I will be interested to see how you get on,

Good luck,

Martin

Martin, was just about to post this and got a notification you had posted :)

Yip, the MAP sensor is faulty, borrowed one today and the car is fine with the GEMS and JECS.

Thanks for yours and everyone's help and input, hopefully I will be able to help someone else one day if they have a faulty MAP sensor :D



[Edited by Scoty - 1/12/2004 5:44:27 PM]

Interesting! My MAP sensor blew up when I inadvertently got the 12v supply touched to the ecu case. Did yours just blow on it's own?

Anyway, glad it's sorted, and you may now consier youself as the GEMS/MAP sensor expert!

Martin

Yes the MAP sensor has packed in on it's own accord.
As far as I can remember, this is the first fault the car has had in 4 years of ownership!!

Ooohhh...don't let the muppets hear you've got notification on, you'll be inundated with mails now... :D:D:D:D

Alan :cool:

Looks like they know already ;) :D :D

woo hoo. when can i get a shot of ya rocket shcoty???:D