944S computer problems

ronniebaldino · 06-07-2003, 09:55 PM

I recently had my car in for service as it was running rich and not idleing as smooth as it once did. They assumed it was the O2 sensor (which was not working) but also tried sending a fake signal to the computer and it failed to adjust the mixture. Based on this they said I needed a new computer $$$$. Could there be anything else going on here? For that matter does anyone have a 944S (1987 if it matters) DME sitting around????

Thanks

bader4 · bader4's Garage

many things could cause a rich condition and thus a poor idle. coolant temp sensor, afm, stuck fuel pressure regulator, leaky injector, etc.

ronniebaldino · 06-08-2003, 09:27 AM

O.K. How do I narrow down the options? Any way I can troubleshoot this down to a likely cause?

bader4 · bader4's Garage

need to check the signals/resistance of each item. I don't have the book here with me, but frwilk nows these systems better than anyone. Pm him and see if he can help.

ronniebaldino · 06-08-2003, 12:26 PM

Could I do that with a decent circut tester? My dad is an electrician so maybe I could pull him in on the troubleshooting. Definetly need someone to talk me through the process though. I am not yet aquinted with the forum (pm him ?? I assume personal message). I was going to sell the car as I had become hopeless. I just want to thank all of you in advance for the huge help I can tell you are all going to be. I just hope I can help some of you out once in a while.

bader4 · bader4's Garage

By pm I do mean Personal message. I am new to these cars although I am an auto tech. I have to research every thing I do electrically. I will try to get you some specifications and proceecdures tomorrow. I have the books at work.

Martin T · 06-08-2003, 01:43 PM

If the temp signal is cold the O2 sensor is ignored, with the engine cold after sitting overnight test the resistance of the coolant temp sender and the AFM temp sender, if they are not the same at ambient temp one of them is broken.

todwic · todwic's Garage

buy a haynes manual.

carsontc · 06-08-2003, 05:55 PM

I think the Haynes manual shudda been standard equipment...in the glove box with the owners manual !!

as usual FRwilk.com has a excellent test for the AFM at:

http://www.frwilk.com/944dme/afm.htm

ronniebaldino · 06-08-2003, 07:39 PM

I have the haynes for the 8V 944. Would it be fine for the 16V??? I read all the info on the site mentioned above and I am thinking this could be the issue. It is a longshot but it would explain why the dealer told me that the ecu wasn't resonding to a fake o2 sensor signal and making adjustments. As I understand it the sensors need to read warm before the ecu even looks at the signal from the o2 sensor. I will look at the Haynes in the morning and see if it will help me test these two sensors. I just can't believe that the dealer wouldn't have known to check these already????? $75per/hr.................
I would love to hear from this FRwilk person as he seems to know everything there is to know about the systems in question. His diagrams made no mention of the 16v so I would love to know if the 1986 version is the same as my 1987 16V. I am so excited to check these all out now....

ronniebaldino · 06-09-2003, 06:53 PM

I just checked the resistance of the temp sensor in the AFM and it was well within spec. I had no luck finding the engine temp sensor or the conecter under the dash for it. I was wondering though. If the engine temp sensor was not functioning correctly would my temp gauge in my dash not work as well cause it seems to function ok. Any other ideas of what to check out?

bader4 · bader4's Garage

The coolant temp sensor is for the engine management system. It is in the block below the tupper radiator hose where it connects to the head, it has a blue connector and should be 1500-3300 ohms at 15-30 degres celsius. The resistance goes down as temp goes up.

Cali56 · 06-12-2003, 06:54 PM

I think check the tps resistance it should read short open short or vise versa, open short open, just as you move the throttle it clicks to another state doesn't change states again until about 3/4 to full open throttle position. the voltage out of the afm is relative to the flap angle its hard to check without the car running, use a volt meter set to measure dc up to 12volts, the signal feeding the afm should be 5 volts the signal out should read a slight increase with increased rpm relative to the flap angle.. a dirty tps or afm connection will mess up the air flow ratio.
a burnt o2 sensor will mess up stuff mid throttle to full throttle under load. all sensors and computer systems must be in working condition to have proper fuel mixtures. they didn't include any that don't do something to conribute. so make sure they all work.
water temp sensor should have resistance relative to the temperature, the airflow meter temp sensor should have resistance relative to the temerature. check with frwilk for the resistance values I think he has all of them relating to the airflow meter. sorry I don't have the values.