HELP... electrical issue or computer issue?

unclemikeys2001 · 03-28-2006, 08:31 AM

I just replaced my inner FP regulator due to it was letting in too much gas. Flooded motor when cold, had irratic idle etc. ...Now that the fuel pressure is sorted out it runs & idles like a champ when warm. However its running VERY lean. ...But when cold it wont start at all unless I give a squirt of ether. Then will die if you even touch the gas pedal, until its warm then runs like a champ again. When warm it really runs great. .....I had a shop look at this & they think I have an electrical issue. There is no response from the coolant or O2 sensor when unplugging & does not alter the idle at all. Also the CO setting on the AFM can be turned all the way rich or all the way lean & this affects nothing. Car runs the same. Although unpluggung this will kill the car so its gettinmg some volts but mabye not the correct volts? I have 2 extra AFMs here & swapping them does nothing so I know this is a good part. He did a volt test on the o2 senser & from the computer side it reads low at .12 volts. He thinks something is wrong with my computer. .....Please someone explain whats going on. Does my computer need swapping? THANKS IN ADVANCE.

nynor · 03-28-2006, 08:34 AM

have you checked the fuel pressure and flow rate at the rail?

bearone2 · 03-28-2006, 08:42 AM

fuel pressure sorted out, is it correct?
have you checked the basic throttle stop position.

clarks garage has a pretty good explanation of setting the tps, which has got to be set right for accel/decel/idling.
for a test, unplug the tps. it won't accelerate right but will run.

the porsche manual recommends not stepping on the throttle when starting.

.12 is lean. when running you'll see .5 to 1.0 showing that the o2 is working.

unclemikeys2001 · 03-28-2006, 08:43 AM

No, I havent checked the pressure at the rail. But still shouldnt altering the C0 setting to max/min affect something? Also by simply unplugging the collant sensor should also have an effect on idle but it doesnt. I will get the fuel pressure checked asap just to find out where Im exacty at there & then update. Should have done that already anyways. But Im thinking my problem is something else. Please keep the ideas coming in. Thanks

unclemikeys2001 · 03-28-2006, 08:47 AM

When I say 0.12 this measurement was taken from the computer side of the plug. The O2 sensor is new & is working (or should be) . My mechanic said that not enough volts is going to the sensor.

nynor · 03-28-2006, 09:06 AM

if your fuel pressure is wrong, your mixture will be wrong.

unclemikeys2001 · 03-28-2006, 09:22 AM

Thanks to all who are helping its appreciated. I wont get down to the car till this afternoon. But in advance so when I get there I will know, what should I be looking for as far as a reading in the fuel pressure? Please let me know in detail. Running, idle, off, etc. Thanks...

nynor · 03-28-2006, 09:40 AM

i believe pressure with pump running should be 2.5 BAR, IIRC. you will need to jumper the fuel pump relay. it should flow at least 800ML in 30 seconds. see clarks-garage.com for a great procedure for checking the fuel pressure.

Razorback1980 · Razorback1980's Garage

What's strange though is that if fuel pressure were the problem, it wouldn't run properly after it warms up. Should run better but still not well. If that's it and it's running too lean, you shouldn't have good acceleration after it is warm. Another possibility might be the temperature sending unit? It should be what's telling the computer the car isn't warm yet and needs extra fuel until it reaches operating temperature.

unclemikeys2001 · 03-28-2006, 12:56 PM

Well, I dont have a fuel pressure tester so Im buying one & making the metric/sae adapter on clarks garage. Will get to testing the pressure soon. In the meanwhile I swapped out my ECU from my parts car & now 1 thing is back to normal. Now the engine dies when you unplug the coolant sensor which is whats is supposed to happen. Before it would have no effect when unplugging & car still ran the same, computer not sending/reading signal. ..Im going to have to wait overnight now to see how she starts when cold. Im keeping my fingers crossed. After reading up at Clarks Garage I think I can rule out the TPS being faulty.

unclemikeys2001 · 03-29-2006, 11:57 AM

Got in this morning once the engine was stone cold & crossed my fingers. She started right up... I hit the pedal a bit & no stalling. Drove right off cold no problem...I drove around & did my errands for about 2 hours & the car runs great at all temps & speeds. Idle is a solid 950 (although my tachs not always working, thats another post) . The car has never run better than it does now. I even took it in today for my long put off emmissions test & it passed with flying colors. ....So today is a good day & the problem was a malfunctioning computer not reading my sensors. Good thing I have a parts car sitting around!!! ...Thanks to all who helped me & directed me to Clarks Garage. The info will all be valuable in the future.

Porsche944 · 03-30-2006, 03:52 AM

The big clue was the reading from the computer side of the O2 sensor. You should have seen 0.45 volts with the O2 sensor disconnected. This is a fail safe voltage. The DME uses this to insure that the engine will always run rich should the O2 sensor fail. Running rich prevents detonation (knock, ping). Running like this for an extended period will eventually clog the cat.

I would venture to guess that your fuel mileage was in the toilet before you swapped the DME....