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911cedric

my 993 runs rough when hot

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Hi there everybody,

i have an mechanical problem with my 993; it's a 1996 carrera 2;

i'd like guys to have your opinion about it.

When i start the engine, the motors runs well untill it gets hot like 5 or 10 minuts later.

Then it runs really rough, not irregularly, but very heavily and loud, like an old diesel.

Acceleration is really poor, but motors seems to runs better at high regime.

It looks like if the mixture would be too lean or too poor and the motor "coughs".

There is no noticable smoke or leak.

When scanned for fault codes, i had 2 strange codes that showed up:

- upstream oxygen sensor cylinder 1-3

- fuel pump relay / final stage

after that i changed, the DME relay, and the four oxygen sensors, but nothing changed at all,

and i even still have the same oxygen sensor error code taht came back.

It could be so many things that i don't really know where to start;

it could be a fuel delivery problem, a defective EGR valve, fuel pump, fuel regulator, temperature sensor,

vaccum leak, worn out valve,...?

i asked yesterday to a Porsche mechanic, and he told me first to change the temperature sensor, which is a very well know problem on 964's and 993's.

I will replace it tomorrow and see what happens; but i don't really feel optimistic about that.

If you guys have an idea about that, please let me know, that could be really helpfull.

thanks

Cheers

Cedric

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Check the drive belt in the distributor and make sure both rotors are turning.

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well,

as expected, i changed the temperature sensor, ... and nothing changed.

By the way, for those who never did it, it's a real nightmare to screw in.

So, i turned my attention on another hitch i noticed when the car runs;

When the car is running, i can ear the intake system blowing air in an unusual way,

somewhere in the distributor circuit. I think there is a leak somewhere as i tested it with

a spray.

It appears that the intake manifold seals let the air go through, so i will replace them all tomorrow,

as it has a heavy impact on the engine idle.

Under the intake distributor, i found an air pump with ducts, and i think this one leaks to.

I will check it all, change the seals, and try to thighten everything better.

This air leak has to be fixed.

By the way, it's a real mess of ducts, and wires everywhere on the intake distributor,

and removing that stuff was a pain in the ***; i expect a great deal of pain when i will have to put it back.

Anyway, i will try to fix the air system, then, if it's not that i will try the fuel system regulator, then maybe ignition,

and if it's still not working i think about hanging myself :cursing:

i will check the ignition distributor by the way, but i think i should better fix that air problem first.

so if you guys can help, please let me know

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yetserday, as i took the car for a ride, the motor was almost running normally at idle.

it was too good to be true,

this car drives me crazy.

it was very difficult this morning to start the engine;

then the car ran rough as always and even stalled at cold.

thought first that my DME relay was dead, but i exchanged it with another one and was the same thing. When hot it was a little bit easier (maybe ) to start.

it must be a related problem.

regarding the wiring harness, there was no recall about that harness on that car; i checked with the vin in a Porsche center.

there are a lot of wiring harness, so did you mean the engine harness or the DME harness?

ok first, i have to tell that the Durametric device i use on that car is a real crap. Slow and erratical communication, and finally failed almost all the time.

Gives wrong informations.

i don't know if i had a bad one, anyway, i'm done with durametric.

only worked on few cars before dying.

I'm about to take back an original PST2, and at least it will be a real reliable professional tool.

So, i took it to a guy i know in the city, with the bosch hammer, he found out that my "temperature sensor was dead"; actually the one i replaced.

Plugged or unplugged the sensor gived nothing.

So it can be the sensor itself, the DME wiring harness, or the DME itself.

I will test it tomorrow with a multimeter and see if i got something in the wiring harness. I hope i won't have to change the DME wiring harness because it's a pretty expensive part; it connects the 2 knock sensors, temperature sensor no.2, and the speedometer sensor.

i don't know if it explains everything, but anyway i have to fix it.

the porsche mechanic told me it's a known problem on 993s.

we'll see tomorrow.

Cheers

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I also have used Durametric on 993's and never had a problem. As for the wiring harness it only affected the early 1995 production run and can be checked by looking at the production date on the wiring harness. The last harness I bought was only $120.00 CDN and a few hours to replace.

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just had an interesting diagnostic..

the Dual mass flywheel could be faulty and give erratic information to the sender.

This could explain the misfire and the difficult starts..

i just wonder how to make sure.

it's a pretty serious repair, and i have to make sure it's the real cause.

i would have to remove the engine.

i should maybe first have a look on the flywheel position sender?

there should be one or two flywheel sensors that send signals to the dme.

if there would be a real problem with the dual mass flywheel, i should probably have a fault code from the dme?

please let me know if there is a reliable way to diagnose this.

Cedric

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