closed loop limit?

[topmech0]

hi guys

i have a 993 C4 (MY 1996 varioram) here in the uk. I went away for 3 weeks leaving the car parked up. returned and after initial starting all seemed fine. Left the car running for about 20mins during which time it began running very lumpy and misfiring. tried to rev it and thick white and blue smoke. I thought possibly fouled up so changed spark plugs,put in fresh fuel and fuel filter. Started car up and running very poorly and slow to rev up with periodically excessive wispy white/blue smoke.

plugged in a friends PST2 and only fault arising is the following;

23 CLOSED LOOP SYSTEM LIMIT

I have not seen or heard of this diagnostic code.

can anyone help??

[Loren]

(Porsche Fault 23) P0159 -- Aging of Oxygen Sensor After Catalytic Converter (Cylinders 4 - 6)

[topmech0]

hi loren

this does not give me a p number code. just the 23.

this is 993 so only has one oxygen sensor. just googled the code and description and it takes me to a chip company??? do you think possibly this is an ECU fault?

am at my wits end with this. Everything on this car is factory standard

[JFP in PA]

hi loren

this does not give me a p number code. just the 23.

this is 993 so only has one oxygen sensor. just googled the code and description and it takes me to a chip company??? do you think possibly this is an ECU fault?

am at my wits end with this. Everything on this car is factory standard

What Loren is trying to tell you is that the PST code 23 is the same as P0159, and indicates the O2 sensor behind the cat on bank 4-6 is on its way out and needs to be replaced.

[binger]

FYI there are four O2 sensors on your 993. 2) before the cat and 2) behind the cat.

[topmech0]

hi all

either you are confusing this with a 996 or the american models are different for your smog laws. Here in europe they have one sensor in the middle of the cat.

This a UK car

thanks

[binger]

Got it as you did not specify ROW car.

[JFP in PA]

FYI there are four O2 sensors on your 993. 2) before the cat and 2) behind the cat.

hi all

either you are confusing this with a 996 or the american models are different for your smog laws. Here in europe they have one sensor in the middle of the cat.

This a UK car

thanks

Got it as you did not specify ROW car.

Actually, it went both ways. North American cars had a single O2 sensor mounted at the cat in 1995, 1996-1998 models have two, one before and behind the main cat on both banks. ROW cars continued to use a single sensor for a longer period, but I am not sure when they switched to two sensors on each bank.

[Richard Hamilton]

All RoW 993 Carreras used DME 2.1 throughout the model history. They did not have post-cat O2 sensors or secondary air injection, as they were not OBD2 compliant.

[JFP in PA]

All RoW 993 Carreras used DME 2.1 throughout the model history. They did not have post-cat O2 sensors or secondary air injection, as they were not OBD2 compliant.

Thanks for that information Richard. After 1996, cars in North America had to become OBD II compliant, hence the switch to two O2 sensors per bank. We recently had a fully restored 1989 Cadillac in the shop that carried a pre OBD I diagnostic system (used a system called Assembly Line Data Link or ALDL) that had one large main cat and had only one O2 sensor ahead of the cat (which happened to be acting up) for a big 5L V8 engine; my how times have changed.

[topmech0]

update;

i plugged in another ECU from another car and it ran perfectly from cold. Unfortunately then it started running badly after 10-15mins..I let car sit and go cold again to see if temperature issue but it runs the same(badly) with both ECU's now!!!! seems both original and replacement ECU have blown? how to find the cause is my question and also aynbody know where to get ECU repaired? I am in London UK

[binger]

I am sorry hear that. I would put the DME back in and diagnose your issue ASAP. I know you had (Porsche Fault 23) P0159 -- Aging of Oxygen Sensor After Catalytic Converter (Cylinders 4 - 6). I would check the resistance in that sensor but I would also check all the injectors too. If one goes south and starts pulling too many amps it can blow a driver in the DME. Once you do get the DME repaired I would be careful not to plug it in to the car until you find what component blew the driver in the first pace.

[JFP in PA]

update;

i plugged in another ECU from another car and it ran perfectly from cold. Unfortunately then it started running badly after 10-15mins..I let car sit and go cold again to see if temperature issue but it runs the same(badly) with both ECU's now!!!! seems both original and replacement ECU have blown? how to find the cause is my question and also aynbody know where to get ECU repaired? I am in London UK

Before I would do that, I would test the O2 sensor in question for resistance and correct voltages; if either is out of range, I would put in a new O2 sensor and try the car with the original DME in place. Just might surprise you.....

[topmech0]

update.... I had a friends car so plugged my 'bad' ECU into it and surpirsingly it worked perfectly so not the problem and the good running for 10 mins with a different ECU was coincidental. now at stage where i think injectors will be next course of action? also may borrow a gauge and check fuel pressure.i had a spare pressure regulator so already fitted that.

thanks

[JFP in PA]

update.... I had a friends car so plugged my 'bad' ECU into it and surpirsingly it worked perfectly so not the problem and the good running for 10 mins with a different ECU was coincidental. now at stage where i think injectors will be next course of action? also may borrow a gauge and check fuel pressure.i had a spare pressure regulator so already fitted that.

thanks

Read my post directly above, as I noted, you probably have a bad O2 sensor, but you need to check it before replacing it...................................

[topmech0]

JFP

as i explained before,the ROW cars only have one sensor in middle of cat. Also if i disconnect it then it makes no difference to running Surely this should make the sensor reading go to lambda 1 safety mode? It made no difference

[JFP in PA]

JFP

as i explained before,the ROW cars only have one sensor in middle of cat. Also if i disconnect it then it makes no difference to running Surely this should make the sensor reading go to lambda 1 safety mode? It made no difference

I'm well aware of ROW car setups, the code you have says that sensor is the problem, either because the wiring harness leading to it is a problem, or the sensor itself is going south. You need to check the sensor and its harness.

[topmech0]

will do that tomorrow but i only had that code once.cleared it and now even with rough running,misfire and sometimes thick white smoke then blue smoke it hasnt returned. I suspect the code was as result of bad running engine and not the cause. the sensor is only a year old and was genuine from dealer. If sensor disconnected surely it goes to set reading and therefore although may not be perfect it would run better? white smoke is indication of what usually in 911?

[JFP in PA]

There are only two liquids in a 993 to burn, fuel or oil. High fuel problems (e.g.: Leaking injectors) would cause pungent black smoke; so it is probably oil.

[topmech0]

final update

thanks for your advice guys but it was a stuck injector on cylinder number 1. I removed them all and took them to injector specialist when put on test rig the injector for number 1 cylinder was like a hosepipe as soon as igniton switched on. the white/blue smoke was excess fuel.I replaced that one and ultrasonically cleaned other 5 and problem solved!!!