bgrabner

Hey there -

Just got the 928 in for inspection and failed emissions testing. I got the car in CA last year, and this is the first time I have taken it in for an emissions test. The only change I made to the car since I got it was putting an RMB on it, and I just put a new MAF on it. Here are my readings:

15 MPH
HC ppm: Limit=103, Reading=250 FAIL
CO %: Limit=0.58, Reading=3.84 FAIL
NO ppm: Limit=778, Reading=215 PASS

25 MPH
HC ppm: Limit=100, Reading=241 FAIL
CO %: Limit=0.61, Reading=2.33 FAIL
NO ppm: Limit=709, Reading=48 PASS

What could be causing te high HC and CO readings? Do I need a new oxygen sensor, or could my catalytic converter need replacing? I searched the archives, but unfortunately found many threads on passing, but not what to do when you fail. Any help is appreciated. Thanks!

Bill

bgrabner

Anyone?

John Speake

Hi Bill,
The O2 sensor is connected in to ECU via the round, 3 pin inline connector that lies on the floor, just in front of the relay/fuse panel. You need to get a voltmeter onto the sensor pin and ground, and this will help you see if the loop is working - with the engine at normal temp. The voltage should vary around 0.2 to 0.8v as the loop keeps the O2 in check. If it just goes permanently high or low, then the loop or sensor is faulty.

bgrabner

Thanks John! I will check that out tomorrow and let you know the results.

Bill

shaaark89

bill,
if you need to try a different o2 sensor (or even cats for that matter) i have a few laying around.

ViribusUnits

It seems like something is causeing your engine to run rich.

Find out what it is, and fix the problem.

Possible things:

O2 sensor
Too high fuel rail pressure
Bad MAF
leaky, or stuck fuel injector
Bad ECU
Bad Temp I or Temp II sensor
Stuck WOT switch

That's all I can think of right now.

bgrabner

Tom - sent you a PM...

Bill

RazorRacer

I just had the same problem with my 1984 928S today. It passed last year, the first year I owned it. The guy said it wasn't the cat.

Bill51sdr

Low NOX... chances are the cat is good as the midbed appears to be working although the hugely rich condition you have could be keeping the NOX low. Definitely check the O2 output voltage. It should be varying between .2 and .8 volts constantly once closed loop is achieved (if possible in this case). I'm willing to bet your O2 is pegged at a low voltage, HOWEVER, before just blindly replacing it make sure you do not have another condition (grounded O2 lead for instance) causing the condition. A LOT of good O2 sensors get replaced out there.

RazorRacer

The O2 sensor is working. It had a low reading cold. As the engine warmed up the voltage increased steadily to 0.8 volts. Do I need to check for a grounded O2 lead?

Could bad gas cause this problem? I have been using 87 octane.

JE928Sx4.

Could be the Injection Brain is starting to go. I had mine rebuilt by Rich Andrade (Elektonic Repair Inc.). Mine was wayyyyyyyyyy off in the same manner as yours but worse. The rebuild has the engine running perfect, emissions wayyyyyyyy under the limits and pulling STRONG!!!!

I'm in Alexandria and am willing to let you swap it out to test.

John Speake

Razor racer,
You don't have a short because you get a reading. But the readong you get isn't correct.

The voltage should vary around 0.3 to 0.8 v as the loop works to try and keep the value at stoich. This only happens once the engine is up to normal temp. though............

If the voltage just sticks at one end of the range, the problem could be ECU fauilure, or a bad connection between O2 and ECU.

bgrabner

Hey John - thanks for the offer I may take you up on it if the O2 sensor isn't the issue. Question for you though - if the Injection Brain is going, wouldn't the car run rough in addition to the readings being off? Since John S. hooked me up with a new MAF, the 928 has pulled strong and idles rock steady...still learning these things, so just wondering how I would diagnose the injection brain..

Regardless, I would still like to hook up with you and see your toys - my next shark will be a black on black 5 speed like yours. Almost swung on the Dulles 928 in another thread here, but I need to get my first one up to snuff before taking on another one!

Bill

Rich9928p

LHs that are on their way out have many different symptoms. Running rich is one of them, early on you don't feel it, but the situation often keeps getting worse until the engine stops running. Other symptoms include a slow death with intermittent stalling. There may be poor idle speed regulation. The fuel pump may cut-out. Then there is the won't start but injectors chatter.

The sad fact is some LH symptoms are subtle and could be caused by other components (bad relays, clogged idle speed regulator, dodgy fuel pump) so diagnosis can be difficult and expensive. I have several customers who elected to have their LH rebuilt as a preventative measure rather than risk failure. Other customers paid over a thousand dollars for diagnosis only to find that the LH is bad.

A Porsche dealer recently contacted me, they plugged in a "factory rebuilt" LH into a customer's 928 an it appeared to be DOA. Ouch.

JE928Sx4.

Actually my failed ECU just had the car running really rich and it tended to stall when stopping after getting up any speed. Otherwise the engine ran pretty smooth.

I do have a new Bosh universal O2 sensor for an S4 (you splice it in). Turns out I didn't need it, and by my latest readings will not need it for a long while.

Sounds good, I'll drop you a PM with my contact info.

Regards,
JE