bdristy

I have a 1990 944S2 Cab which is basically stock with 169K. I have recently failed the VA emission inspection 4 times after trying a number of things and need some advice. The car passed the emission test 2 years ago with all readings way below the limits after replacing the oxygen sensor. I have only put 10k miles in the last two years on this car. The CO reading was high on all 4 attempts. After failing the first time (CO limit/reading was .37/.78 (15mph) and .53/.85 (25mph)) I was told I needed to run it longer (i.e. get it hot) before having it inspected. I did that and tried again and it failed with roughly the same reading (CO was .81 and .78). I then did a basic tune up (i.e., air/fuel filter, plugs, cap and rotor) and tried again, but fail again (CO was .61 and .53 (25mph passed this time)). I then read the bad fuel injectors could cause the high CO and had then rebuilt. The fuel injector report I got back showed the injectors were in bad condition and were restored to factory spec. I was thinking this was going to solve the problem and had the car inspected a 4th time and it still failed with the CO reading going up instead of down (i.e. CO was 1.15 and 1.30), but other two reading, i.e. HC and NO, which were already below limit went down by about 30%. Right now, I am not sure what to try next. I have read it could be the catalytic converter, but there is no power loss. The cars seem to be running great. Some have mentioned the oxygen sensor but I replaced that two years ago. I would not think this would have gone bad in that time period. Someone has mention a bad fuel regulator might be the problem, but I am not sure how you would check or test this. Does anyone have any other advice or suggestions?

VirginiaF1

Suggestions?
Move down here to Richmond... we don't test for emissions.
( Amazes me that govt will allow dump trucks to belch black smoke but still MUST test 20 y.o. Porsches)

1. Maybe adjust your Fuel Quality Switch?
https://rennlist.com/forums/showthre...ferrerid=96487

2. Was your new 02 sensor tested for good conductivity/ground at replacement time?

3. Original factory DME Temp Sensor still in car?

Subscribed.. Good Luck!

joejoe

I just ran into this on my 86.5 928 a few days ago. I pulled MAF check and was good, Checked dampners to see if bad, no also good. Checked WOT and CO setting with Porken Blink'r also good. Thought maybe o2 sensor had gone south, pulled lambda plug and checked (dam) also good. Made apointment for diagnosis at smog shop to tweek idle adjust and co setting. When testing (this was after a slow 15 mile drive to shop and 15 min cool down while there) the car was running numbers near perfect.

I am at a loss as to what the heck changed a gp car to near perfect. What I think and my smog guy agrees is that maybe the o2 sensor was not making good contact and reseating it connected correct or the disconnection of MAF harness and reconnection made a better connection. I really do not know , but as there was absolutly nothing adjusted it is the only thing I can think of.

I would check the o2 sensor (not sure where plug is but should find out as I also have a '90 944 cab) Disconnect plug and with meter check for reading it should be .5 - .8 or so and fluctuate when speed changes (at least for the 928 it was this way) If the same 3 wire plug as on the 928 the black one is to the lambda, of the other 2 1 is voltage to heat up oxy sensor other is ground ( I believe)

+++ check with positive to lead to o2 sensor not computer and ground wire to good grounding source not the ground mentioned above. Check for heater voltage from whereever the 2 white wires come from fuse panel. One will show 12+ volt the other nothing, again use good known ground.

The o2 sensor cold have failed, was it generic? or oem replacement? If generic then it had to be spliced in, and one of the splices could be bad. Hope this helps some as I know (I really do) just how frustrating this situation can be.

xschop

How old was the gas and what percent ethanol? (It causes gelling if it sat for long periods) Make sure you have 10 gallon fresh gas (100% petrol if you can get it) then add 3-4 oz ACETONE. I've passed emissions in Texas this way many times. You just have to have good ign. parts and timing set correctly.

pnbell

Just hold off for about 5 years... then your car won't require emissions testing...

sorry, I have no great advice on this topic other than maybe your 20 Catalytic is no longer performing as it should... It's weird that the other emissions measures are fine though...