Mike Frye

Attached is the first run at the emission test for my 'new' '85 5 spd.
Anybody ever seen anything this high? She was actually running pretty strong, but the exhaust is a killer.





I have since done a complete tune-up and run some injector cleaner through it, but even on my new plugs, I'm getting some serious carbon. I'll post pix if I can later on. And although I can't seem to locate it, I think I have an exhaust leak as well.

FYI- tune up consisted of:
Plugs, wires, caps, rotors,
air filter, air pump filter, fuel filter


I'm going back for a retest in about an hour and we'll see how it does after the tune-up. I'll post the results. If, as I suspect, I fail again I'm going to need some direction on what to try next.

ROG100

O2 sensor or MAF (if the 85 has a MAF)

ZEUS+

Usually retarded valve timing causes rich emissions. I agree with RDG100 suggestions before looking for a mechanical failure.

Scott M.

Bad MAF.

WallyP

The cat will clean up minor problems, but the LH ECU has to hold the fuel/air ratio right at stochimtric. To do this, the Temp II sensor has to tell the ECU the correct engine coolant temp, the MAF has to tell it the amount of air coming in, and the oxygen sensor has to tell the ECU what the ratio coming out of the exhaust is. A failure of any of those components will cause your problem.

Mike Frye

OK,

Here's the update after the tune-up.



Still no good.

I just printed pages 50-94 of my volume 1a manual to see if I can isolate the problem. I'll check on all of the sensors that I can. Is there an official 'Porsche' name or description for the MAF that I'm not seeing? Or maybe a part number?

Andre Hedrick

This explains the gas mileage issue, all these emissions at zero (0) RPM!

Mike Frye

Andre,

You should see how much it went up when it was running!

JK.
I noticed that too, I'm not sure why that was on there, I guess they can manually enter that value and they just didn't bother.

Anyone know where I can find the part number or a different description for the MAF in the manual for an '85?

Also, don't you love the way the manual dictates that in order to troubleshoot, the engine, electrical system and ignition system must be in perfect mechanical condition? If that were the case, why would I be troubleshooting?

John Speake

Have you set up the idle CO as described in the Workshop manual ?

Mike Frye

John,

I see the adjustment instructions in there, but I'm concerned about two things:

1. I'm thinking this was probably set up correctly when everything else was good, and
2. It's more likely that something else went bad, so finding and fixing that should come first.

If you've had experience where this has helped though, let me know and I'll give it a shot.

________________________
One additional point. Could any of the sensors listed above cause the carbon I'm getting on the plugs? When I took out the new plugs to check the compression, there was a lot of carbon in there.




__________________________________

John Speake

If the MAF is aged, then you will find you won't be able to set the CO to the required value. Because you disconnect the O2 sensor for this test, then it will be just a check of the MAF.

When you reconnect the O2 sensor and still measure CO on the test pipes, it should be at the same or similar figure to the one you set. (O2 loop now active). If it isn't there is an O2 loop problem.

If you are feeding the correct stoich mixture into the cats, then if they are OK, the numbers should make the car a pass.

If not, suspect the cats..

Mike Frye

John,

Thanks again, I'll read up on this and give it a shot.

Bill51sdr

Were these readings measured at idle or 2.5k rpm's? You are running very lean, may even be mis-firing judging by the HC readings. The NOX readings you have are partially due to this lean condition. If at idle, the CO adjustment will help, but if this is at higher rpm's that adjustment will have no descernable effect.

Mike Frye

Bill,

They make you get out of the car and they run the test (OK, 1st gear is down this way, and the e-brake, well, there it is, OK, you got it?).
Anyway, they run it on rollers in gear, and I think they rev it up a little, but I couldn't tell you how far. I can't imagine it getting up to 2500, but it may be.

As Andre mentioned, they didn't note the RPMs or speed on the test sheet.

Bill51sdr

Ok, dyno test under load. You have problems that a simple CO adjustment is not going to cure. As stated by others above, may be best to start out by testing the MAF. If that checks out the cats may be deactivated and in need of replacement. The suggestion on the O2 sensor is a good one as well. As the engine is running now, you should be seeing a reading of around .7-.8 volts considering how lean it is. Ideally the sensor should be varying rapidly between .2 to .8 volts if all other systems are operating properly. Good luck!