Idle speed seems to be around 950-1000 rpms when cold and doesn't seem to change from that. I haven't driven the car much so I could be slightly inaccurate on these numbers but I can always check.

Regarding the GT conversion the PO told me that besides the big red brakes, suspension and other add on's that their was a chip of some sort added. I can call him and see what he is exactly referring to since I don't have any paperwork on this specific item.

He did rebuild the motor and it appears as though the intake plenum was "extruded and honed" but everything else seems to be oem and not changed... but I will look into it.

Important Note: This car passed SMOG last year with everything that it has on it currently and new "50 state legal cats" which was my concern as maybe they are not working as effectively now. I am changing the O2 sensor and will continue to look for any air leaks on the fuel rail and also vacuum leaks.

I did ask a couple questions above about doing the O2 sensor voltage check and also what is the best way to use a spray bottle to see where air leaks exist... Any input here?

I will report back on GT conversion and what he knows additional regarding that upgrade/change but knowing it passed last year hopefully will not make any major changes.

Thanks,
Bryan

 

What's your idle rpm estimate based on? If it really is 950-1000, then I'd say that it's either a very non-standard chip or you have a vacuum leak (as more experienced people have suggested above).

If you have a chip there that you don't quite know what's in it, rent or buy a Sharktuner. You should be able to get an actual GT calibration in those. It will also tell you what the actual idle speed is and whether the idle adjustment controller is pegging out at the minimum.

Do you happen to know what cams do you have in that engine?

 

If the car has Autothority chips or clones of them , it's very likely thay are causing high NOx. The chips try to richen the fuel mixture and add ignition advance. Closed-loop mixture controls at test RPM's negate the richer maps that Autothority used, while the timing advance curves raise combustion temps. I bought a set of those chips way back when, swapped the S4 versions for the GT version because of low- to mid-range detonation issues, and finally pulled them out for stock to protect the engine. Take a look at the two controllers, accessible in the passenger's footwell cowl-side hidden by a carpeted cover. The bracket unbolts, and slides to the rear for access. Look to see if the cover tabs have been opened previously. If so, open the EZK box and see if the larger chip in there, the one in a socket, still has a factory part number on it. Alternatively, you can try borrowing a set of known-stock controllers and plugging them in for testing. If the tester doesn't mind the visual impact, you can just pop the connectors off the existing conrteollers and attach them to your test boxes sitting on the floor.

 

He told me:

 

I think that the main difference between '91 GT and S4 engines that causes the peak power difference is the camshafts. If this car still has the S4 camshafts, there's at least one more important step to take to make the engine like GT, in addition to making sure that the two ECUs in fact has a GT calibration (or Sharktuning them to optimal calibration.)

The problem is that GT cams are kind of hard to come by. I would ask around if someone has a set of Elgin 65-6 cams on S3 cores for sale, those are well matched cams for this kind of engine.

 

Update:

Did dome research and I will let you know what I have paperwork on and the dates:

1) MAF sensor - replaced at 106,000 miles by Tilmans in Santa Rosa on 6/3/02. The cost for just the unit was $770.20
2) O2 Sensor - I couldn't find anything showing this has been changed going all the way back to 67,000 miles so this was changed today.
3) GT Conversion - No cams were put into this car differently (from what I can see other than tearing it down) than what it came with.
4) GT Conversion - A chip was put in the car. The previous owner to the last two owners which was prior to 67,000 miles did install a chip. I do have the guys name and he works at a Porsche dealership in LA area so I can call but since this was sooo long ago I doubt all of a sudden from last year it has changed anything that significantly.

After the car passed smog last year in March of 2013 there was some work done but all of it looks to be in great shape (on the outside) and was done at the local Porsche dealership and I know the tech who is very good. It was as follows...
- Fuel pressure diaphram, regulators and dampners were replaced on the car. It was brought in and the notes state "replaced regulators due to not starting and they were leaking causing rich condition".

This is what I know. So far I have replaced the O2 sensor (just happened today so could be the solution), checked for any visual signs of air leaks or anything that would cause this issue. I am hoping since the O2 sensor appears to be very old that it was the cause and I can move. Will update soon after my next smog test... which will be for free this time at least.

Any thoughts? Thanks again for all the help and wisdom. This is why I come here. Now time for a cold one... or three.

Cheers,
Bryan

 

Sorry if I miseed it, but have you put new (copper) plugs in? Other than that, good luck!

 

Sorry, you didn't miss it. I forgot to mention. Plugs are going in tonight.

Coming out: BERU R6 819
Going in: Bosch Super Plus 7900 WR7 DC+

The plugs came from Greg

 

Your MAF is 12 years old - thats about what I'd expect for lifetime (my 10 year old one in my non-cat 89 when I got it could not be adjusted to factory idle-mixture spec). Contact your local JDS vendor (Louis Ott in Oregon?) about MAF rebuilding/replacement.

I'd still also consider replacing the chips with stock ones - I'm not sure how much fuelling changed between GT and GTS, but it seems logical to expect the factory put more fuel into the more powerful engine, and thus could contribute to your lean running.

Sounds like you're on track to figure it out.

 

I think I've said this three times, now.

Run the car. Monitor the output voltage from the O2 sensor with the sensor hooked up to the brain. Report back.

Until you do this, you are just playing a guessing game.

 

I am planning on doing this but unsure where to hook the tester up to. Is there a DIY page someone can point me to? Thanks!!!

I've searched but cant find one.

 

This is an important test.

The O2-sensor cable comes through the side of the tunnel, into the CE-panel/footwell area. Pull out the floorboard and look for it near the front edge of the carpet that covers the side of the tunnel, 2-3" above the floor. It's about a 1/4" diameter black cable, 3 wires.

Follow that past the CE (central electric) panel, it may be tucked under the panel-- find a rubber 3-pin disconnect. Disconnect it, and have a look at the three pins: Two males and one female on one side, visa-versa on the other. The single male or female is the signal wire, the other two are the heater.

Now have a look at the backside of the rubber connector on the sensor side (left side that leads towards the tunnel), you may need to pull back (or cut back) some insulation or a rubber boot to get a look-- you want to find the holes where the wires go in, and stick the red meter probe into the single pin, from the backside. Reconnect the two connectors (orienting the male/female pins carefully), insert the meter probe, and find a nice ground connection for the black test probe (the ECU chassis will work well). Start the car, warm it up, and watch the meter.

As Greg said, you should see the O2-sensor voltage moving up and down a two or three times a second, between (roughly) 0.2 and 0.8 volts. This tells you that the LH is actively managing the fuel, in order to main the proper 14.7:1 fuel ratio.

If the MAF were aged and out of cal, or you had a big air leak, then you would see a constant 0.2 volts (too lean) because there is more air than the LH can compensate for. It can adjust quite a bit, but if things are too far off then it just hits the stops and the sensor continues to holler for more fuel.

I don't recall seeing anyone post a picture, but it is pretty clear once you find the sensor.

The O2-sensor is the Bosch 13048, has the correct connector and grommet.

Good hunting,
Jim

 

Thank you, Jim.

Well written. That would have taken me an entire page.

 

Thank you for taking the time to write this. My GTS arrived this morning and I want to do this test too, before I try to pass smog.

 

As always, Dwayne's camera has been there!

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