mcholdfast

I'm having trouble getting the ROW to pass emissions again. Everything is good except for high NOx levels as usual. I thought the O2 sensor may have been the culprit but a swap with a known good one didn't help. The cats are only a few years old.

I thought I'd swap out the LH with the 89 S4 and see if that helped but when I pulled the LH from the ROW 90 S4, I found some things that don't look normal, to me at least. There are three "modules" that are attached to the LH/EZK bracket, one that is bolted to a plate that was welded on. Another that is just a multipin plug and a third that has what appears to be an adjustment screw. Any ideas what it adjusts? Also, the 89 has the clear plastic relay (?) attached at the bottom which I am accustomed to seeing. The 90 doesn't have one.

I'd still like to swap the brain but I'm a little nervous about doing it after seeing the difference in the two installations. Is it possible that I may damage the 89 S4 brain if I install it in the 90 ROW S4? The noticeable differences are the things attached to the bracket so it may have nothing to do with the brain but given the cost to replace, I want to be sure. Along with everything else, I noticed that the tabs that hold the cover on the LH were all bent upward so that the cover would almost fall off if the mounting bracket wasn't holding it on. It had obviously been opened.

Here's a bunch of pics. Can anyone tell me if these look normal for a 90 S4 and if not, any thought as to what the extra bits are? Does it make sense to swap the LH to help fix the NOx emissions problem? Thanks in advance for any input.

Bill Ball

If they are Random Technology cats, that's about how long they last. We've had a number of local cars fail smog with these cats after only a couple of years.

mcholdfast

Ok, the welded on plate holds the TRW airbag sensor part #92861322002. That was easy enough to figure out and makes sense given the origin of the car. Any ideas about the other two connections?

mcholdfast

Thanks for the info, Bill. My next plan of attack is to swap the exhaust and see if that does it. I would just swap the cats but they're welded on the ROW. I also noticed that there's no airline from the air pump on the ROW.

Rich9928p

All LH fuel injection modules from 1987 onwards are "worldwide" ... there are no differences for different markets. The coding plug (Codierstecker) programs the LH for the different world markets.

The ROW 928s that have no cats nor lambda sensor require CO tuning via the potentiometer (shown in the photo with the flat head screw). The ROW 928 requires periodic manual base CO adjustment to run properly.

mcholdfast

Thanks Rich,
This sounds like it might be the beginning to the end of my emissions problem. Other than a screwdriver, what equipment is required to set the base CO adjustment? Is the procedure documented in the WSM?

MGW-Fla

Mike, wish I could help you with the technical aspects. However, I do have you a solution. Move to Florida where we no longer have emissions testing & instead of worryin about cats, NOx levels, O2 sensors & LH brains, you can just enjoy driving your sharks!!
Plus you will be lots closer to come to Sebring & Daytona!!

Hilton

First step I'd suggest is making sure the coding plug is correct for using an O2 sensor.

Chances are the cats used to federalise the car have been compensating for the O2 sensor doing nothing (assuming the federalisation process wasn't intimately familiar with 928s).

FYI - the potentiometer should be adjusted with an emissions sensor attached pre-cats and airpump, and set to 1.0% CO output. As MAF's age, they go leaner, and the CO will drop and NOx go up. The exhaust test ports attached at each end of the airbox (with grey caps) are for exactly this.

Turning the potentiometer clockwise enrichens the mixture, ccw leans it - you can measure the value across pins 1 and 3.

I just removed all the old non-cat air-pump plumbing on my '89 as I want to remove the potentiometer and fit an O2 sensor to my car when I get an x-pipe. To make sure I wasn't getting wrong info from the O2 sensor, I plugged all the exhaust ports in the heads for the non-cat air pump system (M12x1.5pitch).

Interestingly, the air pump gear came complete with a set of 8 10mm M12 spacers rather like the ones MK made for his brake caliper mod! heh

mcholdfast

Tempting but it's too flat down there. I like having the mountain twisties close by.

dprantl

Can you post all your emissions results? It may help in the diagnosis.

Dan
'91 928GT S/C 475hp/460lb.ft

mcholdfast

Thanks Hilton. How do I find this information?

mcholdfast

Will do tomorrow.
The last time it was tested, it passed the 25 MPH test and failed the 15 MPH test by very little. It was very close. NOx is the only problem. The other tests have always passed with ease. I replaced the O2 sensor and retested today and the NOx was higher than the last time but about the same as it had been in previous tests.

blown 87

One thing we do to "Trick" the test on a marginal car when everything eles is where it should be is to hook up a water bottle with a small orfice, maybe .020-.030, anything that drops the combustion chamber temps will lower that Nox.

May not help yours, but we have made a bunch of cars pass doing this that had marginal converters.

And as Bill said, a couple of years from any after market converter is good, if they make it that far.

One other thing that can help is a good carbon cleaning, like the BG products intake cleaning system.

Anything you can do to take ignition lead and fatten up the mixture will help if the other numbers look good, plus test it cold.

If you need more detailed info on what I am talking about you can call me at the shop, pm me for a number if you do not have it .

Hope this helps

Greg

mcholdfast

Thanks Greg,
Do you have the emissions sensor needed to set the base CO adjustment that Rich and Hilton mentioned in the previous posts? If so, I may take a trip to your shop soon.

blown 87

Yes, but it has been years since I have used it, there is not much in common in a real world test and what you are going to find at the testing station.

If you want to use it you are welcome to it, but it is not going to help you much, what will is having a testing station that is willing to work with you and run in test mode to see what you have, that we do have.

From what I have found there can be a big difference in making one pass and making one run right.

How far off are your numbers on Nox?