Yet Another NOx Fail Thread

[Porsche_monkey]

I failed my eTest on Nox on my 89 3.2 Cab. Everything else is good. Very good.

NOx was at 763 vs. an allowable upper limit of 652.

Ideas:

1. connect the ECU brown 'California' wire

2. get it hotter prior to testing, this car has only seen about 50 miles in the last two years

3. top up with lower octane fuel

4. richen the mixture a bit to raise CO but lower NOx

5. swap the ECU for a stock version (I have a Steve W chip) (I could borrow a stock 84 ECU from a friend)

6. borrow another Cat (I have one on the car, do not know how good it is)

7. Run some 'Guaranteed to Pass' through the engine, (tricky because I do not have valid plates on the car, so I can't legally drive it until I pass the eTest)

8. New O2 sensor

My retest is cheap, under $20. I am thinking of just doing 1, 2 & 3 and going for a retest. There is no limit on how many times I retest, but I have to pass to transfer the title into my name.

Suggestions?

[175mph951]

i would bet that your chip in the ecu is the reason your not passing. ive seen it many times especially with 944's and 951's that are chipped

[Tyson Schmidt]

Nitrides of Oxygen, (NOx) are formed when combustion temperatures exceed a certain point. Lowering NOx requires lowering the combustion temps.

Retarding the timing, richening the mixture, lowering the compression ratio, cleaning out the carbon build-up in the combustion chamber, getting the EGR system working properly (if so equipped), making sure the 3-way catalytic converter is functioning properly (if equipped) all will reduce NOx emissions.

EGR (not a fitment on your '89, but I'm posting this for others) works by introducing spent exhaust gas into the intake charge, thereby mixing a percentage of inert, incombustible spent gas into the combustion chamber. This effectively lowers the combustion temps. It is done only at strategic times, to prevent loss of performance and driveability. It was the introduction of EGR that actually allowed auto manufacturers to begin raising compression ratios again, while still meeting NOx emissions standards.

I think your best bet is to swap in a stock DME or stock chip. Connecting the California brown wire may actually make it worse due to the leaner mixture.

Steve Wong may be able to help by giving you options to retard the timing VIA the fuel quality switch in the side of the DME that can be moved a number of positions. This will alter the mixture, and/or timing to a more favorable setting for reducing NOx.

[longhornchris04]

How "hot" was the engine. My dad failed an emmissions test in his 92 BWM (several years back). They had him take it out on the highway and drive for 30 min... passed with flying colors. You need the engine and the cat converter good and hot for them to work correctly.

Failing that, I'd say swapping the chip would be your best bet as the "least invasive" method. I don't think fuel octane will make a difference. Injector cleaner might - but only if your injectors were clogged and causing the engine to run lean.

[Porsche_monkey]

My engine was not hot enough. In hindsight that was my fault. It will be hot next time, I will make sure of that.

Can I just swap and 84 ECU into my 89? I think the chips are different, but 'box' itself is interchangeable? I need to be able to put the 89 ECU in to the 84 (so he can still drive) and the 84 ecu into the 89 (so I can pass).

[Steve W]

Make sure you drive you car nice and hot before smogging, an hour of spirited driving is good. If you only drive it 5 minutes down to the smog station, you're asking a lot from the car.

You should also probably swap and smog test with the stock chip - it gives you a greater NOx margin from the limit. With the performance chip, there is more ignition advance in the low load regions off idle/lower rpms exactly where they test. This increases engine fuel efficiency and throttle response, but also doubles the NOx levels. The HC and CO levels remain the same because the mixtures have not changed. For most cars this will still pass emissions tests, but if there's just a bit of imbalance with any part of the motor (ie. manifold gasket vacuum leak, or some partially clogged injectors, it can throw the NOx over the limit.) As an example, at a particular test point, while a stock car may test 450 ppm NOx with the acceptable limit being 1100, with the chip it would normally test around 900 ppm. If the mixture is tripped off balance, it doesn't take much to exceed by another 20%. Hope this helps to clarify what is occuring.

[Steve W]

Also, you can swap ecus from one year to another without issues. It all pretty much works the same.

[Porsche_monkey]

Thank-you Steve. I understand the issue. The 84 ECU with a stock chip will go in for a few days.

Maybe the 84 guy will like the chip so much he will buy one from you.

[Porsche_monkey]

Well thanks to Pelican (and Steve W) I passed. Easily. I swapped ECU's with a 1984 over the weekend. Then I drove the car reasonably hard for 30 minutes this morning (and it is cooler here today), then dropped it for testing.

NOx went from 763 to 499.

And, the Steve Wong chip in the 84 worked so well that either my friend will order a chip from Steve or I will never see my own ECU again. That car runs (and idles) so much better with the new chip it's like he had a real tune-up done.

About to change my signature.....