Help!..........Failed Emissions

[SF944]

Help!..........Failed Emissions

Before I go crazy with trying to diagnose the problem, I'm hoping someone out there may have had a similar experience and lead me in the right direction:

The car: 1991 with Dali chip, Comptech exhaust and headers. 93K miles

The problem: "Massachusetts" (tough emissions standards including a dyno run under load) Of course trucks and buses are exempt from emissions testing, but don't get me going on that one......

The results:
HC 2.21 (limit 1.20 gpm) FAIL
CO 6.40 (limit 20.0 gpm) PASS
NOx 0.29 (limit 2.50 gpm) PASS
CO2 240.57

By looking at the HC graph, it appears the highest HC reading occurs early (just off idle?). And, it appears the car has a slight skip and rough idle (I had attributed this to the chip, but I've never driven a stock NSX) -- so much so that the steering wheel and rear spoiler shake intermittently at idle.

The car had been sufficiently warmed up, including a high-rpm highway run, sniffer was put into the right-hand tailpipe (does one exhaust outlet run "hotter" than the other?).

Options:
new plugs? (which ones?) -- (no I haven't yet checked to see if they're gummed up) Should I be running special plugs with the Dali chip? Is the Dali chip known for richening the mixture too much?
If the chip is the culprit, would someone have a stock chip in Mass. that I can "borrow" for the test? (I'm assuming the ECU can be swapped easily, yes?)

Any help would be appreciated. Please don't PM-me, as I havent' figured out how to use it, but to save bandwidth, feel free to email me direct at [email protected]

Thanks in advance. --Scott

 

[NSX-Racer]

I know at least one case where a similar problem with a NSX in Switzerland was solved by simply changing the sparks (OEM platin), but that was a car with stock chip and stock engine.

 

[bayareansx1999]

i remember seeing one of those addictive you can put into your gas tank that can guarantee your car passing smog. i think it was like $20 something dollars though and was on sale at Kragens.

 

[ak]

http://www.autoshop101.com/forms/h56.pdf

I found this online. Was this idle or dyno test?

 

[Larry Bastanza]

ak,

Nice reference, thanks!

There is a few things this can be:

Spark Plugs
Coils
Egr valve/system

I would remove the Dali chip. You really should take the car with the stock chip, since if I recall, there may be some timing changes with the chip (no 100% sure about idle timing though, I would e-mail MJ and ask).

If you have a slight hesitation off idle the engine is not running 100% and any of the above can cause it.

When was the last time the car had a complete service?? plugs/filters/valve adjust/egr checked??

Do you get an engine check light ever?? If so, what codes??

HTH,
LarryB

 

[JPS Europa]

I would agree with Larry as far as making sure you are in the best state of tune and I would also go with the stock chip. Note that not all Mass inspection stations make the NSX do the dyno test. If they think that the car is configured in such a way to make it unsafe or potentially damaged on the dyno, they do an idle only test. This how they checked my car at the Kingston Shell just off Route 3. The manager did not want to do the dyno test even though he had my permission. It would be a 40 minute drive for you.

Oh yeah, High CO is a partially burned gasoline problem. Probably too rich or a weak coil/plug or bad O2 sensor. Although I would expect to see higher HC (unburned gas) with a coil problem, it is not always the case. Does your check engine light work?

 

[SF944]

Thanks Larry, JPS, and others.

I've had no check engine light and unfortunately don't know when the last major service was done.
I emailed MJ at Dali for advice and he seemed to suggest I try the stock chip also.
I plan on checking the plugs this weekend and giving it the once-over in my garage before taking it in for a multi-million dollar valve adjustment. Fingers crossed. How can I check the EGR valve at home??

JPS-- that Shell station you mention may be worth looking into if all else fails, but I'm shooting for fixing the problem first. Would you be willing to lend me your stock chip if need-be?

 

[The REAL nsxtasy]

I've had no check engine light and unfortunately don't know when the last major service was done.

Then it might be a good idea to do a complete major service (like a 30K/60K/90K service. If you don't know whether the timing belt has ever been replaced, it would be a VERY good idea to do so, since it is now overdue on both time and mileage.

taking it in for a multi-million dollar valve adjustment.

A valve adjustment alone normally costs around $300, but it is usually included as part of a 30K or 60K service, which costs $800-1100.