[DML] Re: catalytic converter question

["therealdmcvegas" <dmcvegas@xxxxxxx>]

Did something change in California? I moved to Nevada 8 years ago, but
for as long as I  can remember, Emissions Testing was just the typical
"two speed" test @ both target RPM of 750 idle, and 2,500 reving.
These are performed with the car parked, and not underload, like on a
dyno. Which of course is going to cause higher emissions, since the 
motor is burrning more gasoline to run.

And aside from being on a dyno, there can be other factors involved
here too. How old was the gasoline? How warm was the car? When was the
last oil change?

If a Catalytic Convertor fails, you HCs will go up slightly (remember,
HCs represent unburned fuel in the exhaust), but you typicly won't
fail that portion of the test. You will however fail the remainder of
the tests when it comes to CO percentage, CO2 dilution, and other
gaseous content in the exhaust such as Oxygen, Hydrogen, and Nitrous
Oxide. These will fail, as there are not enough of them, BUT, your
Hydro-Carbons (HC) should typicly still pass. I've only heard of a
Catalytic Convertor failing once, and it happened to be a local owner
here in Vegas. His HC content was great, but the O2 & CO2 was almost
nill.

Now make no mistake, Catalytic Convertors can indeed fail. BUT, if
this was the case with your car, Instead of high HCs & NOx Emissions,
you'd have high HCs, and LOW NOx readings! Your high NOx measurements
tell me that your engine isn't burning all of the fuel that it is
being fed, and that the Cat is having to work overtime, in order to
burn them off itself. If nothing else, it proves that you Cat is in
good working order.

If I were to guess, you prolly have a clogged fuel injector. Here's
why:
The K-Jetronic fuel injection system is entirely mechanical. Rather
than simply telling an electronic fuel injector to open more
frequently in order to deliver more fuel to a cylinder, our system is
based off of residual fuel pressure. increase the pressure delivered
to an injector, and it will open more, to deliver more fuel. And when
trying to perform fuel management simultaniously on multiple
injectors, with a shared feed point, it has to remain a very balanced
system. So if you have a clogged injector, less fuel is going to be
bleed off from what is offered to the 6 injectors, and the remaining 5
are going to have to spread that extra amount between themselves.
Which means their pressures are going to increase.

So, in a nutshell, one clogged fuel injector will result the car
running a rich condition! Wich will cause HIGH HC content in the
exhaust!

We don't measure NOx here in Nevada (not yet), but we do measure HC
ppm. With a fresh tank of gasoline, I can pull anywhere between 90-112
HC ppm on the idle, and have typicly hit between 12-38 HC ppm @ 2,500
RPMs. Higher readings *can* signify the presence of old gas, and I've
seen this with both my own car, and others. BUT all of these readings
were taken without the car under load on a dyno.

My best advice to you right now? MANY smog check stations will offer
you either a "Pass or Don't Pay", or a "Free, Unlimited Retesting if
failure" type of promotion. Go to one of these, and have your car
tested OFF of a dyno before you go any further. And make sure that you
 burn out any old gas in the tank by taking her out on the highway,
and "blowing the cobwebs out." And perform an oil change. Do NOT ad in
any type of fuel treatments, other than Techron! If this doesn't work,
check you fuel injectors' spray patterns, and check into possibly
having them cleaned. DeLorean vendors should offer this service.
Otherwise, your local BOSH parts and service center should be able to
as well, but possibly for a higher fee.

OBD-II= OnBoard Diagnostics (system) generation II. It's a system that
controls everything from ABS, to engine management, and emissions
control for a car. It's more than just EFI, it's also stores info
about failed O2 sensors, etc. There is no need to replace any ECUs on 
your car. They work just fine, as your catalytic convertor does, I'm
certain.

-Robert
vin 6585 "X"



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