[DML] Re: Question for owners with issues.
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[DML] Re: Question for owners with issues.



No problem. All we need to do here is a little bit of proper 
troubleshooting, and I'm sure that your issue is easily resolvable. 
In the process however, forgive me if this post starts to sound a bit 
juvenile. It's not my intention. I just want to explain things of how 
I would troubleshoot your issue, in as simple of terms as possible...




Let's start with what we know to be true about the situation, and 
work our way backwards from there to diagnose what the problem really 
is that's causing the issue.

The issue here is that your car will not pass an emissions test. 
Specificly, the NOx levels are too high, but the CO dilution, and HC 
levels are acceptable.

>From this alone, we know that the Catalytic Convertor on the car is 
working properly. Otherwise, you would have failed the O2 & HC 
dilution levels portion of the test.

We know that an engine tuned to factory spec will pass emissions 
properly. But we have to figure out what variables may come into play 
that would negate those factory settings. We have two options here.
Option 1: Start from scratch, replace EVERY component, and *hope* 
that we happen to fix the issue in the process. The Cons of course 
are that we may not resolve the issue, it's wasteful because we're 
replacing good parts, and it's expensive.
Option 2: Work backwards to diagnose the issue, pinpoint the culprit, 
and resolve it from there. The Cons are that it's just time 
consuming. But it will save you allot of money in the long run, as 
well as many headaches of trying to figure out what the issue is, 
when a "blanket repair" fails.

Now I'm not from Missouri, but I do like to to see things for myself. 
However, we'll go ahead and say that DMC-GG did infact properly set 
the CO mixture, and engine timing properly. After all, we don't have 
any reason to doubt them.

Still, the engine doesn't pass. You have performed a tune-up, and 
even replaced the Catalytic Covertor. Still you don't pass.

Now let's take a step back to square one where we started out at. 
Your NOx emissions levels are too high, even after the work performed 
thus far. So, let's take a look here real quick like:

http://capita.wustl.edu/CAPITA/CapitaReports/EmisTrends/soxnemc.html

Now we know that high combustion temperatures are what cause NOx 
emissions. So what causes a high combustion temps?

The first item is if the engine is running too lean. Now we know that 
a CO adjustment was already performed, so the Air/Fuel ratio has 
already been adjusted properly. But a vacuum leak could also throw 
that mixture off, by introducing unmetered air into the system and 
causing a lean-burn condition (higher combusion temps). So now, we've 
got to check for a vacuum leak. To do so, grab a can of starter 
fluid. Pull a hose off of the Cold Start Tube, and spray some in. If 
the engine idle starts to rev up, then we know that there is a vacuum 
leak somewhere. If not, reconnet the hose, and spray around it, to 
make sure that it's not the culprit.

Now, if a vacuum leak is discovered, repair it, ensure it's gone, and 
start all over again with readjusting the CO mixture, and test again.

If no vacuum leak is detected, then we have to continue on...

One band-aid option is to simply retard the ignition. But we don't 
really want to do that. It's not a factory specification, so the 
engine will not run optimally. Also, it may lead to improper 
combustion, and could adversely affect the other emissions readings.

So what do we do. Well, we know that the engine is running to spec, 
and is in tip-top shape. Perfomance is good, I imagine that your fuel 
economy is also good too. However, we've still got high NOx levels in 
the exhaust. We know that it's caused by high combustion chamber 
temperatures...

Carbon build up. Carbon build up is bad, as you know. Carbon is an 
engine deposit that attaches itself inside of the valves, and the 
combustion chamber. It's bad because it heats up, and will stay hot. 
If there is too much carbon present, it will ignite the fuel, and 
will cause it pre-detonate, before the sparkplug can ignite it at the 
correct time. Carbon also doesn't disappate heat as quickly as the 
iron and aluminum pistons of the engine, so it stays hotter...

Your car has a history of an owner fueling up with too high of an 
octance gasoline. If the octane is too high, it can't fully burn, and 
thus carbon deposits are left behind over time.

It may be entirely possible that you have significant carbon build up 
inside the engine. Not so much that you're getting a pre-detonation 
knock, but enough that the combustion chambers cannot disappate heat 
fast enough, and are in turn keeping those temperatures higher inside 
the engine.

To help get rid of carbon build up, Techron is a great fuel 
detergent. A good dosage, along with some prolonged use of Chevron 
gas will help to give the engine a good cleaning out.

So what other alternative do you have to reduce combustion chamber 
temperatures? Simple! Click on this link, and scroll to the bottom:
http://auto.howstuffworks.com/ignition-system2.htm

By using colder spark plugs, there is a good chance that you'll be 
able to reduce the combustion temperatures, and reduce the NOx levels 
as well. I know that switching to 2 levels colder of a plug, I was 
able to get rid of a mild knock that my engine had.




Now I hope this helps you out a bit. Like I said before, I wasn't 
writing this with a condecending tone. I just wanted to explain as 
simply as I could what troubleshooting steps I use, and how I would 
have adapted them to your issue.

Quick and dirty answer: Get some colder spark plugs, and a big bottle 
of techron. Drive around at least 1 tank, and test the car again.

-Robert
vin 6585 "X"



--- In dmcnews@xxxxxxxxxxxxxxx, "valleyrat12" <valleyrat12@xxxx> 
wrote:
>
> Hello Robert,
> 
> I understand your criticism.  I have owned my Delorean for about 
> two weeks now and am currently waiting for my workshop 
> manual to be shipped out to me from the PO.  
> 
> After the car failed dthe first time I took it to DMC in garden 
grove. 
> they adjusted the fuel mixture and checked the timing to be 
> certain that they were in spec. It failed again after this checkup 
at 
> which point I ordered the tuneup kit and a Cat and O2 sensor 
> from john. Since installing these components the car it has been 
> running really well, however STILL fails smog.  I will again be 
> taking the car to Garden Grove, this time hopefully it will be 
fixed.
> 
> I guess my point is that when there is something beyond my 
> understanding (Fuel Mixture/timing) I DO take it too the experts.  
> Things like tuneups, electrical trouble shooting, etc I can do very 
> well.  The Smog thing I can not figure out, and neither can a lot 
of 
> other "experienced" people I have talked too. that is why I post 
> here. I firmly believe in the power of on line forums like this 
one. 
> Many people with many different experiences can voice their 
> experience.  I then sift through and decide which apply to me.  If 
> you have suggestions for how to better utilize this resource 
> please let me know.
> 
> Nathan Sobieralski
> 2277







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