[DML] Re: Failed emmissions AGAIN

["Dan" <djdanwilson@xxxxxxxxx>]

--- In dmcnews@xxxxxxxxxxxxxxx, "Tom Niemczewski" <tomciodmc@xxxx> wrote:
> 
> One of the reasons for your failed emissions might be the prolonged
use of 
> premium fuel. I am assuming that you mean 93 octane. Higher octane gas 
> causes deposits to form inside the cylinders and in the exhaust
system. That 
> in turn will over time cause the compression to be raised. With that
you 
> will get higher temperatures in the center of the cylinders along with 
> unburned gasoline close to the edges of the cylinders.

How come I've never heard of this? Granted, I'm not a mechanic nor an
engineer, but I'd think is this were true enough to cause problems
this knowledge would be more common than it is.


--- In dmcnews@xxxxxxxxxxxxxxx, "Tom Niemczewski" <tomciodmc@xxxx> wrote:
> 
> The DeLorean engine 
> was designed to use 87 octane gasoline and this is what you should use. 
> Using 93 will just cost you much more and will not do any good for
the car.
> Before you go to test the emissions again make sure to burn all of
the 93 
> you have in the tank and then fill it up with 87. Then go for an
hour long 
> drive at highway speeds. This should clean up a lot of the deposits
left 
> from using 93 octane fuel. From there go directly to the testing
station. 
> Try not to get stuck in traffic as idling for prolonged period of
time will 
> again cause deposits to start forming.
> I posted about the use of 93 gas in the past, but I guess it's a
good idea 
> to mention that again for new members on the list.


Yes, the DMC version of the PRV V6 is a low compression engine, so in
theory I can see why running 87 should not be a problem, but the 3.8
liter V6 engine in my '97 T-bird is a low compression engine too, and
if you run it on 87, like Ford suggests, on days over 80 degrees or
when climbing hills at any temp it detonates like mad. When you run 89
or 91 it does not. I know the PRV is a different engine than my Ford,
but who's to say it would not do the same out here in Phoenix where
it's never cold.

Okay, let's say we have an engine that has been run on higher octane
fuels than required, and it now has these "deposits" built up that
have raised it's compression as a result. Wouldn't suddenly running it
on lower octane cause, or run a higher risk of detonation since you're
now running low octane fuel in a higher compression engine?

Again, I'm not a mechanic, so my knowledge is limited, but I think I
would have heard of this somewhere. Can you point me to an obviously
legit source that will confirm this? I know some GM powertrain
engineers. Next time I see them I'm going to ask them about this.
'Till then I think I will just keep on running my Chevron 91.

Dan W.
VIN 16192
AZ-D








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