Re: [DML] Re: Failed emmissions AGAIN - really long
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Re: [DML] Re: Failed emmissions AGAIN - really long

Hello Dan and others reading this...
First I have to apologize for the length of this post... I wonder how many 
will actually read it all the way to the end ;)

>> ...the answer to that would be that whoever
>> wrote the Owner's Handbook must have made a mistake or just forgot to
>> mention that in YOUR book. I say "your" book because mine clearly
> states
> I have a 1983 Owner's Handbook. Probably the last edition printed. You
> are correct. It does state that on page 40. I however was referring to
> page 39 where is says:
> "Fuel Tank          51.6 litres          13.2 gallons
> (91 octane unleaded only)"
> When I see "91 octane unleaded only" in the handbook of an American
> I now understand the difference between (R+M/2) & RON because I looked
> it up on Wikipedia. I also now see that the Owner's Handbook was
> poorly written.
Exactly... Most people don't know the difference between grades of gasoline 
and they go by the assumption that "premium" or "super" is better. It's 
clever marketing by the oil companies that really works.

>> Is this a bulletproof enough source? :)
> Yes, but looking back on what I wrote I was apparently not clear
> because I was referencing the desire for bulletproof sources on your
> claim of deposits building up due to using higher octane fuel than
> required that leads to emission issues
>> The higher the octane number the less chance for detonation but
>> at the same time combustion temperatures are higher.
> Okay, so wouldn't higher combustion temps burn off these deposits?
> Again, I'm not arguing as much as approaching this from the point of
> view of someone with limited knowledge attempting to apply common
> sense based on what they know.
Ok, you would be right in this case... it seems logical, but you are 
forgetting one thing. In case of the engine the time of the burn is also 
important. This means that all gasoline needs to be burned in a 
predetermined amount of time. Because of this when you use higher octane gas 
there will not be enough time for all the mixture to burn properly. Higher 
octane fuel burns slower and because of that the temperature is higher but 
before all the gas is burned inside the cylinder it is being pushed out of 
the cylinder because the exhaust phase has already started. If the engine is 
designed to use fast burning gas, the slower burning premium will be pushed 
into the exhaust before it has enough time to burn. This will raise the 
emissions. All the unburned gas will end up in the catalytic converter where 
it will be burned up causing the converter to overheat. This after some time 
will cause deposits to form inside the combustion chamber and will damage 
the converter.
Makes sense? ;)

> Also, my previous question still
> remains. If you have an engine that has been run for a long time 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 fuel lower in octane than appropriate for the
> engine's "new" raised compression ratio? I mean, if the deposits
> raised the engine's compression, wouldn't running a fuel that is not
> adequate for the current compression cause knock rather than clean out
> the deposits?
YES, You are right. It might cause knock when you switch to 'regular'. It 
the engine has been run on premium for a long time it will sound much worst 
at first. BUT with the raised compression and now faster burning fuel the 
deposits will be cleared out of the engine pretty quickly. That is why I 
advised to go on a hour long drive at highway speeds. Detonation and knock 
usually occur at high loads (heavy acceleration). Cruising at constant 
highway speed does not put a lot of load on the engine and at the same time 
keeps it running at high RPMs. Great exercise for the engine, clears any 
deposits, moves a lot of gas through the converter clearing it as well.

> Ambient air temp is another factor in detonation. I know this through
> experience, not through a text book. Again, I live in Phoenix,
> Arizona. One mile above hell, lol. I have a '97 T-bird with a 3.8
> liter V6. It's a low compression engine too, and Ford suggests running
> it on 87 (R+M/2) <SNIP>
> Will the PRV V6 do the same? I don't know, but I also do not want to
> find out.
This will probably offend a lot of people but that is my point of view... 
Don't compare Ford to the PRV. Ford stands for Fix Or Repair Daily ;)
But seriously, that doesn't mean all engines will act the same. It all 
depends on timing, mixture, how the valves are set.. There are many 
variables. Ambient temperature might have some effect but not a lot. The 
engine temperature is controlled by the thermostat and it should be constant 
regardless of ambient temp. The slightly higher intake temp will cause a 
slightly leaner mixture, but FI computer should compensate for that. Maybe 
it was just time to get the valves adjusted in those cars? Check the 
maintenance schedule.
Anyway, a little knock is not dangerous to the engine. A little means that 
it is not constant and not very loud. If you only hear it at high loads 
(going up a steep hill) then it's ok. If you hear it often then you should 
check the timing, timing advance and adjust the valves. On some cars the 
valves need to be adjusted very often. I used to have an old Fiat where the 
valves were suppose to be check and adjusted every 10k miles! It depends on 
how the engine was made.

>> And the most important thing - 93 IS NOT BETTER than 87.
> It is if it prevents detonation in your particular engine regardless
> of what a handbook says. I'll take emission fouling deposits over
> detonation any day!
I would say check if everything is as it should be. If the car was designed 
for 87 it should run the best on 87. If it doesn't then something is not 
right. Be it the timing, timing advance or valve adjustment. BTW, timing 
advance is a common problem on the DeLorean. On every DeLorean that I looked 
at the advance solenoid had a vacuum leak! This will cause knock at high 

> By the way, just an FYI. Premium fuel in Colorado is 91 (R+M/2), not
> 93 (R+M/2).
True... I didn't look at where you were. I used to live in FL and got used 
to 87, 89 and 93. Lower octane premium is used at higher elevations because 
of lower oxygen content in the air. 93 plus low amount of oxygen would cause 
an even slower burn adding to the problem.

I would like to congratulate everyone who got this far reading my tech 
stuff. You must be really TOUGH! ;)

Greetings from Poland

Tom Niemczewski
vin 6149 (in Poland!)

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