Techs, I have a fuel question.

[3,503 lbs of trouble]

The following is from the DeLorean Mailing List (the DeLorean version of the CF). It's a reply to a guy who bought a DeLorean in Colorado and drove it home to California where it won't pass emissions. The owner of the DeLorean mentioned the car has always been run on premium fuel to which someone responded with the following:

From: "Tom Niemczewski" <tomciodmc@...>

Date: Fri Dec 16, 2005 8:23 am

Subject: Re: [DML] Re: Failed emmissions AGAIN Tomciodmc

Hello Nathan

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. 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.

BTW, 87 octane in USA is the same as 91 in Europe.

Good luck

Tom Niemczewski

vin 6149 (in Poland!)

tomciodmc@...

www.deloreana.com

Is what he says above true, that running a low compression engine like mine, 8.8:1, on premium will cause deposits to build up that actually raise the compression and cause problems like this guy states, or is he showcasing his Polish education? Basically, will running 91 in a engine made to run on 87 hurt it? I don't think so, but hey, maybe I'm wrong.

By the way, the DeLorean Owner's Handbook, under capacities states "(91 octane unleaded only). Then on the next page it reads "Your De Lorean is designed to operate at factory specification at UNLEADED GASOLINE only of at least 87 anti-knock index (R+M/2) (91 research octane number)." The manual was printed in the UK because it says "tyre" rather than "tire", but the car was manufactured for the US market, not Europe, so if there is a difference between 91 octane in the US and 91 octane in the UK, which one is this damned handbook referring to??!?

What should I be running the car on? 87, 89 or 91? I run it on Chevron 91 now.

[Desertdawg]

Higher octane fuel will cause deposits to form over time...So eventually there wouldn't be any room left for the piston to hit TDC, right???

Then he states that idling in traffic will allow the lower octane to form the same deposits??? So much for the first theory...

I think the doodie is getting a little deep here...

I bet this guy is going to suggest moth balls in the gas tank after the next failed test...

[3,503 lbs of trouble]

I bet this guy is going to suggest moth balls in the gas tank after the next failed test... 

Oh Jeeze!

[BSeery]

usually higher octane is a slower burn, and harder to ignite. Less prone to pre-ignition by a hot spot, high compression or bad timing. There for you could believe that it's a slower burn then maybe it won't burn all the way. Well, I don't know about that. If that was the case then all our Corvettes would run like total crap.

I do agree that putting 91 - 93 octane in anything that isn't 9.75 or higher compression is a waste of money, unless you are towing and putting heavy loads on the engine.

[knkayotte]

Good possibility. Noticed the car was from Colorado, altitude might have been a factor also. High altitude plus high octane fuel in low compression car could lead to carbon deposits from unspent fuel.

Unbelievable how misinformed the public is about the different grades of fuel. With 8.5:1 compression in the 72 Vette I?m running 87 with 0 ping.

Love the people who say every 3rd or 4th tank the put in higher octane to help out their engine when their car is running just fine on the lower octane stuff.

[ICULUKN]

Well.. The first misnomer was that Colorado has 93 octane.. they dont... I lived there for a year in 2001 and they have crappy 91 just like California; and us. Second problem is that this guy doesnt know crap about fuel. It may be true that running 91 octane on a motor designed for 87 will not increase performance, but this is due to lack of timing in the motor to burn the slower burning fuel, not due to deposits left.

[Donbecker]

Did they state any details about what part of the emissions test he failed?

Basically, different things on your car will effect different types of emissions. It's pretty easy stuff.

I doubt that it has that much play in it...

[3,503 lbs of trouble]

Did they state any details about what part of the emissions test he failed?

Basically, different things on your car will effect different types of emissions. It's pretty easy stuff.

I doubt that it has that much play in it...

Here are the threads:

http://autos.groups.yahoo.com/group/dmcnews/message/59529

http://autos.groups.yahoo.com/group/dmcnews/message/59631