Re: [DML] What gas octain to use (Chuck)

["content22207" <brobertson@xxxxxxxxxxxx>]

Several possibilities spring to mind:
- Carbon buildup, as Joseph suggested
- Modified or replacement engine, as Warren suggested (Euro spec
Renault blocks were sold as replacements to the DeLo community in the
mid-late 1980's -- I had one)
- A vacuum leak (see the melted spark plug pic in #5939's photo album
to see what a cracked line to the HVAC switch did to me)
- Over advanced base ignition time

Pull all 6 spark plugs to see what's going on inside your engine. You
need to pull all 6 because a problem in just one cylinder could be
causing your predetonation (a loose fitting spark plug itself can be a
culprit). If they are melted, cylinder temps have risen
astronomically. If they are clean & white, cylinder temps are too
high. You want a tan or caramel color.

Don't assume just because the crank pully points at 13 degrees that
base ignition in fact is 13 degrees -- if the timing scale is off, all
your readings will be off. I ran into this on a car in Charlotte
recently, but off in the other direction (13 degree reading was
actually closer to TDC).

Is your engine hard to start? One of the symptoms of over advanced
base time is hard starting. Does your engine run too hot? Another
symptom of over advanced ignition is excessive combustion chamber temps.

There is a 100% accurate procedure to re-index a PRV timing scale
(short of the screwdriver in spark plug hole method, which I've never
mastered on any engine because of the angle):
- Rotate the engine manually to 20 degrees BTDC
- Remove the block plug closest to the front of the engine (under the
intake manifold)
- Insert a foot long 5/16" drill bit into the hole, letting it ride on
the #6 counterweight
- Continue to rotate the engine until the drill bit drops into a
pre-drilled hole in the counterweight
Cylinder #1 is now at TDC. Move the timing scale to reflect such, and
you're ready to set base ignition time.

Until then I'd recommend retarding base ignition time by ear
(clockwise). Isn't going to hurt anything, and may solve your problem
without removing the intake manifold and muffler (can't reach the
crankchaft nut with a stock muffler in place).

Some people subscribe to the theory that optimum ignition is at the
threshhold of predetonation. Your PO may have been one.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, beatlesra1@xxxx wrote:
> 
> Unbelievable but true..My car will only run on 93 or 94- octane. If
I  put 91 
> in it's knocks like crazy. I've told this to a few of me fellow
Delorean  
> owners and they think I'm crazy!
>  
> Chuck Vin 6125
> DCO
> 
> 
> [Non-text portions of this message have been removed]








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