RE: [DML] Is My Idle OK?

["John Hervey" <john@xxxxxxxxxxxxxxxx>]

Todd, See below:

-----Original Message-----
From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On Behalf Of
Todd Nelson
Sent: Wednesday, June 28, 2006 4:49 PM
To: dmcnews@xxxxxxxxxxxxxxx
Subject: [DML] Is My Idle OK?

List:

The idle on my car seems to be a little rough, this could be due to it using
a very old mechanical fuel injection system or it could be something else.

Todd, Have the injectors been cleaned or checked to see if they are all
matched in pressure and bleed down.

 As this is the only DeLorean I've ever seen, much less driven, I'm not sure
what I should expect from the car as far as idle quality, and startup ease
is concerned.  

Todd, I have had cars in the shop that Idle as smooth as any car should.

When started, which can sometimes take a little help from the throttle
pedal, the idle will fluctuate slightly, according to the in car tachometer
it doesn't appear to be too bad, maybe 50 RPM's.  However a short time later
the idle will sag maybe 150 RPM then pick itself up again, it will continue
in this cycle until I begin to drive it, at which time it may reappear.

Todd, I would consider replacing the 02 sensor and re adjust the mixture
screw.

  Upon inspection of the engine when idling I will notice that it does seem
to shake a little more than I would consider normal.  When sitting at a stop
light you can really feel the car rumble, I kind of like it, but if it's not
normal then I should do something about it.  When I bought the car I noticed
that the cap to the mixture screw was gone, assuming the mixture was set
incorrectly I used the dwell meter approach connected to the diagnostic plug
to watch the readings while the car was at running temp.  Needless to say it
was off, not swinging between 45 degrees.  However I am unable to get it to
a steady swing, sometimes swinging between 45 and 50, sometimes 35 and 40,
sometimes 40 and 50, I will notice this with the screw in the same place.
The mixture screw hole is plugged during these readings, it just seems more
erratic than it should.  This leads me to think there is a vacuum leak of
some kind in the system.  Although this seems unlikely since I have replaced
all of the engine vacuum hoses, intake O-rings, "air horn" paper and rubber
O-rings, cold start valve and tube O-rings, fuel distributor to mixture unit
O-ring and the paper gasket between the two halves of the mixture unit.


Vacuum leaks normally are a steady problem as the vacuum is leaking.


I have used the propane method for finding leaks, but it has proved
unsuccessful.  What seems odd is as a test I removed the air cleaner while
the engine was idling and "squirted" some propane directly in the intake to
see/hear the results, but surprisingly nothing happened, this didn't seem
right to me.  I thought it could be the constant idle speed system
regulating the idle, but this seems unlikely as I wouldn't suspect it to
function that quickly.  At any rate I disabled the system by unplugging the
ISM and manually idling the car by using the "brass screws".  I experienced
the same results.  The only other running problem I've noticed is when
manually working the throttle spool I can just barely hear a quiet pop like
a small backfire, just when holding at a constant high RPM.  When driving
the car it's completely unnoticeable.  Other than that the car runs fine,
acceleration seems good and power seems to be normal.  Then again, I've
never driven another DeLorean.  Any thoughts?

Little pop's in the intake are normally a sign of running to lean and a WUR
needs to be replaced.

John Hervey
www.specialtauto.com


Thanks,
Todd Nelson
1561, Vermont
http://www.rit.edu/~tan5732





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