[T3] Chasing Engine Gremlin - Popping

[Keith Park]

Check you cyl head temp sensor for starters.

Keith


Top Notch Restorations
topnotch at nycap.rr.com 
http://www.a383ina68.addr.com/radiorest/main.htm
71 Squareback "Hothe"
65 Notchback "El Baja Rojo"
65 Squareback "Eggcrate"
87 golf "Winterat"
93 RX7 "Redstur"

-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Robert
Bills 
Sent: Thursday, March 31, 2011 2:19 PM
To: type3-vwtype3.org at lists.vwtype3.org
Subject: [T3] Chasing Engine Gremlin - Popping 


As some of you know, I recently put a '73 Squareback back in service after
14 years of storage by the original owner. Stock fuel injection.
.
The engine starts almost instantly when the starter in engaged.  Idle is
very rough when cold, but evens out a bit after several minutes at a high
idle.  Depending upon how many days the car has been sitting, there is
sometimes a puff of of smoke at cold startup and the exhaust smells rich.
My practice has become to warm up the car at least 5 minutes before backing
out of my driveway.   (I'm in SoCal).  Valves are adjusted; new plugs; dwell
and timing are set to specs.  All factory fuel, injection and hoses are
intact.  No vacuum leaks.  All wiring connections and grounds have been
checked. Fuel pressure is a constant 29 psi. Compression tested 135, 135,
130, 135.  All cooling tin is in place.


Approximately 500 miles ago, I had my work checked by a highly recommended
local VW mechanic who knows the D-Jet fuel injection system well enough to
think that converting to carbs is an admission of failure.  He gave the
engine a clean bill of health, but observed that he felt a "slight flat spot
in the midrange" that he suspected could be related to an injector.  [Not
surprising after 14 years of nonuse].  He suggested that I drive the car
awhile to see if the problem cleared up on its own, stayed the same, or
became worse.


During the last several days, the "flat spot," (slight hesitation after
shifting into 2nd), which had been very minor and easily masked by more
agressive acceleration, has degenerated into a "popping" when I try to
accelerate in 2nd.   This seems to be related to the engine operating
temperature because it happens most during the first 5-10 minutes of driving
(after the 5 or so minutes of warmup in the driveway), even on warm days.
This occurs whether it is the first start of the day, or a start after
sitting several hours in a parking lot following a cool down from a 20
minute freeway drive.   The popping almost never occurs after engine is
clearly warm (although the "slight hesitation" is still there).


The popping concerns me, but I don't have a clue where to start or where to
go from there.  What do these symptoms suggest?  Are these engines really
that cold blooded?
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