andy@utzoo.UUCP (Andy Rubaszek) (09/12/85)
I hope someone can suggest a solution to this one. The car is a 1981 Buick
Electra station wagon with 50K miles on it. The problem is that it pings
under partial load at cruising speed when the engine is hot. It behaves
when cold and under full load (i.e. it downshifts and accelerates smoothly
with no ping when you tromp the gas pedal even when fully loaded AND going
uphill). There is also a barely-perceptible hesitation and then a more
pronounced lack of guts under partial acceleration at cruising speed, but
plenty of power under full throttle. The engine is 5.0 litre.
There is no obvious sign of overheating; fan and belts are ok, thermostat
is not stuck. The carb has been overhauled (one mechanic claimed the mixture
was too lean and that was causing the ping). EGR valve is fine; I replaced
the gasket just in case. Timing is already retarded 4 degrees; loss of power
becomes too noticeable retarding more. Vacuum hose routing was checked.
In short, I don't know where else to look. The only solution I can come
up with is trying cooler spark plugs, but since the car is used a fair bit
in city traffic, I am concerned about fouling and carbon build-up with a
cold plug. (Oh yeah, the upper cylinder area was "de-carbonized" with the
gunk you pour into the carb.)
So... if anyone has had a similar problem or can offer any suggestion, I
would really like to hear from you. Thanks in advance.
Andy Rubaszek @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!andymls@harpo.UUCP (09/16/85)
I had a similar problem on a 78 Chevy wagon. It was a stuck EGR valve. In the summer time with a humid weather there was enough water vapor in the air to prevent the pinging. However in the winter time the pinging would return. At light throttle or heavy throttle there was no pinging. Hav you tryed a super unleaded? Irv McNair
tmorris@convex.UUCP (09/19/85)
There are a couple questions that you could answer that would
help diagnosis of your problem:
1. Did it work fine before , or did you acquire it with this
problem ?
2. Did it occur after a tune-up ?
3. Did it occur with the onslaught of hot weather ?
I used to be a tech for a GM dealership and had to deal with
a quite a few "problem pingers". Here are a few off-the-wall things
that I have located that fixed the ping:
1. The thermostatically controlled air breather valve did not
switch from hot to cold incoming air source.
2. The fan clutch was shot and caused overall higher temps.
3. The cooling system had a circulation problem.
4. The valves had been ground too close and had sharp edges.
5. The valves had deposits that could only be removed by
removing the heads and cleaning with a power wire brush.
(usually the result of a steady diet of cheap gas or
leaking valve guide seals).
6. The a/c condenser was full of bugs , causing higher temps.
7. A defective water pump had a casting defect which cut down
the circulation to the right 4 cylinders.
8. The cruise control had a vacuum leak in the diaphram.
You had checked all the usuals , so I left them out. Generally
what you want to find are:
1. Things that make the engine (or a certain combustion area)
get too hot. Use a gauge to find out.
2. Things that make the mixture too lean AT THE TIME THAT IT PINGS.
3. Things in the combustion chamber that retain or focus heat.
4. Things that prevent the EGR from coming on THE PROPER AMOUNT at
THE PROPER TIME.
There are probably others , but I can't remember them now...
HAPPY MOTORING !