Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

sensor in the distributor that can also be the problem (cars with the crank position
sensor do not have the hall sensor in the distributor).
Hot Start Problem: Power Stage Overheats. [Note from Boris] I had a hot start
problem on my car. It drove me bananas. I would pop the hood just slightly after each
frequent stop, and this reduced the frequency of the problem drastically. Why do you
ask? Volvos, especially the turbo models generate enormous amount of heat once
parked after a drive. This heat has no place to escape. It just sits under hood for a
LONG time and can damage various components. I believed whatever part was
malfunctioning must be under hood and not on relay board. Replaced Hall sensor
needlessly. Problem was in the Power stage. Took it off, cleaned the contacts very
well, and coated with dielectric grease. Next, I coated the heat sink side of it with
thermal compound which to my surprise was not there before. This helps keep it
cooler. For extra protection I taped a styrofoam cup over it (Yes I too can be frugal…)
Problem gone. I was stuck the other day going 11 miles in 3 hours, and the car ran
fine. It was so hot under the hood, I could have baked a good lunch under there.
GENERAL EMISSIONS CONTROL PROBLEMS:
Emission Control Problems: High HC, CO or NOx. Below are some generic
diagnosis notes (non-Volvo-specific) to help you begin pinpointing why you failed the
smog/emissions/MoT etc. tests.
[Excerpted from "Exhaust Emissions Diagnosis: The Precursor to Finding Engine
Performance Problems", Larry Carley, ImportCar, June 2000.
GENERAL DIAGNOSIS. Elevated hydrocarbon (HC) emissions usually indicate
ignition misfire due to fouled spark plugs or a bad plug. But high HC emissions can
also be caused by burned exhaust valves (check compression), lean misfire (check for
vacuum leaks, low fuel pressure or dirty injectors), or rich fuel conditions (excessive
fuel pressure, leaky injectors or a dead O2 sensor).
High carbon monoxide (CO) emissions are a telltale sign of a rich fuel mixture. On
newer vehicles with feedback fuel controls and fuel injection, leaky injectors, excessive
fuel pressure and sluggish or contaminated O2 sensors are all possibilities to
investigate.
Harder to diagnose are elevated oxides of nitrogen (NOX) emissions. NOX levels are
affected by engine combustion temperatures. When the temperature inside the
combustion chambers exceeds 2500°F, nitrogen combines with oxygen to form oxides
of nitrogen, or NOX. Many engines rely on EGR to lower combustion chamber