97 US 850 non turbo starting question

Our 850 was working well. The winter was punctuated by a warm spell with
the temperature going over 65 degrees F - 18C. The warm weather took a few
days to reach a peak, but we dropped off a cliff today going to around
29F - -1.6C.

The Volvo did not want to start at all, and usually it starts with a quick
twist of the key no matter the weather. When, after a few minutes cranking
for 10 seconds followed by 15 seconds of rest it fired up it ran lousy for a
bit, but seemed to clear up in time.

After sitting almost 4 hours in the cold it again fired right up, as it
usually does. My wife said this happened once before when the weather got
much coder fast.

Has anyone heard of this or have any ideas? Need I worry?

Thanks
--Steve

 

What is the mileage? Are there any codes present? When were the ignition
parts last replaced? When the temperature drops the engine coolant temp
sensor signals the fuel side of the computer to increase the injector(s)
pulse width and enrichen the mixture. A slightly enrichened mixture will
fire more easily in the presence of a spark. An over rich mixture will
foul the plugs, which is what happened.

This can be caused by a number of things. Coolant temp increased
resistance: shrinkage at a joint or connector can move the contact
surfaces of the connection to a less conductive area of contact. Usual
sources are computer grounds, circuit grounds, high resistance solder
joints on circuit boards or decreased signal strength from the cam
sensor, engine speed sensor or the mass air flow sensor.

Additional possibilities include a seeping fuel pressure regulator,
cracks in the inlet hoses or an intake manifold leak of some sort
allowing unmetered air into the motor.

Multiprong spark plugs were recommended to alleviate the problem in non
turbo cars, along with a plastic spacer that prevented the timing belt
from jumping on cold starts after an extreme temperature drop. One of
the more interesting properties of rubber is that it tends to shrink
when hot and expand when cold. Consequently the belt tensionser has to
respond in a parallel manner in order to keep the belt tension
relatively constant. Unfortunately the tendency of the tensioner to
stick when cold and old will allow the belt to jump unless the spacer
has been installed to prevent jumping. At any rate, the slight
retardation of cam timing due to belt growth can contibute to hard start
problems if the ignition components are marginal or well worn.

An additonal consideration is that continued rich hard starts will
contaminated the oil with fuel and exacerbate the starting problem as
well as allow increased internal engine wear from decreased lubrication.

If you can't check these things have them checked by someone who is
familiar with the car.

Bob

 

I've noticed that too, in both my 98s. They seems to "learn" exactly
how much fuel is needed on cold start, and swings of more than 10-15°C
seems to confuse them.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

125000 miles

Are there any codes present?

The check engine light is not on--only time that went on was when my wife
did not 'click' the gas cap.


When were the ignition

It had the 120,000 check 5k ago. I do not know exactly what they did
do--but it has always worked fine, the quick temp change seems to be the
triggering event.

When the temperature drops the engine coolant temp

These sound possable--the sudden change in temp has caused a PC board with
differing components to contract at different rates...

These would seem to be faults that would continue to cause trouble. The
problem only seems to occur when there is a sudden drop in ambiant temp. In
the instant case the last time the car operated it was warmish out in the
60's F the next cycle, when the cold start problem occured was at a temp of
about 29F.

After a run of 30 minutes or so and a cold soak of about four hours in the
29 or so F weather the car started fine and ran well. I have not run the
car since this issue arose.

Thanks for the ideas--I will have the car checked out if the problem
re-occurs.
How does the 850 sense ambient temps? Clearly less fuel is required for a
warm outside air temp start of a cold engine then for a cold outside air
temp start of a cold start.

If the component that senses the OAT is a bimetallic device perhaps in time
it gets tired and will react to the changes in outside temp much less in
time...

 

Additional info--

The temps have been between 20 and 24 F and the car has cold started from 8
hr or longer cold soaks flawlessly.

The problem is just limited to the behavior of the car on the FIRST start
after a sudden temp drop.

Any ideas, Please!

 

The primary source of temperature information comes from the engine
coolant temperature sensor. This is an NTC device. The internal
resistance decreases as the coolant temperature increases. The ambient
air temperature is determined by a thermistor in the center of the
intake air stream at the Mass Airflow Sensor. Both bits of informaton
are available through the OBDII Data Link Connector to either the Volvo
system tester, VADIS/iVADIS or the Autodiagnos scan tools. When scanning
the car cold, after a long cold soak, the thermometer on the wall, the
ambient air temp sensor behind the spoiler and the two engine sensors
should all read within a few degrees of each other. In terms of failure,
the ECT sensor has been more problematic than the foil type MAF sensors.
However, both would trigger the MIL if the fault persisted for more than
several seconds.

If when the scan tool connected the readings seem true then the next
step would be to inspect the vacuum line at the fuel pressure regulator
for the presence of fuel. None should ever be there. Intermittent
diaphragm leaks on 850/70 cars are particularly hard to catch and don't
fail often.

Failing that there is a connector or ground problem problem that will
have to be addressed by physically inspecting each one and eliminating
each as a cause until the only thing left is the control unit. The ECUs
are not notoriously weak points, but they hold the highest probability
for defective wave soldered joints.

If the signals for the engine speed sensor or the cam position sensor
were absent, neither would set a code unless the engine were running and
if either were absent there would be no injection. The overrich problem
was quite prevalent in the turbo models and a service kit was provided
as a bulletin fix for them. There may be an ECU reflash available for
your car. There is an updated ECU, most updates address cold start fuel
mapping issues.

Bob