Jim Grant's Tech Tips
Cutlass, Only Runs When Cold
I have a big problem with
my 94 Oldsmobile Cutlass . It will run fine 20 to 50 miles and never miss
a thing! Then it will shut off as if youd turned the key off. It was starting
right back up, but now, it wont until it cools off! Why? Could it be coil
packs? A replacement coil pack is non-returnable if it doesnt fix it.
Everyone I talk to has different answers; I need some help. I'm going to have
a baby soon and I need my car!
It is a rare day that a coil
pack completely fails and then once cooled comes back to life. Generally, a
failing coil pack will cause the engine to skip and misfire like there was a
bad spark plug or spark plug wire. There are 2 components that come to mind
that could possibly cause the problem youre describing. They are the ignition
module or the crankshaft position sensor. The component that is the most troubling
in our shop is the crankshaft position sensor. If crankshaft position sensor
information is lost, the fuel and spark will be turned off instantly as if the
key had been turned off. This sensor also has the irritating ability to get
better and perform as if there never was a problem. The ignition module can
cause problems but is often more flamboyant as it is failing. Both components
are sensitive to heat. Diagnosing either component when they have failed is
not too difficult. When the vehicle is running right, it is only guess work.
If you were to ask for a guess, I would lean towards the crankshaft position
sensor based on past experience, but that is only a guess. One last note, the
crankshaft position sensor is not much money but can be a real bugger to change
if you live in the rust belt.