Have a 97 Cavalier with p0300 (random misfire) and p0172 (rich fuel
condition).I'm assuming the rich fuel condition is a result of the un
burned fuel hitting the o2 sensor post catalytic converter? anyhow,
had it on a scan tool that reports cyl 1 and 4 are missing
intermittently. Changed plugs/wires and the coil pack for 1&4. Still
missing.on 1&4 Changed ignition control module. Still missing on
1&4....
What tells the ign control module to fire the coil pack? Crank
position sensor?

When looking at graph on scantool (Modius Snap On) while attached to
plug wires shows (on 2&3) like EKG blips (even height spikes with
flats between equal spaced).
On 1&4 Some full spikes some half height and some flats where even
spacing would indicate spikes should be.
(yeah, not the correct terminoligy, but I'm doing the best I can...)

I'm about $280 into parts that I didnt need... Anyone got an idea?

Crank sensor or it's reluctor wheel would be the most likely culprits. BTW
misfires will show lean on your O2, because there's loads of oxygen. A P0172
indicates it's adding fuel, which would be consistent.

<jason.e.carney (AT) gmail (DOT) com> wrote

Sounds like dirty fuel injectors to me. It was a problem a couple
years back, GM issued a TSB about it as well.

Chris

On May 16, 3:15 pm, Hal <hala... (AT) gmail (DOT) com> wrote:
I had to replace all 4 injectors this past year... Guess I'll swap 1&4
for 2&3 injectors and see if the miss follows the injectors. If
missfire doesnot follow injectors, how would I check the crank sensor?
Jason