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2002 Envoy sle 4.2 L straight 6. Random misfire(PO300). After erasing codes for several days, I finally took my car on the highway and ran it at high speed(70+) for about 4 to 5 miles. Check engine light came on as before but this time it gave me(PO305). Random misfire cylinder 5. So I switched coil 5 with coil 2. Went back out on the highway and repeated as before. This time it gave me(PO302). This was telling me I had a bad coil. Replacing one coil pack solved the problem. The professionals told me low fuel pressure would not give me random misfire, but rather a O2 code because the engine is running lean. Thank you------------------------------------ thank you very much.
Have fuel pressure tested when no start. Or, if you have no access to pressure test, try removing air intake hose at front of throttlebody and give a good spray of quickstart, or WD-40 with throttle plate open, then try starting. If it fires up momentarily then dies, I'd be looking real close at fuel pump, or at the least fuel filter. The fuel pressure test will confirm.
It is possible that when you had an oilchange the oil used was 10/40 which is correct for this vehicle BUT i would advocate that a thicker oil is used for this mileage say 20/50.
all cars will use/burn oil and i always ask my customers how much oil they put in from the last service so that i can judge what oil to use.Thin oils (5/30)should only be used for new cars,and even then
keep an eye on oil usage/burn.....
We have all read,in various publications that "using the wrong oil can cause damage"but after 40 years in the trade,i have NEVER had a complaint or any engine damaged by this method of filling
at service.(we had forty bays in my last dealership.)
I had a similiar problem with my 2000 Grand Prix, coming home from Michigan. It was found to be the Air Intake Sensor. It is located on the airhorn, between the air filter, & the injector intake. It cost me $360.08, just for the part. It tells the main combustion computer how much gas to give the engine, as to how much air is coming into the air cleaner. With the module bad, it is flooding the engine. Mine bucked me like a bronco for almost 40 miles, on an interstate highway. A 1 hour drive took me 4 1/2 hours to get home. It would be cheaper to have it put on an analyzer, because there are several components that could give the same effect. There is also an oxygen sensor, that is in the exhaust pipe, that could be bad.
Sounds like it has went into "Safe Mode". This is a feature in newer autos that will allow you to drive it to a repair station or off the interstate when the engine detects that it has too many miss fires in a row. Several causes for this, bad gas "water in the gas", burning oil, etc.
There is a possibility that your timing belt has a couple of teeth missing now. When was the last time the timing belt was replaced? The reason for the fuel smell is the engine is trying to fire at the wrong time. It's trying to fire when the exhaust valve is actually opening. Replacing the belt isn't a bad job.