Po 301 blazer 1999 hard start chevrolet v6-4.3l p0301

Q: Po 301

asked by on October 08, 2016

Hesitation rough idle missing hard start when warm mis gets worse code po301 keeps coming up already replaced plugs wires cap rotor injectors egr gasket compression 150 no leak down

My car has 120365 miles.
My car has an automatic transmission.

P0301 is a misfire in number one cylinder. I believe you are already aware of this. A common problem on these is the injector assembly. I would do everything below before I condemn it. If I were there in person, I could tell the difference between a cylinder problem and an injector problem.

You need to perform a leak down inspection. It is not necessary to use the percentage type that tells you how much air is leaking out of the cylinder. You just need about 50 psi of air pressure and a hose that will thread into the spark plug hole. With air pressure in the cylinder, listen from the tail pipe, open the throttle and listen there and listen in the crank case with the oil filler cap removed. If you hear a hissing in one of these areas, you have a problem in either the exhaust valve (tail pipe), intake valve (intake), or the rings (crank case).

You can have good compression even with one of these having a problem. A dynamic compression test will build pressure and small amounts of oil will seal small problems, but this changes when the fuel is ignited and the pressure sky rockets.

Keep in mind, you could also have a head gasket failure. Does the coolant keep getting low? Do the spark plugs have a tinge that matches the color of the coolant? Is the cylinder wet from coolant? A good way to test for this is to warm the motor thoroughly and pressure test the cooling system. A cooling system pressure tester will pressurize the cooling system in the same fashion as what occurs when your motor warms up. Once you have pressure in the cooling system, let it sit for at least five minutes. Sometimes longer. I have let it sit for as much as a day of work, depending on the suspected failure. If you have a head gasket issue in number one cylinder, this will push coolant into the cylinder. You should be able to spray air into it and get some wet coolant blowing around. Do what ever you need to see if there is any coolant in the the cylinder.

If you should require more assistance, I recommend getting an engine is misfiring inspection.

Good luck!

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

The cooling mood on my 2007 chevy cobalt came on out of nowhere. I had a guy pour antifreeze in and it was okay until yesterday.

Hi there. Check the coolant level to see if there is any coolant in the radiator. If there is no coolant in the radiator, then fill up the radiator with water and perform a pressure test. Check to see where...

My passenger headlight keeps going out, then tap it and comes back on?

Hello. This sounds like the bulb filament in the glass is intermittently loose or the plug connection to the back of the bulb is loose, corroded, broken, or intermittent. If the bulbs are many years old, they have probably lost...

Whitish marks on car. Need to find a way to make the paint job look better without getting whole new one

If the damage to the paint is on the surface you can use a good past wax or mile compound to rub off the marks and follow it with a good wax. If the paint has been damaged then a...

Related articles

How to Customize Your Classic Chevy Pickup
There There are some vehicles that stand the test of time, proving they are functional, attractive, and in demand several decades after they were originally manufactured. One such vehicle is the Chevy pickup truck. The Chevrolet lineup has included...
2012 Chevrolet Traverse vs. 2012 Toyota Highlander: Which One Should I Buy?
Large SUVs are a huge and broad market, with a range of different offerings from economy to luxurious. The majority of the SUVs and crossover SUVs offer decent gas mileage, plenty of room for friends and family to ride along...
The 5 Safest Used Cars You Can Buy For Under $20,000
The Subaru Legacy, Honda Accord, Ford Fusion, Chevy Volt, and the Volvo XC60 are five of the overall safest used cars you can buy for under $20,000.