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

Car shaking, Check Engine light on ,brakes are not performed completely,vehicule doesn't take off as easy before 1999 Lexus RX300

Hi there - most likely, your power brake booster has failed. This booster uses engine vacuum to provide braking assist. When the brake booster fails, it both allows air into the engine intake that is unmetered by engine management (causing...

Can cam sensor be damaged by water or removing intake and injectors?

Hi There, Unfortunately, the flooding or water damage may cause the camshaft position sensor to fail or potentially cause starting or misfiring issues. The camshaft position sensor may have also been damaged or not hooked up properly if it was...

How to remove dash wire harness from 1997 chevy c1500

Hi Brandon. Thanks for contacting us today. Unfortunately, since we can't attach files to this platform, your best bet is to purchase a service manual for your 97 Chevrolet C1500 online, so you can review the recommended steps for completing...

Related articles

A Buyer’s Guide to the 2012 Chevrolet Silverado Hybrid
If If you’re looking for a half-ton pickup truck that also gets great gas mileage, look no further than the 2012 Chevrolet Silverado Hybrid. While it has the towing and carrying capacity you’d look for in any regular truck, it...
2005 Kia Sorento vs. 2005 Chevrolet Blazer: Which One Should I Buy?
SUVs are great for playing out in the mud, taking kids and friends around to different places, as well as just running errands around town. While they are not known to be terrific for gas mileage, that problem is negated...
The Best Used Cars to Buy If You Need a Lot of Trunk Space
Many Many people focus more on interior room than cargo carrying capacity. That’s natural if you have a large family or regularly carpool, but what about drivers who need to carry a lot of stuff most of the time and...