Code P0300, car running badly

Welcome to CarPros.

The fuel trims are perfect along with all other things I saw. You want the trims to be as close to 0 as possible, and yours stay well within the specs. What a negative trim indicates is that the O2 sensor is indicating the fuel mixture to be slightly rich, and the computer is trying to compensate by shortening the time the injectors are open. The opposite happens when they are positive. However, as mentioned, your's are good.

Now, have you replaced the crankshaft position sensor?

Take a look through these links:

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works

Often times, a crankshaft position sensor problem is identified with the engine stalling or shutting down when hot. However, that isn't always the case. It can cause a random misfire. Take a look through this link:.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

As far as the ECT reading of 60C, it is reading in Celsius and not Fahrenheit which you already know. That is equal to 140°F. That is not up to operating temp. If the engine doesn't get warmer than that, it can cause issues.

Can you let me know how long the P0300 takes to show up after the code is deleted? Do you feel any misfire while driving? Is that the only code you are getting? I ask because it is possible for a faulty crankshaft sensor will not set a code.

Let me know.

Joe

Sounds like a plan. Also, let me know if you have had any other code show up.

Take care,
Joe

Hello,

The two important PIDs to watch on the live data is the O2B1S1 and O2B2S1. These are the upstream oxygen sensors that your vehicle's Power-train Control Module (PCM) or "computer" uses to adjust the fuel going to your vehicle's fuel injectors. The voltage that they produce should fluctuate from 0.1V to 0.9V. It is reading the oxygen content of the exhaust. The PCM is trying to keep the air:fuel ratio at stiochmetric which the perfect combustion rate. Stoichmetric air:fuel ratio is 14.7:1. This is because at sea level it is 14.7 miles to the top of the atmosphere. So your vehicle's PCM is adding fuel until the O2 sensor reads rich(0.5V - 0.9V) and then it subtracts fuel until the O2 sensor reads lean(0.5V - 0.1V) and then adds fuel until it reads rich and so on. This way it is constantly adjusting keeping the air fuel ratio as close to stoichmetric as possible.
From the video you shot your O2 sensors were working perfectly. Did you clear the Direct Trouble Code out of the PCM when you replaced your spark plugs?

Thanks,
Alex
2CarPros

Welcome back:

The sensor can be tested.

A) Disconnect the CKP sensor harness. Connect an LED test light between battery ground and CKP harness terminal A.
B) With the ignition ON and the engine off, verify that the test light illuminates.
If not as specified, repair or replace the fuse and/or wiring.
C) Carefully connect the test light between CKP harness terminal A and B. Verify that the test light illuminates.
D) If not as specified, repair the CKP harness ground circuit (terminal B ).
E) Turn the ignition OFF and disconnect the test light.
F) Next, connect suitable jumper wires between the CKP sensor and CKP sensor harness. G) Connect a duty cycle meter to the jumper wire corresponding to CKP terminal C and battery ground.
H) Crank the engine and verify that the duty cycle signal is between 40-60%.
I) If it is not as specified, the CKP sensor may be faulty.
J) Next, connect a AC volt meter to the jumper wire corresponding to CKP terminal C and battery ground.
K) Crank the engine and verify that the AC voltage signal is at least 10.0 volts.
If not as specified the CKP sensor may be faulty.

__________________________

To determine duty cycle, you will need a multi meter. Most have a DMM setting to measure frequency.

I attached a couple pictures with the wiring to the CKP you may find helpful.

Let us know.

Joe

Not a problem. Let us know what you find.

Joe

Welcome back:

My next suggestions are these. Since everything electrical and fuel related are within spec, I would check engine compression and confirm the catalytic converters are not plugged.

https://www.2carpros.com/articles/symptoms-of-low-compression

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

________________________________

Here are the specifics on compression. The specs are listed in these directions.

ENGINE COMPRESSION TEST
1. Disconnect the positive ignition coil wire plug from ignition coil.
2. Disconnect the fuel injector electrical connector.
3. Remove all the spark plugs.
4. Block the throttle plate wide open.
5. Charge the battery if the battery is not fully charged.
6. Start with the compression gauge at zero. Then crank the engine through four compression strokes (four puffs).
7. Make the compression check the same for each cylinder. Record the reading.
The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one cylinder is 1035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi). (1035 x 70% = 725) (150 x 70% = 105).
8. If some cylinders have low compression, inject approximately 15 ml (one tablespoon) of engine oil into the combustion chamber through the spark plug hole.
Normal-Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking-Compression is low on the first stroke. Then compression builds up with the following strokes but does not reach normal. Compression improves considerably when you add oil.
Valves Leaking-Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
If two adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the two cylinders.

Let me know what you find.

Joe

Welcome back:

The compression specs are in a previous response. You got me stumped. See what happens when checking the catalytic converters and let me know.

Joe

Hi Guys,

I was just reviewing this one and it looks like the short term fuel trims are just fine at idle. You show them bouncing around 0 and then dropping to about -2. This is ok as the PCM will be able to adjust for this and will not directly cause a misfire. Remember that the PCM uses the IAC, MAF, MAP, Baro, to calculate what the air/fuel ratio should be. It then monitors the o2 sensors to see how it did. The goal is to stay at 14.7:1 and a short term fuel trim of zero is this ideal state. So the fact that it is bouncing back and forth from positive to negative shows that the PCM is able to add and remove fuel in order to keep it around 0.

Also, the PCM on these older engines can only control fuel to match the amount of air that is coming in. So an accurate air flow is crucial. Based on these numbers on the recordings that you have, it looks like the volumetric efficiency at idle is about 54%. This number seems off so I am thinking you have a MAF sensor issue but I see you replaced it. So let's run this test at wide open throttle so we can see what the VE is at that point. A healthy engine should be between 75-90% efficient at WOT.

If you can take that scan tool and write down these numbers while doing a WOT stab, it should help point us in a good direction. DO NOT hold it at wide open in order to get all of the numbers. Do one at a time and record the highest number that you see for each.

We need:
IAT - Note if it is F or C. Either is fine, I just need to know which.
RPM -
MAF - Include the measurement because it matters if it is g/s or lb/min. Either is fine, I can do the conversion.
Engine size is 4.3L

Just make sure you get me the Mass Air Flow and not the Absolute Pressure sensor.

Multi cylinder misfires codes with no specific cylinder misfire code, is saying that the PCM is not seeing a crankshaft acceleration after it fires the spark plug on various cylinders. However, it is not a consistent misfire. Meaning any given cylinder gives the PCM the expected acceleration but then on the next stroke it does not. Usually, these are related to fuel delivery or air delivery.

It could be a restricted converter so if you just pull out the upstream o2 sensors and run it and see if it smooths out. If it does, then a restricted converter is your issue. If it does not, can you reinstall the o2 sensor and perform the wide open throttle stab and record the numbers above?

Thanks

That is great. Based on these numbers you volumetric efficiency is 68%. This is not horrible but it is a touch low.

What this means is there could be a restriction in the air intake system, a malfunctioning MAF, or exhaust restriction. Most likely exhaust because you replaced the MAF and your short term fuel trim are a touch on the negative side.

Before you go any further, remove the air filter and inspect the intake snorkel then just run it at idle and see if it clears up a little. I assume it is missing at idle based on what you said earlier. Also, remove the upstream o2 sensors and see how it runs.

Lastly, if you can find your compression readings that you mentioned earlier that would be great. Hopefully you have them on all six cylinders.

Let me know and we can go from there. Thanks

To answer your question about the MAF. I am concerned about this. In my experience it should be around 2 g/s at idle and then climb when you accelerate. Your MAF is around 5.5-6 g/s at idle. This means the PCM is seeing a larger amount of air coming in and it thinks it needs to add fuel in order to achieve the 14.7:1 ratio. Hence your short term fuel trim being a little rich and the PCM commanding it to go lean. I think this command to go lean is actually what is causing your misfire.

Anyway, removing the o2 sensor and running it will prove out a clogged converter. It could still be carbon on your valves that is restricting flow but this is unlikely to cause a bad misfire as you describe.

Have we checked for a flat camshaft? I would remove the valve covers and confirm the springs and lobes are in tact. Please let us know what you find. We are interested to see what it is.