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Gary
Gary, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 894
Experience:  Senior Technician
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DTC code P0302, cylinder 2 misfire. Having trouble finding

Customer Question

DTC code P0302, cylinder 2 misfire. Having trouble finding the source. Plus in cold weather it is hard to start. please assist
Submitted: 1 year ago.
Category: Pontiac
Expert:  Gary replied 1 year ago.

Hi there,

I had one customers car with P0304.

Swapped all parts around, was partly unseated exhaust valve, from failing retainer, lucky for owner I found it.

I would do a compression test and a leakdown test.

Swap the injector to another cylinder, and how old is the fuel?

Gary

Customer: replied 1 year ago.
It has a direct injection system, so how dose that work, i know it uses a pump to put high pressure into the cylinders. But is there a physical injector that dose this, if so where is it located at?
Customer: replied 1 year ago.
Oh, and the fuel is fresh, how much compression should the cylinder be at?
Expert:  Gary replied 1 year ago.

The spark plugs are easier to pull than the injectors.

So let's pull the plugs out and do a compression test.

Shouldn't be more than 10% variation across all cylinders. 160-190 psi would be typical.

If cylinder 2 tests low, a leak down test will then show where the loss is going.

The injectors are under the intake manifold in the cylinder heads.

Gary

Customer: replied 1 year ago.
The compression test shows 120 psi across all cylinders with no variation. Should i test the fuel pressure at the port? if so what should the typical reading. That way i can eliminate the pump from a possible problem.
Expert:  Gary replied 1 year ago.

Hi Roy,

If the compressions are close to even, I would still do a leakdown test.

Does the original no.2 spark plug look any different to the rest of the spark plugs?

It will not be furl pressure, since it occurs on one cylinder only.

If the engine is at a continuous misfire, it could be flooding the cylinder with fuel, or not enough, or no fuel. So could be an injector issue, have seen a few direct injector issues, or it could be a PCM.

Can you reexamine the no.2 spark plug, current and original?

Gary

Customer: replied 1 year ago.
The spark plug on cylinder 2 looks fine and the cylinder leak down test showed the same compression reading, but now i have the DTC P0101 and P0102. So i now have problems with the MAF sensor. Could this be the stem of the problems. I cleaned it out with sensor cleaner, and it ran ok for a while, then codes P0101, P0102, and P0302 are back. Should i replace the MAF sensor, also could this be because i changed out to a K&N air filter? Should i go back to a paper filter?
Expert:  Gary replied 1 year ago.

Hi again,

The MAF DTCs are the result of incorrect airflow, cylinder 2 is the cause.

My bet is you have a "riding" inlet valve, not seating while the motor is running.

Please read again what I wrote on the 7th December:

I had one customers car with P0304.

Swapped all parts around, was partly unseated exhaust valve, from failing retainer, lucky for owner I found it.

I would do a compression test and a leakdown test.

A compression test may not reveal your fault if there is a loss. A leakdown test is a completely different test procedure using a different tools etc.

I would make sure the MAF is clean with a MAF cleaner, and the K&N filter is at the minimum oil amount.

Some guys tend to overoil them.

Did you want to swap No.2 injector to another cylinder?

Do you want to try another PCM?

Gary

Customer: replied 1 year ago.
well did the leak down tests again all was good on number two cylinder. I did find a leak in the innercooler. This could cause the MAF to mess up, which causes the fuel system to have problems, in turn could make number two cylinder have problem if it is the weakest cylinder. im running the monitors now, all i have left is the evap monitor and then i can confirm the fix is done.
Expert:  Gary replied 1 year ago.

Hi again,

The intercooler leak would have to be a fairly big leak to measure lean at idle, and would be a massive leak under boost, which then has the engine going fuel rich with low power, black smoke etc.

Is NO.2 cylinder the "weakest", if the compression AND leakdown tests are as good as the rest of the engine?

If you are confident you have found an issue, then I do hope for you, that you are right.

Gary

Expert:  Gary replied 1 year ago.

Hi Roy,

How did you go with your problem?

Hope I was of some help to you.

Gary