Recurring Po301
 

Hey Gents, hoping you guys can point me in the right direction here.

Important notes:

The code usually only appears during warm startups. (Ex: I drive somewhere, let the car sit for 5-10 minutes, then restart it.)

Before the code appears, the engine shakes a bit harder than normal at idle, as if there was a vacuum leak.

Otherwise, the car performs just fine. She pulls hard, and there's no evidence of a lack of power.

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With the above info, here's the rundown:

Over the past year or so, I've been getting a recurring PO301 code on my car. It started off relatively infrequent. It popped the code, I'd reset it to see if it happened again, and it wouldn't appear for weeks.


About 3 months ago, it started to get more frequent, so I started troubleshooting, here's a bulleted timeline:

- At first, I thought it was the coilpack. I had one die before, and replaced it with an aftermarket Denso Unit. I warrantied out the coilpack, and the light went away for a while.

- The light came back, so i tried swapping the injectors and plugs to cyl 3. A few days later, I got a PO303. This led me to believe that it was either the coil or the plug, so I warranted out the Coil again, and got new plugs. That was 2 months ago, I haven't seen a 303 since.

- Light stayed off a couple weeks, then returned. I started to get concerned that i might have a more serious issue, so I rented a compression tester (which was brand new when I got it). I ran the test, and got 63PSI on cyl 1. Interestingly, I only got 60PSI on cyl 3, which hasn't thrown a code (except for when it had a bad coil/spark on it).


After this, I'm not sure about my compression test results. I fear that either I did something wrong, or the tool i had was malfunctioning. I'm planning on having a shop run it to verify my results, but before I start dropping money, i wondered if any of you had ideas or thoughts for me.

Thanks in advance for any advice!

That seems like low compression to me.

^It does, but as I said above, the car doesnt seem to be experiencing any power loss, and Cyl 3 is not experiencing any issues. Hence why I think that the compression test results are wrong.

Get a different tester, get someone who has done it before, or take it to a local shop?

Ran a second test with a better gauge, i'm showing 130PSI on Cyl 1 & 3, testing 2 & 4 now.

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Edit:

Completed the full test, every cylinder came in at 130PSI (+/- 1). I've ordered a leakdown tester, and contacted Injector Dynamics regarding testing injectors.

I should note, the test was done on a cold block - I wasnt able to test it hot - not enough room to get hands in there without serious burns.