Code 303. - Toyota Tacoma Forum
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#1 (permalink) Old 01-25-2013, 03:08 PM
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Code 303.

I own a 1998 Tacoma 2.4l, with approx 368,000 miles on it. Been getting a 303 code. I've eliminated the ignition, checked the compression and I've got low compression on #3 cylinder, 150 psi on 1,2 and 4, 115 psi on #3. I will be adding a little oil into the cylinder and pray that it is only a burnt valve. If it is a bad set of rings I will probably replace the engine and add a few mods to increase the performance. Any thoughts from the members would be greatly appreciated.
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#2 (permalink) Old 01-25-2013, 04:14 PM
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Re: Code 303.

You seem to be on the right track ...

P0303 is specific to cylinder #3, and compression is one of the probable causes of a cylinder-specific misfire.

Minimum acceptable pressure on your engine is 127 psi in all cylinders, and all cylinders (per spec) should be within 14 psi of each other.

If adding oil into cylinder #3 causes a higher compression reading, it's likely to be the rings or a worn cylinder bore. If adding oil causes no change in the compression reading, it's most likely to be a valve or a blown head gasket.

Good luck with it ...

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#3 (permalink) Old 01-26-2013, 08:39 AM
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Re: Code 303.

Hello Enola: I just added oil to the #3 cylinder, no increase in compression. A few questions, if it was a head gasket wouldn't there be a loss of water/coolant? A gasket change would be sweet on my wallet! Do you know of anyway to verify either gasket or valve leakage? If it is a valve, can the head be rebuilt reliably? I really do not want to be without this ride for long, my F-150 is a gas hog, lol... Thanks in advance for any info.
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#4 (permalink) Old 01-26-2013, 10:40 AM
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Re: Code 303.

I don't know of any way to tell for sure (valve(s) versus head gasket) without pulling the head. If you remove the head, you're going to need to replace the head gasket. So it seems to me you're looking at a new head gasket one way or the other (i.e., whether or not head gasket leakage is causing the compression loss).

This means the only remaining question is whether or not you've got a valve problem (sticking valve; burnt valve; whatever ...). You really can't tell without pulling the head.

If you're going to have to pull the head, you might as well invest in a valve job (regardless of how much valve damage / wear there may be). My own experiences (a long time ago) led me to make a rule that it's wise to do a valve job whenever the head is removed. Nothing is as maddening as having to pull a head off a second time 'cause you were trying to be too tricky the first time.

Yes - one would think a blown head gasket should result in loss of oil and / or coolant. But it's possible for the 'seal' (between head and block) to be leaky for "gases" without much fluid transfer.

It's still possible you have ring failure / damage in #3 that's severe enough to prevent the added oil from giving you temporarily better compression in that cylinder.

At 368,000 miles, I wouldn't rely on a piecemeal approach (fixing one little part at a time) - I'd go for at least valves and rings all at once on general principles. I've seen too many cases where being too optimistic and trying to get by with fixing just one thing ended up costing more than doing it all the first time.

Just my .02 ...

Yes - the head can be reliably rebuilt provided it's not structurally damaged (e.g., cracked, badly gouged).

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#5 (permalink) Old 01-26-2013, 12:48 PM
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Re: Code 303.

Thanks for your two cents Enola. Reliability is my main concern. John...
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#6 (permalink) Old 01-28-2013, 12:24 PM
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Re: Code 303.

Did you do a leak down test?With 368K miles I would plan for a rebuild on lower end and top end that is if you plan on keeping the truck.Most people jump ship when big things break but you find out its cheaper to keep her for the long run that is.
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#7 (permalink) Old 01-28-2013, 03:53 PM
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Re: Code 303.

Turbostang, could you explain a leak down test. As you can see I have kept her for the long haul, bought her brand new! Would love to put another 300k on her. I know it is clutch time and a new timing chain is in order. Seriously thinking of a new engine, any good word on Japanengines.com? 2k for new! Thanks, John...
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