Terrible engine sound prius 2008 (fault code: P0304)

does the car burn any oil?

 

What is the oil level at? Has it been low for a long time?
Let us know what happens after moving around ignition coils to determine if misfire moves to different cylinder or not?

 

if the oil level drops on the dipstick between oil changes, it is burning oil. you can track it if you wish by googling the dipstick measurement from high to low and how many quarts it equals

 

Always love it when you start preaching about dipsticks!

 

let's not get thrown into the politics thread

 

Maybe next step is doing a compression test in maintenance mode?

 

I don't know if there are factory spec numbers for compression on a new engine, but that wouldn't matter anyway. Piston ring and valve seal wear over time will always reduce compression but the engine will still run well if all cylinders are wearing pretty evenly, so on a compression test you're looking for consistency between the cylinders. Get yourself a compression tester (I have this one), unplug and pull all the ignition coils, pull all the spark plugs. This also gives you a chance to make sure they were installed well, make sure you put some dielectric grease inside each coil boot before reinstall if you didn't before.

Ideally you will also unplug each fuel injector to save gas and prevent explosions, but as there's no spark with the coils unplugged it shouldn't actually matter. This is an extra safety measure.

Then you handtighten your compression tester into cylinder 1. On a normal car, you would then go crank the key for a 5-count so the starter will turn the engine over and build pressure. Write the number down, repeat again on cylinder 1 and write that down, then cylinder 2x2, cylinder 3x2, cylinder 4x2.

The cranking procedure is different on a Prius. You have to put the car in inspection mode (ICE always running) to do the test. Then you hold the start key for a 5-count to crank it.

So with your compression gauge all set up, sit down in the driver's seat, the procedure is:

1. Press start once, then twice, with foot off brake to enter ready mode
2. Now press and hold brake with your LEFT foot
3. Press gas twice
4. Shift to neutral
5. Press gas twice
6. Put it back in park
7. Press gas twice. Now you are in inspection mode and ready for the compression test.
8. Now with foot still on brake, press & hold start button for 5 seconds. After about 1-2 seconds it will start cranking. After 5 seconds it will stop cranking and your dash will light up with error lights, but that's fine. Test is done!
   
9. Record your compression, release pressure, repeat on same cylinder. Now do the same 2x test on all cylinders.
10. Your two tests on each cylinder should be roughly the same. If you're getting different results between tests, repeat as many times as needed on each cylinder until you know you're getting it right.
    
    If you see something like 150-150-150-120, with lower compression on cylinder 4, that would definitely explain your symptoms. Let us know what you see. A head gasket and a head job a) might not even be indicated, and b) is NOT engine broke. Getting the head pulled, valves machined, head inspected, gasket replaced, is a huge job but it's a big step short of a shot engine. That might be like $1000-1500 at a cheapish independent shop, whereas an engine swap would be more labor and the price of a new used engine.

 

My recent problem with my 2008 with 195k turned out to be 'bad injectors', misfire code on 1 and 3, rattle shake at idle, and it would seem to run fine at higher RPMs and idle fine most of the time. In the process I also changed plugs, coils, cleaned the MAF and throttle body. I never did the compression test or the combustion gases coolant test, but both of those are easier than changing the fuel injectors so to may want to try those tests first.

 

A blinking check engine light usually goes along with misfires. Reading the ECM codes will confirm whether this is the case. Maybe there will be other or different codes that can direct where your attention should be focused.

 

You should suspect a blown head gasket at this point. The Gen3 has an issue where the EGR valve gets plugged up, leads to overheating, leads to warped head, leads to coolant leaking into cylinders, leads to hydrolock and destroyed engine. There's no particular issue like this in Gen2. It is possible that low coolant caused overheating which caused a warped head/blown head gasket which caused low compression.

Get yourself some Toyota coolant (Zerex is the off-brand you can get at Napa, OReilly, etc but I always order Toyota brand on ebay) and/or some distilled water, check your coolant daily. You can get a cheap tester to test for exhaust fumes in your coolant also if you want. Also, since Prii stupidly don't have a temperature gauge, it can be helpful to keep a scan tool that can read temp plugged in and showing temp while you're driving.

Looking back at your first post, this started in the MIDDLE of a drive...that might be the drive where you lost all your coolant or your thermostat was stuck closed or something??? You may have been experiencing severing overheating and a warped head right during that drive.

Anyway if I were you I would either a) take it to a shop or b) top off the coolant and do a SHORT drive with a temp scanner plugged in and see what happens

 

I don't know, read the manual. If not, this is a cheap one that does show temp.

Note that you can't actually top off very low coolant by filling the reservoir. You have to fill through the radiator cap and fill it to the brim, then start the engine and get the air out and keep it filled. This is best done with a funnel like this one.

 

Pink/orange is probably OEM. I would stick with that. Get it from a local dealer if you're in a hurry. Yes, do what you described and run the car for maybe 10 minutes with the heat up all the way to reach operating temp (coolant at like 180F) so the thermostat opens and the coolant circulates through the heater core. Does the misfire go away when you rev up? If so I would top up the radiator (and reservoir to the full line) with the car off, then with the reservoir cap ON and the radiator cap OFF turn the car on in inspection mode and rev it up if needed to reduce the misfire. Keep your foot on the gas for a couple minutes. Then get out, top off the radiator, and back to the gas pedal if necessary to rev it up to keep it from misfiring as much as possible. Keep doing this for ~10 minutes, keeping radiator full.

Eventually thermal expansion of the coolant will have it "boiling" out the radiator cap. At that point, shut the car off, get the radiator cap back on (wearing a glove, duh) and let it cool down. As the coolant cools and condenses the radiator will suck more in from the reservoir and stay full.

Then start it up, go for a drive with your scanner plugged in, and see what happens.