Thread: Code P0303, and p0300

I dropped #3 cylinder, and I am a bit stuck. I replaced all coil packs, and tested each new pack for spark, each one will throw a spark 1"+, I replaced the #3 plug with a known good plug, I replaced #3 wire, and still dead cylinder. I did a compression test on the cylinder and it pushed out 145psi on the gage so the cylinder has compression. I ran the motor for about a minute and felt the exhaust ports, and it is for sure #3 cylinder, I have 5 burnt finger tips to prove it.

The only thing left to fire a cylinder is fuel. Is it possible to have an injector go bad where it wont put fuel in the cylinder? What is the best way to test/check injectors.

Thanks for any input or ideas, things to check. I am kinda stuck on this one.

I put a new injector in and the cylinder is still down.

Gonna recheck everything, I have to be missing something.

Could be the ignition control module.

Rechecked everything, and I am stuck.

New parts installed:
All coil packs
New set of stock wires
New set of Autolite 606 plugs
New injector on #3 cylinder

I have done the following checks:
Checked spark with inline spark check device, it shows #3 is firing the plug.

Put a noid light on the #3 injector connector and it shows the wiring harness is pulsing the injector. I have not done an ohm reading on the new injector yet, but its new it should be fine.

Done a compression check on #3 cylinder, it shows 145psi, and I also checked #5 for comparision, it showed 145psi, so compression is ok.

I lifted the vavle cover up enough to get my fingers under there to feel the push rods, and both the intake and exhaust were moving up and down, so the cam is not flat. I couldn't get the cover totaly off because the front dogbone mount was in the way. Now maybe, it has broke a rocker arm and not opening the exhaust valve. That I will tear into tonight to verify if something broke there.

Is there anything else I am missing, or should be checking?

never assume that new parts are automatically good. This is the only time I don't like BOOB's (bad out of box)........I would check as much as you can to ensure that the new parts are good........are you positive that there is ample gas pressure at the injector location? Just some thoughts.......

Fuel pressure is another thing I have to check. I am going to go buy a gage tonight on way home and check pressure at the rail, and see. I will also ohm out the new injector to verify it is good.

If those two things check out, then I am going to get the valve cover off, so I can visually verify the exhaust valve operation, and check for broke parts.

Thanks for the advise.

Problem found, it was a broken exhaust valve spring. The spring had not collapsed so it was allowing for a good compression check, but wasn't enough pressure to allow the cylinder to fire.

Now question is this should I just replace the broken spring, and not worry about the others, or should I replace all of them. I am planning on a cam upgrade sometime in the future, but right now I running a stocker. I would hate to break another in a week or so. I am also going to back down the shift points to 5700rpm instead of the 6k it is at now.

Thanks to everyone who gave me advice.

how many miles are on your current springs in there?

Your sig has no mods of cam or rockers? Assuming these are stock springs w/o any mods...

I'd swap all the springs, retainers and valve seals. Go with something like 105#'s and LS retainers. This way in the future if you plan on modding, everything is all set and ready to go.

The car has 150K on it. The valve trane is all stock. I was planning on putting a low mileage short block in it, and having the heads gone thru at the machine shop. Then put in maybe an XP cam, and good springs. I will probably end up putting another 30k on the car before any of that happens though.

So is it worth messing with putting good springs on now? I dont have the heads off of the car. I will be putting the springs on with the heads on, and filling cylinder with air.

I do plan on backing down the shift point from 6k to about 5700 so as to hopefully help from breaking more springs.