Started my car today and it was idling like crap for about 10 seconds on the verge on dying (500rpm). Then the check engine light lit up and threw the P0300 code. I check the wires and all seems to be snug. Should I check the plugs...?

 

Anything recently done to the car or a recent fuel fill before this occurred? Any other codes? I seem to remember that a 300 code will also provide information on the offending cylinders.

 

Yeah...the 300 code is an engine misfire. I get it on occasion during initial code start up (after a headers, head/cam, intake install)...I clear it away and nothing occurs for the rest of the day.

However, you stated your car was running terrible...what have you changed?

 

Look on the rear of the driver's side head for the two ground wires there. Make sure they didn't come lose. If you added headers and so on, make sure no wires have touched them and burned. Bill Curlee has posted many times about this happening.

 

 

Damaged or loose spark plug wire or injector connector is usually what I find for P0300.

I'd start by twisting and seating all plug wires at both ends, then removing/checking/reinstalling all 8 injector connectors.

Corrosion on the injector terminals most often the culprit on cars where no modifications were done recently...the things get damp and corrode, and the act of removing and reinstalling scrapes off enough to get a good connection.

Damaged/loose plug wires is most often the culprit on recently modified cars. It's important to push and twist the plug wires until you hear a nice positive click, both ends.

 

Thanks a lot guys. I havent changed anything recently on the car Ill recheck all the wires, etc.

 

It ran terrible for about 10secs. then the rpms jumped up to 8-900 and everything was fine excluding the code and CEL.

 

As you're reinstalling the injector connectors, a small dab of dielectric grease on the harness connector terminals is a great thing. It will help create a barrier to moisture entry after the connector is re-seated.

Just grab a tube of dielectric grease at the parts store, and apply a pea-sized dab on each of the two terminals on each connector.

 

This is most likely a fuel issue then (low fuel pressure), a leaky injector can cause this too till the rich cylinder(s) clears up. P0300 is RANDOM MISSFIRE the other P030X codes are per cylinder where X is the cylinder #. I would bet on fuel presssure or injectors on this one. Get a fuel pressure guage on it if it continues to happens and see what the fuel pressure is on startup.

Once the CEL is set, it takes severla drive cycles to clear on it's own or you can clear it through the DIC or scan tool.

 

I just cleared it through the dic. Ill check the fuel press.

 

While you have the guage on, record the fuel pressure readings *after* you shut off the engine. Properly sealing injectors should keep >40psi fuel pressure at the rail for at least a full minute after the fuel pump is stopped. If the pressure drops significantly below 40psi as soon as the engine and pump are stopped, it's a dead giveaway that an injector is not properly closing.

Let us know what you find, I see from your posts back in March/April that this has been an ongoing problem and it must be getting frustrating.

Assuming no findings from the fuel pressure tests, a really good series of posts including a tech bulletin about P0300 can be found at the link below.

It describes the same injector terminal corrosion issue I covered previously for you, as well as a known wiring harness abrasion issue inherent to certain models.

http://www.digitalcorvettes.com/foru...threadid=38483

I haven't encountered the harness abrasion problem myself, but evidently it exists on some cars.

Everyone I've helped with P0300 has found either a loose/damaged spark plug wire or an injector terminal covered with corrosion.

If you can get a proper scantool, you can pull up all 8 cylinders' misfire history counters and see exactly which one(s) is/are having issues in most cases. These counters have helped me find interesting things such as individual injectors not flowing properly but not setting a P-code on the DIC, loose/damaged plug wires setting P0300, etc.

 

Ill check around for a good scanner. I hooked up a fuel press gauge and its stable at 61psi at idle and has been holding 43psi for the past 30mins. I also checked just one of the plugs and it looks perfectly fine. Ill keep digging in there for any corrosion.

 

Good data. The injectors aren't completely ruled out just yet, but they're low on the list.

After you've verified all plug wires are firmly seated on both the plug end and coil end, and you've removed/inspected/reattached all 8 injector connectors, let us know how it runs and we'll go from there.

 

I just hooked up a boost gauge to check vacuum. Is 18-19 good @ idle? Jumps to around 10 when I blip the throttle to 3k.

Next, reseating injectors.

 

bump.

 

Bump what? All 8 injector connectors removed and re-seated? All 8 plug wires pushed and twisted to ensure proper seating?

 

^ yeah I reseated all 8 and it holds >40psi after I shut down. Im guessing my vacuum is in the norm too.

 

Remove each spark plug wire and measure resistance using an Ohm-meter. Record each wire's resistance and report back.

Be careful with your meter's probes, don't just smoosh them all the way to the bottom. Contact the sides of the terminals same as a spark plug or coil terminal would do, so you get an accurate reading.

 

^ i have no clue on how to do that.