Blinking Check Engine light

TedSJr · January 30, 2020

I have a 2003 2500 HD 4WD with 6.0 Gas V8. The check engine light periodically will begin blinking. It can blink for 2 minutes or for an hour, then it may quit for days. It has been doing this for months. My mechanic put it on the analyzer and got a Code 300. He said it is a misfire but he cannot pinpoint where. He suggested changing wires, plugs, coil packs, etc. Before I start replacing parts, does anyone have any thoughts? I've read where people say you should stop driving the truck immediately but, like I said, it has been doing this for a while and I have no problems in performance or gas mileage.

Formulabruce · January 30, 2020

Mine does that, same code but its the fuel vent system and seem to only do it when the tank is full, or near full.

newdude · January 30, 2020

Blinking = Bad. Its misfiring which is bad.

You can start with plugs/wires, but might want to check the intake manifold gasket beforehand as they do leak on those year Vortecs and cause misfire codes.

BlancoSilverado · January 30, 2020

Blinking CEL doesn't always mean that its a misfire. It letting you know that there is something wrong and continue driving as is can lead to permanent damage to the driveline (engine/trans) components.

Abeyance · February 3, 2020

I am currently fighting this exact same issue, which seems very common based on all the posts about it all over the internet.

Check engine light blinks, mostly but not exclusively, at idle. It also idles around 500 RPM, which I believe is a bit low and at times seems like it's going to stall but never quite does.

Computer shows a code P0300 (Random/Multiple Cylinder Misfire Detected).

So far I have done the following, which has changed nothing:

New spark plugs
New spark plug wires
Cleaned throttle body
New idle air control valve
New PCV valve
New fuel filter
Added a can of Sea Foam to fuel tank (unknown quantity of old gas in tank)

Next up, I'm going to borrow a fuel pressure gauge and check that. If the numbers don't look right, then I'll probably try a new fuel injection pressure regulator and/or new fuel pump. If the numbers do look right, then... I dunno, maybe an EGR valve or MAF sensor or new coil packs or...?

Colossus · February 4, 2020

With the sea foam in there, drive it a bit hard, hard accelerations to get the RPMs up. that's where the seafoam will do the most good at cleaning things up.

tlaw91 · February 6, 2020

Blinking = Bad. Its misfiring which is bad.

You can start with plugs/wires, but might want to check the intake manifold gasket beforehand as they do leak on those year Vortecs and cause misfire codes.

Totally agree!!

The op and the other guy who has already fired the parts cannon should replace the intake gaskets. They are a common failure part with this age/mileage on this engine and year. Also gives you a chance to replace the knock sensors and valley plate gaskets.

Hope this helps

-GM Technician

Sent from my iPhone using Tapatalk

Abeyance · February 9, 2020

Ok, before I order any more parts for my parts cannon, including intake manifold gaskets, I checked the fuel pressure, which I'm told can also be the issue behind a P0300 code. Here is what I found, at the schrader valve on the fuel rail:

Key on, not started: pressure went to 50, then slowly dropped back to zero. Not sure if it was supposed to, but it did not hold pressure with the key in the on position

Starting and idling: pressure was consistent at 50
Running, feathering the throttle: pressure bounced between 48-52

Those numbers seem a bit low, but I don't know if they're low enough to indicate the issue is there. Hoping someone can tell me if my test results indicate anything, if not I'll probably just move forward with the intake manifold gaskets and a bit of prayer.

dj_bosse · February 9, 2020

You said there's been no change in performance or gas mileage when the light is flashing. Can you actually tell that the truck is misfiring when the light is blinking? This may sound like a stupid question, but on my 06 2500 and my cousin's 04 2500 we both had "ghost" P0300 codes, where there wasn't a noticeable misfire (no shudder or anything). Both of ours ended up being the crankshaft position sensor. Did a relearn on the sensor and the P0300 cleared and hasn't come back (~6 months since performed relearn).

Edited February 9, 2020 by dj_bosse

davester · February 9, 2020

That fuel pressure is a bit low, as it should be about 60 psi. I know on my truck with the returnless fuel system, it's supposed to hold pressure for some time (as in, stay close to 60 psi for more than a couple minutes after turning the key off). I don't know how your system should behave, as yours has a return fuel system, with the fuel pressure regulator operated by vacuum.

Given that with the engine off you can't get over 50 psi, I would suggest replacing the fuel pump to get it higher (as that seems to be the max pressure your current FP can put out).

That said, your engine should still run reasonably well, since it looks like it can maintain that 50 psi, so the ecm can readily compensate for the slightly lower pressure by keeping the injectors open a bit longer (happens automatically in closed loop mode) by adjusting fuel trims.

Edited February 9, 2020 by davester

Abeyance · February 9, 2020

Quote

You said there's been no change in performance or gas mileage when the light is flashing. Can you actually tell that the truck is misfiring when the light is blinking?

Yes, you can tell. Whether the light is flashing or not doesn't seem to make any difference, it always feels like it's misfiring (shuddering, low on power, slow to accelerate, stumbles and almost dies when you come to a stop, etc).

Quote

Both of ours ended up being the crankshaft position sensor. Did a relearn on the sensor and the P0300 cleared and hasn't come back (~6 months since performed relearn).

I assume there are instructions around here somewhere on how to do this relearn? Or is it a dealer only procedure? At this point I'm willing to try just about anything as I'm running short on patience and thinking about fire-bombing the thing.

riverbanks · February 9, 2020

Takes a good scanner to do relearn,I agree with low fuel pressure,time for a pump

dj_bosse · February 10, 2020

I had access to a SnapOn scanner (for free) so that's what I used. There is a way to do it without a scan tool, but you need a lot of open road without any lights or stop signs which can make it difficult to complete the relearn. I'm sure if you took it to a shop for them to relearn they'd charge you a full hour labor even though it takes no more than 10 seconds to complete.