Cel Flashing

59ih340 · October 29, 2009

I've had this problem for a bit,'03 6.0L at 70 the cel will flash randomly then go out sometimes it will set a P0300 code,most times it won't set anything.I changed all the coils and injectors with new ones it runs smooth has good power.Still getting the cel flash at 70. I just got new scanning software and I can now pull history easier.

This mifires are 0 to a couple hundred for cyl 234578, Cyl 1-23888 misfires, Cyl 6-29592 misfires.I picked up 2 new plugs to throw in,but what sticks out to me is the problems are cyl 1&6. The 2 cyls firing 180* off from each other. Does this seem more like a bad sensor? need for a crank relearn? or just a coincidence?

bmgmike · October 30, 2009

I've had this problem for a bit,'03 6.0L at 70 the cel will flash randomly then go out sometimes it will set a P0300 code,most times it won't set anything.I changed all the coils and injectors with new ones it runs smooth has good power.Still getting the cel flash at 70. I just got new scanning software and I can now pull history easier.
This mifires are 0 to a couple hundred for cyl 234578, Cyl 1-23888 misfires, Cyl 6-29592 misfires.I picked up 2 new plugs to throw in,but what sticks out to me is the problems are cyl 1&6. The 2 cyls firing 180* off from each other. Does this seem more like a bad sensor? need for a crank relearn? or just a coincidence?

I have a 2003 Silverado 2500HD 6.0L, 136,000 miles that doing the exact same thing. It was flashing constant at 70, changed the fuel filter and now it flashes but it intermintent. If you find out what it is I would love to know. Someone else on here has the same thing but I don't know if he got it fixed or not.

59ih340 · October 30, 2009

Where the problem is only at higher engine speeds and I can watch the misfires mainly on Cyl 1 and Cyl 6 ( firing 180* off from each other).I have a feeling the camshaft position sensor is breaking up @ higher rpm. I picked up one today and will try to put it in over the weekend. as soon as I do, I will rescan it and let you know what I find.

59ih340 · November 1, 2009

Cam position sensor rescanned Cyl 1-8 ALL 0 misfires.

bmgmike · November 1, 2009

Cam position sensor rescanned Cyl 1-8 ALL 0 misfires.

Great you figured it out, what kind of scanner do you have, would like to see which are misfiring on mine. Where did you get the sensor and how much did you pay? Again good job.

59ih340 · November 2, 2009

Cam position sensor rescanned Cyl 1-8 ALL 0 misfires.

Great you figured it out, what kind of scanner do you have, would like to see which are misfiring on mine. Where did you get the sensor and how much did you pay? Again good job.

I just started using OBDScan-APEX. It's really cheap if you have a laptop The software and computer hookup is around $140. and the GM enhanced software is on sale now for $40,The GM enhanced is pretty good,it will read and clear abs and aibag codes too.So for under $200,if you have a laptop or can get your hands on one it's a pretty cheap way to go.Www.obdscan.net

The sensor I got @ Advance Auto parts it was about $42 and The easiest way to change it is pull the intake manifold off so you can get at it easy.You could probably reuse the gaskets,but I threw in some fresh ones (about $40).It took me about 2hrs.(but I was in no hurry, could have done it in an hour)

buck-brandt · November 5, 2009

The 5.3s actually had problems with misfires and rough idling. A common cause is bad intake gaskets sucking air.

bmgmike · November 10, 2009

The 5.3s actually had problems with misfires and rough idling. A common cause is bad intake gaskets sucking air.

Update, took it to the dealer, diagnosed as vacuum leak or cracked intake, hope it is gaskets, will let you know.

Nytemare · November 10, 2009

Hey does anyone know if this is a problem with the 4.8's also...the gasket thing I mean.

My truck sometimes stumbles on idle...for the most part the roughness is almost gone...but its not as smooth as I'd like it to be.

bmgmike · November 12, 2009

I've had this problem for a bit,'03 6.0L at 70 the cel will flash randomly then go out sometimes it will set a P0300 code,most times it won't set anything.I changed all the coils and injectors with new ones it runs smooth has good power.Still getting the cel flash at 70. I just got new scanning software and I can now pull history easier.
This mifires are 0 to a couple hundred for cyl 234578, Cyl 1-23888 misfires, Cyl 6-29592 misfires.I picked up 2 new plugs to throw in,but what sticks out to me is the problems are cyl 1&6. The 2 cyls firing 180* off from each other. Does this seem more like a bad sensor? need for a crank relearn? or just a coincidence?

How did you come to the diagnosis of the cam sensor?

bmgmike · November 21, 2009

The 5.3s actually had problems with misfires and rough idling. A common cause is bad intake gaskets sucking air.

Update, took it to the dealer, diagnosed as vacuum leak or cracked intake, hope it is gaskets, will let you know.

Replaced the cam sensor and new intake gaskets, still doing the same thing. Dealer said the intake could be warped. Any other ideas.

59ih340 · November 21, 2009

The 5.3s actually had problems with misfires and rough idling. A common cause is bad intake gaskets sucking air.

Update, took it to the dealer, diagnosed as vacuum leak or cracked intake, hope it is gaskets, will let you know.

Replaced the cam sensor and new intake gaskets, still doing the same thing. Dealer said the intake could be warped. Any other ideas.

Are they checking with an actual vacuum guage,or are they just guessing? it should be around 17-22 in-Hg.(maybe 12-15 with a leak)There is also a TSB GM technical service bulletin #06-06-04-046 concerning bad grounds in the main harness. That throws p0300 codes due to poor pcm grounding. how's the fuel pressure?

minibike132 · November 21, 2009

The 5.3s actually had problems with misfires and rough idling. A common cause is bad intake gaskets sucking air.

Update, took it to the dealer, diagnosed as vacuum leak or cracked intake, hope it is gaskets, will let you know.

Replaced the cam sensor and new intake gaskets, still doing the same thing. Dealer said the intake could be warped. Any other ideas.

Are they checking with an actual vacuum guage,or are they just guessing? it should be around 17-22 in-Hg.(maybe 12-15 with a leak)There is also a TSB GM technical service bulletin #06-06-04-046 concerning bad grounds in the main harness. That throws p0300 codes due to poor pcm grounding. how's the fuel pressure?

A gauge isn't really a good way to check for a leak.

minibike132 · November 21, 2009

I guess I should expand on that. It isn't very accurate if you have a good scanner you can do a much more accurate diagnosis with a can of map gas or brake cleaner.

What I usually do on these motors to find a vacuum leak is pull up the fuel trims and o2 sensor data. I pull the vacuum line to the booster for a quick second to make sure both banks go lean fast like they should. Then I put a quck blast of brake clean into the air filter box to make sure they go rich quickly and evenly. If that checks out then the o2s are reporting like they should, if one is slow then address the slow sensor first.

Then look at fuel trims again, anything positve indicates low fuel delivery or a vacuum leak. If it is only one bank then most likely a leak, if both are lean most likely fuel (on this motor there isn't very much in the way of external vacuum stuff that can leak causing both banks lean other models are different). If one bank is lean start spraying that bank till it goes rich, bingo you found your leak. If not start looking at other things that would cause a lean condition.

Usually a vacuum leak large enough to cause a miss on this motor will cause a P0171 for a lean condition before it missfires, I would be looking more in the low fuel volume direction if it were me but I guess we all do things differently.

59ih340 · November 21, 2009

A gauge isn't really a good way to check for a leak.

They could use fuel trim data...but that could be thrown off by a hundred different things(weak fuel pump,bad grounds,o2 sensors....) and not give actual vacuum readings.

That's how they threw gaskets at it and it's not fixed. should they just put a manifold on it bill him and still not have it fixed. I'm just trying to get info on how they are determining it's a vacuum leak.