5.3 vortec heavy misfire under load

[Trav]

What are you talking about?

The problem is reduced coil saturation time combined with the greater voltage requirements of the eroded plugs.
No one said it couldn't be a fuel or the knock sensor issue but he didn't post any codes or FT data.

Buy this book. Seriously many trade schools use this book.

http://www.amazon.com/Automotive-Technol...ystems+approach

 

[turtlevette]

Originally Posted By: Trav
What are you talking about?

The problem is reduced coil saturation time combined with the greater voltage requirements of the eroded plugs.
No one said it couldn't be a fuel or the knock sensor issue but he didn't post any codes or FT data.

Buy this book. Seriously many trade schools use this book.

http://www.amazon.com/Automotive-Technol...ystems+approach


Reduced coil saturation? There's one coil per cylinder, way more time than you'll ever need. Older systems provided very hot spark with a single coil. The wire on the ls is very short so there is almost no loss. It should be a bullit proof system.

I learned my ignition stuff from a guy on the vette forum who did skunkworks stuff.

http://www.corvetteforum.com/forums/c3-t...ys-like-me.html

 

[Trav]

It doesn't matter how many coils there are. You need to read some books or take some classes.
Going by your theory spark plugs should never need changing as gap erosion doesn't create any problems. LOL

Quote:
I learned my ignition stuff from a guy on the vette forum who did skunkworks stuff.

 

[turtlevette]

Originally Posted By: Trav
It doesn't matter how many coils there are. You need to read some books or take some classes.


Sure it does. There's 8x more time for the coil to charge. All those ugly coils are mounted on the valve cover for a reason. It almost doesn't matter anymore that there is gap erosion. Spark plug changes are becoming a thing of the past.

 

[Trav]

Quote:
It almost doesn't matter anymore that there is gap erosion


Whatever you say. Go and argue with NGK. BTW buy that book.

Quote:
As spark plugs grow older, they lose their sharp edges as material from the center and ground electrodes is slowly eroded away. As the gap between these two points grows, the voltage required to bridge the gap increases proportionately. Even the best ignition systems will be strained to supply enough voltage to completely burn the fuel. It is at this point, when fuel is being left unburned, that the time has come to change spark plugs.


http://www.ngksparkplugs.ca/tech-info-spark-plug-faq.cfm#sp16

 

[Warstud]

EASY....Your Intake manifold leaks.

 

[The_Eric]

Originally Posted By: Warstud
EASY....Your Intake manifold leaks.


Doubt it. A manifold leak's effects would tend to diminish as the throttle was opened.

 

[ls1mike]

I have had manifold gasket leaks in an LS. I would have to be pretty bad in an LS to cause a miss. Usually you get a rough idle and diminished performance.

 

[meep]

ignition misfires increase with load, more noticed at lower rpms when air/fuel density is higher; the problem in this case is found on the high tension side of things.

been there, done that, own the t-shirt, wore it out and moved on....

 

[ls1mike]

Well since I don't see an LS motor in you signature I can tell you I got a different t-shirt that reads something totally different than yours.


LS motors with a bad coil, wire, or bad plug will miss under load and high up in the RPM it is their nature.

 

[SteveSRT8]

Originally Posted By: ls1mike
Well since I don't see an LS motor in you signature I can tell you I got a different t-shirt that reads something totally different than yours.


LS motors with a bad coil, wire, or bad plug will miss under load and high up in the RPM it is their nature.


I've got a driveway full of them. Run many many many into the ground from brand new. In a duty cycle so tough that all other mfgrs chuck the warranty.

Vacuum leaks in the intake to cylinder head gasket? Common and mostly not a problem, fuel trim usually shows these.

Ignition problems? Unheard of. I have run stock plugs past 250k with no misfire. Wires are many times difficult to detect. Coils throw a code almost instantly.

OP simply hasn't given us enough to do any serious diagnosis here...

 

[ls1mike]

Originally Posted By: SteveSRT8
Originally Posted By: ls1mike
Well since I don't see an LS motor in you signature I can tell you I got a different t-shirt that reads something totally different than yours.


LS motors with a bad coil, wire, or bad plug will miss under load and high up in the RPM it is their nature.


I've got a driveway full of them. Run many many many into the ground from brand new. In a duty cycle so tough that all other mfgrs chuck the warranty.

Vacuum leaks in the intake to cylinder head gasket? Common and mostly not a problem, fuel trim usually shows these.

Ignition problems? Unheard of. I have run stock plugs past 250k with no misfire. Wires are many times difficult to detect. Coils throw a code almost instantly.

OP simply hasn't given us enough to do any serious diagnosis here...


That is not what I am saying. Igintion problems are few and far between I agree, but I have been around and raced with enough of them and my own to know if you do have a miss because of how they make power it will show the miss under load and usually above 3000 RPM. Coils will throw a code, but the plugs and wires, if they are bad will sometimes throw a CPS code.

 

[SteveSRT8]

Don't worry Mike, I am in complete agreement with you!

 

[meep]

Originally Posted By: ls1mike
Well since I don't see an LS motor in you signature I can tell you I got a different t-shirt that reads something totally different than yours.


LS motors with a bad coil, wire, or bad plug will miss under load and high up in the RPM it is their nature.


Hey hope I didn't come off as smug -- I was more annoyed by earlier comments suggesting misfires had nothing to do at all with rpm / density. I usually don't post here when I feel that way but I saw several folks trying to help and being told they were wrong. it bothered me.

in totally stock applications, I find spark weaknesses first show up under higher loads at lower rpms' as the spark has alternate paths to take with the resistance through greater fuel/air charge increases. problems with wires, caps, plug insulators show up there and are more pronounced until the downshift either covers it up or gets to a higher rpm/less density load allowing the spark to go where it's supposed to. Just ran into this very thing last month in a friend's yukon.

 

[ls1mike]

No I didn't mean to either, but I am on my 5th LS powered vehicle, and what he is describing in my case has been bad plugs/plug wires. But it was generally after 150,000 miles unless, like the picture I posted, I used sub par plug wires for towing.

 

[turtlevette]

Originally Posted By: meep


Hey hope I didn't come off as smug --



I couldn't care less. And I don't care what you think of me either.

Its about determining the most likely cause of the described problem. A fuel issue is much much much more likely to be load variant than spark. What you are saying happens only when the spark energy is right on the hairy threshold which is a special condition and not very likely. These things go through fuel pumps rather predictably and fuel filters clog more often than ignition problems.

I like the way Steve says I have an obvious lack of experience for saying the ignition is bullet proof then the next post says he's never had an ignition problem and runs his plugs 250k miles. We have some very emotional people here who can't see thru their personal feelings and use logic.

 

[SteveSRT8]

^^^That was my personal experience with dozens of LS powered trucks.

It has nothing to do with the OP's issues, and your theory on fuel pump partial failure is nuts. Fuel pump in these vehicles is either good or dead, no in between. And half a million miles on one of my best trucks with no clogged fuel filters either.

We have a lot of elitist idjits on this board that imagine they are the smartest man in the room. That doesn't make it so, and anyone can browse the net for obscure diagnoses...

 

[Trav]

Here is the thing, if someone changed the plugs and didn't use a platinum OE spec plug and used copper instead set at a wide gap then it can cause problems in a short time. So can a cracked insulator or bad wire/coil.
With the information we have its a guessing game, FT data, misfire count, OBD II codes, service history, etc would help.

+1 these fuel pumps do seem to die without any warning at all.
There is no point in trying to educate this guy, he wont even believe what NGK the makers of the OE Delco plugs put in black and white.

 

[SteveSRT8]

Agreed. It is an open discussion!

But trying to figure out a problem over the computer is ridiculous anyway. Add in a couple of inexperienced fools trying to make wind and it gets even harder. I normally don't even try...

 

[meep]

There's another possibility we haven't covered--- predet due to carbon buildup or a hotspot such as a poorly seated exh valve. That would do exactly whats listed above and could be informally tested by a tank of 93 octane....