My brother has a 2004 Tahoe z71 with the 5.3 vortec that over the past year or so has developed a heavy misfire under load like pulling a trailer or sometimes just pulling away from a stop quickly. He thinks its a knock sensor is bad, he replaced one about 2 years ago but he thinks he may have pinched a wire for one of the knock sensors when he reinstalled the intake manifold. Would one dead knock sensor cause misfire on an engine under load? Personally i dont think the sensor is his problem but he swears up and down that it is
5.3 vortec heavy misfire under load
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sounds like an ignition coil breaking down to me.
Without knowing much else, what you described sounds like a plug/wire/coil issue. Best thing would be to get a scanner on it that reads cylinder misfires or contribution and narrow down the hole.
As for the knock sensor, circuit problems should set a code.
As for the knock sensor, circuit problems should set a code.
Originally Posted By: 55Test
My brother...swears up and down that it is.
Have him replace it on his dime and time.
If it's all fixed take him to dinner and give him $250 T&M. Deal?
My brother...swears up and down that it is.
Have him replace it on his dime and time.
If it's all fixed take him to dinner and give him $250 T&M. Deal?
When was the last time this thing had a new set of plugs? Definitely sounds ignition related.
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Originally Posted By: The_Eric
Originally Posted By: turtlevette
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Yes it certainly can be.
Nope, spark doesn't care until cylinder pressures get crazy high. He could pull the codes and settle this easily.
Originally Posted By: turtlevette
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Yes it certainly can be.
Nope, spark doesn't care until cylinder pressures get crazy high. He could pull the codes and settle this easily.
Fuel issue is my guess as well. He does get an error code for a knock sensor and his Scangauge shows one knock sensor isn't actually doing anything, it always shows a value of 0. When he first bought the Tahoe it had a similar sputtering issue, he replaced the front knock sensor (the one closest to the front of the engine) and it ran great after that, he pulled a double-axle uhaul car trailer with an old Ford farm tractor that must have weighed 6000+ pounds like it wasn't even behind him. He also says his fuel mileage has gone down noticeably since the misfiring has returned
Quote:
Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load.
http://www.aa1car.com/library/cm1196.htm
While it could be fuel with the limited information we have here the obvious questions are how old are the plugs and what codes are stored.
After that regular diagnostic steps inc FPT will reveal the problem.
Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load.
http://www.aa1car.com/library/cm1196.htm
While it could be fuel with the limited information we have here the obvious questions are how old are the plugs and what codes are stored.
After that regular diagnostic steps inc FPT will reveal the problem.
ls1mike
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Originally Posted By: turtlevette
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
I have had 4 LS equipped vehicles and a ignition issue most certainly can do this in these vehicles.
My current 2500 HD is a 6.0 and would run great until I got the trailer hooked up and hit a hill or had to really mash the go pedal. I would get a really bad miss. Here is what I found.
This was an aftermarket plug wire. They do not use the heat shield like the wires from the factory. Turns out is a great plug wire for the Trans Am, but the heat of towing ruined them in the truck.
OP what are the truck details? Miles?
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
I have had 4 LS equipped vehicles and a ignition issue most certainly can do this in these vehicles.
My current 2500 HD is a 6.0 and would run great until I got the trailer hooked up and hit a hill or had to really mash the go pedal. I would get a really bad miss. Here is what I found.
This was an aftermarket plug wire. They do not use the heat shield like the wires from the factory. Turns out is a great plug wire for the Trans Am, but the heat of towing ruined them in the truck.
OP what are the truck details? Miles?
Originally Posted By: turtlevette
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Obvious lack of experience here. This is an excellent example of bad internet counseling!
Anyone who tunes cars KNOWS ignition misfire can and does occur during heavy loading...
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Obvious lack of experience here. This is an excellent example of bad internet counseling!
Anyone who tunes cars KNOWS ignition misfire can and does occur during heavy loading...
Originally Posted By: SteveSRT8
Originally Posted By: turtlevette
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Obvious lack of experience here. This is an excellent example of bad internet counseling!
Anyone who tunes cars KNOWS ignition misfire can and does occur during heavy loading...
Yup - common knowledge with experience.
Originally Posted By: turtlevette
I'm going to disagree with everyone and say its the fuel pump. An ignition issue would not be load variant.
Obvious lack of experience here. This is an excellent example of bad internet counseling!
Anyone who tunes cars KNOWS ignition misfire can and does occur during heavy loading...
Yup - common knowledge with experience.
If he's worried about the wire harness, then he should pull the intake. Not a big deal as I'm sure he knows. 10 minute or less job. A common problem with these engines is for water to get in and rot the knock sensors out. Dorman makes a replacement harness if his was damaged during install or by corrosion from water.
Originally Posted By: ls1mike
This was an aftermarket plug wire. They do not use the heat shield like the wires from the factory. Turns out is a great plug wire for the Trans Am, but the heat of towing ruined them in the truck.
This makes me glad that I've been using ACDelco wire sets on my 5.3's.
This was an aftermarket plug wire. They do not use the heat shield like the wires from the factory. Turns out is a great plug wire for the Trans Am, but the heat of towing ruined them in the truck.
This makes me glad that I've been using ACDelco wire sets on my 5.3's.
It does sound like a coil. I drove myself nuts with the F350 when it blew out a coil towing. Bad misfire below 3000RPM, but would run fine above 3000.
And, typical Ford, it doesn't throw a code for it.
I'm not familiar with GM computers but I could see it causing an issue too if a knock sensor wasn't working.
And, typical Ford, it doesn't throw a code for it.
I'm not familiar with GM computers but I could see it causing an issue too if a knock sensor wasn't working.
If an ignition system can't properly fire a plug that has erroded 10-20 thousands then its a poor design. The difference in cylinder pressure between idle and full acceleration in a passenger vehicle does not present that much more resistance across the gap. You'd see it if you added nitrous but its not that different during the range of normal operation.
Let's have him pull the codes and see who's right.
Let's have him pull the codes and see who's right.
Originally Posted By: ls1mike
My current 2500 HD is a 6.0 and would run great until I got the trailer hooked up and hit a hill or had to really mash the go pedal. I would get a really bad miss. Here is what I found.
Looks to me like it got a little too close to that miter saw.
My current 2500 HD is a 6.0 and would run great until I got the trailer hooked up and hit a hill or had to really mash the go pedal. I would get a really bad miss. Here is what I found.
Looks to me like it got a little too close to that miter saw.
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