spark knock

ignent · April 18, 2005

Got a problem with spark knock under 3/4 throttle with no load on level ground and have tried everything I know to do. I have a 6.0 2500hd and have replaced the plugs,pcv,wires,fuel filter and air filter. I have also gone from 87 to 89 octane gas but nothing! Can anyone lead me to something I am missing? I can't afford to start running 93 octane and am to the point of getting rid of my baby. HELP!!

dewfpo · April 18, 2005

Decarbonizing the cylinders sometimes helps if carbon is the problem.

If carbon is not the problem....

It could be a bad MAP (manifold absolute pressure) sensor. If it's reading the wrong pressure, it allows too much spark. Often does not set a code in the ECM. Need a scan tool to check it.

DEWFPO

Haulin' 8.1 · April 18, 2005

Check the fuel pressure.

mmmikkke · April 18, 2005

Hmm... Ver-r-r-y int-er-est-ing. 3/4 throttle. Probably just short of going to a "full rich" air/fuel mixture. So it sounds like maybe you have a cylinder that's running "lean". Could be a bad intake manifold gasket, or a defective intake manifold "casting".

I'd take out each plug and look for the one that's indicating the lean burn. Concentrate your attention there.

I bet it's just 1 cylinder.

snoman · April 18, 2005

Got a problem with spark knock under 3/4 throttle with no load on level ground and have tried everything I know to do. I have a 6.0 2500hd and have replaced the plugs,pcv,wires,fuel filter and air filter. I have also gone from 87 to 89 octane gas but nothing! Can anyone lead me to something I am missing? I can't afford to start running 93 octane and am to the point of getting rid of my baby. HELP!!

<{POST_SNAPBACK}>

Given today full prices, premium is not that much more percentage wise and you may actual break even with higher grade gas because of improved engine performance. It sould like you run it hard and if you have big tires with stock gearing the engine is wotking harder and more prone to knock. I use premium in both of my 4x4 GM SUV's and have for years and they run better and never knock either no matter what I do. Some brands of plus are little better than regular and you might even try mixing 50/50 regular premium for the same price as plus and which will yeild a higher octane too

dewfpo · April 18, 2005

Could be one dirty or faulty injector as well. Not putting enough fuel in, cylinder runs lean and pings.

DEWFPO

snoman · April 18, 2005

Could be one dirty or faulty injector as well. Not putting enough fuel in, cylinder runs lean and pings.

DEWFPO

<{POST_SNAPBACK}>

Not too likely here because if it was that lean the engine would feel a bit ruff too.

facn8me · April 18, 2005

Must get tiresome correcting everybody Snoman.

mmmikkke · April 18, 2005

You should still start by looking at the plugs. When you take them out, note which one came from which cylinder. Look for either a brown "baked" plug, different from all the others, or one with excess carbon on it.

Heck, you might find out that you have a cracked insulator on one plug, and your problem will be solved.

Lean or not, look at the plugs.

The reason I think it's a lean problem is that it's happening mostly at 3/4 throttle. The spark is advanced, the vacuum is near zero, but the mixture is not at full rich. Take it to full rich (full throttle) and the ping goes away (as far as we know). So it's a carbon-based preignition most likely, either from a hot (lean) cylinder or from a cylinder that has a carbon deposit on or near the plug.

Butch 02 Denali · April 18, 2005

Got a problem with spark knock under 3/4 throttle with no load on level ground and have tried everything I know to do. I have a 6.0 2500hd and have replaced the plugs,pcv,wires,fuel filter and air filter. I have also gone from 87 to 89 octane gas but nothing! Can anyone lead me to something I am missing? I can't afford to start running 93 octane and am to the point of getting rid of my baby. HELP!!

<{POST_SNAPBACK}>

The #1 cause of pinging is a dirty mafs. (and the cheapest and easiest to fix too!)

The second most likley cause is a clogged or sticking EGR valve.

Because your ping is at light throttle, I would lean toward the EGR as the culpret!

As mentioned, still a good idea to pull the plugs and see they are all burning even. Clogged and mismatched injectors are high on the list too!

snoman · April 19, 2005

Must get tiresome correcting everybody Snoman.

<{POST_SNAPBACK}>

Not as tiresome as ignoring the obvious. If it had some of the injector problems that are being suggested here, the engine would "feel" different too and not just ping. Some people are just hung up on trying to burn the cheapest gas they can find (not realy refering to the thread starter) and then blame the engine not the gas when it knocks and when last I looked the manual says minimum recommand octane is 89 not 87 and it does say MINIMUM which means there can be times when more is needed. I do not burn 87 in any of my newer 4x4's and never have. The only 4x4 I use 87 in is a old Jeep with a carb and a AMC 360 in it with 8.25 to one compression and I used to use 86 in it too before Sunoco stopped carrying it. It liked the low octane stuff.

Haulin' 8.1 · April 19, 2005

We've been discussing this quite a bit lately. So here's a greatest hits selection lol:

I've been able to correct this twice here lately by raising the fuel pressure, but that was on trucks where the pressure was known to be below spec. There are numerous causes of spark knock. You should take it to someone who can and will be able to find and repair the cause.

In the meantime read through these posts:

What is spark knock, what causes it, and how to determine and remedy it:

http://www.gm-trucks.com/forums/index.php?showtopic=40531

and

Fuel pressure's effect on detonation resistance with real world results on a 6.0:

http://www.gm-trucks.com/forums/index.php?showtopic=39982

Vernon

ignent · April 21, 2005

Thanks for all the help I believe I will let a shop put it on a scan machine. If I continue with this myself my next question would be... why won't it start? Cya