Knocking when giving it gas

On my 04 it has started making a constant knocking noise only when I give it gas forwards and not as loud backwards and it will stop as soon as I let off the gas. I’ve been to a couple different mechanics and nobody seems to know what it is.

 

I'll guess.

You have carboned up pistons (at least 1 or 2). This raises compression and absorbs fuel, creating detonation condition.

If you run a tank of premium E0 fuel and the noise is gone, or greatly lessened, this will verify.

If that's what it is, report back and we'll tell you how to fix it and prevent re-occurrence.

 

Thanks. I have not had a tune up since ive have it but I have only had it for about 4 months. I have gotten gas all over from NC to GA it’s all the time.

 

when I fill up today I’ll run premium and get back to you

 

Why should this make a difference? Ethanol fuels are less energy dense, that and having to spray more quantity of it actually makes them ideal for reduction of detonation. It's the reason you see high performance boosted cars running E85 and E90. That said, what is written on the pump is what it is ethanol quantity or not, 91 is 91, it's mixed to be at least a minimum of what is written on the octane sticker.

 

Have you ever had an exhaust leak before to know what one sounds like?

 

exhaust leak

No I have not. But wouldn’t it always be making that noise if it is started? It will only do it when I’m driving and pushing the gas pedal. Not sure if that makes a difference.

 

Exhaust leaks are more of a tick than a knock, but they track well with throttle position and are often very faint at idle. Is the knock present when not moving?

is it present under light load if you take off slowly? Not to undermine the posters above, but a knocking detonation at part throttle is unlikely unless the truck is running VERY badly.

 

You are correct. The important part for this 'guess' diagnostic is the 91 octane.

IF it were to turn out that carbonization were the problem (or part of) I have found the E-0 can be a somewhat useful part of the home brew cleanup process.

 

Have you tried to run a mixture of 91 plus E90?

Will running E90 hurt the fuel components? Lines or injectors?

 

Our trucks aren't really set up for flex fuel, if you're not running a modern pump it will hurt it over time. The rubber lines will be okay as long as you don't run it exclusively. PTFE lines are recommended for extended use. OEM injectors probably don't have the flow capability to run it exclusively, you have to spray a lot more than just gasoline. Obviously a tune is required. I run E30 in my BMW with a tune adjusted for it and can pull down. 420hp with no timing corrections, lets me run 21psi all the way up to my 7500rpm limiter on a 10.2:1 compression engine haha. The ethanol is so knock resistant, but you have to up the injection duty cycle cause it's so much less energy dense than gas. Laymen's terms, it's like having meth injection except you can adjust for it accurately with your fuel map and spark map and monitor it within your afr map. So you get more bang for your buck... Literally... Vs meth

 

No the knock is non existent when not moving. The knock is the same if I take off slow or fast light load no load heavy load it’s constantly there

 

You say no noise not moving.

Does revving motor in neutral, not moving, create the noise?

If you are at speed on the road and coast in neutral, any noise?

 

idle for my truck is 750rpm once I hit the gas pedal at 1000 rpm it’s knocking

 

Mmmmm

 

Correct no noise not moving reving does nothing at all. If I’m driving just as soon as I let off the gas pedal it stops so I can coast and I won’t have any noise

 

I think we're gonna need a video or sound clip cause it's sounding like a failing flex plate by your description

 

https://youtu.be/jCCed4pVFg0

 

filled up this morning with premium fuel and it made no difference at all.

 

What are your fuel trims? This will tell you if your looking in the right direction
Scanguage will tell you,
Does not sound like an engine knocking tho