Loud Tapping

Reimenizer · 05-19-2008, 04:57 PM

My Dads 2002 GMC Duramax has a VERY loud tapping sound. It has 114k miles on it and is bone stock. He tows a 30 ft fifth wheel that weighs about 12-13k. Of the miles it has towed about 35-40k miles (of the 114k).

He bought the truck new and ever since new it had this tap. The tap has gotten louder over the years. Now it has gotten real loud (gradually). He has had it to the dealer since mile #1 and they say it is just the way the engine sounds.

It does sound like a typewriter and gets worse under load. Coasting the sound goes away. The dealer still says it is normal? He reports no loss of power.

I have to say that when I heard it...it does not sound good. Early on I even told him that these valve trains are noisy. I saw the truck 50,000 miles later and it got much worse. I have a '05 Duramax (I know they are different). This is not a faint noise...it is LOUD. He says it is one valve (put the old 2x4 on it to hear where it was coming from. Dealer says normal. I say it is not right.

Are these valves adjustable? He lives in Eastern PA...what should I tell him to do. Is there something he can buy to test for what it is for sure? My Dad is mechanically inclines but diesels are not his thing. Now a 1952 Pontiac he is good with. I have a brother that lives up there that can help with the testing. The dealers obviously do not know what to do and he does not have confidence in them? Yeah, now the repair is on him.

I did search the forums but all I saw was injectors and what was pretty much greek to us newbies. Help. Thanks in advance. Seems like a great forum. Reimenizer

**deeretracks** · 05-19-2008, 05:17 PM

Sounds like the pilot injection to me....Mine dose the same thing and thanks to this crap that they are calling diesel fuel it is louder under a load. try running a good fuel additive in it like staydine or powersurvice and see if it helps. I run powersurvice in every tank and its has helped.

**Bryan@ATS Diesel** · 05-19-2008, 05:22 PM

Its not the valves.......Its called "Pilot Injection". Basically what it's doing is injecting a small amount of fuel into the cylinder during the compression cycle as the piston is traveling upward which in turn ignites the fuel. This way, when the main injection pulse comes on, the fuel is being shot into a flame. The reason for this is the effeciency aspect.......Its completely normal in the duramax motors and amazingly so, the dealer ship is actually right with telling you what they were trained to tell you....."Its normal, Don't worry about it"

FYI......Fuel addatives will not make this sound go away. Its programmed into the ECM and will fade in and out depending on your boost, throttle position and RPM. The harder you are getting into it, the less you will hear it.......Mostly under light to moderate throttle is when I notice mine.

samdweezel05 · 05-19-2008, 06:38 PM

My 03' makes the same noise and as stated above the sound goes away if you keep your foot in it. My cure is keep my foot in it so I don't hear the sound.

Phil

Reimenizer · 05-19-2008, 08:24 PM

Can the ECM be adjusted to reduce this extra fuel? Does the injector need to be replaced?

**Bryan@ATS Diesel** · 05-20-2008, 07:59 AM

Its not an injector issue. Its a table that is built into the programming in the ECM...........It can be adjusted to a point but I personally wouldnt get rid of it.

**IdahoRob** · 05-20-2008, 08:06 AM

Get rid of the pilot injection and it will sound like a 12 valve cummins and run worse. Pilot injection is the reason that these new common rail trucks are much quieter.

Pilot can be changed (added, extended, turned off, etc.) I run pilot until about 2500rpm then it turns off on my race tuning, but stays on other wise.

On your 05 LLY do you notice the engine get louder at 2500rpm or so? Is this the same kind of sound your dad's makes? If so, that is pilot injection turning off.

Reimenizer · 05-20-2008, 05:18 PM

Rob, mine does not have the tapping like my dads at any RPM. My dads is a distinct tap from one side of the engine. To me it sounds like a valve tap. I am no mechanic like most of the people on that post. My Dad seems to think it one of the injectors malfunctioning. I did call him last night with the above postings and he thinks it could be this pilot deal.

One thing I do want to clarify. This tapping is not just some tapping. It is distinct and very loud. I tow a 5th wheel too and run into plenty of D'max motors in the camp grounds. I have never heard this engine sound out of any of them. I guess what I am saying is that I am not exagertaing the tapping sound. I am not picking this thing a part saying it needs to be as quiet as a Lexus motor. This is a loud tap and is not faint in any way. My Toyota van with 150k is starting to have a slight tap when started cold until warm-up. This tap sounds like what used to occur with those big block 455 motors in the 70's. My 05 LLY has all kinds of internal engine noises. I consider them normal for the engine. This tap is not normal. I know it is hard to describe in text without hearing it.

Since GM does not know how to diagnose these engines (the ones near him)...where does one bring it? A local diesel mechanic, Detroit Dealer, etc. Reimenizer

Reimenizer · 05-20-2008, 05:59 PM

I searched to net and see a bunch or service bulletins issued by GM regading the injectors of this engine. From the description it seems that this might be the issue. It is not a recall but certainly there was an issue with these injectors. True?

**IdahoRob** · 05-20-2008, 06:01 PM

Hmmm, ok this does not sound like pilot then. Has the dealer checked balance/return rates on the injectors?

Next thought, could it be an exhaust leak? Usually you'll see soot where it is leaking.

I have a friend with a 2002 LB7 that has, what sounds like, the same issue. Does not affect driving, but is much louder than any other Dmax that I've heard. He lives out of town, so I've not had time to play with it to find the cause.