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View Full Version : Need Help Diagnosing Tapping/Knocking Noise



ponyXpress
05-23-2002, 11:53
Hi everyone-

Great board! I've been reading you-all for over a year and finally had to take the plunge.

I've searched this thread and have not been able to find any info on my problem, so I was hoping someone could help.

I own an '01 Duramax/Diesel Ext. Cab and last fall started getting a tapping - maybe loud enough to be called a knocking - when towing loads under stress (up hill/passing). My trailer probably weighs about 10,000 - 13,000 lbs.

This noise keeps time with the RPM and starts out an annoyance, but can get quite loud on the big hills. Seems to sound metalic in nature and seems to be coming from just in front of dash, in center, down low. This truck not make this noise for the first 14,000 miles of it's life. Milage is now around 30,000.

Took my dealer's diesel mechanic for a ride with trailer in tow and was able to reproduce the noise. He called GM and says GM knows of 2 problems - one tapping (described in detail elsewhere on this thread) and then also the knocking problem. GM is autopsying engines with these problems to try and figure out what's going on. Meanwhile, they say to keep driving it.

I am getting ready to leave on a solo trip from mid-Atlantic to Oklahoma with horse and trailer in tow. I really would like some opinions on whether this noise could turn into my rig going kerpluey in the middle of nowhere.

Does anyone have experience with a problem like this one? Any advice on what to do next? :confused:

Thanks for any help!

NutNbutGMC
05-23-2002, 16:52
^............. Search and ye shall receive knowledge on this unheard noise... ;) I saw a thread just last week on this very thing. Hope this helps.

[ 05-23-2002: Message edited by: NutNbutGMC ]</p>

Searay90
05-23-2002, 20:24
Have you tried running some cetane boost when towing your trailer?

D-max Man
05-23-2002, 20:36
Sounds like it might be an injector leaking at higher pressures. This will make a noise like a rod knock but higher up in the engine.

Have the dealer manually boost the fuel pressure with the Tech II and see if the noise comes back. If so there is a procedure in SI-2000 (dealer knows whit SI 2000 is) to find which one it is.

[ 05-23-2002: Message edited by: D-max Man ]</p>

ponyXpress
05-24-2002, 07:38
In order -

For NutnbutGMC: Thanks for the tip! I saw posts regarding the tapping at lower RPM, but did not see anything I thought would help me. Must've missed it - I'll look again.

Searay90: No I haven't tried cetane boost but will look into that. I'm just a lil ol farm girl who loves her truck but lacks the knowledge/experience you all have. Thank you.

D-Max Man: Will do. Thanks!

Does anyone think I should postpone this trip until this is resolved?