Odd Noise w/ hesitation, what is it? (Please Read)

Z71mudder · August 17, 2003

Well, today, I finished up my front end mods and went to wash the truck! After I washed it I went for a little drive. While I was out, I noticed an odd sound. It sounded like an airplane engine winding up when I gave it some gas. Also, along w/ the sound there seemed to be some hesitation, as the throttle response wasnt as crisp as usual! The same has happened before, like in the mornings in the winter, but it had always fairly quickly worked itself out, but it had a chance to warm up today and only did this after the car wash. Im just concerned because I could never get it to quit. I didnt drive alot afterward so maybe I didnt give it enough time, but Im stumped! Does anybody out there know whats goin on? Id really appreciate the info, thanks!

Will

Butch 02 Denali · August 17, 2003

Will,

Is sounds like you have a leak in your intake between the throttle body and the mafs. Do you have a K&N FIPK by any chance? They are known for leaking at the throttle body. Otherwise check all the connections and the tube itself, it could be cracked.

Butch 02 Sierra Denali

Victory Red · August 17, 2003

Nice lookin truck man. I checked out your site. I don't mean to get this thread off topic, but do you have anymore pics of your stereo install? Did you remove the plastic cover over the jack storage area to give you more room? It's hard to tell in the one pic you have on your site.

vortec4800 · August 17, 2003

I have the exact same problem. I first noticed it a long time ago and it only happened rarely. Now it happens all the time. It sounds like a lot of air wooshing when you hit the gas, and it feels like power is cut in half. I've been looking for the source of the leak for a while now, but can't seem to find it... I think I'm just going to replace the stock air tube with one of the aftermarket ones that doesn't have a resonator, hopefully that will fix it up. If anybody has any suggestions to help us, that would be great.

Z71mudder · August 17, 2003

Hey thanks for the ideas to check out guys! Ive been told everything from transmission to fan clutches so I dont know what it is! About the speakers, yes i removed the cover off the jack stuff! Again, thanks for the ideas guys, Ill just have to try and figure it out! Ill get some more pics of my speakers and stuff sometime!

Will

Shaners · August 17, 2003

There is no doubt that if the fan clutches are engaged for some reason, that your truck will feel like it is a "dog". If the fan is turning with the clutches engaged, you will hear a woosh of air from under the hood, that will correspond to the RPM's.

Z71mudder · August 17, 2003

Well, I just went for another drive to try and figure out what it is, and Im just stumped! I turned off the AC, the radio, and it still made this annoying humming sound. Whenever I would rev the engine the hum would get louder up to the point to where the exhause drowned it out! The hesitation doesnt seem as bad but still this hum! Does anybody have any inklings as to what it might be? I dont have KN FIPK or anything like that, the engine is completely stock other than the drop in KN filter and the single in/dual out flowmaster exhaust! Anybody?

Will

ps-shaners, what you said sounds erily similar to what mine is doing, as I said above the sound gets louder as the revs get higher to the point of being consumed by the exhaust note. do you think that is probly the culprit, and if so, is that a problem or just something that happens on these hot summer days?? Thanks again for all the help guys!

Shaners · August 17, 2003

Sounds like the cluthes on the fan are engaged....

If I park my truck at night with a "hot" engine, the clutches engage and the truck "roars" the next morning for a few blocks...

If the truck is run in town on a hot day and never gets up to speed to keep the air flowing through the radiator, then the clutches fully engage,and the fan really sucks the power from the motor....

vortec4800 · August 18, 2003

Fan clutch hm? That does actually make sense, I live in Arizona and the first time I noticed it was when it was like 115F outside - what bothers me is it also does it sometimes in the evening when its not so hot out, but it mostly does it during the day. Would you be able to visually tell if the fan clutch is engaged? I didn't actually realize there was a clutch between the fan and the engine, just thought it was a direct drive... The fan is always moving in there from what I can tell, does the clutch just make it turn faster for improved cooling?

Z71mudder · August 18, 2003

Those are some good questions vortec4800! Also, I just installed the bolt-over billet grille on my truck on Friday, and then noticed this on saturday! Do yall think the possible added restriction from the bolt-over grille + the fact that the last couple days have been the hottest thus far here (mid 90s) might be whats causing it? I think if it doesnt stop Im just gonna take it back to the dealership and see what they can do for me since Im still under warranty! Whatd yall think?

Will

Shaners · August 18, 2003

The fan does always turn, but there is a viscous clutch that engages under warm operating temps. When that clutch engages, the fan will "Roar". The fan also robs 10-15 HP, so if you are running the A/C too, then you are really bogging down the performance of your truck.

The old 4.3L in the S10 trucks and Blazers really "roared" all the time because of the fan...

chevy38fan · August 18, 2003

I had to replace my fan clutch in my 1994 K5 Blazer because it went out and the engine constantly overheated because it drank (literally) coolant(actually I never let it get to that point, I had a gallon of Anti-Freeze/coolant with me at all times, lol). That's when I found out there was a fan clutch.

also my fan clutch never kicks in during hot weather, mine only does it in the morning when its really humid out. never during the day though.. odd???

99silveradoz71 · August 18, 2003

The old 4.3L in the S10 trucks and Blazers really "roared" all the time because of the fan...

Ah yes, I miss the roar of the 4.3 in the 92 Jimmy each morning.

robz71 · August 18, 2003

Im with the others probably your fans because I know that when its hot here and I turn on my a/c my truck has a different sound to it and doesn't seem to have the power.

01BlackZ71 · August 18, 2003

I've noticed several times that once I start my truck, turn the A/C on, then back out of the parking spot and start driving off that once I reach around 10-15 mph I hear this really strange sound, it sounds like a real small airplane taking off, it's really difficult to describe in words, but anyway, it "takes off" in like a second and I never hear anything else. I've heard the fan kick on when the temps get above 90*, and it sounds like it's really pulling some air around. Also, maybe once in a very long while, my truck will slightly hesitate when throttle is fed to it coming off idle (like when you're pulling onto the highway from a stop sign). Any of this connected? And finally, on occasion, when the truck is started it stumbles around for about two seconds while the RPMs drop to like 250 and it almost dies, but then it like "realizes that it's going to die" and starts running normal. Not really any big deal to me, just embarassing when your friends are around. My Dad talked to the dealer about his truck, and they told him something about carbon deposits and the engine thinking it's misfiring when it really isn't, so it dumps in a bunch of fuel and only makes the problem worse. It was something along those lines. Anyway, sorry for the long post, and other than these minor things, and the fact that it uses more oil than I would think it should, my 2001 5.3 liter has ran great for 20k miles. Thanks guys, I enjoy reading all the forums here, keep up the good work.