what sounds like sticky valves, but isnt? car in Park, no knocking. Car in drive, knocking, when accelerated, it gets worse. could it be alternator related, crossed spark plug wires? Cant pin it down..need help!! I've tried the engine cleaners that are supposed to release sticky valves. No luck, unless of course it isnt sticky valves at all. I dont understand why it only makes the sound when it is in Drive or driving.

 

cracked flywheel ?

 

not that I can see. There is the tiniest bit of play in the water pump flywheel, but actually I just found a vacuum line break..so i'm hoping that will help a little. Not a valve train issue; used a sounding rod.

 

Only in drive, not in park. Then it must be either driveline, or related to putting a load on the engine. I'm assuming the sound matches your engine speed rather than your road speed, that rules out the driveline. So it must be engine or transmission. Hmm... need more info.

 

yeah....i found a broken vacuum hose, replaced that, but still no difference. It almost sounds electrical in origin but I just cant pin it down. It is definately coming from the engine top end. The car just keeps running worse every time I take it out now. Can't figure it out. Can a faulty or almost failing alternator cause this problem?

 

if its a valve sticking than it would sound like a diesel , thats the best way to describe it

 

no, nothing like that. just an accellerated tapping whenever I accelerate, only happens in drive or reverse. No tapping in nuetral or Park. very strange and very frustrating

you can email me directly at jimmeeker2003@yahoo.com if you have a good solution

 

Upon further reflection, it's seeming more like detonation could be the trouble.

 

yea is it more of a "pinging" sound

 

I put in new spark plugs, No Gap Bosch Platinum about 150 miles ago. I pulled the plugs, they were all clean, no evidence of oil, carbon buildup, anything. Do you think I should replace them with OEM spark plugs?

 

The problem with platinum plugs is they get hot, and they stay hot. This can cause pre-ignition, which makes noises. I think you should install the plugs GM recommends for your engine, and see if that helps.

 

This is the kind of thing you should have posted in the beginning. The more gas you give it, the easier it is for it to pre-ignite, and the hotter the plugs get. More rpm also makes the plugs hotter. This is why the problem is less at idle.

 

sorry. but thanks for the help. and those hot plugs would make that tapping sound?

they were definately hot; the plug wires where they plug onto the spark plug were VERY hot. wow...hope this helps the problem. So this would even cause hesitation and poor performance?

 

Keep in mind also the more gas you give it the more force is generated in the cylinder which in turn can make bottom end issues more noticable and also in the valve train as theres more force acting on the valves and theres also the increase in RPM to contend with. You wouldnt think it would take more force but keep in mind in the real world cumbustion can be continueing after the exhaust valve is open even if only slightly so and the piston is comming up with more force also while the intake valve is open even if only alittle bit.

 

That's all valid, but the bigger issue is that preignition starts the burn too soon, this builds cylinder pressure too soon, and that pressure is fighting the piston's rise to TDC. Yes, the burn needs to start before TDC, but the goal is to have peak cylinder pressure about 15-20 degrees after TDC, not before or at TDC. The noise could be hammered bearings, but overstressed valvetrains tend to be quiet until something fails. Preignition also happens very fast. Like detonation. Normally, the fuel does not explode, it burns very fast. But detonation is such a fast burn it qualifies as explosion. This is like smacking the piston with a sledgehammer. The piston rocks in the bore so hard it makes the audible knock.

 

Yea but usually detonation causes more of a pinging sound. It very well could be though and judging but the hot plugs i would say its a possability that should be explored but idk. A tapping is usually indicating a problem happening once rhymithcally when a valve operates or a cylinder fires where as detonation would likely be more of universal to all cylinders kinda problem. Im not saying it cant be detonation i sincerly hope it is as thats usually an easy fix i just always have to play the devils advocate and throw out some ideas.

 

Thanks. I'll put in new plugs and post a response this weekend

 

If the problem isn't what I think, I'll admit it and apologize for costing the OP a spark plug test. There's always one cylinder that runs hotter than any other. Usually a bigger problem on carbureted cars with OE intake manifolds.

 

Maybe I'm way out of the ballpark here....but only happens when in drive...but not in park and get louder the more you press accelerator....and maybe you've already checked this..but thought I'd throw it in there, Could it be that you have a cracked exhaust manifold/leak in headpipe/or bad exhaust manifold gasket. That's just what it sounded like to me....sometimes it's hard to find the cracks and leaks on those...but thought I'd just put that out there for ya. sometime the simple answer is the correct one. When you put a load on motor the exhaust escapes in the leak...when your giving it more gas...it pushes more exhaust...causing more leaking. (sometimes they sound like a tick or knocking sound).

 

OMG!!!! i am haveing this same problem 305 tbi, my dad had told me on mines it might be a burnt valve.in park every thing is fine you can rev the motor up and no problems accure. drive its sounds more boged down rpms drop at stop lights car has no power behind it anymore and if you try to accerate to much you hear a popping sound almost like a rod knocking car jerks around then stops and start accelrating some times its makes like a compressed air comeing back thru the intake sound. driveing at a steady speed you look at the rpms and they just move around alittle and the exhust stinks.i had pulled the dis cap off and the #5 point was burn replaced the cap and 3 days later is burnt the #5 point again. is this all the same stuff you have happing?

 

IMO...your car sounds like the timing is off....just my opinion of course....check your base timing...and what motor is in yours....carb. or fuel injected??

 

wow, lots to think about. I know the exhaust is fairly new and have done a block test to see if air is pushing back out near the headers but nope; same noise. It does seem to be coming from the driver side plug area, possibly the no. 2 plug. It has a new dist cap, rotor, timing just adjusted, new plug wires, new plugs (hopefully the cause of the problem). I'm probably going to run out right now and get plugs since I can do that in about 20 minutes. And, I'll post a pic of the car...its a beauty...been garaged for 13 years....

 

Exhaust leaks have a way different sound than lifters or valves or preignition. If you ever take your exhaust manifolds off the heads the factory put them on, even if you buy gaskets, you must take your manifolds to be resurfaced back to flat. I've resurfaced hundreds. You'd be surprised how far they warp.

 

its fuel injected and just had the timing set

 

very similar, but not as bad

 

OK, REPLACING PLUGS HAD ZERO EFFECT. Maybe it is a small exhaust leak...frustrated!!! I guess I have nothing left to try that can save me some money, so I'm going to take it to a shop I suppose.

 

Well, removed everything again and this time found TWO leaking, cracked and practically nonfunctioning vacuum hoses. The first to the PVC valve, which was laden with varnish and probably hadnt been changed in some time. This vacuum hose was barely hanging on by a thread. While I was changing that one, noticed that it connects into the engine block nipple and that connection hose was "rigged" and was just barely sitting on the nipple; so im replacing that and hope all will be well and running again by tonight.