AmorgetRS

iTrader: (6)

My engine decided to start making a new weird noise today. It is make what sounds like a knocking sound at ~2,000 rpms while in 1st through like 3rd gear. It does not make the noise on the highway, nor at idle, it has to be under load. It also doesn't make the noise while accelerating or decell, just the normal "maintain speed" load. The engine is a 96 or so truck long block in a 1988 Trans Am w/ a T-5 and the stock TPI setup.

Does anyone have any thoughts? It is hard to pin point where the noise is coming from because it doesn't do it in Neutral and I not big on trying to ride under the hood :-) Yes, it has plenty of oil in the system that looks nice. It's not frothy, really dirty, or low.

Thanks,
Douglas

Gramps

iTrader: (1)

you got yourself some knocking, its when your gasoline detonates before it should, making the pistons rattle, its very bad for your car, but it should flash a code if something is wrong with the knock sensor(if you have one), try running premium gas for a change, see if it does anything.

AmorgetRS

iTrader: (6)

Never thought about that. I am amazed it is knocking that much as it has never happened before, I wonder if an injector isn't doing well or something. I guess I'll be pulling some plugs this weekend and making sure everything is firing correctly. I do have a knock sensor from a 350 TPI motor and I guess I should hook up my laptop and see if it is displaying any knocking.

Thanks!
Douglas

Gramps

iTrader: (1)

im actually willing to bet more money on your knock sensor or your timing system. is your timing ok?, can you set it properly? if one of those things goes then your engine will not be able to adjust for the knock, it usually retards the engine until its stops pinging, but if the system isnt working then it cant adjust the timing, and your pooched

Grim Reaper

By the way you describe it, it does tend to sound like detonation. The best way I can describe detonation, is it sounds like marbles rattling around in a tin can. If that's what you are hearing, then detonation is most likely your problem.

I don't know if you have a "tuned" eprom, if you do, someone may have reduced the max amount of retard the ECM can pullout when the KS detects knock. Also, the KS works on "harmonics". In other words, it hears differently than we do.

A KS will pull out timing way before you'll ever hear it. But, if it is "maxed" (like running a bad tank of gas...which isn't that uncommon these days), then the KS becomes saturated and goes "deaf". That is generally when you begin to hear it.

Get a fresh tank of the highest octane gasoline from a known good gas station that you can get in your area. In BC, they can get 94 Octane at Chevron. If that doesn't cure it, then it's most likely not detonation.

If the sound is "rythmic", (ie. it may occur under load, but the noise is a occurs in a rythmic fashion) that usually indicates a mechanical problem. It may be the start of a main bearing on it's last legs, a lifter going bad, your lifters needing adjustment or your timing chain slapping against the side of the timing cover.

AmorgetRS

iTrader: (6)

I haven't checked the timing, but nothing has changed on the car. It wasn't doing it one day, and after getting it a little overly hot because the car got stuck in the snow in my driveway, it started doing it. It is hopefully going on the lift tomorrow and I will see if maybe I fried some knock sensor wires or something like that, plus check my timing.

The sound isn't like marbles, it is coming from one spot in the engine, but I can't track down what that exact spot is. From what I can tell is the the passenger side that is making the noise. The best way I can describe the sound is "piston slap" or it sounds like a diesel.

My EPROM is the stock 305 (AKFU) bin with the timing, fuel, PE, and some other tables copied into it from a stock 1988 350 bin that I found on Moates site (I think). I did all the tuning with the chip and I know I didn't mess with its ability to pull timing.

I got a new full tank of gas from a different gas station, but it started when a tank was about half empty, so that would be really weird, imho.

It is based on RPM, but since it mostly goes away at higher RPMs it is kinda hard to tell if it is 100% rpm or not. I am a bit worried I may of damaged something mechanical though. I am thinking I am going to pull my valve cover and see if I can see anything going on with the lifters. I am also going to see if having the car on the lift and running I can track down the noise using a extension to listen for the noise as it may just but that it is quieted down a lot when idling or at rpms. The car does not feel 100% to me, but when it is making weird noises sometimes the mind plays tricks.

I'll know more later today.

Thanks!!
Douglas

AmorgetRS

iTrader: (6)

Okay, so without hooking up the laptop yet here is what I have found.

Timing is right where I set it (stock, 6 degrees base irrc).

I pulled all 4 plugs on the passenger side, everyone of them looked good. Light brown, no damage, no soot, no white powder. As I remember if you ping/detonate you can see it on the plugs as little pits or some sort of damage, but I saw nothing odd about any of them. All were gapped correctly, also.

While the car was running I used an extension as a stethoscope it listen for any mechanical noises... nothing. Just swish swish swish, no ticking, clicking, clanking. I am pretty sure I'd be able to hear any quieter metal on metal noises using that method.

So, next I hook up the laptop and see what I can see...

coolrimsatleast

I've got the same type of sound in my 3.4. I can control the rythm of it by speeding up or slowing down. If I let up on the gas or give it more gas it goes away. Mine happens at 1500-1700 rpms. It drives me nuts. I need to get a truck like I want that I can drive while I tear into the engine and start looking at stuff. I backed off the base timing to about 6 1/2 degrees and it still did it.

thepoz89

dumb question but have you checked your oil level?

AmorgetRS

iTrader: (6)

Good luck, I think I am going to have to do that when the weather gets nicer and I can start commuting on my motorcycle again.

No such thing as a dumb question! But yes, I have checked my oil level. It is right where it is supposed to be.

So, to continue the saga I hooked up the laptop to the car, took a look at everything and it seemed in spec. I revved it up, no spark retard due to knock in the lower RPMs, though I had a couple degrees when I revved it way up and let off. So, by that I think my knock sensor is working, and pinging isn't the problem. I jammed the throttle open to hold it at about 2,000 RPMS and got the noise to appear fairly loud. I tracked it down and it seems to be coming from the back of the engine or the flywheel/clutch region. I am wondering if cam bearing or the end of the crank bearing (no idea what it would be called) went or something like that. I may end up pulling off the transmission and seeing if I can find anything not right.

Is it okay to run the engine with no transmission attached?

Thanks,
Douglas

thepoz89

you should be fine w no trans

Gramps

iTrader: (1)

no tranny is just fine but id imagine youd have to find a way to support the engine...i could be wrong but doesnt the tranny support the engine as well??? abubuca you have a very interesting problem here, i sure wish i could hear it for myself, mayb a sound byte is in order?

AmorgetRS

iTrader: (6)

I was thinking about that... I have a digital video camera that I can use to make a short video of the car on the lift so you can see and hear where the sound is coming from.

You guys are correct, the transmission does support the engine, but I can support the engine using a jack and some wood or something of the sort.

Thanks for your continued ideas,
Douglas

Gramps

iTrader: (1)

sounds like a good idea...keep us updated amorgetRS

AmorgetRS

iTrader: (6)

Videos:

http://amorget.pnw3.org/88TA/EngineTop.mpg <--- 12 megs

http://amorget.pnw3.org/88TA/EngineBottom.mpg <---- 3 megs

The best place to hear the noise is in the top engine video toward the end after I rev it up a little. There is a nice whining noise also, that is my power steering pump. You might also be able to hear my injectors, they are very loud and from a LS1. The mic exagerates a lot of the other noises, but listen for the knocking noise.

Gramps

iTrader: (1)

im gonna put money on your rod bearings. usually a lifter will only make it noisy on the top end(and you lose power), but the knock is very clear on the bottom (after screwing with the audio settings). you should probably take out the engine and put in your other one. itll give you the chance to fix that bearing and replace the others, chances are that if 1 is bad, soon another one will go bad.

my 2cents, pull pan and check for a bad bearing, if one is found then replace motor with other one.

AmorgetRS

iTrader: (6)

Thanks for all your help. I really do appreciate it. I will deffinately go with your idea and check for a bad bearing. I should probably also drain the oil and see what I find in it, too...

vorgath

Your engine sounds like mine did, before it seized up completely.