First: I have and 89 Firebird 305 Automatic Trans.
The car has been sitting for quite some time.
Ive replaced all the basics like plugs, oil, fuel pump, etc.

Now: When i start it up, it sounds decent, a little rough, but it seem fine. An odd gas smell arrises when i accelerate, and on DECELERATION the engine makes a slight knocking sound. I can not figure out what it is. possibly the knock sensor is bad? I dont Know. Please help, i have to drive this vehicle all the way to phoenix, wich is about an hour n a half long drive, and i REALLY dont want to be stranded on the side of the road. . .

Thank you in advance for any and all reply's, help, wisdom.
Matt

 

The knock sensor is for adjusting the ignition timing to prevent preignition. I've never heard of an engine that pings when you let up the throttle.

What does your oil pressure do under these conditions?

 

Are you sure you are hearing a "knock" (as in pre-ignition knock)? When decellerating, this would be extremely unusual. Normally, knocks would be heard when accellerating.

It may be you are hearing some backfiring that is being muffled by your exhaust system. If that is the case, there is probably something wrong with your fuel delivery or ignition. First step is to have someone read your car for any codes it is throwing. It may indicate a specific failure (O2 sensor, etc.). If it does not, and you are smelling gas, it could be that the TBI is not "misting" the fuel properly after sitting around without being run.

 

check your torque converter bolts ..i just replaced flywheel in my brothters truck doing the same thing cept his was cracked in all the around where it bolts the crank..you can check a suspected crack with silver or golt metalic paint after its been wire brushed off..my camaro sounded like a rod knock but thank god it was just loose torque converter bolts. hope this helps

 

it could be alot of different things, an engine knock would get faster as your rpms rise, so i highly doubt its an engine knock, maybe a bad belt tensioner?

 

You can hear it at idle, it sounds like a "knock" to me. . . But when you accelerate you can hear it as well.

Thanks for all the advice

 

mat my brothers truck sounded just like as your describing. it would be worth the 15 minutes it takes to check the converter..i was ready to pull the oil pan on my brothers truck and just pulled the dust cover off and took a flashlight and wire brush and there it was.. I brushed what i could off and sprayed some silver paint on the suspected crack and man it was a relief that i didnt have pull the pan and check rod bearings ..if you do find the problem keep me posted anyway.

 

Thanks man, i appreciate the advice and il deffinately take a look at it first thing tomorrow morning

 

Im beggining to think i might have a failing converter all together. The car shifts really hard, and at first i thought it was the motor mounts. when the vehicle shifts it makes a loud noise and feels like it shakes the whole car. I have the replacement ounts, i just havent put them in yet. If that doesnt fix it, then it must me either my TC or my trans...

 

I have a similar issue, not a thirdgen but...
I have an 86 K5 Blazer 5.0 4 speed standard, Edelbrock carb, Accel HEI.
Also sat for years before I got a hold of it. Starts runs smooth, great torque (for a 5.0)
But in neutral if I rev the engine I hear a knock on decel. Probably not a pre ignition but maybe a physical metallic clash.
Unfortunately my oil pressure gauge doesn't work at the moment. Plan to fix that to check the pressure.
Luckily the K5 doesn't have a cross member in the way for dropping the oil pan.
Only things I can think to do is check the oil pressure or maybe have a rod bearing going, although that is the only noise. A single (I believe) mechanical knock on engine decel. With decent understanding of the inner workings of a SBC, it makes no sense to me.

 

Take a wood broom stick (or even a dry tree limb), press one end to your ear and touch the other end to random parts of the engine (be real careful not to put it into a belt or other moving part). Its the poor man's way of listening to the engine and pin pointing where the knock is at idle.

First thing first drain the tank and put new fuel in it you are smelling old gas

Based on what you said.
sticking lifters (can't recall if 87 305 was hydraulic lifters but assume so)
valve blow by due to having some rust on the valve seats
acorns or other animal installations in the exhaust

The hard shifting could be the TV cable out of adjustment or could be a trans issue
the loud bang when it shifts is the transmission mount on the cross member

Its likely running rich due to bad gas, old o2s sensors, and other random things (vacuum leaks) witch will cause it to pop on deceleration, especially if the cats missing or gutted. With the old gas you are probably also ending up with un-burned fuel in the exhaust.