MechCD

I've been looking into this a bit and I'm getting scared.

I have some engine knock when I accelerate. Whenever it idles or stays at a non accelerating stance, there is no knock. When it does, it isn't blaring loud, more like a sort of rumble I guess.

Everybody has been telling me to use higher octane gas. I'm using 87 right now. I don't want to work around the problem. I think there is something else wrong that I can't afford to fix . I will try 89 next tank, but I thought a LO3 was supposed to run good on 87....

What should I be checking? The oil pressure is a bit high when it starts, around 45, then it backs down to 30-35 where it stays until the next very cold start. My dad did put a tad too much oil in, I'm thinking I should drain a little off, but I don't think that is the direct source of the problem.

I could do some ALDL logging, or dig through old logs, but I simply don't know what to look for.

Just for stats, its a '90 TBI 305 V8. Runs around 650 RPM on warm idle, around 900 RPM on a cold start, going down to 650 RPM within a minute or so.

Thanks

dimented24x7

iTrader: (2)

what does it sound like? Is it a high pitched ping or possibly, as one person described it, three rocks in a coffee can being shaken sound. Thats typically what detonation sounds like. But if its a low piched metallic sound then its probably trouble, like possibly worn rod bearings. Of caorse, it could also be other things on the drivetrain as well.

AJ_92RS

That dimented guy is probably right about something else, like a rod bearing or something in the drivetrain.

The only reason I say this is... the knock sensor should hear the knock WAY before you do, and retard the timing enough to stop you from being able to hear it.

Are you getting a SES light?

dimented24x7

iTrader: (2)

thats if the k/s is still functional. The computer has a routine at high throttle loads to check the sensor and if it doesnt pick up knock it will set a code 43. Even with a dud sensor though it shouldnt have much, if any detonation at all on its own unless you changed the timing. AJ is probably right, its probably a mechanical problem more then anything else.

Jukka

But it appears only on "light" acceleration. If i step on it it won't knock. It knocks only i press gas pedal extreme slowly down.
Can this happen because my engine gives little amount of blue smoke when starting and it has done almost 200 000 miles. Could it be because carbon deposits in cylinder heads?

MechCD

Same situation as Jukka... 291,xxx miles

It isn't high pitched at all. Thats why I said it was more of a rumble.

Now the SES light would stay on I hope. I don't exactly look at it a lot while drivinh, but I do look around at my gauges at red lights and such. It's not the drivetrain, you can't feel it, but you can hear it in the front.

But now that I think of it, you only hear it when driving...... I doubt its the drivetrain because once I stop accelerating (steady throttle), it stops making noise.

The knock sensor must work because there are tons of knock on the ALDL log, but once again, I don't know how many are normal.

BTW, I'm very engine stupid

How hard are rod bearings to change? Compared to say clutch work and changing struts If it's harder or close to changing the clutch, I'll have a shop do it.

and finally, should I not drive it to school everyday? Thats something I need to know very quickly.

dimented24x7

iTrader: (2)

well, id say you definatly got your moneys worth out of that engine. Replaceing the rod bearings would go along with a complete engine rebuild, ie: have the crank turned, block machined and heads + block magnefluxed, hot tanked, and all that other good stuff. Id say retire that motor and let it rust in peace. Probably your best bet would be to get a crate or used longblock 350.

dimented24x7

iTrader: (2)

as long as your school isnt too far it probably wont be a problem. My beater has been doing that for two years now and it still runs. Have a backup plan though in case it spins a bearing or suffers some other failure.

MechCD

Crud man.... I can't retire it, I just bought it a few months ago....... It has to bring me to the moon and back

How about getting an estimate and seeing how long I won't be able to buy meals?

School = 5-15 mins away
I go straight there in the morning and go a round about way with no stops to avoid traffic on the way home.

and putting $5 worth of 89 seems to have helped. I didn't think it would mix that quickly.

Would a tune up possibly lessen the problem? I'm honestly on a shoe-string budget here and I can't afford to get another car/engine. I think a new engine would cost more than the car did

MechCD

Heres a thought out idea.

Since it doesn't do anything strange in idle, it's drivetrain related. Slowly raising the RPMs in neutral doesn't cause any noises.

It also rumbles bad in 5th.

Wouldn't rocker bearings make noise on idle too? I went and looked up their function and location.

How about u-joints? Something that didn't get aligned when I put a new clutch in? I used the alignment tool that came in the kit and that was it. Everything else just got bolted back on.

Maybe I should throw a post over on another forum because this is starting to not be TBI engine related.

dimented24x7

iTrader: (2)

if its more of a rumble then it might be something else. Since its ok at cruise the u-joints are probably ok but id start seeing if you can id where the location of the noise is. That will at least tell you whats causing the noise.

MechCD

Thats where I'm lost, I can't figure out where its coming from. It sounds almost towards the front. I have to have the windows closed and be on an empty road to hear the sound

The 5th gear rumble is clearly underneath, but I can't feel it throught the shifter.

I hope it isn't something around the clutch, I don't know if I can handle taking all that hardware out again.

MechCD

Just for the books, my was putting 86 in there...... After a full tank of 89 and then topping with 87, it has been running like a dream. I really thought something was wrong, but it turned out to be cheap gas