89 IROC, 350 TPI, 30 or 40 over, pretty much stock - nothing fancy. Rebuilt little over a year ago.

When my car is rolling and the gas is floored and the rpms are about 3500-4000 AND UP there is this kind of rattle. But if I back off the gas just a little, but still accelerating, the sound goes away, its loud enough that you don't have to try to here it.

Anyone have any idea?

Thanks for any thing.

I am pretty sure its not just something bouncing around in the engine comp.

THanks.

 

detonation?

 

Rattles and pings and knocks like that are the scariest noises to hear. Where does it sound like its coming from? I know thats just as hard of a question because things can sounds like there coming from all over the place. Just to be sure, check all the bolts on your pulleys. I though my engine was knocking and ready to **** the bed until I found a loose bolt on my harmonic balancer. Boy was I relieved. Try to pinpoint the sound as best you can. Open the hood, rev the engine and listen. Then we might be able to help you more.

 

i have the same problem. i just had a new tranny put in like a weeks ago and when ever it gets past 3500 RPM i here a very fast vibration noise. from inside it sounds like its coming from in side the engine compartment, but outside it sounds like it is from under neathe by the cat. so i have no idea???

 

Well see here's the tricky part. I can Red line the engine in Park or Neutral and the engine sounds perfectly normal and strong.

But at speeds above about 35 or 40 is when it makes this sound.

Its a rattle or a tapping noise. There is no shake-shimmy-vibration. But I think I can feel it through the gas pedal a little but that may be my imagination.

Here's another clue, if you will. It only happens when I am already moving. . . . .

When i take off from a dead stop, or very slow roll, the engine is perfect until I hit the top of second gear, or maybe its third gear, even at high RPM in first gear there is no problem, and by then I am already moving pretty good.

I'll try to pin point the circumstances a little better.

Thanks for all the help everyone.

 

Sounds like spark knock to me. You usually only hear it when the engine is under a load, hence the absence of the noise when in neutral or park. I used to get it quite often in a Ford Ranger I had, as well as my 91 Jimmy. Ususally putting a grade of higher octane fixed it temporarily (i.e., switch from regular to mid-grade or premium). I'm not sure what would remedy the problem on a more permanent basis. I could be wrong, but that's what I'd try first!

 

Ok, this definitely sounds like a tranny problem now. You might have some chipped teeth somewhere. I know I don't have the knowledge you need but the guys on the Tranny board might. Go ask there is you haven't already.

 

Spark Knock is caused by fuel igniting prematurely. This could be due to lower octance (easier burning) fuel, or over advanced timing. Retarding your timing will help the problem. However this sounds more like a tranny problem since there are no rattles or knocks in Park. It sounds like it only rattles in one gear while moving. A friend of mine used to have a old POS motorcycle that had a chipped gear. He would always skip it because when it engaged it rattled like hell. It still worked though... just noisily. I'm sorry to say it but thats what this sounds like.

 

Oh yeah.... I forgot. Do you have an aftermarket exhaust? If you do check all the bolts everywhere along with its clearance. Exhaust rattling and rubing is a very common problem, and whats more is that it can sound like its coming from all over the place. Also only happens somtimes at odd times, such as a certain RPM but only while moving. It happend to me, turned out just to be loose clamps.

 

what octane gas do u use? i really really think its spark knock..

 

I would have to agree on the spark knock theory. Poor gas, too much timing, and carbon build-up are some of the causes. Mist some water down the intake while its running and see how much crap comes out the exhaust. You may have gotten some bad gas, toss in some octane boost and see what happens.

 

Its spark knock, I know, i've been there


The reason you dont hear it in 1st or when yo punch it from a stand still is the load difference...

WOT in 2nd is more load than WOT in first, the gearing is working against you just enough late in second to throw it into detonation


I once heard detonation reffered to as sounding like "marbles" sound familiar?

 

mist some water? Are you serious? maybe i should mist some water down my carb while its running to clean stuff out? Lol ive never heard of that, does it really work? nothing horrable happens?

 

BOOM!! The car blows up!!!

No really, it's fine. Haven't you heard of water injection?

It's actually better for EFI than carb cleaner is. Especially for TPI. And there's less chance of causing a fire. I've had that happen (on a carbed motor). It looked cool as hell, but at the time I didn't think so.

Just make sure you rev the motor while you're doing it.

And it can be a spark knock like the guys said. And like tpi_roc said, you may only hear it in 2nd or 3rd because of the load.

I was told by my granpa to think of it like you're riding a 10 speed. The slower you go, and try to accelerate in 8th-10th gear, the more it burns your legs, and makes you tired faster. But put that bike back in 3rd or 4th gear, and the bike seems to move faster than you can pedal!!!

AJ

 

Throw in some better gas or octane booster and see if it goes away.

 

yes it sounds like spark knock. You'll have to go for a higher octance gas.
Also, did you change the spark plugs? Do you know if they did during the rebuild what heat range they put in?

 

Don't be fooled because you think your running 91 or 93 octane either. Cheap gas is exactly that. I would think if you had a bad planetary gear you would hear it in that gear every time, no matter load or speed. I agree with most of these guys that its detonation. Ford is catching hell right now with alot of there cars, they cut it too close on the compression and getting complaints about detonation on 87 octane. People don't realize that for 2 bucks a tank they can run 93 and never have a problem, lots caheaper than 2 grand for a motor.

 

Ford is saying bye-bye to four of their cars.

Too bad they didn't cut any SUVs, the peckerheads...

 

I agree about the SUV's, gas hogs like that are the reason they can't build more sports cars.

 

I Realize This post has been going for a week but I don't get a lot of time to get online. I thank everyone for replying.

So Knock/Detonation is a bad thing? Just kidding. I do use regular gas. If I change to higher octane, will the knock stop, or does it just depend on how "bad" the knock is?

I have changed spark plugs since the rebuild, even though the mechanic did too, but that was just for peace of mind. I used the recommended type. Anyone got any suggestions otherwise?

What is THEE BEST way to rid the knock? Timing? I have not checked the timing since the rebuild. New engine? I wanto to build one soon anyway (don't we all) Just gas? But is just uping the octane good enough?

Thanks everyone.

oh what about the knock sensor?

I'm looking for ANY ideas.

 

Yeah, higher octane should help. Do you know what compression ratio you're running? Maybe too high for reg. gas. The knock sensor should be on the passenger side of the block, threads into a coolant passage, but I'm not sure on those, someone will correct me if I'm wrong.

Edit: If you pull timing out you're kinda crutching the problem, unless you got way too much, that is. I run about 10* advanced base timing, lots of guys run that I think.

 

Has anybody stopped to consider that the timing is a mile off or the knock sensor is shot or both? If you're hearing the car ping, then the timing is WAY off. The computer can retard your timing up to (I think) 12 degrees, so if you're pinging, then your car isn't getting retarded, or your timing is so far off that even with the 12 degree retard it still pings. A lot of grease monkeys try to set the timing on these cars the old fashioned way: Turn it till it pings then back it off. You can't do that on these cars and get good results.

Check your timing, and if it's where it should be, replace your knock sensor.

 

Yeah, the timing scenario occurred to me as well. But, true to my lazy nature, I usually check the easy stuff first. I'd change the gas, if that doesn't work, move on to other possible causes.

 

The only reason I say bad gas is because its happened to me several times before. Out on a road trip and fill up at some backwoods place, pull out and get down the road, engine starts pinging. It may be timing and it takes 2 minutes to check, but unless its off, I'd personally try different gas first. If you pull timing or the computer pulls timing, you're losing power and fuel mileage.

 

Jza Ford may be saying bye bye to four of theircars but they're introducing 5 to 6 more
Atleast here in Europe

 

I can relate to whats going on. I believe I know the difference b/w ping and rattle. Pinging sounds like pinging...and rattling sounds like rattling.

My L98 Automatic has both. Pings during normal operation, but rattles only at WOT after shifting into 3rd, and sometimes at top of 2nd. Always it is accompanied by black smoke. My assumption is fuel is not being burned. I need to adjust my timing and/or change my plugs. The plugs will fix it I am 100% sure...both the pinging and rattling...which I believe are both related.

 

Actually, I advance it until I see knock counts in the ECM (with a scan tool) and then back it off. While it's possible that I might have a little too much timing, as long as I'm not getting spark counts it shouldn't hurt anything except power.

Besides, my timing gun broke.