Rattles When Foot On Gas Pedal

[Wilfred]

Hello

I have a 90 LS400, when accelerating theres this rattle in the front end. when its just rolling to a stop or no gas, then the rattles gone. Its only when u give it gas u hear this constant metallic sounding rattle.

Anyone else have this problem or know what it is. Starting to get paranoid

Thanks

[LinuxFan]

And you are still driving it?

Brave soul you are... when you first heard this you should have pulled off the road then and checked it out thoroughly. I experienced this before -- once it was the lug nut not being tight enough and the next it was a bad wheel. It could be a lower ball joint also.

It could be anything.

What is worth noting is that it should not be doing this and since it is doing it, something is not right -- so have it checked out ASAP by a certified mechanic. Yours and the car's health depends on it.

[larryp]

Linux is right - could be anything, but you need to find out before damage is done. Did you have A/C button on? Bad compressor makes a similar sound that fluctuates with engine RPM.

[nc211]

Heat shield on cat converter loose?

[Econ]

Eeep. Rattle when accelerating? Something like change rattling around under your hood? I would hope not - that's likely a rod knock, and those aren't any good.

Does the rattle vary in frequency according to speed of the engine or speed of the car? Or does it vary at all? Do you notice a difference on windy days vs. calm days?

[Wilfred]

I haven't tested it between windy v calm days. Weather in Australia is always the same...sunny.

It is like a penny rattle and i couldn't remember if it vary in frequency but i got a feeling it did when i was accelerating.

The sound is still there even when A/C is off. The compressor has had oring replaced.

Whats a rod knock?

[nc211]

the sound of pending engine death.....throwing a piston through one of the piston walls. :( My guess however is something has wiggled loose. A component or heat sheild or something like that.

[Wilfred]

Its not that bad is it? Its not that loud

This morning i took it out. Started it cold, ran it till its warm. The rattles gone. Seems quite weird. Any more ideas brainy?

The only other thing this morning i did was check the oil levels and they were all perfect and hit the battery terminal covers so its secured.

Thing is car only has done only 63000km too

[nc211]

It could be anything. I seriously doubt it's a rod knock if you've maintained the oil changes. I mean, you've changed the oil at least more than 3 times ever right? It's some bolt or something. Go have a mechanic look underneath it.

[Wilfred]

Got a friend who knows much more about cars than me to check it out He says its engine "ping" and reckons its because i use unleaded rather than premium unleaded. We put octane boster in it and i'll see if that fixes the trick. Went for a drive after putting the stuff in before not a long one the ping was still there. Maybe take longer for the octane stuff to work. But its definetly an engine ping and not rod knock cause he says rod knock is much louder.

Anyone else had pinging problems before? Another suggestion is spark plugs possibily. But im hoping it is just bad fuel.

[Wilfred]

Apparently we have bad fuel quality in australia

[Econ]

Pinging (also called detonation or pre-ignition) is caused when the fuel combusts early and unevenly. That rattling or knocking sound you're hearing is the piston & rod being shoved back the 0.1mm or so of play they have so hard and fast that you can hear it over the sound of the engine operating. Not a desireable state to be driving around in, but waaaay better than rod knock.

The following is a brief fuel quality/octane rating primer based on what I can remember and is in no way inclusive of all information or definitive. Check Wikipidea for some additional info --

Fuel quality shouldn't affect pinging, but octane definitely does. There's two methods for measuring octane in fuel, if I remember correctly, and I don't know the difference between the two. However, their results (octane rating) are very similar.

Higher octane fuel burns more uniformly, and some claim more slowly (though we're talking about fractions of a second). Some engine designs (such as high compression engines) need this uniform burning characteristic in order to ensure they run optimally.

Pinging is eliminated because the higher octane fuel is less likely to combust early (detonate). Sometimes the combination of the temperature in the cylinder and the pressure the air/fuel mixture is subjected to can cause lower-octane fuels to spontaneously combust (much like how a diesel engine works, except diesels do this on purpose). The fuel burns in one area before the spark ignites it, and works against the upward momentum of the piston.

Sometimes octane boosters work. Sometimes they don't. It depends on how well you mix them in with the fuel. If it is indeed pinging, I would do two things: 1) Wait for your tank to go nearly empty before filling it up with premium, and 2) Dump a container of BGK44 (made by BG Products) to clean out your injectors and any potential carbon build up from the pinging.

[Wilfred]

After driving it with the octane booster it still pings however doesn't seem to be as much as it used to.

Is there anything else that could cause a ping? Anything else i could check.

Or does octane booster take some time to work? Or will it take a couple of tanks of premium before it will go away.

Im not spose to use the car when pinging occurs yet i need to get rid of the unleaded, what a dilema!

[Econ]

Ok, should have looked at my information before. I don't think it's pinging because the 1990 LS400 is equipped with knock sensors. They're sensitive siesmic sensors designed to pick up on the vibrations caused by engine detonation (pinging) and are linked to the ECU, which will accordingly dial back the injector pulse width to reduce pinging until it's gone.

So, given that detonation is avoided by the knock sensors, which compensate by reducing power, I'm going to guess that it's something else.

Once, after I had worked on my intake manifold on my other car, I heard a tapping noise coming from the engine bay when I was accelerating. Sometimes when I was cruising, but not as often. Turns out (after six weeks of freaking out) that it was a throttle cable that I forgot to re-attach to a bracket that was tapping on my hood. When I accelerated the engine would twist in it's mounts and the cable would bounce up and down. Frustrating.

Without hearing the noise, this is going to be much harder to diagnose. Does the metallic rattle sound occur whenever you accelerate? Or can you accelerate gently and avoid the noise? What about when your foot is on the floor? Does the sound ever get louder?

Check your spark plug wires to ensure that they're all tightly secured and there isn't too much dieletric great in the boot. This problem generally causes more of a knock and less of a metallic rattle, but could definitely be the culprit.

Also, seriously consider having a certified mechanic look at it if this continues to be a problem after 1 tank of gas.

[Wilfred]

The sound only happens after driving it till its warm. Sound is not there when cold, or when warm initially only after driving for a while. Then it comes whenever u accelerate. Because of that i don't think it could be something loose because if it is it should do that when its cold too.

I noticed that the exhaust is extremely hot after parking the car because you can hear a lot of excessive metallic ticks from underneath the car. Could this have anything to do with it?

Thanks Econ by the way

[KY350]

Wilfred - if its pinging caused by using unleaded fuel instead of PULP, then a tank of PULP should fix it. I'm also in Aust and we may not get as good fuel as the Japanese or even the Americans, but our fuel quality is not so poor that it would produce pinging.

Your owners manual states to use either 95 RON or 98RON fuel as a minimum depending on the age of your LS. For some reason, you descided to use regular unleaded petrol. Why???

The 4 major fuel companies all have 98RON fuel available now and have all had 95RON for over a decade. Even our remote country towns carry 95RON fuel, so try using the recommended fuel to see if your problem disappears.

If you use a couple of tanks of PULP and the problem persists, then I'm guessing your problem is not related to low octane fuel.

[ArmyofOne]

Wilfred - if its pinging caused by using unleaded fuel instead of PULP, then a tank of PULP should fix it.  I'm also in Aust and we may not get as good fuel as the Japanese or even the Americans, but our fuel quality is not so poor that it would produce pinging.

Your owners manual states to use either 95 RON or 98RON fuel as a minimum depending on the age of your LS.  For some reason, you descided to use regular unleaded petrol.  Why???

The 4 major fuel companies all have 98RON fuel available now and have all had 95RON for over a decade.  Even our remote country towns carry 95RON fuel, so try using the recommended fuel to see if your problem disappears.

If you use a couple of tanks of PULP and the problem persists, then I'm guessing your problem is not related to low octane fuel.

←

wilfred, you stated that it only does it when its warm...its not pinging then. pinging would be more pronounced at cold startup.

[914lps]

I said it before I'll say it again. Those bottles of booster are a waist of Money. Try the better gas. Look if your gas is rated at 87 octan and you ad a booster that states you will get 10 pionts more from it, it does not take 87 octan to 97. It takes it to 87.10!!!!! A total waist!

Back to what the noise is. Have someone look at it when it is making the noise. Could be so many things! Including the fan hitting the cover. It could even be a motor mount and something is hitting when the egine is given gas... Lots of things..

[Wilfred]

Thanks

I didn't get an owners manual when i got the car so i really didn't know if it needed PULP or not.

But thanks for your help. If problem persists then i'll take it from there.

Army of one. Do you have any idea or hazard to take a guess what it is. It definetly on happens when warm and never cold. Even when its warm and idling in neutural and u step on gas, u can't reproduce the sound. But its definetly like a pinging ticking and only happens after a long drive.

[ArmyofOne]

Thanks

I didn't get an owners manual when i got the car so i really didn't know if it needed PULP or not.

But thanks for your help. If problem persists then i'll take it from there.

Army of one. Do you have any idea or hazard to take a guess what it is. It definetly on happens when warm and never cold. Even when its warm and idling in neutural and u step on gas, u can't reproduce the sound. But its definetly like a pinging ticking and only happens after a long drive.

←

that right there rules out a rod bearing. if it were a rod, it would do it, irregardless of whether the tranny is engaged. so your engine is ok down on the bottom.

what it may be, is ylour valve clearances have come out of adjustment. but then, that should be constant all the time as well. having to guess without hearing the sound is like trying to pin the tail on the donkey, i (we) may not even have it right.

does it become more pronounced when the engien is revving in neutral, any particular speed this happens at? even at idle?

could be a ticking fuel injector...in fact, i would be willing to bank on it. i dont know exactly what causes that, but it has to do (i think) with the injector delivering the fuel too early or too late.

the unltimate test of your internals and what they are doing woudl be a compression test, there is no other way short of tearing it apart. do a compression test. if you have no compression on one cylinder, you have a dead cylinder and a rod bearning gone. but that probably isnt the case. also with a blown bearing, you would have metal shards in yoru oil and possibly bubbles in your oil too.

since you have dual overhead cams, my thoughts here are:

Camshaft Bucket (lifter) tapping.

Valve clearances out

Ticking fuel injector.

just a hunch here... fill up your tank with the premuim gas, and before you drive anywhere other than home (while the tank is still on full) reset the ECU by pulling the negative battery cable off for a few minutes (10 should do it). this will cause the ECU and more importantly, the Electronic Fuel Injection System, to reset. just a hunch, but it cant hurt.

[Wilfred]

Thanks i'll try that and yeah it does normally pronouce itself at about 2000rpm. It does happen later too but its loudest around there plus also as the engine revs quicker the engine is louder so its harder to hear. But it doesn't happen when car is in neutral. Only after driving for a while especially at 2000rpm.

[ArmyofOne]

Thanks i'll try that and yeah it does normally pronouce itself at about 2000rpm. It does happen later too but its loudest around there plus also as the engine revs quicker the engine is louder so its harder to hear. But it doesn't happen when car is in neutral. Only after driving for a while especially at 2000rpm.

←

thats key because its at the beginning of the powerband, the very beginning.

good info.

i would shoot for injector. try resetting the ECU. see what that does. even if it only makes it better for a minute, thats a minute we have to figure out which one is causeing the problem.

any hesitation or rough idle from this? try holding the gas with the car in park at 2000 or near there...notice a misfire? try to hold the revs as steady as you can and reallly feel for it.

if no, do the same in drive, but DONT do this for long, only about 10 seconds, as it could overheat your tranny if you arent careful. the only reason i reccomend this is because it may be an "under load" type of situation. that is to say, it will only do it when the engine is being used to pull the wieght of the car.

[Wilfred]

Thanks

Yep i noticed it shakes a bit and can feel it through the steering wheel at 2000rpm (while in neutral). When u drive to 3000rpm, as u take off your foot off gas, and it goes past this one point around 2000rpm, it shakes and theres a hiss sound from underneath the car like from exhaust. when u just rev it to 2000rpm and when u let off when the shake occurs, u still get that hiss sound. Maybe theres a bit more clue.

Would the fuel injector cleaner products help do you think?

[Wilfred]

After unplugging the negative terminal for about half an hour the sound still remains.

[ArmyofOne]

Thanks

Yep i noticed it shakes a bit and can feel it through the steering wheel at 2000rpm (while in neutral). When u drive to 3000rpm, as u take off your foot off gas, and it goes past this one point around 2000rpm, it shakes and theres a hiss sound from underneath the car like from exhaust.  when u just rev it to 2000rpm and when u let off when the shake occurs, u still get that hiss sound. Maybe theres a bit more clue.

Would the fuel injector cleaner products help do you think?

←

hmm...

sounds like you timing may be off a degree. if the belt has jumped a tooth, it will cause this. the engine only running rough at certian times. is it pretty consistent?

either way its evident that you aren't doing any SERIOUS damage to the engine by driving it. i wouldnt put a rediculous amount of miles on it, but you are probably ok until you can afford to have whatever it is diagnosed. if you can now, take it somewhere.

without hearing it it will be almost impossible to tell.

a malfunctioning fuel injector isnt goin to be helped by fuel injector cleaner, but you can try. if it is just carbon build-up, i have a solution to this that will work 10x better. if you know how to change a spark plug you can do this. PM me for it. but if the injector itself isnt working correctly, more than likely its due to the injector being bad. this is fairly common and not nessecarily hard to fix either.