A Helicopter Under My Hood? Well..it's Very Small

[clacey]

I have a 90 LS 400 with 213,000 mi. Under acceleration it makes a tapping sort of sound. It does not happen when the car is in park and you rev the engine. It only happens under pretty heavy acceleration while driving. When inside the car, it sounds as though it is coming from the right side of the engine or maybe this is just where the sound is coming through from the engine compartment. Since it happens while driving and not just revving how can I tell if it is noisy valves or bad manifold gasket???

There must be an easier way than to stick my head under the hood while I accelerate to 80 down the freeway.

Any input??

Thanks,

CL

[bartkat]

Since it happens under load, it could be preignition knock.

[clacey]

preignition knock?? How do you check or fix that? Is the timing off? I am about to change the distributors and caps will this help?

Thanks,

CL

[wwest]

213,000 miles, just as likely, or more likely a rod knocking.

[tansupplyman]

with that mileage you should use 20w50 Castrol also--certainly in Tx.

$0.02

[clacey]

Thanks everyone for taking the time to respond.

One other thing:

it gets much better as the engine reaches higher rpms. It is more noticable at lower rpms when you punch it. It seems to clear up as the engine gets rolling. It also is not a sharp knocking sound it is more dull sounding. It's hard to explain a sound in a letter. I hope this added info helps. I'll bet this thing hasn't had a tune up in 120,000 mi. I just bought it from my brother for $2,500.00. It is in awesome shape. Not a bad deal at all. the interior and paint is emaculate except for the yellow on the bumpers.

Thanks,

CL

[Lexus.]

could be the speedo cable

[bartkat]

preignition knock?? How do you check or fix that? Is the timing off? I am about to change the distributors and caps will this help?

Thanks,

CL

Could be too much timing advance or some carbon buildup in the combustion chanbers. When you do the new distributor, you'll be setting the timing so that should tell you if it stops pinging.

I think there are some fuel additives that might clean out some of the carbon, the injectors, etc. I'd try that too.

The other possibilities that people are coming up with are far more serious and more expensive to fix, so I always try the cheaper and easier ones first.

[Steve]

i had carbon build up in my Soarer... was very pingy.. changed fuel grade and gave it a good run and is now fine.

[mig25]

:chairshot: Be careful if you use heavy oil. Eg (20W50) I would never use such oil in my Lexus. Unless I drove in the Sahara desert for extended periods of time.

Heaviest I would recommend , would be 10W30.

The engine oils have no relation to noise in the engine. Also, if your car is well maintained, the mileage should not mean anything.

It could be the valves that need adjustment. Most of the times the noisy ones are from cylinders number 5 and 7.

It is always a good Idea to have your valves checked anyway, regardless . Check the bolts on the exhaust manifold, if one of them is loose it could leak exhaust gases, thus causing the noise.:chairshot:

welgaby@msn.com

[VBdenny]

You sure someone didn't put regular gas in the car? It will make a racket if that happens.

[clacey]

I smell a bit of exhaust when I sniff the passenger side of the engine, which is where the sound seems to come from. I'll probably replace the manifold gaskets on that side. It shouldn't be that difficult or expensive for me to do. We'll see what happens then.

Yesterday, I cleaned the screen in the power steering solenoid. WOW! What a difference that made. No more spongy steering.

[jzz30]

i think what you are hearing is valve chatter. i have this problem also. when under a bit of load like going up our steep driveway it chatters a bit. i thought it might be in need of a valve adjustment but i took everything appart but every thing was all within tolerences. so well in was in the process of a timing belt change so just put the valve covers on and went on with it but after i finished i was looking at the owners manual and it said that valve chatter at low rpms is normal or can happen or sumthin like that.

[Rice]

I have a 90 LS 400 with 213,000 mi. Under acceleration it makes a tapping sort of sound. It does not happen when the car is in park and you rev the engine. It only happens under pretty heavy acceleration while driving. When inside the car, it sounds as though it is coming from the right side of the engine or maybe this is just where the sound is coming through from the engine compartment. Since it happens while driving and not just revving how can I tell if it is noisy valves or bad manifold gasket???

There must be an easier way than to stick my head under the hood while I accelerate to 80 down the freeway.

Any input??

Thanks,

CL

Yiour car has all the symptoms of leaking EGR pipe. Mine has the same thing, so I know. It may sound like exhaust manifold, but chances are that it's the EGR pipe. You can only find out by lifting the car and have someone give it gas while you listen.

[tansupplyman]

Rice--did you replace the EGR pipe yourself--was it a problem??

[Rice]

Rice--did you replace the EGR pipe yourself--was it a problem??

I did not replace it yet, but it's on my to do list.

Here is why. There are two of them - one on each side. They go from exhaust pipes just before the 1st catalytic to the egr system. That places their attacment points between exhaust pipes and transmission with about 1-2 inch clearance. If the bolts that hold then break off during removal, the tranny must be removed in order to drill out the studs. This may become very expensive and I am not ready for this contingency. Pipes themselves are about $85 each.

[clacey]

Rice, I believe you are correct. I changed the starter about 3 wks ago and had to bend it out of the way a bit. I saw a little puff of smoke from the back of the engine when I started it, which is where the EGR pipe is. Are these things brittle? Is there anything attached to them?

Thanks for the replies.

CL

[Rice]

Rice, I believe you are correct. I changed the starter about 3 wks ago and had to bend it out of the way a bit. I saw a little puff of smoke from the back of the engine when I started it, which is where the EGR pipe is. Are these things brittle? Is there anything attached to them?

Thanks for the replies.

CL

Yes, they are brittle, especially on older cars. They are subjected to very high temps in addition to mechanical bending during engine operation. As the result, they rust and develop leaks.