rwmj5

I couldn't find anything on this elsewhere in the forum but hopefully someone on here knows whats going on- I have a 93 LS 400 with about 134000 miles. It runs absolutely smoothly and there are no problems with the performance of the engine at all (I'm getting 21 MPG highway) However, there has been one problem with the car ever since I got it. On 3/4 or full throttle acceleration, starting at about 2000 rpm and ending around 4000 rpm, there is a sound coming from the engine. It is a hissing sound mixed with a high pitched metallic rattling. It is not present at any other time during the operation of the car accept at the engine speeds and high throttle settings as I mentioned, and the sound always goes away after the engine revs past a certain speed. I know someone with a 94 LS 400 with the EXACT same problem, so I know it is an issue with this particular model. The only question is, does anyone on this forum happen to know what this is?

(No it has nothing to do with the air conditioning)

rwmj5

Could the PCV valve be rattling? Or maybe a leak around the hose that attatches to the PCV valve or in some other hose?

Brandicus

iTrader: (6)

are you sure its actually a problem or do you think its the noise the LS makes when it smells BMW and mercedes exhaust ?

sha4000

iTrader: (1)

you should be getting more mileage than that on the highway in my opinion.the hissing sounds like you might have a vacuum leak, but your car should idle rough if thats the case. definitely check the pcv and all other vacuum hoses at idle with the car in park and listen to your engine closely

ychachad

The hissing may be a sticky serpentine belt. Did you use any belt dressing in the past?

rwmj5

I don't think it's the serpentine belt, I just had the timing belt changed along with the serpentine belt a couple months ago. since 21.5 MPG is low, what is the expected gas mileage for someone averaging 80 in a 93 LS 400 with 140000 miles?

UTA LS

I got 19.75 with 50/50 driving around town and on the highway, 21.5 mpg doesn't seem too far off from where you should be. its a 4,000 lb car with a 4.0L v8, don't expect the world.

Its not a honda civic

rwmj5

Thats exactly my line of thinking. I'm actually pretty pleased with 21.5, especially seeing how the EPA value is 23 MPG and that test is done at less than 60 MPH.

btw I just sold my 40 MPG honda civic three weeks ago