Rokas

Soon I will be opening up the engine to my 95 LS400 with 200k miles and while one of my goals is to change the timing belt and water pump, I have a very bad vacuum leak somewhere inside the engine. When I say inside, I mean somewhere you can't see it without removing at least the throttle body.

At this point, it has gotten so bad that the car barely chugs to 25mph!

I want to know what is likely to be the culprit so I can look for it when I do the timing belt. If I can't fix the leak, there's no point in doing crap!

Anyway, thanks for any suggestions or pointers.

Should I use a dye first?

timmy0tool

iTrader: (7)

you can't add dye to air...which is what is leaked when there is a vacuum problem.
BUT what makes you think it's a vacuum problem? do you hear an audible hiss in the engine?

I would try to fix the car's inability to go faster first before tackling a timing belt job.
start with the ECU. inspect it for leaking capacitors:
https://www.clublexus.com/forums/ls-...capacitor.html

spuds

Following....looks like this will be a good learning thread.

Yamae

I suspect that the gasket used for the intake manifold is causing your problem. You can check it using a smoke machine.

Rokas

Thanks man. That's the type of info I need!

Yes there is a hissing noise... A loud one. And guys, of course I wouldn't do the belt if I can't fix this but I'm hoping to do both. The belt is so old (over 200k miles) that I'm afraid to drive the car period.

Anyway, it was hissing for a long time and the other week it went from a hissing sound to a straight up loud blowing air... Hard to describe...

​​​​I had a (real) mechanic come by and that's what he diagnosed. He was able to show me how there is a certain noise if you give the car throttle and release it real quick - you can hear it sucking in air unevenly.... Kinda like a gurgle.

Scotty Kilmer (YouTube) showed how you can use a cigar for the smoke. What is a good vacuum line to do this with? I've learned a lot but some things still elude me. You smoke the car by unhooking a vacuum hose and putting the smoke in there, correct?

I'm trying to get the car to StereoRob's where I can work on it. I'll figure it out (especially with his help) with you people's help and post pictures and everything for the future.

The intake manifold gasket might actually be the problem... The hissing is definitely coming from that area and it's not a visible hose so good chance that that's what it is. Thank you.

Any time I can't find good info on something, I always add it to my site when I figure it out so people can immediately find it in the future.

And what I said about the dye - I was tired. Leave me alone. :P

Rokas

What is this in reply to? I can't understand what you're trying to say in the context of this thread.

EthanS

Use a spray can of carburetor cleaner with the straw nozzle for precise spraying, and see if the engine bogs down when spraying in various locations to locate the leak?

Rokas

I'm glad you brought that up. I've done that both with starter fluid and carb cleaner and I suppose the leak is hidden somewhere because I got NOTHING. I even sprayed pretty big areas (while trying to avoid electronics) and didn't hit anything.

I'll ask the new owners when they fix it. I bought me a nice, white '96. Very happy.