Can anyone explain a 'squeal' from the Throttle Body?

[BigBen]

OK, this one has me scratching my head:

'95 GMC Yukon with the stock TBI 350. 238,000 miles.

I've been getting a 'squeal' when I'm driving. It happens at about 1300 to 2000 rpm and only under moderate load.

It won't do it in neutral, and it won't do it under hard acceleration. Mostly just at crusing speeds with enough load to maintain velocity.

I thought it was the alternator at first, but it's not making the sound.

If I'm rollin at about 45 I can get the pitch to change by just lightly altering the accelerator position... not hard enough to change speed, but it will alter the pitch of the squeal.

I've listened and listened. I had my Girlfriend hold the brake down in reverse and rev it to 1500 while I listened. As near as I can figure... it seems to be coming form the Throttle Body????????

One last thing, when I shut the engine off, it makes on last squeek, just as the engine dies.

If anyone's got any ideas, I'd love to know. This is driving me crazy!

Thanks,

-Ben

 

[4X4HIGH]

Vacuum leak. Change out the TBI base gasket and check all vacuum line connections.

 

[BigBen]

Hmmm... hadn't thought about a vacuum leak.

Performance hasn't suffered.... but is it possible to have a vacuum leak and no performance change / Check engine light?

 

[southernspeed]

Yeah, the ECU will compensate for a small air leak.

 

[Cowboy_80]

if it's just enough of a leak to make it squeak...

 

[longbedder]

If you happen to have WinALDL cable and software, hook it up and look at your BLM numbers. If they're consistently above 128 for a static condition you've got a vacuum leak for sure.

I bet the other guys are right, though. I had a little cap pop off once, and it made a helluva whistle under load.

 

[Thunder]

Probabally the TB base gasket. But check all the vaccum lines too.
Mine had a nice whistle when the base gasket went out.
I have found the GM gaskets work the best and last the longest.

 

[BigBen]

I'm pretty sure mine is OBD I... and I don't have WinALDL anyway
(EDIT: This was dumb on my part. I now know that WinALDL is for OBD I... and I'll be building a cable soon)

I'll take a look tonight.

What's the consensus on spraying stuff around the gaskets while the engine is running to test for leaks. I've heard of guys using starting fluid, but I dont' remember if that's a good idea or not??

Thanks for all the help guys, I'll keep you posted!

-Ben

 

[Cowboy_80]

spray it. It's the easiest way to locate a vac leak. if the engine revs up, you're close...

 

[Thunder]

You can also use water in a spray bottle. It is way safer than starting fluid which is highly flamable. RPMs will usually go down if there is a leak.
Or you can just change out the TB base gasket. With as many miles you have on your truck it is most likely shot.

 

[BigBen]

Good call guys.

I used the water trick and the first spot I hit (Front right corner) the engine almost died and came back to normal.

Looks like I'll be getting a gasket at the dealership tomorrow (if they have 'em) and replacing it in the 10 degee weather we're going to have here this weekend.

I'll let you know what happens.

-Ben

 

[BigBen]

It's stinking cold out in Michigan right now.

 

[BigBen]

Well, none of the local dealerships had a gasket... so I got a FelPro and put it in today.

Bad sounds are gone and the Yukon is running better.

Thanks for the help

-Ben

 

[jonrpick]

A friend of mine would use CO2 in a can to find vacuum leaks... doesn't leave a mess and isn't flammable. Again, RPMs should drop if there's a leak.

I think the stuff he used was for blowing dust out of electronics or something.

 

[BigBen]

That's a good idea. I've got a couple of those compressed gas dusters that might do the trick.


Just wanted to say Thanks again to the "Brotherhood". This is just one more time that my $25 annual membership probably saved me over $100 in auto repairs!

-Ben

 

[Thunder]

Glad you got it fixed.

 

[BigBen]

Me too.

The other good thing here is that I learned about WinALDL. For some reason I thought it was for OBD II... .oops. I've been reading up and I'll be building a cable in the next few days so I have another diagnostic tool.

-Ben

 

[Thunder]

Great! Winaldl or a good scanner is a good tool. Need it if you want to do your own work. Having it will save you a lot of time and frustration when you have a problem. It is a great free program. If everyone who had TBI would use it there sure would be a lot less posts about "Why is my TBI running like crap?"
Even if you dont understand the data it gives right off the bat. You can post it up here or in the injection forum. Many people can help you out.

 

[jonrpick]

Glad you got it fixed Ben.

I'm considering a TBI conversion in the future, and after seeing WinALDL mentioned, I think I'll get it too when I do the swap.

Seems to be well worth it.