Ok another problem with this little truck is a hissing noise behind the dash and it dies in reverse if you dont give it a bit of gas.

Suspected problems might be a vaccum leak somewhere. I dont think the EGR valve is bad, but im sure it would be good to get it cleaned.

How hard is it to get to the vaccum hoses? Whats worse case scenario?

The truck is an 89 Chevy Tahoe 4x4 Blazer 4.3 litre

 

Sounds like you have narrowed it down pretty well. If it is a vacuum leak, I would not hesitate to replace every line with new rubber vacuum line. In the engine compartment, this should not be too bad to do. Under the dash you really only have to worry about the one line that leads to the HVAC vacuum controls.

There could be more than just vacuum lines contributing to a vacuum leak issue. The TBI base gasket on these motors likes to leak at times. You may want to just replace it. It is not too expensive.

If you have a propane torch handy, you can use it as a vacuum leak detector. With the engine running and the torch valve open slightly, but not lit, trace along all of the vacuum lines and around the base of the throttle body. Listen for a change in the engine noise. If you notice a change, there is a leak at that location.

 

Thank you so much for your suggestion!

Do you think perhaps it may be a vaccum leak thats plaguing the 4x4 unit as well? I does not want to shift into 4HI, it goes to 4Lo just fine but its a real pain to get it back into 2HI. [>:]

If its not hoses, is there a part or a series of parts I chould check or replace?

 

The HVAC and 4wd systems get their vacuum from the same source (same line out of the intake). So yes, it is very possible that a vacuum leak is causing all of your problems.

There are only a few locations where a vacuum leak typically manifests itself. Lines and TBI gasket. It could be caused by a failed component under the dash, a failed intake manifold gasket, or a failed vacuum actuator for the front axle, sure, but you need to put on your detective hat and sleuth this out.

 

Ok found the problem!

The vaccum hoses to the Cruise Control were loose, I removed them cuz there was something under the dash not connected and i didnt feel like tearing it apart to reconnect it. I dont use CC anyhow. So we just capped off the CC under the hood.

Then ther ewas another hose going to another place which i ahve no idea what it does but it was a solid plastic hose and it was broken so I replaced it with a rubbe rhose and it works fine now.

Now we found another leak lol!

Its under the carb where it connects to the engine. Gonna get a new gasket on there this week prolly.

Still lugs out in reverse though, might have to do with the leak. But it is really working alot better now that the first leak has been taken care of.

I didnt have a propane torch but my brother brought over some stuff that i sprayed onto the engin block and the engine revved up, thats how we found the gasket leak.

Thanks for the help!

Nina