I was really bored at work today and in a hurry to get what I can use out of my ***** vacuum hose set on... (which isn't much..it's not worth it. Can hardly use any of it..sizes are all wrong)... Well I disconnected the vacuum line to the cruise control package completely, because my cruise control doesnt work..cable is shot..so what's the point right? Since I didn't have any vacuum line plugs, I cut a small piece of my new spiffy blue vacuum line, and wrapped the end in electrical tape..slipped it over and idled the car...it was sealed. So driving home, I pull into the driveway, park it, and I notice the car's idle kicked up suddenly and I hear a hissing noise as the car's idle gets a little erratic.. So yeah, the tape had opened up at the end... My only question is...if it's leaking vacuum, why did the idle kick up? I thought vacuum leaks caused a very slow idle and stalling, not a fast idle? Just figured I'd ask....knowing is half the battle ya know.

Thanks!

 

because your MAP sensor detected a load change (change in vacuum)

the more air (load) it senses, the more fuel its going to tell the computer to injector (as in when you accelerate)

 

Ok....that makes sense... So, an MAF car won't do that same thing then will it?

 

well, a MAF car still has a MAP sensor, its just not its "primary" basis

a MAF system looks more at the MAF than the MAP, the MAF sees the actually amount of air coming in

MAF systems are more forgiving as to larger mods, in other words with some work (say a cam) you prolly wont need a custom PROM (unless you go to extreme)
BUT, you have the big-*** MAF sensor in the way harming air flow

thats why most hi-performance engines are usually MAP (speed density) based

 

I didn't know the MAF cars had the MAP too....I gotcha now. I've heard they both have their advantages, but it's a lot easier to do homemade intake using an MAP system.....

 

yeah, pretty much all GM OBD-1 cars had a MAP (it was called several different names, all the same function really) even carburated cars, TBI, etc.

 

Yeah....so they all got the MAP, but in MAF cars they were used for different lesser purposes, whereas when the MAF was eliminated, they became primarily used to measure air intake...now I know how that part works...they indirectly measure air intake by measuring the pressure inside the manifold and comparing it to a table programmed into the prom right?

 

its actually the absence of pressure


-pressure=vacuum

 

You just HAD to get technical on me didnt ya? At least I've got the right idea... You know what I mean!!

 

The quick way to tell if you have a vacuum leak on a carb car, is to put a rag over the carb, if the idle goes up, you have a leak, if it dies, your Ok.

 

What do you mean, just put a rag over the carb with the air cleaner off?

 

Yeah...I dont know crap about carbs, but I figure if it's got a rag over the top w/o air cleaner and no vacuum leaks, it'll choke and die...but if it has vacuum leaks, the engine vacuum is going to pull in air through the leaking part and keep the car from dying...at least as quickly..depending on how major the vacuum leak is. But engine vacuum is a very powerful thing..try slipping off a small vacuum line so it's only connected to the manifold and put your finger over it..sucks like crazy...

 

hmmm, ok, i'll try this tomorrow, thanks for the tips!

 

Once you confirm you have a leak, the fast way to find it is to use Gumout Carb Cleaner Spray. Spray everywhere (around the carb, hoses), (aviod the sensors) and when find the leak the idle will go down, then repair or tighten to fix.

 

I've found the leak! look at this thread, i put a picture of the hose that's not hooked up, can ya help me out?

Another vacuum leak thread!