Vacuum leak question

monsterstang70

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Jun 24, 2004

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Amityville, NY

Sep 23, 2004

#1

• Sep 23, 2004

• #1

Im about to purchase a s/c 88 mustang hatchback, here is a quick run down on the mods. it has 50 lb injectors, novi 2000, in line fuel pump, mass air conv. , 373 gears, alum driveshaft w/ loop, brand new centerforce dual friction clutch , new msd wires, dart stage 3 heads, cobra r's needs new rear tires, the car needs finishing , it has a vacum leak somewhere , the radiator( triple core alum) has a small hole, also you need a s/c belt. The problem is that the car surges and dies at idle if you dont keep your foot on the gas. What kind of vacuum leak would cause the car to do this?
Sorry for the lenght
Thanks
Jhery

 

jrichker

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#2

• Sep 23, 2004

• #2

Use a vacuum gauge ($17 at most auto parts stores) to determine if a leak is present. You should see 15"-19" of vacuum at 650-725 RPM.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will speed up. Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Fire is an excellent hair removal agent and no eyebrows is not cool...

 

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fost9508

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#3

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• #3

sort of off topic, but I work in the energy industry and to check vacuum leaks we use shaving cream. Anybody ever hear of using this under the hood?

 

monsterstang70

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#4

• Sep 23, 2004

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lol 1st time i heard bout using shaving cream on a engine.

 

bgjohnson

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johnston,iowa

Sep 23, 2004

#5

• Sep 23, 2004

• #5

never heard of that method but it makes sense, and hey guys don't forget that he has a pretty big blower with a nice looking combo sucking in alot of air. I hear that SC'ed engine can have an idle problem like the one you described, I know that some people put a hole in the throttle plate to take care of the problem. but I'd also check your IAC and make sure the throttle body is clean and free of build up.

 

D

Daggar

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#6

• Sep 23, 2004

• #6

fost9508 said:

sort of off topic, but I work in the energy industry and to check vacuum leaks we use shaving cream. Anybody ever hear of using this under the hood?

Click to expand...

So how does that work?

 

monsterstang70

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Sep 23, 2004

#7

• Sep 23, 2004

• #7

bgjohnson said:

never heard of that method but it makes sense, and hey guys don't forget that he has a pretty big blower with a nice looking combo sucking in alot of air. I hear that SC'ed engine can have an idle problem like the one you described, I know that some people put a hole in the throttle plate to take care of the problem. but I'd also check your IAC and make sure the throttle body is clean and free of build up.

Click to expand...

How big of a hole in the throttle plate and exactly where on the plate?

 

monsterstang70

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Sep 23, 2004

#8

• Sep 23, 2004

• #8

jrichker said:

Use a vacuum gauge ($17 at most auto parts stores) to determine if a leak is present. You should see 15"-19" of vacuum at 650-725 RPM.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will speed up. Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Fire is an excellent hair removal agent and no eyebrows is not cool...

Click to expand...

Would you happen to know of any common places of vacuum leaks and if they leak is by the manifold or tb, would a new gasket fix it?
thanks
Jhery

 

F

fost9508

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Sep 23, 2004

#9

• Sep 23, 2004

• #9

Well giving it some thought it would probably be a little more messy then spraying oil on the joints. Anyway what we did was spray on the shaving cream and where ever a little volcano appear you had a leak.

 

S

smac61

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Sep 24, 2004

#10

• Sep 24, 2004

• #10

Just a thought....before drilling a permanent hole in the throttle plate, I would consider installing the idle adjuster plate. Costs less than $20, and if it doesn't solve your problem, you're not stuck with a hole.

 

deftsound

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#11

• Sep 24, 2004

• #11

man ive had more problems with vacuum leaks then i ever want to have again, first of all, check the vacuum hose coming out of the front of the intake manfold from underneath it, secondly, check to make sure your pcv valve is functioning properly and that there are no cracks in the hose, thirdly make sure your intake manfold is torqued down to about 18 ft lbs...

 

bgjohnson

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johnston,iowa

Sep 24, 2004

#12

• Sep 24, 2004

• #12

actually the bypass idle plate is 32 shipped and it doesn't solve all problems, but it is a good option I didn't list, but I agree with SMAC61. I have the plate and it didn't help my idle much, the good things about it is that you can adjust your idle without readjusting the TPS. but if you close off the throttle plate like the instructions say, somtimes(this happened to me) it will cause a sticky throttle, like you have to get past the point of vacuum then is moves freely.

 

J

jerry beach

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Sep 24, 2004

#13

• Sep 24, 2004

• #13

jrichker said:

Use a vacuum gauge ($17 at most auto parts stores) to determine if a leak is present. You should see 15"-19" of vacuum at 650-725 RPM.

Fire is an excellent hair removal agent and no eyebrows is not cool...

Click to expand...

Sounds like you are speaking from personal experience there, I have been on fire many times. Mostly from welding, shirt catches fire, easy to put out

I dont think a vac guage will tell him much. With so many mods, it will likely be out of stock specs anyway. With the S/C he may see boost at idle, I have no experience with them. I would find out if the car has been professionally tuned, and if it ever ran right. Its likely this guy has been chasing the problem for quite some time and has given up on it. Unless it was really cheap, I would steer clear of it. Also make sure he has reciepts on all the engine parts he says are in there. I agree with the guy who said clean the TB real good. Thats a great place to start with idle issues.