Finding Vacuum Leaks - Chevelle Tech
Troubleshooting Diagnosing problems done here.

 11Likes
  • 1 Post By SSJohn
  • 5 Post By Dave Ray
  • 1 Post By nashville beth
  • 2 Post By LeoP
  • 1 Post By DUTCH MAX HEADWORK
  • 1 Post By Dave Ray
 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 10 (permalink) Old Jul 16th, 19, 3:41 PM Thread Starter
Tech Team
Mike
 
Join Date: Jun 2013
Location: Boston
Posts: 727
Finding Vacuum Leaks

I'm pretty sure I have a vacuum leak somewhere given my poor idle and performance with my aftermarket FI. I used some carb cleaner and sprayed around the base of the throttle body. i also sprayed where the intake meets the heads and didn't hear a change in performance. Anyone have a punch list of most prone leak areas and what they'd check first? also, is carb cleaner good to use or should i use something else?

67 Chevelle 454, M21
Gen IV 454 (out of C30 ), 390 heads 1.88/2.19 valves by Vortecpro, with ISKY Hyd Roller cam (at 050 218 int./228 exh, lift 530 int./552 exh.), RPM performer intake, Fitech 600HP, Dougs headers, and M21, Gear Vendors OD, 3.73's, UMI Suspension, Viking coilovers.
mdelgado is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old Jul 17th, 19, 12:17 PM
Tech Team
John
 
Join Date: Dec 2012
Location: 55.916, 10.733
Posts: 490
Re: Finding Vacuum Leaks

Old timers trick:

Take the air cleaner off and cup your hand. Slowly put your hand over the fi barrels. Engine must be running. If the engine smooths out and gains rpm, you have a vac leak.

I absolutely hate (and refuse) to spray anything flammable on the exterior of a running engine.
hydro462 likes this.
SSJohn is offline  
post #3 of 10 (permalink) Old Jul 17th, 19, 2:59 PM
Senior Tech Team
 
Join Date: Apr 2012
Location: Yerington, Nevada
Posts: 1,576
Re: Finding Vacuum Leaks

I like to temp fate, I use UNLIT propane to sniff out air leaks.
Dave Ray is offline  
 
post #4 of 10 (permalink) Old Jul 18th, 19, 8:32 AM
Lifetime Premium Member
Don
 
Join Date: Mar 2013
Location: Michigan's U.P.
Posts: 661
Re: Finding Vacuum Leaks

X2 on the propane,thats what we used in our shop.
Don B is offline  
post #5 of 10 (permalink) Old Jul 18th, 19, 9:26 AM
Lifetime Premium Member
Beth
 
Join Date: Oct 2010
Location: Nashville TN
Posts: 1,254
Re: Finding Vacuum Leaks

Quote:
Originally Posted by Dave Ray View Post
I like to temp fate, I use UNLIT propane to sniff out air leaks.
X3

Places I have found before : shaft bushings in a throttle body/carb, power brake booster, split accessory hose, intake manifold
LeoP likes this.

67 Chevelle convertible, 138 vin, original 4 speed, bucket seats, 12 bolt, Marina Blue with black interior
nashville beth is offline  
post #6 of 10 (permalink) Old Jul 19th, 19, 8:54 AM Thread Starter
Tech Team
Mike
 
Join Date: Jun 2013
Location: Boston
Posts: 727
Re: Finding Vacuum Leaks

No luck yet. But I'm just seeing your advice now. so I'll try your suggestions this weekend. I was trying starting fluid around the intake and tb mount and no change. I'll try picking up some propane too. Should I disconnect the booster and plug the hole to test the booster? Right now the booster and pcv are T'd on the intake. All vac holes on the FI are capped.
Would a header leak cause this? I do have some ticking under the hood..

67 Chevelle 454, M21
Gen IV 454 (out of C30 ), 390 heads 1.88/2.19 valves by Vortecpro, with ISKY Hyd Roller cam (at 050 218 int./228 exh, lift 530 int./552 exh.), RPM performer intake, Fitech 600HP, Dougs headers, and M21, Gear Vendors OD, 3.73's, UMI Suspension, Viking coilovers.
mdelgado is offline  
post #7 of 10 (permalink) Old Jul 19th, 19, 10:58 PM
Lifetime Premium Member
leo
 
Join Date: Oct 2003
Location: Southwest Florida
Posts: 13,107
Re: Finding Vacuum Leaks

The booster and PCV Tee'd in is your vacuum leak,the booster goes on a dedicated vacuum source. Change the PCV system off of the booster line and your problem will be solved and good luck!!
davewho1 and 68-13427 like this.

Leo Paugh
Maryland Chevelle Club #017
A.C.E.S.#3731
progress has little to do with speed, but lots to do with direction

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
LeoP is offline  
post #8 of 10 (permalink) Old Jul 20th, 19, 1:21 AM
Lifetime Premium Member
Al
 
Join Date: Apr 2011
Location: SO CAL...Huntington Beach and Rancho Cucamonga
Posts: 4,901
Garage
Re: Finding Vacuum Leaks

I found a vacuum leak at the intake to head gasket by first checking the plugs. On short runs or lots of idle time showed oily, but the oil cleaned up on long runs and the plugs looked lean compared to the others. So I tried to figure out WTF. I pulled the PVC and plugged it. Then sprayed carb cleaner into the valve cover, after a few seconds the rpms would increase slightly. That told me I had a vacuum leak or bad valve seals/guides and maybe sucking oil at other times. Pulled the manifold and found the leak at the gasket. The intakes were pulling vacuum and oil through the lifter valley.
hydro462 likes this.
DUTCH MAX HEADWORK is offline  
post #9 of 10 (permalink) Old Jul 20th, 19, 3:09 PM
Senior Tech Team
 
Join Date: Apr 2012
Location: Yerington, Nevada
Posts: 1,576
Re: Finding Vacuum Leaks

DUTCH gives a good answer, again. Look at the plugs.

Case in point, one year when I still lived in So. Cal., I had to go through the Socialist by-ennial smog torture tests with my first year 2.8 V6. Engine had developed a single cylinder miss. So, I get in there one day, and go testing, plug wires, plugs (found the lean cylinder, number 6, driver side rear). Looked at cracked this or that, loose whatever, couldn't find it, dead plug wire, cap, name it. Then, it hit me, the only thing I didn't check was the EGR valve, mounted just over the number 6 inlet port. I pulled the valve, liquid checked it in my solvent tank, leaks, not giant ones, but 3 fairly bad ones. New replacement EGR valve, smog check, passed with flying colors, to the point the inspector grilled me on what I did to make the ting pass, because NONE of them he has ever tested, passed. I never did get to the point of the EGR valve in the story to him.

Nope, never did think to use my propane method on that leak problem, probably would have showed it up a lot faster if I had.

On the propane, I use a hand held propane torch, UNLIT, UNLIT, UNLIT. I also use that method down the carb if I think there is a lean condition from the carb jetting at a designated throttle opening, very low flow propane down the air inlet with throttle held at a set RPM the leanness seems to be. Engine loads up, too rich, engine speeds up, too lean. Besides, burned propane smells better than gasoline.


Also, when I propane check, I leave the brake booster fitting in the booster, and check the whole power brake system as assembled.
hydro462 likes this.
Dave Ray is offline  
post #10 of 10 (permalink) Old Jul 22nd, 19, 12:03 PM Thread Starter
Tech Team
Mike
 
Join Date: Jun 2013
Location: Boston
Posts: 727
Re: Finding Vacuum Leaks

Thanks Leo, I'll put my booster dedicated to the fitting on the intake, and the pcv to the fitting on the throttle body.

In regards to plugs, earlier this year I was chasing a rough idle. but only on the drivers side. I'll attach a pic of the plugs. My timing was way off somehow and after adjustment it seemed to go away, but still a little rough. I'm beginning to wonder if I should just pull the intake and reinstall with some sealant around the ports for added insurance

Unfortunately didn't mess with the car in the 100 degree heat here in new england. Went offshore fishing where it was cooler



67 Chevelle 454, M21
Gen IV 454 (out of C30 ), 390 heads 1.88/2.19 valves by Vortecpro, with ISKY Hyd Roller cam (at 050 218 int./228 exh, lift 530 int./552 exh.), RPM performer intake, Fitech 600HP, Dougs headers, and M21, Gear Vendors OD, 3.73's, UMI Suspension, Viking coilovers.
mdelgado is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.

Email Address:
OR

Log-in










Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome