Finding a vacuum leak - Pirate4x4.Com : 4x4 and Off-Road Forum

Wilson · 06-13-2009, 02:55 PM

I'm having a problem with a lean condition with my EFI setup. I've hosed it down with carb cleaner and used a MAPP gas torch trying to find a leak and did not. I also did a compression test, which came back good, and leads me to believe the HG is not blown. The bad new is that I should not start and run the vehicle because the tcase had to go back to AA for repair (auto trans). Anything else I can check or tests that I can do? Chevy SBC, if it matters.

Whitetrash303 · 06-15-2009, 12:34 AM

Check your brake booster. They go bad and cause vac leaks that you'll never find by spraying.

Wilson · 06-15-2009, 05:51 PM

No booster, twin willwood manuals. Would it be possible to ahve a leak on the inside of the galley and have it scavenge air from within the engine? About the only place I can think of at this point, but hate to tear it down again on a hunch.

billymarr · 06-15-2009, 06:00 PM

yes you could have a vacuum leak in the valley and be sucking air through the pvc valve or breather.

Bubba_Jeep · 06-16-2009, 08:57 AM

I've read that you can test for vacuum leaks under the intake manifold by injecting propane into the valve cover.
Personally, I find that approach a little "scary".
Give it try, and report back--if you are able!!

zukesofhazzard · 06-19-2009, 12:50 AM

What symtoms are you getting? I assume you checked fuel preasure and volume, but would it be possible to just simply have a bad IAC solinoid or fuel preasure regulator?

Urban Wheeler · 06-21-2009, 05:30 AM

Quote:

Originally Posted by Wilson

I'm having a problem with a lean condition with my EFI setup. I've hosed it down with carb cleaner and used a MAPP gas torch trying to find a leak and did not. I also did a compression test, which came back good, and leads me to believe the HG is not blown. The bad new is that I should not start and run the vehicle because the tcase had to go back to AA for repair (auto trans). Anything else I can check or tests that I can do? Chevy SBC, if it matters.

Is it TBI or something else? Check and make sure everything is tight and the gasklets are sealed well, check hoses for cracks, check all you unused vacuum ports are plugged, etc. I don't think this is your problem since you've been using carb cleaner and mapp gas.

I wouldn't worry about the PCV, it is supposed to pass air from the engine into the intake.

Do check that your injectors are working, with TBI you can use a timing light. Otherwise, you can use a meter to make sure you have power to all your injectors. (GM TBI supplies power to the injefctors, and the ECM grounds them.) Check your fuses, too.

I worked on a motor with a lean condition, turned out to be bad wiring to the injectors.

f250rollinon37s · 06-22-2009, 08:13 PM

he is running a massflow setup now - i think its the same one ?

wilson ? lean when? at idle, off idle - cruz, WOT ?

06-13-2009, 02:55 PM	#1 (permalink)
Wilson Registered User Join Date: Sep 2001 Member # 7233 Location: Paradise, CA Posts: 17,161	Finding a vacuum leak I'm having a problem with a lean condition with my EFI setup. I've hosed it down with carb cleaner and used a MAPP gas torch trying to find a leak and did not. I also did a compression test, which came back good, and leads me to believe the HG is not blown. The bad new is that I should not start and run the vehicle because the tcase had to go back to AA for repair (auto trans). Anything else I can check or tests that I can do? Chevy SBC, if it matters. __________________ [COLOR=Red][SIZE=4]ECV 7-11[/SIZE][/COLOR] Serving up a Tsunami of Swagger

06-15-2009, 05:51 PM	#3 (permalink)
Wilson Registered User Join Date: Sep 2001 Member # 7233 Location: Paradise, CA Posts: 17,161	No booster, twin willwood manuals. Would it be possible to ahve a leak on the inside of the galley and have it scavenge air from within the engine? About the only place I can think of at this point, but hate to tear it down again on a hunch. __________________ [COLOR=Red][SIZE=4]ECV 7-11[/SIZE][/COLOR] Serving up a Tsunami of Swagger

06-15-2009, 06:00 PM	#4 (permalink)
billymarr Registered User Join Date: Jun 2005 Member # 49353 Location: Afghanistan from TX Posts: 125	yes you could have a vacuum leak in the valley and be sucking air through the pvc valve or breather. Last edited by billymarr; 06-15-2009 at 06:00 PM.

06-16-2009, 08:57 AM	#5 (permalink)
Bubba_Jeep Registered User Join Date: Oct 2004 Member # 37184 Location: Santa Barbara, CA Posts: 1,323	I've read that you can test for vacuum leaks under the intake manifold by injecting propane into the valve cover. Personally, I find that approach a little "scary". Give it try, and report back--if you are able!! __________________ 88XJ, Chevy 5.7L, Edelbrock MPFI, NV4500, Atlas, D44's, high steer, ARB's, 7" custom semi long-arm 3 or 4-link lift, BFG 33x12.5-15's.

06-22-2009, 08:13 PM	#8 (permalink)
f250rollinon37s MASTER TECH Join Date: Oct 2005 Member # 54844 Location: Northern cali Posts: 3,435	he is running a massflow setup now - i think its the same one ? wilson ? lean when? at idle, off idle - cruz, WOT ? __________________ BSW Racing, Calrocs Super mods 12 & ? Driver: Aaron Whitehead - Driver: Joe Hutchins Spotter: Adam Kovarik - Spotter: Dustin Knight Crew Cheif: me fuckers build up of the truggy /forum/ford/544813-update-pics.html Last edited by f250rollinon37s; 06-22-2009 at 08:15 PM.

06-15-2009, 12:34 AM	#2 (permalink)
Whitetrash303 Hardcore Web Wheeler Join Date: Nov 2007 Member # 102426 Location: Denver Posts: 992	Check your brake booster. They go bad and cause vac leaks that you'll never find by spraying.

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