Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   Pelican Parts Forums > Porsche Forums > Porsche 914 & 914-6 Technical Forum

LinkBack Thread Tools Rate Thread
Thread Post New Thread    Reply
Registered User
jamcleod's Avatar
Join Date: Nov 2001
Location: Vienna, VA
Posts: 916
Send a message via AIM to jamcleod
Question vacuum leaks/vacuum gauge

with the frequency of posts about searching for and fixing vacuum leaks for our cars, why hasn't some troubleshooting technique using a vacuum gauge come up? i have an old fuel pressure (range for carbed engines)/vacuum gauge i got along time ago and i know i've seen troubleshooting in repair manuals (Lash for one...) i hooked it up "t-ed" off the fuel pressure regulator (74 L-jet) but honestly don't know what i'm looking for/at. with concern about fixing vacuum leaks, wouldn't the gauge be the first indicator if vacuum is not what it should be at idle, for example? what should it be at idle?
Old 12-28-2002, 07:50 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
VARam1500's Avatar
Join Date: Aug 2002
Location: Central Virginia
Posts: 186
Unmetered air the the problem. Vacuum leak is the difference between metered air and actual, used-for-combustion air. I think your idea is a good one in theory, but to find a way to measure the difference between what the ecu sees and actual is a tough nut to crack. Not to sound like a smart answer, but if it could be done in a practical manner Mr. Bosch would have loved to know how. It's a valuable piece of information that would allow the ecu to figure air/fuel ratio with highest precison.

I'm sure there's good insight from Mr.'s Anders, Darling, and others on the subject. I hope they chime in!

'75 1.8L L-jet 914
Old 12-28-2002, 05:32 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
pbanders's Avatar
Join Date: Jan 2001
Location: Phoenix, AZ
Posts: 1,113
Send a message via Yahoo to pbanders
Unmetered air is a problem with L-Jet, but not necessarially with D-Jet. Air leaks in D-Jet cause a high idle condition, but the mixture is correct. Air leaks in L-Jet cause a lean mixture condition, causing idle and part-load drivability problems.

The problem with using a vacuum gauge for detecting air leaks is twofold. First, what is the "normal" vacuum level at idle? It varies from 14 to 18 in. Hg, depending on the condition of the motor and its temperature. Non-stock cams drop it lower. Secondly, let's say you do know what the "normal" level is, and you measure a different value. What have you learned? Not much that's useful. What you need to do is to find the source of a leak.

Various ways to do this have been suggested. Most involve spraying a combustable around suspected areas and noting whether the engine speed changes. Carb cleaner, starting fluid, propane, etc. have been suggested. This method locates the leak location quickly.
Old 12-28-2002, 07:27 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)

Thread Tools
Rate This Thread
Rate This Thread:


All times are GMT -8. The time now is 12:55 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.