Vacuum Line Routing for Jeep Engines
258 I6 and 304/360/401 V8 in CJ and FSJ
One of the most confusing aspects to tuning up an engine from the late 1970's and 1980's is all the early attempts manufacturers made to improve emissions with various vacuum-operated devices. In some cases (especially early-mid 1980's), it almost looks like they designed the system by simply throwing a handful of spaghetti at the engine and saying, "Route the hoses like that."
The best way to understand where everything goes is to get a copy of a factory service manual (FSM/TSM). Two good sources of these manuals are Amazon.com and Z&M Jeeps. Since these are pretty expensive (but worth it!), I've scanned a couple vacuum diagrams from my 1977 TSM and my 1974-80 parts manuals. I'm sure this collection isn't complete.
EGR (Exhaust Gas Recirculation)
Here is the vacuum diagram for both the I6 and V8 engines. This was the same throughout the 1974-80 model runs for all Jeep models. If your EGR vacuum line has a red & blue delay valve in it, the blue side should point toward the EGR valve and the red side should point toward the CTO switch.
PCV (Positive Crankcase Ventilation)
Here is the vacuum diagram for both the I6 and V8 engines. This was the same for all Jeep models, at least in 1977.
Fuel Vapor Storage Canister
Here is the vacuum diagram for both the 1977 I6 engine. This system first arrived in California FSJ and all CJ models, and was later added to 49-state FSJ's.
Distributor Vacuum Advance
Here is the vacuum diagram for both the 1974-80 I6 engine. Here and here are the vacuum diagram for both the 1974-80 V8 engines of various configurations. In these V8 diagrams, the vacuum line to the base of the carb on the manifold actually indicates ported vacuum, not manifold vacuum. Yes, it's confusing. Also, in these diagrams "10-20-40" and "10-25-45" indicate FSJ's, while "80" indicates a CJ. "E/CALIF" means "except California," while "CALIF" indicates a California-only model. "LHDC" indicates "less (without) heavy duty cooling" package, while "WHDC" indicates "with heavy duty cooling."
There are a few other diagrams out on the Net that are also useful.
Amazon.com sells factory service manuals for lots of different Jeep models at great prices.
Here is another scan from a similar manual detailing the vacuum diagram for a 1979 California V8 FSJ with auto tranny and heavy duty cooling.
Here is another set of scanned pages outlining the vacuum routing for mid-1970's Jeep engines.
Here is a poor-quality scan of the V8 vacuum diagram from a 1984-85 FSJ manual.
Here is another scan detailing the 1978 EVAP (charcoal) canister ports.
Here is a scan detailing the AIR injection pump setup.
And of course, there's always Tom Collins' site, which contains scans from TSM's from several different years. It's geared toward FSJ's, but will mostly apply to CJ's, too.
In the lower right corner of Joe Gorfinkle's site, you'll find lower-resolution scans from a 1976 TSM of much of the info that I scanned from my '77 TSM above.
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originally written 6 Mar 2004
last updated 12 Aug 2011 Obi-Wan (email@example.com)
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