1972 Ford LTD Vacuum Leaks

LANEJAGUAR

MEMBER
1972 FORD LTD
V8
2WD
AUTOMATIC
132,000 MILES

I have a 1972 Ford LTD with a 400 cid motor. I have a rough idle/engine stall problem. So far, I've replaced the spark plugs, plug wires, alternator(for a different problem), voltage regulator. Timing has been checked and is normal. I had another friend look at it and he suggested that perhaps I have a vacuum leak in the carburetor area or elsewhere. Any guidance you could give me would be appreciated.

Friday, June 26th, 2009 AT 4:47 PM

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

A rough idle or stalling. A performance cam with lots of valve overlap can give an engine a lopping idle, but so can a vacuum leak. A really serious leak can lean the air/fuel mixture out to such an extent that an engine won't idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can the wrong PCV valve (one that flows too much air for the application), or a loose PCV hose. The rough idle in these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, enough, in fact, to cause a vehicle to fail an emissions test. Vacuun leak at vacuum hose to brake booster or booster itself is leaking.

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Friday, June 26th, 2009 AT 5:32 PM