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Old 05-26-2012, 06:39 PM   #61 (permalink)
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Quote:
Originally Posted by Grant-53 View Post
. Since the van is my wife's car I might ask you to refer to Mrs. MAP sensor.
That will open a can of worms!!!!!

I can only imagine the computer programming logic on a female MAP !


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Old 05-26-2012, 09:12 PM   #62 (permalink)
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Old 05-28-2012, 06:02 PM   #63 (permalink)
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Quote:
Originally Posted by mwebb View Post
a missing vacuum line on a speed density system such as your s will NOT cause lean condition
A vacuum leak can cause a lean condition, depending on where in the system the leak is. Leaks right by the intake valve do not have as much of a chance to propagate back up to the manifold, and can cause a lean cylinder.

However, most vacuum lines will be hooking up to the manifold itself, so your point is right on the money.


O2 sensor feedback has a limited amount of "control authority". In general, it cannot change the base mixture so much as to prevent the engine from running, at the very least. So a very very lean condition will make the O2 circuit go to full enrichment, but it might not be enough.

Again, though, this is a "corner case" and is not that likely to be what is actually happening when a vacuum hose is disconnected. But it is possible.
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Old 05-29-2012, 03:56 AM   #64 (permalink)
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Quote:
Originally Posted by some_other_dave View Post
A vacuum leak can cause a lean condition, depending on where in the system the leak is. Leaks right by the intake valve do not have as much of a chance to propagate back up to the manifold, and can cause a lean cylinder.

However, most vacuum lines will be hooking up to the manifold itself, so your point is right on the money.


O2 sensor feedback has a limited amount of "control authority". In general, it cannot change the base mixture so much as to prevent the engine from running, at the very least. So a very very lean condition will make the O2 circuit go to full enrichment, but it might not be enough.

Again, though, this is a "corner case" and is not that likely to be what is actually happening when a vacuum hose is disconnected. But it is possible.
it wouldn't make a lean condition in a speed density system; that's fuel is controlled by map, intake temp, water temp, and o2 sensors(most systems are 2 or 4; unless your talking obd1)

map= manifold air pressure
vacuum leak= lower vacuum pressure
most engines run around 20 inches if you have a vacuum leak(by the way he said 15 inches) it would cause the engine to run rich, no matter what the intake or water temp was, and the 02 is for trim(long term/short term) or where in the system the leak is unless it's behind a valve

1.by the way i was running around with a vacuum leak(and no decent amount of heat for march) for a month; high idle and pig ass rich.

2. plastic vacuum lines are crap, they break or wear through faster, and melt easier. than rubber

a maf(mass air flow) system on the other hand, a vacuum leak can cause a lean condition.

some_other_dave; do you drive a chrysler product?

Last edited by baldlobo; 05-29-2012 at 04:06 AM..
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Old 05-29-2012, 06:38 PM   #65 (permalink)
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Sorry, I meant to say "A vacuum leak on a MAP-controlled system...". I have found that air leaks that are close to the intake valve actually do affect the mixture. Checked with a WBO2 meter, and because the car idled like crapola.

This is in a VW-based car, and a relatively-ancient one at that. (The finest 1960s-vintage analog electronic fuel injection!) It has fairly long intake runner pipes from the manifold to the intake ports (on the order of 14" or so) and our working theory was that the "false air" didn't really have time to propagate back up to the manifold to be measured by the MAP sensor.

As I said, though, simply dumping air into the manifold (e.g., disconnected vacuum line or a deliberate leak of some kind like "evap") will not affect the mixture. So you are correct in the case we were actually discussing--just not necessarily in all other cases.

-soD
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Old 05-29-2012, 11:26 PM   #66 (permalink)
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02 sensor in chrysler has around 25% FT authority

02 sensor in chrysler has around 25% Fuel Trim authority
before the system will set DTC s for rich or lean condition
some have even greater authority depending on the system ... unlike VW .

with such a huge correction authority available rich or lean condition DTCs in crysler are rare
in my experience

on speed density systems
( systems with MAP sensor and not MAF sensors )
intake manifold leaks at the manifold to cyl head area can cause misfires
and may not have too much effect on
MR or MRS MAP sensor 's input depending on weather or not the leak reduces
acTual
MAP pressure or intake vacuum in the intake

VW will set FT limit DTCs at 12%
older CIS systems were very sensitive to vacuum leaks at the injector or intake to cyl head seal area
CIS systems had no 02 sensor therefore , no Fuel trim correction .
that began with CIS/E such as it was .

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