2005 Grand Caravan SXT / engine detonation and some noise = ?

Hi,

I own a 2005 Dodge Grand Caravan SXT / 3.8L

Last fall I've noticed some strange noise:
- it is a blowing sound (like a pressurized air escaping from
somewhere)
- I can clearly hear it only from inside, with all windows closed
(i.e. when no outside noise is heard)
- it cannot be heard under the hood or from outside / probably because
other engine noises are masking it
- it apparently comes from where the hood release lever / parking
break release lever are located, but noise source is somewhere deeper
- noise changes with engine revs not only when I step on gas, but also
when I'm driving down the hill on an "L" gear, which makes revs go up
without touching the pedals

It did not lead to any problems, and my mechanic did not find anything
suspicious, so I left it as is (again, _since_last_fall_)

Now when summer weather finally came and it is very hot outdoors,
there is a significant detonation in the engine; the hotter it is
outside the more heavy detonation is, beginning from about 23..24
degrees Centigrade.

I know that one of the reasons for detonation is overheating in
combustion chamber; another is lean mixture (which in turn can be
caused by excessive air being sucked inside). Engine itself is not
overheating; at least temperature gauge shows the same temperature as
it did last summer, when everything was Ok in hot days.

Taking into account that strange noise that started last fall, I
suppose that the symptoms are interconnected, provided that since last
fall there were no hot days before summer.

My mechanic did his best with combustion chamber cleaner, injectors
cleaner etc. etc; When a "check engine" lamp turned on I had to
replace the faulty EGR valve - I was sure at that time that this valve
was the main reason for the detonation, but I was absolutely wrong -
nothing changed except the "check engine" lamp went off.

* * * * *

If anybody have ANY ideas how to diagnose/eliminate the problem, I'd
highly appreciate it.
Or maybe just point me to the community/forum where the issue can be
further discussed.

Thanks !!

 

I'd wonder about a leaky brake booster. If you hold the brakes on and
turn off the engine, does the pedal effort start getting markedly
harder? If that's what it is, this won't be a subtle effect:
unless you've got a pretty strong leg, it'll be nearly impossible to
hold the pedal down.

 

I'll check your assumption first thing in the morning.
By the way sometimes (though not too often) I notice that braking is
somewhat soft and not as efficient as it should be... Not really bad
but like, you know, if rotors and brake pads are wet during a good
rain. I didn't pay much attention to it, but I'll now get into it and
check the brake booster anyway.
Does brake booster leakage cause other symptoms like brake fluid
consumption etc.? I check level periodically and it's Ok all the
time...

Thanks Joe !

 

Not an assumption, a hypthesis to be tested.

Brakes feel soft when wet because there's less friction. Not related
to the booster.

Not the symptoms you're asking about, no. A leaky master cylinder can
cause a booster to fail, but not the other way around. But a leaky
booster is a vacuum leak, and the other symptoms you reported earlier
(detonation, etc) could be consistent with a serious vacuum leak.

 

Brakes feel soft when wet because there's less friction. Not related

Sure, I know that. I was using this case just to explain how my breaks
are behaving sometimes - in dry weather.

 

I'd wonder about a leaky brake booster. If you hold the brakes on and

Nope
Brakes are Ok, absolutely no change to pedal feedback when I turn off
the ignition...