Backfiring

Hmmm ... check your ignition timing yet?

Funny you would mention the EGR.  I've heard conflicting stories
about the effectiveness of it as a pollution control device.
Moses Ludell's Jeep book says that the EGR actually lowers the
temperature inside the combustion chamber, and as such makes the
engine burn cleaner ... but Jack Clifford from Clifford
Performance say's "it's a crutch for poorly designed
aspiration (carb/intake) system" and a properly
designed/tuned system will burn cleaner without it.  (Since
Clifford sells manifolds, headers, cams & fuel systems, I
could have predicted that! )

One thing is certain, if the EGR carboned up, it *will* allow
excess exhaust gasses back into the system.  Usually removing the
vacuum line won't have much effect, since the vacuum operates a
bellows (diaphragm?) that opens up a pin shaped valve.  If it
does have an effect, then maybe the bellows is leaking ...
causing a vacuum leak. To test, beg/borrow/steal a vacuum tester
and hook it up to the EGR. Pump it up to about 5, and see if it
leaks out.  If not, the bellows is OK.

The next thing to do is check out the pin, and it's seat, to
ensure that it seals off the line properly.  Clean it out ...
anyways! Now, something that a lot of us overlook is back
pressure in the exhaust system.  It shouldn't be more than 7 lbs,
I think.  If so, either the exhaust system or the catalytic is
clogged.  Remember that an improperly running engine can very
easily cause a catalytic melt-down.  If you have to replace a
cat, that's the symptom. You've got to make sure you find the
cause!  It usually is one or a combination of the misc things
we've talked about on this list! Check it out, cause it'll cost
you another catalytic if you don't.

 John Madill

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If you can get rid of your rough idle and problems at higher
RPM's with the EGR disconnected, then you have a bad EGR. Since
EGR is a SMOG device and its function is to lower the combustion
temperature, it should not cause any serious problems other than
higher emissions. If you live in CA you will not pass the SMOG
test with EGR disconnected since it is one of the first thing
that is checked.

Siamak Navid

------------------------------

Air from the smog pump will cause a backfire on decelleration.
Make sure the bypass valve is working. It is in the hose that
runs from the smog pump to the AIR manifold (it has a vacuum line
on it.) The vacuum source is manifold, not ported. Apply 22"
vacuum to the fitting and make sure it will hold vacuum. With the
vacuum applied, the valve should close (preventing the smog pump
from pumping air into the manifold).

Lenny

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        I can tell whenever I have a exhaust manifold leak
because I start backfiring like an old model-t. I replace the
manifold gasket and it stops. Which brings up another question.
Anyone out there know how to seal headers up well? I have a 225
v6 and always seem to have leaks, even with new gaskets. Warped
headers maybe?

                                          Bruce D. Osborn