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TR7/8 fuel injection

To: british-cars%alliant.com@eddie.mit.edu
Subject: TR7/8 fuel injection
From: mit-eddie!emx.utexas.edu!jatc@EDDIE.MIT.EDU (James TenCate)
Date: Thu, 26 Apr 90 15:12:13 -0500


Whew!  Lots of neat talk about SU, Z-S carbs, Webers etc.  Almost
makes me wish for my TR7 back (but only a little :-)  Now for
something completely different.

I've got a problem but first, some background:  My TR8 has fuel
injection.  For the second time during my brief ownership of the
car, I've had to take the whole fuel injection system apart.
First time I had all sorts of leaky seals to replace, and the
second time I had to actually replace an injector.  I was truly
awestruck when I pulled all 8 injectors out together (still
attached to the fuel rails) and thought how much it would cost to
replace ALL of them should I drop them!  I was pretty speedy this
time too (write me if you want tips on things NOT to do :-)

I got everything back together and presto, car started right up.
I was pleased.  However, after it ran for a while, I noticed that
the idle speed wasn't where it had been before:  it went from
about 850 RPM before to 650 RPM now.   Hmmmm.  Got out the fuel
injection trouble shooting guide in the shop manual.  I've come
to two completely opposite conclusions (1) there was an air leak
(somewhere past the airflow meter, probably between plenum
chamber and intake manifold) BEFORE I took everything apart and
(2) there is an air leak NOW, not before.

Here's the problem. (10 pts)  Suppose there IS an air leak
between the plenum chamber/intake manifold (I have good reason to
suspect that area).  Will that make the idle speed go UP or DOWN,
everything else being equal?  Why?

The car currently lacks low end power and has kind of a flat spot
(it drives just like an Alfa) so I'm inclined to say that I have
an air leak NOW.  That of course means spending another weekend
taking it all apart again, cleaning off the thin blue film of
Permatex between plenum chamber and intake, and redoing
everything (heavy sigh).  By the way, there is normally NO gasket
between the plenum chamber and the intake manifold but WITHOUT
something like Permatex, the car behaves like a stock TR7, i.e.,
no power at all.  Clearly a good seal is important.

Anyone?

jim
jatc@emx.utexas.edu


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