I’m at my in-laws for thanksgiving so I volunteered to help them fix their
’96 Ford Taurus but I’m a little puzzled and need some expert help.
Failing smog test:
There seems to be a problem with the EGR system , the check engine light
comes on and the car, of course, is not passing the Orwellian California
smog test. I looked at the report from the failed smog test: P0401 “Insufficient EGR flow detected”. Actually the tailpipe emissions measured
are within spec but the mere fact that there is a 401 code is considered a
smog test failure.
In trying to diagnose the problem, and looking at the “typical EGR system
description” in the Hayes manual, I can identify 4 possible causes:
1. The EGR valve is not working
2. The EGR valve is working but the EGR exhaust tubes are clogged up (I’ve
seen this in an old Mustang I once had)
3. Everything is fine but the EGR backpressure sensor is not working and
is lying to the computer telling it that there is no flow.
4. The EGR valve is not getting a vacuum signal to open in which case
either a) the vacuum solenoid is not working or b) the vacuum line to the
EGR valve is clogged or broken or c) the computer is not giving the right
electrical signal to the EGR solenoid to open.
I decided that I could easily look at 1,2 and 4 (cause 3 seemed a lot more
difficult to explore because this car has the Duratec 3.0L 24 valve engine
so the backpressure monitor is in some inaccessible location below the
So I first explored cause 2… I took out the EGR valve and the short
exhaust path from the EGR valve to the intake manifold looked
unobstructed. So next I started the engine. Sure enough, I heard the
exhaust noise coming out of the EGR line, but in any case I stuck a
flexible metal line into, it in case it was clogged. Not much crud came
out so seems like the exhaust path is open.
So now I looked at cause 1… as I had the EGR valve disconnected, I
connected it to the vacuum line and looked at the plunger inside the valve
expecting to see the vacuum lift the plunger at least some but nothing
happened. I revved up the engine and still nothing happened. My brother in
law had already bought a new EGR valve so with the engine running, I hooked
up the new EGR valve to the vacuum and still the EGR plunger did not move.
I disconnected the EGR vacuum hose and put my finger on it and I can feel
some very faint vacuum pulsing but it seems to me quite weak, besides I
can visually see that the EGR valve plunger is not lifting at all.
So based on the above evidence, am I looking at cause 4 or am I missing