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stem (use a mirror if necessary). It should move, then return. If it doesn't,
remove the hose and feel for vacuum as you rev it again. If you find some, the
valve's at fault. If you don't, check out the controls (see step #3). Of course, if
you're dealing with one of those Ford pressure-operated units, you should feel
pressure instead. If you found no vacuum at the valve and there's a
thermostatic vacuum switch in the hose, pull off the source line and feel for
vacuum above idle. If you find it, but none gets to the valve with the engine
warm, the switch is faulty. On all but the positive backpressure and
pressure-operated types, you can use a hand-operated vacuum pump to test
valve action. The engine should roughen and maybe die off when vacuum is
applied at idle. This is especially useful on valves with an enclosed stem. A
note on cleaning: GM says never to use a solvent to dissolve deposits in an
EGR valve, but Chrysler tells you it's okay providing you're careful not to get
any on the diaphragm. With most specimens, you'll be cleaning the pintle and
valve seat with a dull scraper or wire brush, and knocking out loose carbon by
tapping the pintle. But these parts are expensive, so a more satisfactory
means of cleaning them is desirable. Some GM versions, for instance, can be
disassembled for this purpose. Just make sure you don't damage the seating
surface in the process, and that you scribe marks so you can get it back
together in the proper alignment’
(Autosite, 2003).
10.5 Modifications
Excess EGR (failure mode 2) can severely reduce the driveability of the vehicle. In
this case one work-around is to disable the EGR system entirely, so that it operates
in mode 3. It should be noted that this has some negative consequences: hotter
combustion temperature and the possibility (presumably small) of reduced engine
life. Also, this will be an illegal modification in countries with emission control
legislation.
The work-around is achieved by either plugging the vacuum line (j) or blanking the
pipe between the exhaust manifold and the EGR valve (k). If the EGR valve is stuck
in an open position then plugging the vacuum line will be ineffective and the blanking
method is the next option. If blanking is used, then a substantial plate of several mm
thickness needs to be used. The temperature of the exhaust gases is probably
around 500 deg C if not higher, and this will readily melt aluminium (melting point
300 deg C) and erode through thin sheet steel. It would also seem sensible to place
the blanking plate at the EGR valve end of the pipe, not at the exhaust manifold, as
this reduces the temperature to which it is exposed. Stainless steel would be the
preferred material for a blanking plate and could be quite thin, with mild steel as a
second choice (several mm would be necessary). Aluminium, tin can, plastic,
silicone or gasket materials would be inappropriate.
Mitsubishi recommend replacing rather than disabling the EGR valve, for both
technical and environmental reasons.