[Shotimes] 93 SHO Failed Texas State Inspection

[Bob]

High NOX indicates high combustion chamber temperatures which usually means
that the engine is lean, so I wouldn't suspect that the pressure is too high
as long as you haven't done anything to set the pressure higher using an
adj. FPR.

During testing, the car should be fully warmed up, so the EEC strategy you
are in during testing is warm cruise.  If the car is not fully warmed up,
the EEC-IV could be in cold driveaway strategy which causes the EEC to lean
out the mixture to warm the engine as quickly as possible.  Assuming you're
in warm cruise, the EEC-IV computer is trying to keep the air fuel ratio
(AFR) close to stoich. at around 14.7:1.  It does this based on voltage
outputs from the following sensors: mass air flow (MAF), throttle position
sensor (TPS), engine coolant temperature (ECT) sensor, air charge temp (ACT)
sensor, and the O2 sensors.  If the car has EGR, the valve position sensor
is also used.  Each of these sensors can modify what the EEC does.  For
instance, a high coolant temp will cause the engine to run richer and scale
back the spark advance.

It is worth mentioning that you should buy high quality gasoline for the
test.  While the SHO performs better with premium due to the EEC providing
greater spark advance, in this case, I'd try a high quality mid grade, since
premium fuel actually has a lower specific gravity which means the engine is
seeing less fuel by volume.

Does the car throw any codes?  Not all codes cause a check engine light
(CEL/MIL).  If you have a voltmeter or an LED, it's not hard to check the
codes.

If the car has an EGR system, that would be the first thing I'd check and
clean.

If the O2 sensors have over 70,000 miles on them, they should be changed.

I would clean the MAF wire with electronic contact cleaner spray.

Unmetered air leaking into the intake can also cause the car to run lean.
So listen for vacuum leaks.

During testing:
	Make sure the person doing the test is holding the throttle at a constant
RPM during each test period.
	If the car can run the 25 mph in two different gears, select the gear where
the numbers are the lowest.  IOW, look at your test results, and if the
lower NOX numbers ocurr at higher RPMs, see if the person doing the test can
run the 25mph test in 1st, vs 2nd.  If the RPMs go out of range, then
there's not much that can be done, and the car will have to be run in
whatever gear will keep the RPM in range.

 Good luck,
	-- Bob

> -----Original Message-----
> From: Anthony del Busto
> Sent: Sunday, December 18, 2005 5:36 PM
>
> I took my 93 in for the state inpection and couldn't believe that
> it failed.
> It failed the Nox(ppm) on both the high (25mph) and low (15mph) speed
> emission results.  Am I correct to assume that the engine is not
> burning the
> fueling efficiently?  Back in October I replaced the original
> fuel pump with
> a new 155 ltr/hr fuel pump.  Could this be the culprit?  Should I intall
> check the fuel pressure and install a fuel regulator if pressure too high?
> New wires and plugs (all Ford OEM) recently installed as well.  Please
> advise.
>
> Tony
> 93 mtx (stock)
> 122k
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