Ontario emission test, FLUNKED, then PASSED, then PASSED again, WHY?

This car flunked the Prov. of Ontario's Drive Clean Test (ASM2525 test)
and then passed it 12 minutes later, and then passed it again 12 minutes
later. The only difference was the gear that the car was operated in. In
the first test the car was operated in 3RD gear (1800 RPM), and in the 2
following tests the car was operated in 2ND gear (2700 RPM). The ASM2525
does tests at 40KPH (25MPH).

Why did 2ND gear make the difference?

The problem area in the first test was NOx.

The details:

1987 Honda Accord S (Hatchback), 5 Speed, carburettor. Manufactured in
Japan. 1987 CANADIAN Emission Specs. (less emission components than
similar USA market 1987 Accords).

The fuel in the car was premium grade gas. The EGR valve had been serviced
in previous week (minor deposits cleaned out). The ignition timing was 2.5
degrees retarded from the retarded range of the spec. (timing spec. as per
hood label, 20 degrees BTDC plus or minus 2 degrees, both hot advance and
cold advance hoses connected, at 750 RPM). The timing was 15.5 degrees.

The speculation was that the cat was hotter during the second and third
test. The car has the original (simple) cat. It is unknown whether the
original cat is a reduction cat.

Another speculation was that there was more EGR flow at the higher RPM.
The car was road tested later with a MityVac tee'd into the the EGR vacuum
signal. The EGR pintle has approximately 0.50 inch full lift (0.50 inch is
more of a guess) at 5.50" to 6.00" HG. Repeated road tests showed
2.50",2.70" HG at 1800 RPM, 3RD gear (40 KMH, 25 MPH), and 2.90",3.05" HG
at 2700 RPM, 2ND gear (40 KMH, 25 MPH). A higher vacuum signal was there
at higher RPM's (although only slightly).

TEST NUMBER ONE (3rd gear)

40 KMH(25 MPH)
HC ppm limit 130 Reading 45 result PASS
CO% limit 0.73 Reading 0.03 result PASS
NOx ppm limit 1482 Reading 2084 result FAIL
RPM Reading 1826 result VALID
Dilution 13.23 result VALID

CURB IDLE
HC ppm limit 300 Reading 40 result PASS
CO% limit 1.5 Reading 0.00 result PASS
NOx not tested at Curb Idle
RPM Reading 798 result VALID
Dilution Reading 12.70 result VALID

TEST NUMBER TWO (2nd gear)

Lost the results... they were similar to test number three

TEST NUMBER THREE (2nd gear)

40 KMH(25MPH)
HC ppm limit 130 Reading 33 result PASS
CO% limit 0.73 Reading 0.03 result PASS
NOx ppm limit 1482 Reading 1069 result PASS
RPM Reading 2721 result VALID
Dilution 12.62 result VALID

CURB IDLE
HC ppm limit 300 Reading 39 result PASS
CO% limit 1.5 Reading 0.00 result PASS
NOx not tested at Curb Idle
RPM Reading 748 result VALID
Dilution Reading 12.30 result VALID

Note: ppm = Parts Per Million

Any ideas?

M.A. Stewart

P.S. Please don't reply by e-mail to cf005... the spam filter bounces all
incoming e-mails.

 

it was lugging the engine. not good for vacuum operated stuff, like EGR