Emissions test from hell . . .

[gale]

So last Sunday I took the wife's m50 for the mandatory bi-annual emissions test. I took it out on the interstate & got it good & hot. It passed the tailpipe emissions but flunked the gas cap vacuum test. Then the b*tch (car) overheated when driving home to swap gas caps from my e32.

I never made it back for a re-test that day but instead, removed the thermostat and waterpump for inspection -- spun the plastic waterpump impeller on the shaft and the thermostat wouldn't open until 12 degrees F hotter than it was supposed to.

AutohausAZ came thru with new parts in short order. Installed a new waterpump with a metal impeller, and new thermostat & aluminum t-stat housing for good measure. Got a new gas cap too.

Back to re-test: gas cap passes, tailpipe emissions flunked, barely passed at high speed, idle failed hydrocarbons -- WTF???

3rd try: New spark plugs, fresh oil change and new air filter, did a "Shogun re-set" (disconnect the DME for 10-15 seconds). Go back to the emissions place for a re-test and this time it passes fine.

The car runs great now, better than it ever has. Temp needle is straight up 12:00 o'clock, idles smooth, has more pull.

Thoughts:

I'm thinking that when it overheated and threw a 1223 DME temp sensor code, that it must have gone open-loop and caused it to fail emissions the 2nd time and clearing the DME fixed that. I took the temp sensor out and it was well within spec at both ends of the temperature range, about 320 ohms at 180F & Bentleys says 270-400 is where is should be.

1. For anyone with a newly acquired m50, check your water pump. The original factory impellers were plastic up until 95 or 96. Throw it away and put a metal one in. Get a cast aluminum thermostat housing while you're at it, to replace the plastic one that will fail one day.

2. Do a "Shogun reset" before getting an emissions test.

3. Keep a spare gas cap in the glove box when getting an emissions test.

[Hector]

For the HC and CO categories, my car passed with pretty wide margins but barely passed in the NOX category.

[Ross]

I'm in agreement with your thoughts on the retest.
If it makes you feel better consider that one of my cars flunked a gas cap test. I flipped the gasket over on the cap and had the "technician" retest it and it was satisfactory but the pinhead refused to pass the car as the "cap" hadn't been replaced. I nearly strangled the moron.

[winfred]

should of said let me check the glove box for the "other cap"

I'm in agreement with your thoughts on the retest.
If it makes you feel better consider that one of my cars flunked a gas cap test. I flipped the gasket over on the cap and had the "technician" retest it and it was satisfactory but the pinhead refused to pass the car as the "cap" hadn't been replaced. I nearly strangled the moron.

[Barney Paull-Edwards]

Whats a "gas cap test" and how do they test it?

[dacoyote]

Whats a "gas cap test" and how do they test it?

They are testing to see if the gas cap holds pressure...

[Mordan]

They are testing to see if the gas cap holds pressure...

Curious, how do test THAT? I never heard of this on the continent (europe)

oh yea! you remove the cap and use a special pressure-test device ?

[dacoyote]

Curious, how do test THAT? I never heard of this on the continent (europe)

oh yea! you remove the cap and use a special pressure-test device ?

It depends on the state... some states take it off and test it.. other states put a big vacuum hose around it...

[Ross]

It is an evaporative emission test. If the seal for the cap is NG the evap. system is nonfunctional.

[attack eagle]

around here if the cap is attached to the car and they don't want to move the test computer, they "test" the cap by reusing the test cap from the machine.

In 6 years I have only had a cap tested once on one car.