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95 Safari W failed emissions high HC and high NOx no codes


mallenfam
06-09-2010, 04:24 PM
Failed Colorado emissions test for the first time ever (tested every two years). High HC and NOx twice legal limit. Code reader threw no flags, just standard 12 code indicating proper function.

3 years ago (16k miles ago, now total milage is 121k) installed AC-Delco Professional Platinum 41-803 plugs, wires, cap, rotor. Replaced fuel pump with AC-Delco unit <10k miles ago.

Seems to run fine, but sometimes seems a little slow to fire up. Found that tube at evaporator cannister connection (engine side) had rotted, so replaced it hoping that was the culprit, but failed test again. Haven't pulled engine housing to inspect rear of engine yet (daughter who drives the van is bringing it over tonight).

Suggestions on what to look for please -- thank you!

mallenfam
06-10-2010, 01:37 PM
Additional info: the rotten purge cannister hose looks to be on the gas tank connection, not the upstream engine side, so probably did not cause a vacuum leak contributing to the first emissions test failure.

The emissions test is performed on rollers where the vehicle is "driven" by a technician following a predetermined varying speed profile for a 4-minute period.

The HC plot over the 4-minute period has weird rate spikes about every 15 seconds that don't seem clearly connected to the test speed parameters or the graph on how a "normal" vehicle should perform.

The NOx is only about 25% above limit, a bit spikey, but somewhat related to how a "normal" vehicle should perform.

The CO2 level is fine and acts like the normal vehicle would.

The CO level is a bit high (but passes) and is also strangely spikey during the test run.

mallenfam
06-10-2010, 01:57 PM
One more point (perhaps the smoking gun?):

This van has a slight intake manifold leak to the cooling system as confirmed by a Used Oil Analysis and the fact that a small amount of coolant is steadily consumed (perhaps 1 or 2 ounces per 1000 miles). This has existed for several years, but since this is an old vehicle that only sees a few thousand miles per year and is hard to work on, I had just kept the oil changed usually every 2000 miles. However, it went about 4000 miles this time immediately preceeding the emissions test.

Could the coolant leak have significantly reduced the effectiveness of the catalytic converter? Can anything be done to rejuvinate the catalytic converter or must it be replaced?

old_master
06-10-2010, 05:09 PM
Without seeing the actual numbers, (it's only an educated guess) the catalytic converter is failing, or has failed.

CO2 is an excellent indicator to determine if the air fuel mixture is where it should be.
HC is unburned fuel and NOx is a normal result of EGR operation. The catalytic converter is designed to reduce both HC and NOx.

The small coolant consumption you've indicated will not harm the converter if in fact it's being burned. Usually when the lower intake manifold gasket leaks coolant, it will leak externally or internally into the oil, not into an intake runner. As far as rejuvinating a converter, no, it must be replaced if it's faulty.

The code reader will not show a code for a faulty converter. Your vehicle is equpiied with OBDI and does not have the capability to monitor converter performance. Probably be a good idea to have a competent technician, with the proper test equipment, check it out before throwing big money into a converter. Keep us posted.

mallenfam
06-23-2010, 02:10 PM
The over-limit NOx (something like 4.9, i don't remember if the units were grams per ...), HC (about 4.0), and somewhat elevated CO (but normal CO2) led me to believe that the catalytic converter was the most likely culprit.

I found a shop that welded in a new cat for only $180 total. Although they predicted before doing the work that the small, but longterm, coolant consumption had poisoned the cat, they found that the cat internals had nearly all disintegrated away.

I then immediately drove it for 30 minutes out to the emissions test facility and crossed my fingers that (1) the cat was the problem and (2) that the new cat would be adequately functional in such a short period of driving.

Success - NOx, HC, and CO were all down by a factor of 4 and the vehicle passed.

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