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Aug 10, 2009, 1:10 AM

Post #1 of 3 (7602 views)
vehicle inspection Sign In

1994 buick regal 3.1 liter 124,000 miles has problem passing hydrocarbon part of inspection. 220ppm is acceptable. i am now at 393.ppm. i went to inspection and passed co because i put a new oxygen sensor on. i failed the hc with a 238ppm at this time. i had new plugs put in the platinem kind. went back through inspection and failed with a275ppm. i drove it on the expressway and went back another day it failed with 320ppm. i next changed the thermostat. drove it to ispection left car running in line for about an hour before my turn came failed with 329ppm. went back 2 days later and shut the car off every two cars and starteed up about three cars before my turn for inspection and this time it went up to354ppm. my next step is to buy a cat.converter or egr valve or what running out of money soon. i changed oil and filter and this did not help.

(This post was edited by nightwork on Aug 10, 2009, 3:07 AM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 10, 2009, 2:26 AM

Post #2 of 3 (7599 views)
Re: vehicle inspection Sign In

If you continue just throwing parts at it, then you will run out of money.
HC is unburned fuel so you can put all the Catalytic Converters that you want and it still won't pass. Try a coupls simple things first.

Change the engine oil. It gets raw gas dilution and will cause High HC

Ignition misfire is a common cause so make sure the ignition wires are in real good shape. If they have over 50K on them, then replace them.

Make sure the engine is reaching full operating temp and it has the correct thermostat.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Veteran / Moderator
DanD profile image

Aug 10, 2009, 6:34 AM

Post #3 of 3 (7585 views)
Re: vehicle inspection Sign In

All good points Hammer Time.

High levels of hydrocarbons could also be due to a small continual amount of burning engine oil. I’m not talking billowing blue smoke or even a measurable amount of oil missing on the dipstick; but enough oil consumption; that along with the normal amount being produced during combustion; could cause your car to fail.

Allowing your vehicle to run, while waiting for your turn on the machine; is likely one of the worst things to do. As long as the temp gauge is in the normal area and if the test center that is performing the test; are doing it properly; they will (or are suppose too) precondition the vehicle before testing. In other words making sure the engine and converter is up to operating temperature. All the machines I’ve used, give the inspector an option of performing a conditioning cycle as the inspector enters the vehicles information into the machine. This conditioning cycle will run the vehicle up to speed on the dyno for a minute or so to warm things up.

Most any vehicle’s engine (especially 1994 and older models) will begin to load up the exhaust system with emissions due to the low rpm of an idle. The converters will cool off and shut down if idled to long; same goes for the single wire O2 sensors, they will go off line, if the exhaust cools below 450degrees. Once that happens the computer looses its ability of fuel control and will run the engine using a fixed set of values. Likely rich because the computer programming thinks; it has a cold engine to keep running; when in fact it’s only the exhaust system that has cooled. If you still feel the need to keep the engine running; hold the RPM at 1500 rpm plus, just before the inspector gets his hands on your vehicle.

Before you condemn the cat; have it tested by someone that has a gas analyzer. It’s a fairly simple test; drill a 3/16 test port hole in the exhaust pipe in front of the cat (Pre cat). Bring the vehicle up to operating temperature and take a sample of the exhaust gases at the test port. Now plug the test port (self tapping bolt) and take a second gas sample (Post cat) at the tail pipe.
With this math formula; Pre minus Post, divided by Pre, multiplied by 100 will give you the percentage of the converter’s efficiency. Anything below 70% efficient is considered weak and could use replacing.

One last thing; if you’re going to replace the converter; good luck finding an efficient after market replacement. I’ve done a lot of testing on converters and have yet found an aftermarket that was any better then about 75 or 80 % efficient.
An OE converter for this old of a car is pretty expensive; I would suggest a universal converter; the biggest one that you can find, that’ll fit.

The aftermarket converters that are listed and sold as per application; well I believe that it’s not the engineers that decide which goes with what vehicle. It’s the bean counters in the accounting office that decides this. This is just my take on this but; they must look at these converters and say; if this vehicle is running 100% as intended then this much of a converter or converter contents (Platinum Rhodium and Palladium) will do. Where are we ever going to have a piece of machinery that will run 100%, 100% of the time????
The vehicle manufacturers knows that it can’t or doen't happen; look at the size of converters they install at the factory. They are usually twice the size of the aftermarket.

Sorry for the ramble; but I still left out a lot of points I was trying to make.
Good thing EH!!!!!!! LOL


Canadian "EH"

(This post was edited by DanD on Aug 10, 2009, 6:49 AM)


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