Fiero Emission Control

Notice! It is a violation of U.S. Federal law to remove, modify or disable emission control devices. Some states, like California, have laws above and beyond Federal regulations.
Fiero has very little in the way of emission control hardware. There is only the catalytic converter, EGR valve and a fuel vapor recovery canister. None of which require rocket science to fix. (In California nearly all parts of the engine are regulated. Make sure any aftermarket parts you install meet CARB requirements.) There’s also the PCV system. Almost forgot that one.

Catalytic Converter

The catalyst is used to burn off excess fuel and oil that escapes normal combustion. The catalyst usually fails in one of 2 ways. It either disintegrates or gets plugged up with soot. In extreme cases the guts can melt. (Usually if it disintegrates it blocks up the exit port.) The catalyst needs to be replaced when it fails. You can’t fix it.
You want to know which way it failed. If it fell apart then you can likely just replace it but if it’s blocked up with carbon or melted then try to find out why before you install a new one. If the motor is running rich, burning oil, or leaking coolant then these problems must be fixed before the new catalyst is installed otherwise you’ll wreck the new one in short order.
A quick way to test the catalyst is to measure backpressure at the O2 sensor port. According the June 2001 issue of Motor…
With the engine idling, the pressure will usually be below 1 psi on a good system.
Backpressure reading over 1.5 psi is cause for concern. Next, bring the rpm to 2000 and check the pressure again. A good system will usually show less than 2 psi. If the pressure is over 3 psi, the catalyst is most likely going south.
Of course most people don’t have the fancy commercial one of these lying around, but they can be made. You’ll want to use some metal or high temperature flexible tubing to keep the gauge away from the worst heat. You also want a gauge made for low pressure, something with a 5-10psi top end.
You can use an old O2 sensor or spark plug to fabricate the exhaust fitting.
If the catalyst croaks… Once the catalyst is off make sure it hasn’t blown its cookies down the exhaust pipe. With Fiero’s exhaust setup, you can probably suck the stuff back out of the muffler with a shop vac. (Empty the vacuum before starting so you can tell what came out of the exhaust.) If you don’t check for this you could fry the new catalyst. At the very least the exhaust will still be restricted and likely hurt performance.
Many people think the catalyst does nothing but rob performance. Once upon a time this may have been true but today’s high flow catalyst units present very little restriction of exhaust flow. In the vast majority of cases you gain nearly the same performance increase with a new catalyst as having a straight pipe.
·     A straight pipe may give a HP increase but can reduce low-end torque in many engines.
· A straight pipe on an engine with backpressure EGR may also cause odd problems. These engines must have some backpressure to operate properly.
It is illegal in some places to put used catalysts in the trash. Even when it isn’t illegal try to dispose of it at a muffler repair shop or some other place that will send them to be recycled. (They recycle both the metal and the catalyst material.)


Note! An altered or defective exhaust system can screw up operation of the EGR valve on the L4. How much depends on the specific alteration or defect.
The EGR, Exhaust Gas Recirculation, valve is used to limit emissions and to prevent engine knock. On V6 the valve is ECM controlled but on the L4 it is operated by a combination of engine vacuum and exhaust back pressure.
There’s not much to go wrong with the valve. It can jam or leak which is usually caused by carbon and rust in the valve base. The diaphragm that moves the valve can deteriorate and leak. That’s about it. (In one odd case, I had the return spring or something in the vacuum chamber broke.)
You have to watch that the valve is connected to the right vacuum source. That information is on the VECI, Vehicle Emission Control Information, label on the deck lid. Hooking it up wrong can make it open at the wrong time or not at all.
The main problems with this valve on the V6 are that the valve plumbing likes to crack and the ECM control solenoid likes to get trash in it. The cracks of course hurt engine performance, if the car even runs with these vacuum leaks.
The control solenoid can sometimes be cleaned but you have to watch what you clean it with. You want a plastic friendly solvent that leaves no residue or lubricant behind to collect more dirt.
If you suspect EGR valve problems, take it off and inspect it. The gasket for the L4 valve is only about $1.00. I imagine the V6 one is about the same. (FelPro gaskets…) Always install a new gasket if you remove the EGR. A small exhaust or vacuum leak can cause major hair pulling…
Carbon or corrosion on the valve can hang the valve open or shut. You may be able to clean carbon off with EFI system or Carburetor cleaner. Corrosion will usually mean valve replacement.
Shake the valve. Noise is bad… Nothing in it should rattle.
Push the diaphragm up. You may have to carefully use a tool of some type. (A stick of Plastic or Wood is probably safer than metal.) Does it move smoothly and return to the closed position by itself? If not the valve probably needs replacement.

When does EGR open?

That depends on the EGR in question. I can tell you when it should definitely NOT open. It should not be open at idle or at WOT. Otherwise… On the ECM controlled ones it will open whenever the ECM is programmed to open it.
On backpressure ones, like the Fiero stock 4 cyl, it will open at certain combinations of vacuum and exhaust pressure. Exactly when those conditions will be met is hard to say. It will vary based on the condition and configuration of your car and you driving habits.

Service Warning!

Many replacement EGR valves are of the universal type and come with metering washers that are affixed to the valve prior to installation on the car.
These washers MUST be staked in place. Do not depend on the gasket to hold them. If the washer comes loose it will screw up the metering allowing more exhaust gas flow than it’s supposed to. The washer could even fall into the motor and cause major damage.
To stake them down place a punch or the corner of a chisel in the base of the EGR valve next to the washer seat. Hit the punch to dent the valve base and force metal toward the washer. Do this in at least 3 locations around the washer.
Record the number of the original valve to both the sticker included with the valve and a permanent location on the vehicle or in some other place you can find it again. The label often fades. You’ll need the number if you ever have to replace it again.
To select the correct washer you need the code stamped into the OE EGR shell…

Fuel Vapor Canister

The Fuel Vapor can is a little confusing for many people. It is simply a can of charcoal with a vacuum controlled air vent stuck on it. The emission control purpose of the canister is of course to prevent fuel vapor from leaving the gas tank but it also saves you money if it works right. Fuel that evaporates from your tank costs money and gives nothing in return. The canister catches this fuel and lets the car use it. It’s a small amount at any one time but over the life of a car it can really add up especially in hot climates. A canister that is working right will not hurt performance and will add ever so slightly to your MPG.
The Canister Purge uses two vacuum lines. The large one goes to manifold vacuum and carries the fuel vapor into the engine to be burned. The small one is the control line and goes to a port on the throttle body that opens upstream of the throttle butterfly. When the throttle opens beyond a certain range the purge control valve opens and allows manifold vacuum to draw the vapor from the can.
The only maintenance the canister needs is periodic checking of the vacuum lines and filter. There is a floss filter on the bottom to trap large dirt from entering the can and plugging it up. That filter needs to be kept clear of major trash and should be replaced once in awhile or when damaged. (The filter costs
about a dollar at Wal-Mart.)
There are only a couple things that can go wrong with the canister. It can be damaged by cracking the thing or by over filling the gas tank. “Topping off” the gas tank can force fuel up the vent line into the can and ruin it. While the fuel pump nozzle is supposed to shut off when the tank is full, they are often bad and can pressurize the fuel tank enough to force fuel up the vent. Certain types of “Vapor Recovery” nozzles are great for this.
The purge control valve can fail or its line can be connected to the engine wrong. Either can cause problems. The routing of these lines is also on the VECI label.
The fastest way to test for drivability problems caused by the vapor can is to disconnect and block both vacuum lines. If the problem stops, the vapor can is bad.

How does the canister work?

This explanation is based on an article from Motor Magazine or Motor Age that I can’t find anymore…
The canister is filled with high-grade charcoal similar to a gas mask. When fuel vapors expand out of the fuel tank, they cling to the surface of the charcoal.
The important thing here is that fumes don’t soak into the charcoal grains like most people think. This “small” fact is what makes the whole canister possible.
When the canister is purged fresh air is sucked thru the canister, which knocks the fuel molecules off the charcoal and caries them into the engine. Canister purge in older cars, including Fiero, is usually controlled by a ported vacuum signal from the carburetor or throttle body. In many newer vehicles the canister purge is controlled by the ECM/PCM.
If liquid fuel gets into the canister it will soak into the charcoal just like lighter fluid does in your grill. Once that happens the charcoal is ruined. Even if you could dry out the liquid fuel, the carbon won’t recover.

PCV system

The Positive Crankcase Ventilation system is both an emission control and a significant improvement to engine longevity. The job of the PCV system is to remove fumes from the crankcase and burn them. These fumes pollute the air and if not extracted from the engine they promote contamination of the oil and varnish on internal parts.
There are 2 major parts in the system, an air filter, and the PCV valve. Make sure both are clean and that the vacuum line(s) and vent hose are sealed.
The PCV valve should be replaced every couple years at most. There is a spring in the valve that is critical to proper operation. The spring will weaken over time. A bad PCV valve is hard to detect. The obvious test of shaking it only tells you it’s not stuck closed. It won’t tell you the spring is weak.
Make sure you clamp all the joints in the PCV line. The rubber parts can’t be trusted to seal themselves. Don’t over tighten the clamps or you will damage the soft parts.

Emissions Service Parts

Note: Be careful buying PCV parts for the 87-88 4 cylinder motors! Many parts books incorrectly list them as using the same parts as the older 4 cylinder engines. Double-check them against Grand Am or Olds Cutlass Calais of the same years.
I had a heck of a time finding the correct PCV filter for my DIS motor until I looked it up under the Olds line. I’ve noticed some parts catalogs also list ignition parts wrong as well.
This is a quick list of stuff I’ve seen listed and where. I’ve seen AC Delco emissions parts for DIS 4 at Parts America. I imagine they cover other years but I didn’t feel like checking them all. (I think the same vapor can is used in all Fiero.)
The part numbers for the DIS motor parts…

As far as I can tell, the AC EGR is an OE matched unit. (At least that’s the picture they have on their web site.)
GM Parts Direct lists the Vapor Canister for about $25. (Use GM # 17075840)
They don’t have the EGR valve.
No AC Delco part was listed for the one V6 I looked up. (86 GT) Because the V6 valve is ECM controlled it’s not as critical who made it as long as the new part is high quality and provides the correct gas volume.
If you can’t find a stamping number to use for universal EGR’s, try using the information listed with Niehoff Ignition’s parts. Here’s the info they list on Parts America for an 86 GT with their part # FE134A valve. (I’ve never use Niehoff stuff but there catalog info is handy. They are the only one I’ve seen so far that lists data like this.)
[E. G. R. Valve] OE Number 17085897; Orifice Number 11; Use EGR Valve Gasket {FE302}; Use EGR Tube Gasket {FE354}
Notice the OE stamping number above. You could use that bit of info for any universal EGR. (The one you have may use the same metering washer or a different one. Get that info from the chart that comes with the new EGR.)
The V6 EGR solenoid I found listed under “Vacuum Regulator Valve” in the Fuel Injection parts. Parts America says it usually ships in 5 business days.
AC DELCO 214-361 $102.99 [EGR Vacuum Regulator Solenoid Valve] GT, SE Listing
Everyone who’s got them likes Rodney Dickman’s catalyst kit. It has the needed stainless steel adaptors needed for installation.


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