Walker Support

Exhaust 101

Inspections

Inspection of the exhaust system is recommended whenever a vehicle is in for service and there is a ready opportunity for a quick look (i.e., the vehicle is up on a hoist). The basic inspection is to see if there is deterioration of any exhaust system components. Deterioration may not always be obvious, such as through the appearance of holes and flaking rust, so close inspection is necessary.

The most general way of determining deterioration of the basic exhaust parts (pipes, muffler[s], resonator[ s], brackets, clamps and hangers), is to visually look at them, and also to tap them with a small metal ball peen hammer or similar tool. The sound of solid metal should be heard in the pipes, and the muffler(s) and resonator(s) should have a solid sound, without rattles, or excessively flaking metal.

Other areas to look at include:

• Joints and welds where pinholes sometimes develop, indicating the early signs of system deterioration.
• Heat shields - these often come loose as noticeable by their rattling.
• Black carbon deposits - indicating spots where exhaust is escaping.

Finding a system that is nearing failure provides the opportunity for business and, at minimum, gives the customer a "heads up" that may influence their decision as to where the eventual exhaust system repairs will be made.

TROUBLESHOOTING AN EXHAUST SYSTEM

Customer complaints about vehicle performance may include a "no start" condition, poor fuel economy, sluggish acceleration, off-idle hesitation or power loss at around 50 miles per hour. Quite often an engine will start and idle in a normal manner when the exhaust is restricted. Once the throttle is opened, the excess backpressure caused by the restriction prevents normal engine operation. The converter may have a melted substrate and/ or is clogged. Before replacing the converter further tests are required.

Raw fuel can cause a converter to overheat and meltdown. An overheated converter is usually caused by an air/fuel mixture or ignition problem. Diagnostic tests are required. Engine problems must be corrected before the converter is replaced.

When an engine is cold, most cars produce an odor that's characteristic of hydrogen sulfide or rotten eggs. If the odor persists after warm-up, the most likely culprits are a misadjusted air/fuel ratio and/or stuck choke, choke pulloff valve, heat riser valve. Failure to fix an underlying engine problem could lead to converter over-heating and substrate meltdown, if it has not already occurred. Inappropriate catalyst loading on the O.E. converter could also be the problem.

• Ford had this problem on Taurus and Sable vehicles.
• Incorrectly specified PROM (Programmable Read Only Memory) chips in engine computers created odor problems for GM.

If either situation occurs, it is likely to be a car dealer warranty problem.

Converter failure before 50,000 miles is most likely a symptom of another problem. Failure of an OE converter is usually due to an out -of-spec condition in the engine, which introduces an overly rich mixture of exhaust gases into the converter. It is critical, therefore, that before any of the tests can be considered conclusive, the vehicle engine must be properly tuned and all emission control devices in working order! Before performing any emissions tests, it is also important that the vehicle engine is warmed-up to running temperature. This requires running the vehicle for 15 to 20 minutes with its heater turned "off": this is especially critical in cold weather and on four- cylinder vehicles.

It is also important to remember that simple failure of an emissions test is not grounds to replace the converter without establishing "legitimate need".

GENERAL INSPECTION OF AN EXHAUST SYSTEM

Inspect components for deteriorated or broken welds, cracked joints and corrosion damage. Be aware that damage or deterioration in these areas could allow exhaust fumes to enter the passenger compartment of the vehicle. Inspect:

• Exhaust pipes
• Exhaust gaskets and seals
• Catalytic converter(s)
• Muffler(s)
• Resonator(s)
• Tail pipe(s)
• Hanger or brackets

Inspect the exhaust system for any of the following concerns that could cause poor sound quality or vibration:

• Leaking joints, seals, or components
• Binding of components
• Grounding (metal to metal contact between the exhaust system and other vehicle components)
• Excessive vibration or movement of the exhaust system
• Torqued or twisted exhaust system hangers or brackets

Grounding can be a major concern to driver and passenger comfort. Check the system for the following conditions in the event a grounding concern is evident:

• Loose or damaged pipes
• Loose or damaged clamps and brackets
• Loose or damaged heat shields
• Loose or damaged exhaust seals/connections
• Loose or damaged flange bolts

Be aware that alignment of components is critical to proper exhaust system operation. There should be no excess stress or pull on mounting hardware when the exhaust system and vehicle are in their at-rest position.

Lightly tap the converter with a rubber mallet or thump it with a properly gloved hand. Use Caution: Remember the unit may be hot! Use a heat resistant glove for protection.

On a properly functioning monolithic or honeycomb converter, the sound should be a solid thump. If you hear rattling noises or banging around, it possibly means that the substrate ha broken-up. The unit will have to be removed and visually inspected to confirm this problem.

Check that the noise is not the result of loose shields or other loose components in the exhaust system. If you confirm that the substrate has broken-up, check pipes and muffler for loose pieces which may have become lodged in these components.

SIMPLE EXHAUST DIAGNOSTIC TESTS

Pyrometer Heat Differential Test

The conversion process produces heat. So, exhaust gases entering the converter should be cooler than the gases exiting the converter.

The heat differential test measures the surface temperature at the inlet and outlet bushings of the converter. If conversion is taking place, then the outlet bushing reading should be higher than the inlet bushing reading.

Different pipe wall thicknesses and corrosion, along with different heat transfer rates, may cause inaccurate results, however. So, the U.S. EPA recommends that this test be used only to prove that a catalyst is good. Make sure that the engine is fully warmed up and running. Make sure the heater is OFF. Using a pyrometer, read and note the temperature of the pipe just ahead of the converter inlet. Read and note the temperature at the outlet pipe. Calculate the difference between your readings. If the outlet reading is higher than the inlet reading, you can be assured that at least some conversion is taking place. On well-tuned, newer vehicles, the catalyst can be fully functional at only a 20° difference.

An excessive heat differential of more than 5000 F, is an indicator that there's an excessively rich fuel mixture in the exhaust stream. This can cause excessive heat in the converter and result in substrate damage or meltdown.

Check the vehicle's fuel system for out-of-spec conditions. After fuel system repairs or adjustments are made, recheck the converter with the pyrometer. If both readings are nearly identical or the outlet is cooler than the inlet, rapid oxidation may not be occurring. You should check that the Air Injection Reactor or Thermactor is operating properly. The converter may simply not be receiving enough air to support oxidation.

Engine Vacuum Test

The intent of the vacuum test is to determine if there is a blockage or restriction in the exhaust system. It may or may not indicate converter problems.

Ideal backpressure levels vary from one application to another. Different size engines have different flow rates and so do their exhaust systems. Check manufacturer specifications. Readings also depend slightly on where in the exhaust system they are taken. This test can be performed using any suitable engine vacuum source, including the carburetor, intake or injection manifolds. After the pressure gauge is connected to a vacuum source, readings are noted at a variety of engine speeds.

To perform the vacuum test at the intake manifold, start with the engine off, and disable the EGR valve by removing or disconnecting its hose or one of its solenoids. Connect the pressure gauge to the manifold and take an idle reading with the transmission in neutral. Turn off the engine and disable the EGR valve by disconnecting its vacuum hose. Plug the hose. With the transmission in neutral, take another reading at 2500 to 3000 RPM. Read at variety of other engine speeds.

To perform the vacuum test at the injection manifold, start with the engine cool, and remove the air injection check valve. Connect a rubber adapter cone to the check valve connection. Then, connect gauge hose to the adapter.

As engine speeds vary, readings should initially drop slightly, then rise to within 2 to 3 inches of the vacuum level established at idle. Any sudden drop of over 10 inches of vacuum may indicate a blockage problem. Erratic swings of the vacuum indicator may indicate periodic blockages caused by loose components temporarily blocking the exhaust system.

Remember that vacuum levels are also affected by factors other than exhaust system restriction, including valve and ignition timing.

Inlet Backpressure Test

These tests are used to determine if blockages exist in the converter that is creating excessive backpressure. They can also be used to determine blockages or restrictions in a muffler or other exhaust system components.

Inlet backpressure can be read either at the O2 sensor or at the pipe just ahead of the converter inlet. To connect the pressure gauge at the O2 sensor hole, start with the engine off, and carefully remove the sensor. (penetrating oil and a rocking motion may help).

All O₂ sensors use an 18mm-thread hole, so one adapter fits all applications. Install adapter in the hole and tighten to manufacturer specifications. Then connect the gauge hose to the adapter.

To connect the pressure gauge at the inlet pipe, start by drilling or punching a small hole into the pipe in front of the converter. Caution: DO NOT punch or drill a hole in the converter body! Attach pressure gauge to the pipe by a self-tapping hollow nipple or hollow tapered metal tip.

To perform the inlet backpressure test, begin by reading and taking note of pressure at idle and at full throttle "goose" or 3000 RPM. After taking an inlet measurement, install the O2 sensor; or plug the pipe hole with a self-tapping screw-in plug or weld.

At idle, the gauge should read zero inches of pressure. During the momentary full throttle, pressure should not exceed 4 PSI. If the gauge reads 5-6 PSI, at full throttle, blockage probably exists down stream of the test point. If blockage is indicated, use the Outlet Backpressure Test to isolate the blockage point.

Outlet Backpressure Test

Drill or punch a small hole in the outlet side of the converter. Attach the gauge to this outlet port. Run the engine at 3000 RPM or full throttle "goose" and note pressure reading. After completing the test plug the outlet test hole. Pressure drops from the inlet readings greater than two PSI indicate that blockage is probable within the converter.

"Sniff" Test

This test measures the levels of HC, CO, CO2 and O2 gases coming out of the tail pipe. Using this data, you can isolate problems under the hood and under the vehicle.

State EPAs do regulate which analyzers may be used in the repair and testing of vehicles within their jurisdiction. They may also limit what kinds of problems an analyzer can be used to diagnose and how it is calibrated.

Both the analyzer and vehicle need to be warmed up for about 20 minutes. Make sure vehicle is at operating temperature.

Excessively rich mixtures are beyond the capability of the catalyst to convert. Even if the converter is working to specifications, measurable levels of pollution will be noted at the tail pipe under these conditions. The validity of this test to isolate a converter problem depends on a properly tuned and operating engine. Fortunately, a gas analyzer can first be used to locate engine problems.

Following manufacturer's instructions connect analyzer to exhaust pipe. With the choke wide open, idle and timing set, read and note the levels of Oxygen, Carbon Dioxide, Hydrocarbons and Carbon Monoxide produced by the vehicle.

Compare your data with the Primary Causes of High Gas Levels, listed below. The chart will help isolate engine emissions control problems. There may be more than one engine related problem, in addition to a failed converter.

Primary Causes of High Gas Levels

HIGH HC LEVELS	HIGH CO LEVELS
Needle and seat leaking Broken spark plug wire Vacuum leak, resulting in lean misfire Float level out-of-spec Fuel mixture too rich Cracked distributor cap Worn rings - low compression Fouled plug Bad valves or damaged Converter malfunction	Low idle speed Inoperative air pump Clogged air cleaner Clogged PCV valve Out-of-spec choke Idle mixture out-of-spec Carburetor malfunction Converter malfunction Other emissions device worn

After you've made sure that the engine is properly tuned and again running at operating temperature, record the levels of all four gases. If CO levels are high when the engine is in tune, then the converter probably needs to be replaced. Higher than normal HC levels mean that the converter may have to be replaced. A pyrometer test should be done to confirm the need.

INSTALLATION PROBLEMS

1. Verify the application in the catalog. Do not overlook any footnotes that will influence installation.
2. Intermingling of competitor's parts could cause a system to not fit the application properly. The reason for this is that many OE exhaust systems leave the factory as a single welded unit - there are no breaks in the system. For aftermarket purposes, this type of exhaust system is sometimes impractical. To make installation easier for the installer, aftermarket manufacturers produce replacement parts in smaller pieces that are easier to handle and install. Not all exhaust system manufacturers break the OE system at the same points. This difference in connection points sometimes creates complications when mixing aftermarket components from a variety of manufacturers.
3. Always check parts for damage before installing them. Sometimes parts are damaged during shipment. Minor handling damage to pipe ends or muffler bushings can be easily repaired with tools available in the Walker® product line.
4. If a new part is being used with existing parts in the system, make sure the old parts are in good condition. A broken pipe end could cause the system to be too short.
5. If the muffler and pipe were originally welded assemblies, and the catalog does not recommend replacing both parts together, be certain the cut-off was made within one-half (1/2) inch of the weld.
6. Make certain that the vehicle has not been modified in any manner that would void the catalog listing. A frequent example of this are engine swaps, header installations, etc.
7. Is the part designed in such a manner that the inlet end can be confused with the outlet and the part could be installed backwards? Most Walker mufflers are marked to designate the outlet end and it is easy to see if the muffler is positioned correctly.
8. Is the muffler rotation correct? Many mufflers can be installed 180 degrees rotationally incorrect, causing fit problems with the rest of the system.
9. Check the silhouette of the vehicle. Does the exhaust system hang too low? The top of the exhaust pipe should not be visible when viewing the vehicle from the side.
   CAUTION: MINIMUM CLEARANCE FOR ANY PART OF THE MUFFLER TO THE UNDERBODY OF THE VEHICLE SHOULD NOT BE LESS THAN ONE (1) INCH.
10. When a heavy-duty clamp is required, the clamp should be torque down to approximately 40 foot-pounds to ensure a tight seal. If the seal is not airtight, loosen the clamp, rotate it 180 degrees and then tighten it again.

EXCESSIVE NOISE

1. Ensure application matches the catalog listing - year, make, model, engine - and that all pertinent footnotes have been considered.
2. Do not accept "broad" application information in the catalog listing header. When receiving a noise complaint, obtain the exact model, make, year and engine information.
3. Note catalog listing or bulletins to see if any of the parts have been superseded. In the catalog, these are noted with an "or" listing. The alternative part may have better acoustical performance.
4. If possible, a record of exhaust system complaints and solutions should be maintained to determine if the problem is really with the part, or if the specific vehicle or installation procedure could be at fault.
5. Ensure that part numbers have not been transposed.
6. If possible, place your hand on the tail pipe and try to move the system from side to side, and up and down, to determine if the system is hung securely and not grounding or touching the under-body of the vehicle.
7. In the case of a noise complaint, start the engine in an open area and allow it to warm up. Once the engine reaches operating temperature, listen to the exhaust noise and decide whether or not you agree with the customer's complaint.
8. If the noise is a popping sound at the tail pipe end, check under the hood and determine if the engine is equipped with an Air Injection Reaction (A.I.R.) pump. If an A.I.R. pump is present, disconnect the belt from the pump. If the noise ceases, the valve in the pump is faulty and should be replaced. If the vehicle is not equipped with an A.I.R. pump, the problem could be in the engine. A compression test should be made.
9. Should further investigation be required, place the vehicle on a lift, raise the vehicle, and inspect the exhaust installation. Check for the following:
   • Grounding
   • Broken hangers and insulators
   • Loose/leaking joints
   • Muffler and resonator installed backwards
   • Missing converter
   • Resonator substitute pipe in use
   • Worn out heat riser
   • Engine with faulty timing
   • Use of an "economy" or performance muffler
   • Alterations to the original installation

All of these conditions can lead to complaints concerning excessive exhaust system noise.