INTER-JECT TeamTalk with Leo Karnauchow           
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As part of receiving calls for diagnostic advice from our members to related fuel injection problems there is one I would like to point out which concerns me most of all, as many members spend huge amount of unpaid diagnostic time to track down that elusive engine performance problem.

In most cases they're continental vehicles or fairly late model vehicles fitted with electronic engine management systems and, as such, it's usually the electronic bits that cop the blame.

Well, not so. In fact, in the majority of cases it's the basic principles of the 4-cycle combustion engine that fail, just like they did prior to all those electronic bits fitted years ago.

Intake, compression, power and exhaust --- still the basic ingredients required. One of the basics often overlooked in later model vehicles is the exhaust system. With the introduction of a catalytic converter to motor vehicles, the exhaust system has become a critical part of a vehicle's trouble shooting and diagnostic procedure.

So, let's take a look at some of the more common problems you may encounter, and diagnostic procedures which I have done in the past.

1. Rule ONE. Any non genuine exhaust system fitted to any continental vehicle is suspect to engine performance problem. This is for Diesel, Petrol EFI or K-Jetronic vehicles as they are fitted with specially factory tuned exhaust systems. Only one part of the exhaust system if interchanged with aftermarket non genuine replacement muffler or catalytic converter for example can sacrifice in engine performance.

2. Nature of complaint, when the problem started, what has been done the vehicle and who has done the work. | Please check this for your Diagnostic requirement | Take extreme care if customer has themselves changed the leaking exhaust manifold gasket. An unnoticed back to front fitted or wrong type manifold gasket can block off 1/2 of the exhaust or the intake port and robe engine performance. Check if work has been done lately on those items first as it has revealed many times the cause of performance problems.

3. What you see is definitely not always what you get! Testing catalytic converters for blockages still remains a mystery to some repairers and is the most frequent phone enquires to INTER-JECT's technical helpline.

Most repairers still rely on the "thump" test to see if the converter core has broken up or a visual inspection to detect deterioration of the core. Heat testing to ascertain operating efficiency and back pressure testing to detect blockages requires specialist equipment like the INTER-JECT machine with pressure gauge and sensitive flow meters, which unfortunately exhaust shops don't posses.

This applies to general repairers also and can result in incorrect diagnosis of converter problems. A recent example was when a general repairer was trying to remedy poor performance in a vehicle by tuning with no effect. The converter was suspected and removed for visual inspection.

Looking in either end of the converter the core appeared normal for the vehicle's mileage and light could be seen through both ends. Eventually the vehicle was brought to INTER-JECT attention for performance checks with the LB-291/2F. After all initial basic checks all appears OK. Further test with the equipment for exhaust back pressure indicated extreme high flow off scale and high pressure 35 Kpa (5 psi) with the indication of a blockage within the converter, contradicting the visual test and no lose particles were evident in the converter using the "thump" test method.

Based on the results of the back pressure test, a new converter was fitted and the vehicle performed normally. Believing your own eyes, they must be playing tricks on you!! To reveal this phenomenon, it was only by dissecting the converter case for closer inspection of the core.

The core | link to the picture | actually come apart in the hands due to a fracture that had occurred right through the core. As you can see in the illustration the centre of the core had suffered a meltdown, but still allowed some light to enter the cavity (it looks like an internal white ants nest) in the centre of the core created by the meltdown, giving an illusion that it wasn't blocked.

Without an actual back pressure test with the INTER-JECT equipment, this faulty converter would have been very difficult to diagnose and simply relying on what you see may be full of pitfalls.

4. BLOCKAGES

Hidden problems lurk in air-gap pipes. The trend towards the use of air-gap (one pipe inside another) pipes has brought with it a new failure problem that results in excessive back pressure.

Highlighted by poor engine performance, the collapsing  | see picture | of the inner pipe restricts the flow of exhaust gases and causes excessive back pressure within the exhaust system. Hidden from view, this fault has thrown many repairer into wrong diagnosis and caused the replacement of perfectly good parts.

New converters and mufflers are often fitted trying to correct poor engine performance when a simply, correctly carried out back pressure test procedure could have pinpointed the fault as a collapsed air gap pipe.

There are many theories as to what causes the internal pipe to collapse, but the fact is it does happen, and Exhaust, and Automotive Specialists need to be on the lookout for it.

How to test for restrictions USING THE INTER-JECT BACK PRESSURE TESTER LB-291/2F 1. Use the Oxygen sensor mounting hole for connecting the equipment supply hose into. Alternatively drill a hole in a convenient place in the engine pipe in front the converter.
2. Attach the hose from the pressure/flow tester LB-291/2F to the temporally pick up point.
3. Start the engine. Pressure on the engine at idle should not exceed 1.25 psi or 8.9 Kpa. System flow indicator, if fully turned on shall not exceed 60 L/h.= 0 Pressure reading. Pressure at 2500 rpm should not exceed approximately 3 psi or 20 Kpa. System flow indicator, if fully turned on shall not exceed 120 L/h.= 0 Pressure reading.

4. If the test reading is not excessive, weld up the hole ensuring standard safety procedure is followed and damage to electronic components is guarded against. Alternatively, a screw can be inserted in the hole.

5. If the reading is excessive, remove the rest of the exhaust system downstream from the converter and re-test.

6. If the converter is blocked, the pressure and flow will still read over the limit. If the reading drops then the restriction is in the muffler, or some part of the system downstream of the converter.

7. Mufflers, converters, etc. can also be tested by taking comparative readings in front or behind the suspect component, ensuring that any holes (other than the one the equipment is attached to) are plugged.

8. NOTE: This procedure only indicates whether or not the converter is blocked---- it will not indicate if the unit is functioning efficiently or not. Use our OnLine technical help support!