Part 1. Reduced fuel flow due to a restricted inlet screen. Sluggish plunger movement due to contamination.

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Verity Dean
6 years ago
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1 More about the author /instructor SCREEN Part 1 There is not a good way to check the fuel distribution per cylinder. The intention of this session is to discover and pinpoint whether distribution is equal for all cylinders. This marvel of modern ingenuity is subject to failure due to no fault of its own! There are several excellent ways to check electrical functions However no easy way to test mechanical failures like Reduced fuel flow due to a restricted inlet screen. Sluggish plunger movement due to contamination. Improper seating of the pintle valve due to dirt particles. Deposits on the nozzle affecting the spray pattern. After 40,000 or more miles of driving, adding contaminants with every fill up, deposits are bound to get trapped in the fuel delivery system which alter the flow. This not only affects fuel economy, but it also adds to vehicle maintenance cost. 1

2 When the vehicle left the factory, it was calibrated to perfection and this was programmed in the computer as ZERO or 128. Any compensation for deficiencies is first recorded in the SHORT TERM FUEL TRIM. When this STFT reaches a limit, it will dump the data into LONG TERM FUEL TRIM or LTFT, for a permanent recalibration. When fuel is added, this indicates that somewhere a lean mixture was created and the computer is compensating. 2

3 No code set. No misfire. No customer complaint. No drive-ability problem. Therefore, most techs don t bother to hook up a scope to do a snap-test. Yet it is like a cancer, eating away inside the engine with excessive carbon buildup. undetected? When the customer does not experience a problem or is not aware that the brain inside the car is crying for intervention, this information is often ignored. If some injectors flow at reduced efficiency, the computer will increase injector on time to compensate. CONSIDER what this will do over time? This increase makes the good injectors too rich, creating excessive carbon deposits. To O2 Sensor Cat. Converter -- Valve Stem -- EGR Valve etc. To what extent is it the obligation of the technician to offer to correct the problem before major expense will occur over time? Will the customer appreciate his concern, or will the car owner feel someone is trying to sell something? 3

Justifying a scope hookup in order to check it out and then proving it, is something else. 139 The objective is to identify the location. Then pinpoint the cylinder affected.

4 Hook up and set up the scope. Do a snap-test. Freeze the scope pattern. Scroll back to event. Identify the problem. Compare this with scan tool and COP-III Knowing from the fuel trim that a lean condition is being compensated is one thing. Justifying a scope hookup in order to check it out and then proving it, is something else. 139 The objective is to identify the location. Then pinpoint the cylinder affected. The only significant observation is a high Long Term Fuel Trim. This indicates that fuel is added to compensate for the lean condition. The problem could be caused by one or more lean injectors or an intake leak. The scan-tool by itself only indicates there is something off balance, but it cannot pinpoint where and how. There has to be an easier way to locate and verify the problem. 4

5 Use the scanner to qualify a need for service by reading the Long Term Fuel Trim. Find the lean injector(s) by driving the computer lean until misfiring occurs. Use the scanner to identify the restricted injector(s) or locate the proximity of the vacuum leak. If the scanner is routinely hooked up the time is reduced to 5 minutes. The objective is to identify a fuel delivery problem and follow a simple sequence to locate and pinpoint the problem. Ground connection. Tap into negative side of Fuel Injector. Hold button to add FUEL. Piggy-back Fuel Trim Generator. CONNECTION SPY. You lost contact when LED is off. EXTRA FUEL BOOST. Use sparingly on negative trim only. The COP-III was designed as a link for Coil-on-Plug diagnosis with a scope. However, with an additional unique adapter it becomes a valuable tool to pinpoint functional problems for display on the scanner. The hook-up is to one single injector. 5

Hook up and set up the scanner to misfire count. Connect Fuel Trim Generator Push the button. Identify problem. Evaluate corrective action.

service to the customer but also creates more business.

This is just enough to allow the long term process to drive the leanest cylinder or cylinders into misfire.

6 Hook up and set up the scanner to misfire count. Connect Fuel Trim Generator Push the button. Identify problem. Evaluate corrective action. HOW IT WORKS Time is of essence and since the scanner is plugged in for almost any drive-ability related problem, a few additional steps not only provide a service to the customer but also creates more business. In order to trick the computer to reduce fuel, we use a COP-III attachment to introduce a metered amount of enrichment. This is just enough to allow the long term process to drive the leanest cylinder or cylinders into misfire. This misfire can be detected by the scan-tool and the problem is identified. The metered amount of adding fuel has to be precise. It is important to be small enough to prevent that cylinder from getting too rich and foul out the spark plug, yet rich enough to trigger the O2 sensor to demand the computer to keep reducing the fuel until the leanest injector misfires. 6

Since the test results depend on the O2 sensor, it is advisable to test for response and range at idle.

Since the O2 sensor is the main player in the showdown, it is essential to validate its accuracy.

To get an accurate response, this test is performed without rapid acceleration or change in RPM.

7 Since the test results depend on the O2 sensor, it is advisable to test for response and range at idle. NOTE: The fallacy of a quick acceleration is that it may shock a lazy O2 sensor into responding. Since the O2 sensor is the main player in the showdown, it is essential to validate its accuracy. Observing the O2 scope pattern on a scope with a direct hookup is preferred over the processed O2 data from the scanner. To get an accurate response, this test is performed without rapid acceleration or change in RPM. A quick one second bump on the red button shows all we need to know about rise and recover. A customary snap acceleration may shock a lazy O2 sensor into response which is very inaccurate. A better way is a little bump on the pushbutton without raising RPM, and looking for response and range of pre-cat and post cat O2 sensors. 7

Notes When the numbers Since are the high test or positive, the system is adding results fuel depend and on obviously the O2 sensor, it is is compensating for a lean condition.

acceleration is that it may shock a lazy O2 sensor the numbers into responding. increase at high speed or remain the same, proceed to identify the faulty injector or injectors.

IMPORTANT: This test is only effective at idle. Hold the button depressed and watch the misfire counter on the scan-tool up to a fixed number.

8 Notes When the numbers Since are the high test or positive, the system is adding results fuel depend and on obviously the O2 sensor, it is is compensating for a lean condition. advisable to test for response and range at idle. the numbers decrease at high RPM, return to idle NOTE: and push the button to The fallacy of a quick locate proximity to the leanest cylinder. acceleration is that it may shock a lazy O2 sensor the numbers into responding. increase at high speed or remain the same, proceed to identify the faulty injector or injectors. VACUUM LEAK: Using the FUEL TRIM GENERATOR and COP-III is recommended to identify the cylinder which is mostly affected by the leak. This will narrow down the location. IMPORTANT: This test is only effective at idle. Hold the button depressed and watch the misfire counter on the scan-tool up to a fixed number. That number may vary with engine size but is around 70 on one cylinder or a total of 70, spread over several cylinders. 70 It takes 70 misfires to create enough O2 to offset the HC created by the Fuel Trim Generator. Once the number of effected injectors is established, the customer can be advised of the options, such as: cleaning, replace one or all, new or rebuilt, etc. 8

9 all cylinders are misfiring with a low count? Answer: all injectors are equally contaminated, if the Long Term Fuel Trim still remains high! Quality control after chemical cleaning: How do you know that the job is successful? Answer: When all cylinders misfire at a low count, and the Long Term Fuel Trim is near 0 or 128. only one cylinder misfires but the count is not even close to 70? Answer: You are connected to the lean injector. OBSERVATIONS This concludes trouble shooting POSITIVE Fuel Trim. Proceed to session 2 Trouble shooting NEGATIVE FUEL TRIM. 9

Catalytic Failures. Engine running too hot.

Catalytic Failures. Engine running too hot. Catalytic Failures It is not uncommon for technicians to misdiagnose a driveability or emissions issue by blaming the converter. In many cases, it s not the converter s fault, but rather one of the engine