Presentation is loading. Please wait.

Presentation is loading. Please wait.

Hit the arrow key to start! EXPLORING COMBUSTION BEHAVIOR THROUGH THE EYES OF A SCOPE SECOND EDITION.

Similar presentations


Presentation on theme: "Hit the arrow key to start! EXPLORING COMBUSTION BEHAVIOR THROUGH THE EYES OF A SCOPE SECOND EDITION."— Presentation transcript:

1

2 Hit the arrow key to start!

3 EXPLORING COMBUSTION BEHAVIOR THROUGH THE EYES OF A SCOPE SECOND EDITION

4

5 We know that THE OBJECTIVES OF THE COMPUTER AND SENSORS are aimed at.... MAXIMUM COMBUSTION EFFICIENCY... …and it happens right here!

6 GAP PRESSURE HC Internal K.V demand = ONLY PRESSURE & FUEL WILL VARY WITH RPM. Therefore KV demand varies accordingly. Constant Variables

7 GAP PRESSURE HC If we must compare… If the scan-tool looks at O2 to measure fuel efficiency, it does so after combustion is completed. The scope looks at fuel efficiency before combustion, during combustion and after combustion Plus… it does so per cylinder!

8

9 Fuel delivery equal for all cylinders. Perfect conductivity from point of ionization to the end of the firing time. Hydro-carbons are all consumed when the plug stops firing. SUPER-IMPOSED SCOPE PATTERN

10 Is this is a lean fuel mixture? 1. Obviously a single cylinder problem. 2.Computer control problem ruled out.

11 At the ionization of the pressurized gasses, the AIR-FUEL-RATIO was not lean. For the first 25% of the firing time, the A.F.R. is still normal. The coil energy is prematurely absorbed, due to lack of conductivity. This is not a lean mixture, but rather an absence of sufficient hydrocarbon.

12 1.Road Test? (Customer complaint- Missing at Hi RPM.) 2.Look at paraded pattern? 3.Scope O2 sensor? 4.Current ramp injector? 5.Scope injector pattern? - 6. Cylinder balance test? -

13 Are we ready to diagnose? WORN CAM LOBE CLUES Correct A.F.R. at start. Verify: Power performance test - low vs. high speed. Lower KV demand Why…? Not enough HC to maintain firing...

14 1.Road Test? (Customer complaint- Missing at Hi RPM.) 2.Look at paraded pattern? DONE 3.Scope O2 sensor? 4.Current ramp injector? 5.Scope injector pattern? - 6. Cylinder balance test? - DONE

15 1.Road Test? (Customer complaint- Missing at Hi RPM.) 2.Look at paraded pattern? 3.Scope O2 sensor? 4.Current ramp injector? 5.Scope injector pattern? - 6. Cylinder balance test? -

16 Verify: Power performance test - low vs. high speed.

17 RULED OUT: Lean fuel mixture Low compression CONFIRMED Lower fuel volume

18 What is the SNAP-TEST? A sudden acceleration & deceleration. Ideal objective: When 2000 RPM is reached simultaneously with less than 4 inches vacuum. Ideal objective: When 2000 RPM is reached simultaneously with less than 4 inches vacuum.

19 Force the highest possible KV demand under any driving condition. HOWOn ACCELERATION, at W.O.T., before itRPM increase, timing is still near TDC. worksThis, plus high volumetric efficiency & a lean mixture, create an extremely high KV demand.

20 Force the lowest possible KV demand in the combustion chamber. HOWOn DECELERATION, at closed throttle ITand high vacuum, before RPM drops, a WORKSmaximum timing advance, plus rich fuel mixture, create the lowest possible KV demand.

21 @ idle @ 2000 RPM 8 KV 6 KV The objective of the snap-test is to fool the computer. Before the snap-test there was no apparent problem at low or high speed.

22 NEXT CASE SNAP ACCELERATION is too fast for the fuel trim to respond and the lean injector is exposed. Note the high KV demand and the short firing time. Snap-test result At any steady speed, the computer is back in control and covering up for the lean injector. @ 2000 RPMVerify

23

24

25 All cylinders are driven lean except # 3 IN F.0. None are lean at the start of the spark line. Lower KV supports richer fuel mixture. CONCLUSION!!! @ 2000RPM

26

27 Escaping gasses passing the flame front.

28 Conclusion… RESTRICTED EXHAUST!! …And the scope shows reduced Hydrocarbon… We must conclude there is also reduced Oxygen. If the evidence clearly indicates THIS IS NOT A LEAN FUEL MIXTURE… On all Cylinders

29 Without dropping the exhaust. Without drilling holes. Without removing O2 sensor. Without a test drive. Allow a evaluation for each positive confirmation.

30 Vacuum gauge response sluggish. More turbulence on scope at high RPM. Cylinder balance test worse at high RPM. Inhibiting EGR valve improves performance. 30 % Minimal effect on O2 sensor. 30 % 20 % 130 % CONFIRMATION

31 Inhibiting EGR valve improves performance. What do we expect to see? Of course, in order to see any effect, we must be at a speed when the EGR valve is functional and that is not at idle! If the EGR normally re-circulates about 7%, just imagine how much exhaust is dumped back into the intake with backpressure. Temporarily inhibiting the EGR function for test purposes should not increase RPM with more than 5%. (100 RPM @ 2000)

32

33 Compare cylinders and isolate the odd one. Make note of difference at low versus high RPM. Determine at what speed is worst pattern. Select the worst and the best cylinder. Perform power test at that RPM on both. Record test results on those two cylinders.

34 KV DEMAND - Higher - Lower - Equal. FIRING TIME - Shorter - Longer - Turbulence - More slope down left - More slope up right - Good conductivity - Poor conductivity.

35 REASON IT OUT! Put all the information together and pinpoint the problem based on logical deduction.

36 PROVE YOUR POINT! Disable injector, EGR valve or O2 sensor, etc. Perform snap-test. Compare low & high RPM. Enrich fuel mixture, etc.

37 Dissecting and accumulating information. Conclusion based on analysis. Experimenting at various speeds & loads. Disconnecting or disabling to observe reaction. Experimenting at various speeds & loads. Disconnecting or disabling to observe reaction. Verify and qualify to pinpoint malfunction or component. Verify and qualify to pinpoint malfunction or component.

38 If this is a representation of all cylinders superimposed, there is no need for further diagnosis. 1. Adequate ignition to burn all the fuel. 2. Fuel delivery equal for all cylinders. If a SNAP-TEST reveals no problem and the O2 sensor verifies computer control, all requirements of ignition and combustion efficiency are met.

39 Includes a 125 page notebook. You have just watched a sample of scope pattern interpretation.


Download ppt "Hit the arrow key to start! EXPLORING COMBUSTION BEHAVIOR THROUGH THE EYES OF A SCOPE SECOND EDITION."

Similar presentations


Ads by Google