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| Improvised oscilloscope probe for Automotive ignition analysis. |
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| tautech:
--- Quote from: soldar on January 04, 2019, 08:30:20 am ---If the spark has enough voltage, and it should, and it only fails under load, that means is is not high enough to spark through the compressed mixture or it is sparking somewhere else. Some spark plugs can be defective and the spark jump internally. Or if the plug's cap are not good the spark can be jumping totally outside the plug directly to the block. Or it can be inside the coil. But you say all these items have been replaced.... Yeah, it's no fun troubleshooting something which happens only under heavy load. --- End quote --- Depends on how hardcore your setup is. Add some logging to a race car and examine a pass and the issues generally stand out like a sore toe ! ;D |
| Jim-0000:
--- Quote ---Add some logging to a race car and examine a pass and the issues generally stand out like a sore toe ! ;D --- End quote --- Can you explain what this means to a "non racecar" experienced, but otherwise generalist mechanical person please? (I have maintained my own road vehicles for over 60 years. The very few times I went to a mechanic in remote locations etc., the job was not done properly!) So I sympathise with vk6zgo in reply #13. |
| tautech:
--- Quote from: Jim-0000 on January 04, 2019, 08:54:22 am --- --- Quote ---Add some logging to a race car and examine a pass and the issues generally stand out like a sore toe ! ;D --- End quote --- Can you explain what this means to a "non racecar" experienced, but otherwise generalist mechanical person please? (I have maintained my own road vehicles for over 60 years. The very few times I went to a mechanic in remote locations etc., the job was not done properly!) So I sympathise with vk6zgo in an earlier post. --- End quote --- Full logging of all systems can get pretty complex with sensors all over the vehicle and they can help fine tune most of a cars performance. All I’ve had experience with are on door slammer drag cars but one of the most telling are EGTs that not only give feedback on tune vs load but when they might drop unexpectedly against another cylinder indicating what’s generally an ignition problem. They are great when doing dyno runs to optimise tune at all points over the rev range. So what might you log ? RPM Boost Fuel pressure TPS Driveshaft RPM (slider clutch slippage) Suspension (launch squat and bumps in the pass) Battery voltage etc etc For the guys right into it, logging is of paramount importance to squeezing what’s possible out of any setup. |
| joeqsmith:
--- Quote from: Jim-0000 on January 04, 2019, 08:23:20 am --- --- Quote from: joeqsmith on January 04, 2019, 04:38:21 am ---Coax is RG400/U. I have a trimmer cap up near the clamp to trim the voltage level. The large braid goes to the block, the clamp goes around the plug wire. As mentioned, this forms a capacitive divider. I feed this into a 50 ohm termination (built into the scope). I test the ignition parts off the engine. --- End quote --- Where did you buy the clamp please Joe? --- End quote --- A friend of mine had given me a couple of those. As the paper mentions, a clothespin would work fine. --- Quote from: tautech on January 04, 2019, 09:20:24 am ---So what might you log ? RPM Boost Fuel pressure TPS Driveshaft RPM (slider clutch slippage) Suspension (launch squat and bumps in the pass) Battery voltage etc etc --- End quote --- :-+ A few others I look at are: EGT, exhaust pressure, oil pressure, AFR. I have had similar problems under load where the motor would stumble with nothing to do with the electonics. Just thinking about pressure for example... The exhaust pressure is roughly equal to the intake, if things are matched. Once the pressure was high enough, conditions were just right and the motor would stumble. The exhaust valves were sticking open. Bigger springs.... As pressure goes up, it puts a strain on the ignition parts. No surprise. You can see how it arched under the boot and etched the side of the plug. To combat this, the gap had to be closed down. Fuel type and amount of fuel ... is another fun one. As the pressures go up, this adds to the fun... Shown is another test jig to evaluate wideband sensors. |
| floobydust:
The coil primary waveform is also very useful, it's how modern ECU's do real-time misfire and ignition fault detection. Electronic ignition clamps the primary voltage to just under 400V, so max. output voltage is limited compared to points. There's two grounds in a car. One high-current ground is from engine block to battery, and the second smaller ground is from the engine block or battery to the car body/chassis. This is for the in-car loads like fuel pump, ignition, lights etc. A common mistake is forgetting the car body ground which the ignition module may not have been grounded to the block. The firewall is no good unless you have the ground strap from block to body. You can't rely on current flow through motor mounts and U-joints etc. Flipping the carb around, it would mean poor mixing in the intake manifold? I don't see a single carb used on the Holden hi-perf mods. If possible you can fit an O2 sensor and see each cylinder firing lean/rich to check balance. Maybe joe has tried this. Otherwise you'll blame the ignition system when nothing is wrong with it. |
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