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Finding an air suspension leak using diagnostic computer


Barry

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On 10/2/2018 at 9:23 PM, Barry said:

How does that even happen? I like to play around and experiment with things as learning but I’ve never wiped an ECU! I didn’t even know it was possible! Maybe he was trying to do a reflash?

Easy. Most Launch (and other) computers have the ability to reset the KAM memory, but if you get it wrong, you lose all programming for the basics like idle speed, fuel trim look-up tables, basic ignition timing settings, and a lot of other things besides. 

However, I did not have the software to reprogram the KAM memory, so I had to deliver the car to dealership 60 km away, and provide the client with a rental vehicle for two days. Good thing he was a long-time customer, but he was still not happy about the affair. 

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23 hours ago, Barry said:

Read my disclaimer, last paragraph. 

I have already acknowledged your point. This article is just a basic lesson in some things you can do with your computer. For fun and nothing else. 

Next thing I plan to show is relative compression testing using graph overlays if you don’t have a compression tester gauge. I’m just waiting for a suitable car. 

There are so many things you can do with a diagnostic computer and if you’re a bit nerdy like me, there’s a lot of fun to be had. When the fun is gone from working on cars then what’s left? Sure as hell in UAE the salary isnt the motivation for doing it 

I agree that diagnostic computers can make life a lot easier, but for compression testing, a compression tester is the way to go unless you are waiting for a car with an HCCI engine. These have compression sensors in the cylinders, so I would be interested to see your screenshots. 

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2 minutes ago, treks said:

I agree that diagnostic computers can make life a lot easier, but for compression testing, a compression tester is the way to go unless you are waiting for a car with an HCCI engine. These have compression sensors in the cylinders, so I would be interested to see your screenshots. 

The way I do it is to overlay battery voltage on a trigger from one of the coils. Shorten  the time on the graph so you’re just viewing 2 engine rotations on one sheet. You will see the cranking voltage drop as each piston enters the compression stroke. Using the mark from the coil trigger as the starting point, you can apply the firing order and work out which cylinder is which according to the voltage fluctuation. When a cylinder has less compression, you will see the cranking voltage a little bit higher. Same as a traditional compression test, the injector and fuel pump fuses should be removed so you can crank without firing and you should be using WOT.

Using a compression tester is definitely the way to go to get accurate pressure readings but for an initial quick diagnosis of low pressure in a cylinder, a relative compression test using the computer is a quick and easy way to confirm that there is a problem without having to remove spark plugs, coils etc. saving time and time is money in this game. Once you know there’s a problematic cylinder, if you don’t need actual pressure readings, you can skip directly to a leak down test to see if the problem is in the top, bottom or side of the cylinder. 

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