My first relative comp test using just the test leads

[stioc]

I'm not a pro, just a huge car enthusiast and a tinkerer. I've been wrenching on my own cars since my very first car 20 years but just getting into the lab scopes and diagnostics. Recently purchased a Modis and just captured my first 'practical' waveform on a 2001 Nissan Pathfinder.

Channel one is using just the test leads at the battery (filter on, AC coupling on, inverted waveform, 1V scale) and channel two is back probing the control wire on cyl 1 COP using a 2v scale. Pretty neat because until recently I thought I had to have a high amp clamp to do this.



Thanks for sharing here because little by little I'm learning from your guys' experience- as well as from youtube.

[b-kenny2]

Great job,Stoic I'll give that a try, then I'll pull a spark plug and do it again just to see how it compares to an amp clamp pattern. Thanks for sharing.

[kirkbarrow.garage]

Great job,Stoic I'll give that a try, then I'll pull a spark plug and do it again just to see how it compares to an amp clamp pattern. Thanks for sharing.

Hi b-kenny2, DO NOT under any circumstances connect to the lead that goes to a spark plug.
You will discover what 30,000 volts can do if you are careful, and will not survive if you are not.
The only way to monitor the voltage is by using one of the adaptors that Snap On may possibly provide for you to buy.

[stioc]

@ b-kenny2, thanks. I'd love to hear what you find if you get a chance to post it.

@kirk, I think what he's saying is that he'll do the same test as I did but on the second test just pull a spark plug out to simulate a low-compression in one cylinder to see if the waveform changes. If it does then the voltage test is reasonably reliable as an amp test. The voltage test being much simpler, quicker and no need for the amp clamp.

[Dr Dave]

1v?

1 v scale ? if you connect to battery arent you geting 12v 1 v scale won'y you be not able to see?

[Steve6911]

Dave

You may have missed the part in the settings that the Scope was AC coupled. The settings that were given were very good but they can vary a bit from car to car. I do my testing at the DLC with a DLC breakout box. I find batteries are getting harder and harder to get to and most of the time the DLC is easy. However the patterns will be slightly different so pick one way and stick with it. I use this test any time I get a vehicle with a dead mis-fire, it has saved me many times when I was told "its got a mis-fire just put a coil and plugs in it". Not so easy when the upper plenum has to come off. I have to "poor" examples of this test as I did not intend them for display, I do not invert my pattern so the draw is down and not up, I also don't turn the filter on. Again these shots were just quick confirmation. The first had low compression in two cylinders the second was a bad coil so the pattern is good.

Bad.BMP

Good.BMP

Sweep, filter, invert pattern are all things that can be played with until you comfortable do this test and see what is right for you. It takes less then 5 minutes from set up to break down and for me it works well. Just one more tool in the toolbox

[Steve6911]

This one might be easier for you to see the pattern, This is a good running vehicle, just in today for PM. I have the setting as they were posted and adjusted my sweep to be easier to see.


32308001.BMP

Notice I did not trigger off of anything so if I had low compression in a cylinder I would not know which one. Again, I use this just as a fast test.

[BRIAN617]

2005 Duramax LLY

This is a result of only one quart of water in lower rad hose...

[Witsend]

This is a result of only one quart of water in lower rad hose...
03-23-2018 07:43 AM

I think I might want to determine what caused the consequential head gasket failure and then take a look at the cylinder walls of that cylinder with a sewer camera through the glow plug hole if able to get piston to bottom.

[BRIAN617]

This is a result of only one quart of water in lower rad hose...
03-23-2018 07:43 AM

I think I might want to determine what caused the consequential head gasket failure and then take a look at the cylinder walls of that cylinder with a sewer camera through the glow plug hole if able to get piston to bottom.

Cab already in the air, engine getting replaced. We already knew it was junk, but I wanted to catch and image to post.

[Steve6911]

Nice shot Brian!

[BRIAN617]

Guess I should've pointed out captured via my OTC DLC breakout box with test leads, 1v scale, AC coupling and 2s sweep me thinks.

[Witsend]

Cab already in the air, engine getting replaced. We already knew it was junk, but I wanted to catch and image to post.

You already knew it was junk , however other than just being your typical high mileage GM product, lol , anything else cause that engine to get hot and overheat times before it finally blew the head gasket, that will still be there and cause the replacement engine to get hot? Clogged radiator ?, Electric fans?, debris built up between condenser and radiator ,even an exhaust restriction ?

[BRIAN617]

You already knew it was junk , however other than just being your typical high mileage GM product, lol , anything else cause that engine to get hot and overheat times before it finally blew the head gasket, that will still be there and cause the replacement engine to get hot? Clogged radiator ?, Electric fans?, debris built up between condenser and radiator ,even an exhaust restriction ?

This guy knew there was a coolant leak/head gasket problem but kept putting water in it and leaving the cap loose until it finally just quit.

I plan to clean radiator before it goes back together.