Advanced ignition diagnostics with a scope

[slipnfall]

Hi Folks, I'm no mechanic by trade, but have always wanted to properly diagnose ignition problems myself. I come from an electronics background, so I'm curious to know what a proper ignition signal should look like. Here are some questions to maybe get this started:

1)Regarding the equipment you use: are they simply glorified oscilloscopes, or do they have other advanced functions not found on a typical scope? Can a commercial oscilloscope be used?

2)What's the normal peak-peak output voltage for most 90's Nissans?

3)What are characteristics of the signal that indicate problems? Obviously misses, or low amplitude, but anything else? Flat peaks, or more triangular? I guess I'm interested more in each individual cylinder's signal, not their relation to one another.

I have a nice analog oscilloscope, but obviously need to pick up a high voltage probe(thus Q #2). Any inside would be greatly appreciated!

Cheers,Jamie

[slipnfall]

Since posting I've learned a few things in general about ignition system diagnostics. First, current characteristics are very important. Anyone know what the current limit is on a 240sx, and the typical rise time? Looks like I'll be buying a current probe before anything else!

[elwesso]

If you'd like , i can move this to the engineering forum, where Q45tech may see this and give a better reply... Let me know and ill pull the trigger!

[slipnfall]

Sure go ahead. I figured this was something mechanics do on a regular basis.

Thanks!'Slip

[slipnfall]

bump... I had hoped this would be something pretty basic for a competant & up-to-date tech.

I have done all the reading I can, but don't know the spec's for our Nissans.

[Q45tech]

http://www.picotech.com/auto/automotive ... nload.html

http://www.interro.com/wav.htm

[Q45tech]

Many times necessary to build your own specs [oscilloscope waveforms]from a known good model of the same year.

Coil on plug dignosis proceedure:http://www.asashop.org/autoinc/feb2003/mech.cfm

I have found that for a lot of people (probably more than you would guess) it's a big deal if their stations are all screwed up and the clock is wrong. For some people this can shake up their whole world.

http://www.asashop.org/autoinc...h.cfm

[slipnfall]

Thanks for those links, very helpful reading material! As soon as I finish reading over them I'm sure I'll have some more questions.

I also found this one to be quite usefull: it has user(of their products) submitted tech articles, and one is aimed directly at Nissan ignition diagnostics.

http://www.aeswave.com/TechNotes/index1.htm

I purchased a pretty basic handheld digital scope, a Fluke scopemeter. 50Mhz x2 ch, but it's the econo version... no advanced math or trace cursors... but at least I have a bit of storage now.

I'm not sure I understand your last quote: when you say station you mean work station (bay?). Were you diggin for information at work?

Cheers!Jamie

[Un4Scene]

I didn't bother to see what the links are too, so I apologize if I'm repeating anything you've already learned. But in my experience when diagnosing an engine ignition system on a scope the technician doesn't generally look for specific numbers. There are a few shortcuts you can use to check things even if you don't have a scope. But when a scope is used it's usually just to compare the readings between the cylinders. I'm no electrical wizard, but I'm guessing thats where the proprietary automotive testing equipment comes in. I've used a hand held Snap-On unit and a full size shop diagnosis computer, and both of them had special leads going to the distributor or coil wire (to tell when the the coil is firing), and to the plug wire for the #1 cylinder (for timing measurment), and to to the sparkplug wires (to tell the strength of the spark). The leads are basically just a clamp that measures the electrical feed passing through the wire it's clamped on, so I doubt you could even get an accurate measurment since it's reading through heavy insulation and shielding. There are different systems that require different types of leads as well, (curse Ford and their damn Triton engine!) but I've yet to see them on a Nissan. Once you get the cylinders showing on the scope you compare them to one another. Most of the time any problem will be obvious. It gets a little tricky sometimes if, for example, you have a cylinder misfiring at random, in which case it may only show on the scope when it misfires. The old Nissan VG30 motors were particularly known for bad ignition coils And the easiest way (that I'm aware of) to find out which one is bad is to disconnect 1 plug wire at a time and test drive the vehiole till you find one that makes the vehicle act differently. Thats a fairly unique problem though, since often times the coil would act perfectly till the engine was under load. Ahh, enough rambling. I hope this helps answer your questions.

[Q45tech]

Radio stations...............it was a quote about how owners get upset if a tech discos the battery and the radio presets disappear because many people don't even know how to set radio or clock. You would think the lost a child or something serious.

People don't realize you can sync scope and look at each O2 sensor to see the result of each cylinder combustion.

You can buy special sparkplugs with built in pressure sensors or a fiber optic to measure the optical spectrum of the combustion event.

http://www.swri.org/3pubs/ird2...5.htm

Unfortunately technicans are not electronic engineers and have to buy their own tools....................most solutions are simple anyway. The design is good, just replace the worn defective components.