XTool, Relitive Compression Test / Power Balance Test

I think the Toyota software has some kind of testing like you're talking about I don't know about dropping individual cylinders and all that I think usually a scope you do that with or you did do that with in the old days I don't know what they do now compression is too easy to check generally speaking you know you have it or you don't If it can blow your finger out of the way generally it should be able to run not necessarily well matter of fact I can't think of the last time I've even done a compression check per se even on small engines like lawn mowers and chainsaws to be honest about it I usually put my finger over the spark plug hole turn the flywheel around and see what I've got I guess after doing this for a very long time pretty good indication of what you got going on No there are no numbers but I don't need something to give me numbers per se I guess if you wanted to check cylinder to cylinder but generally speaking when things like that start to go on you're so far down the list on things wrong it's going to be interesting find out whether the people are going to fix the stuff usually not.

 

Relative compression is one of my "favorite" tests to run on a scope. Lots of good data in that waveform.

However, I was never able to get anything useful on a Prius. I scoped the HV battery feed while commanding a "cranking" compression test. It seems that the inverter switching electronics "smooths out" the current draw. Might get something from an amp clamp around a feed wire to MG1, but that's a PIA to access.

That said, you might get a little something by unplugging injectors one at a time (in maintenance mode) and seeing how much RPM drop you had before the ECM compensated.

If I remember, unplugging a coil causes the ECM to shut the engine down (if it loses the IGf signal from the coil, it won't trigger the injectors - weird Toyota logic).

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I believe you all checked out any of these pocket scopes that are all the rave on the internet and wherever they are now FNI RSI comes to mind Very colorful display and all kinds of functions that can fit in your pocket they seem pretty cool I've never spent much time with oscilloscopes and looking at waveforms personally but I guess it's going to come back into popularity again with electric cars waveforms and all that.

 

Firing order for most Toyotas is 1342 if I'm not mistaken and then a 1NZ would almost never need to worry about compression but in the 2ZZ I imagine it's quite a bit of worry. The same 2ZZ in Corolla almost never has to have a compression check well nothing ever has to have one but I mean on a Corolla you don't ever hear of a shop thing but we need to run a compression check on the Corolla but apparently in the Prius mechanics and people want to know something. I've never done a compression check on any of the Prius that we've owned so far . And I have and owned the whole sap-on compression test set I've rarely used it on any engine to be honest about it

 

Some "direct" (high pressure) injectors have their characteristics defined by a code, and that needs to be entered into the ECM if an injector is replaced. That isn't needed for normal port injectors.

Engine rotation is CW.

ThinkDiag has pretty much every menu function that Techstream does. The only downside is that you have to pay a subscription every 12 months or it stops working (except for generic OBD2).

So yes, it has the "compression test" function (spins the engine at 250 RPM - be sure to READ the service manual instructions - sometimes the scantools get this wrong & it won't work).

A leakdown test is useful, as long as you understand it's limits. (got a GM 3.6 right now with a hard miss, no compression on #6, but leakdown is 4% - care to guess the cause?)

I LUV scopes. Have many. Pico's my favorite.



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I was intrigued here at first by the smoothing behavior you think happens in the inverter IGBT's and assorted other electronic components in there. Mostly due to all the fuss in the 13 pages of @AzusaPrius thread edit> titled> project lithium smoother test, and how it went way off the rails after the recent report of a nexcell melthdown in an ole Gen 2 and the appearance of honda insight engineer mutter and his interest in putting nexcell out of business or should I say compete with what mudder calls defective by design.

Ok not that that's out of the way,\
The real thing I"m interested in learning more about from your post is if the IGf signal is at all related to the IGBT.s inside the inverter, because from watching Professor Kellys video about the inverters, I have the impression that the IGBT's are one of, if not the, the big player in the conversion and stepping of the hi voltage both ways, in and out of the motors and battery.

 

You can run what tests you want. (Make sure to "force charge" the HV battery before doing compression tests). IMO, if fuel trims are "ok" and has no noises, then perform routine maintenance and don't worry about it. There's a reason why I have owned various Toyotas (and 1 Honda) for the past 25 years. In general, they "just work".

I got my 2006 with 160k on it. Dipstick had no varnish on it (decent oil change intervals) and I haven't had to go inside the ICE. Now approaching 230k. (Have done cooling & A/C work, tune & fluids, brakes, exhaust, as well as CM repair & HV battery - but not ICE).

Engine direction is CW when looking at the front - harmonic balancer.

The GM 3.6 has a broken valve spring. It can barely close the valve at rest, and air pressure during leakdown holds it shut. However it can't control the valve dynamically so it leaks when cranking or running. Nice fluttering needle on a vacuum gauge.

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Different "IG" and different "smoothing". The ECM has 4 IGt circuits - a control for each of the 4 ignition coils to command it on and off (to "fire" the coil and produce a spark). The coils each send a signal on the IGf (feedback) circuit to confirm that it did switch on and off as directed.

If the ECM doesn't receive a IGf signal, it can shutdown the fuel injectors. I might expect it to kill only the "affected" cylinder, but many times I see it shut down all injectors (ie, unplugging one coil will stall the engine).

This has nothing to do with the switching transistors (IGBTs) inside the inverter.

Normally when I perform a "relative compression" test, I use a scope with an amp clamp to measure the (12V) current used by the starter motor as I "crank" the engine. As each cylinder builds compression towards Top Dead Center, starter draw increases, then goes down as it passes on to Bottom Dead Center. So there are a series of "peaks" as you look at the amperage waveform. 1 for each cylinder in order, then the cycle repeats.

If all peaks are even with each other, then compression is the same for all cylinders, "relative" to each other. Anything abnormal merits further testing. Here's a typical waveform. So, compression affects starter current.

Now on the Prius, the HV battery supplies power to the inverter for MG1 to spin the engine. I measured current from the HV battery while commanding a "compression test", but could not see ANY pattern that correlated to ICE compression (even pulled 1 plug to create a 1 cylinder "loss of compression"- should be obvious). My equipment is pretty sensitive, but no dice. I guess that MG1 current is "too far removed" (lots of capacitance and inductance) from HV battery current. Thus my "smoothing" comment.

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from #10 above


"The GM 3.6 has a broken valve spring. It can barely close the valve at rest, and air pressure during leakdown (testing) holds it shut. However it can't control the valve dynamically so it leaks when cranking or running. Nice fluttering needle on a vacuum gauge."

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