Techstream EGR Valve Blockage Data

FWIW the Wikipedia page on EGR says that recirculation isn't done at idle because it causes roughness. Does this mean that in your test, the smaller the valve opening that causes rough idle the *better* your flow?

 

Thanks for the data!

Are you sure on the direction? I confess my assumption was the opposite, 110 fully open, idle normally closed or nearly closed at 1. Takes very little opening to roughen or kill the idling engine (you're letting the cylinders fill with stuff that won't burn).

That would seem to suggest that mine is a little less occluded at 143k than yours at 104k, a little odd, but who knows what environmental / driving style / etc. issues might figure into that.

 

You seem to be assuming that large EGR volumes are possible at idle, which isn't the case. Just opening the valve a small amount is enough to kill an idling engine.

 

The "EGR flow sufficiency" monitor was a good find that I hadn't noticed myself. I was wondering why the value had units of pressure, Then it hit me that the ECU must be using the manifold absolute pressure sensor to detect the EGR flow, and that would be why the Gen 3 engine has a MAP sensor and the Gen 1 and Gen 2 (no EGR) did not.

Sure enough, when my engine is idling (warmed up, and really idling, not charging), Techstream reads the MAP at about 4 psi (absolute, like the name says, so really a vacuum reading, about −10.7 psi compared to atmospheric).

As I work up the EGR valve steps, right around step 15 or 16 the MAP reading will go up to 5 psi or even 6: that is, less of a vacuum, as now there is exhaust gas entering the manifold in addition to the air coming in the throttle body.

If I go up to higher EGR steps, the throttle also begins to open further (as the ECU tries to keep the engine from stalling from breathing non-burnable exhaust), so that also contributes to the MAP reading going up (a/k/a reducing the manifold vacuum). But the earliest increase in the MAP reading seems to reflect the inflow of exhaust gas, as the higher EGR step numbers open the valve more.

 

True, and for similar reasons, I do not see how this method can be a good test for blockage of the EGR heat exchanger. That restriction might be lower than the restriction of the valve at the level you measure with engine idling, yet too severe to pass needed EGR flow rate with the engine working harder.

 

Well, that's exactly the point of soliciting more data (ideally including some from people who have recently cleaned or replaced the system).

Until we have more of it, the question will remain one on which anyone's guess is as good as anyone else's.

 

Just a thought about the MAP sensor: if you've not cleaned the intake manifold recently, and/or don't have an Oil Catch Can installed, that sensor is likely to be oil soaked. It's near the intake manifold nadir, almost in the "pool", and the PCV inlet is spewing oil vapour directly above.

It seems pretty durable, but maybe it's readings could be thrown off by being oil soaked? Who knows.

 

The other day, for the first time since I've owned the car, I fished a vacuum hose down through the throttle body and sucked the "pool" out into a brake bleed jar. It was a mite underwhelming, maybe a ml.

 

How many miles? That pool might be the tip of the iceberg, just the stuff that hangs around. The intakes get pretty gunked up, and the egr passageways, one per port.

 

i don't think this "test" is valid. here is why: the results are dependent on RPM. when i initially did it with gas pedal slightly pressed to keep ICE idling, the RPM was 1400-1500 and there was no roughness up to value #44. i aborted because i started smelling strong sulfur from exhaust.

then, i did it again after waiting for battery to discharge forcing ICE to run. this time the RPM was about 1100. the idle was gradually different after like 15 and rougher after 20 and started to be irregular after 30. near 40 the engine started shaking bad and i felt it was unsafe to continue. i aborted at #42 and gradually went back to #1 to make sure the engine works fine.

is there a way to force ICE on from the techstream? also, i missed the EGR values. i have an older version of the software i guess.

 

IS there a Torque Pro gauge that will read EGR and MAP values on a 3G Prius? I have the the Prius specific gauges and there are EGR gauges, but they dont give me any readings.

Or will they only display in Techstream?

Thanks!

 

I don't think anyone is remotely close to proposing it as a "test" yet, precisely because it can't be validated without collecting data first, just like most any other test for anything.

1. Hey, our lab has invented a way to test blood for cholesterol!
2. Great! Let's collect those measurements from a lot of people whose cardiovascular history we also know.
3. Ok, we've got a big pile of measurements now and the health histories that go with them. Does there turn out to be enough of a correlation to tell us anything useful?
4. Hey look, it turns out there is!
5. Great! Let's start using this test in routine physicals.

Right now with this measurement, we're at the very start of step 2. The very, very start, since right now we only have two or three data points, and none yet from a car whose EGR condition is independently known. It would be most useful to start getting some reports from people right after thorough cleanings.

Right, in any kind of data gathering like this, it's important for everybody to report under consistent conditions. My report was foot off the go pedal, strictly the ECU-controlled idle RPM (which is pretty stable, so makes a good repeatable choice). Nothing wrong with reporting more data under other conditions, as long as results at straight idle are included, so the data points can be sensibly compared.

It is probably also important to specify the engine temperature. I don't think I reported that in my post, but I think I made sure to be at operating temp (around 90°C). Maybe I'll check again at some point and be sure to report that part.

I think it does offer a way to enter "maintenance mode" (and I think it's in the utility menu for the hybrid control ECU, not for the engine ECU) ... but there's also a way to do the same thing using some shift lever movements and go-pedal presses before starting the car. That mode keeps the engine running, ideal for this kind of a test.

That's my working assumption, which also has some support in the manifold-pressure measurements in #6.

If Techstream will show them, they exist as PIDs, but it's possible nobody has successfully reverse-engineered those unpublished PIDs yet. I have the greatest respect for the folks with the patience and chops to do that.

 

I can pull some info from mine... haven't cleaned it yet at 170k.

Pixel 3a XL ?

 

what was that RPM again?

 

If you leave the go pedal completely alone and keep your foot someplace else, you get the idle RPM that is actively feedback-controlled by the ECM. Once the engine has warmed to operating temperature, it's around 1000-1100 ish. If the battery decides to charge, the ECM opens the throttle a bit to maintain the target RPM. As you progressively open the EGR valve, the ECM will also notice the RPM drop and open the throttle trying to hold the target RPM.

Those are the conditions I would recommend for reporting, because they are easy to get, and repeatable.

 

I can confirm that Torque is able to read EGR (step and commanded%) and MAP on my gen3s. I have a 10 year old cheap OBD2 adapter with the paid version of Torque. I suggest searching for the monster thread on custom PIDs for the gen3. However note that it's no longer necessary to import usbseawolf's custom PID sheet. The paid version of Torque now has built-in a "predfined set" for each of Prius Gen 2, Prius Gen 3, and Prius PHV. You add them via main settings->manage extra PIDs->3-dot menu->add predefined set.

Also I think "EGR commanded" is generic - it's not even a custom PID. If you can't even view that one then your problem is not with custom PIDs, it's something to do with your adapter and/or Torque. Good luck!

 

Thank you wheezyglider! Yes, I got it running. Not sure how to read the EGR step command% though.

 

OK, how do you define the end point of the test? you said the engine was close to stalling, but it dint stall, did it? it never stalled for me either. sounds subjective to me.
i'll repeat it tomorrow with clean EGR system.