Techstream EGR Valve Blockage Data

Are you thinking a new PCV won’t deliver as much oil/water goop to the intake? A couple of thoughts:

1. PCV valves are pretty bulletproof; a shot of brake/carb cleaner and they’re likely like new. The spring might get slightly fatigued, not sure.

2. I don’t see a new one reducing the goop much, if at all. Oil Catch Can will, though they’re not going to stop all of it either. They are effective enough to be worthwhile though. (Said the man with dual Morosos, lol.)

If/when you have the intake manifold off again, I would check all its metal embeds, and whatever screws into/through them. Maybe hit them all with WD40.

 

Well, really, if a passage was 100% plugged anywhere in the EGR system, that's what you'd see; the ECM would command the valve open, and there wouldn't be any flow. The monitor test would catch that, of course, the next time it ran, because the test value would be lower than the min value, so P0401 would be set and the ECM would start backing off on ignition timing, sacrificing some performance and efficiency so as to be protective of the engine.

The little passages in the IM may be subject to another failure mode that isn't as nice as that. Suppose they clog up unevenly, so a couple are very clogged and a couple are not very clogged.

Then you can still get the intended amount of EGR flow overall—there's only that one pressure sensor, so as long as the overall pressure in the manifold changes the expected amount, the ECM can think things are fine. Because of the passages being a little clogged, it might open the valve a little farther, but it ends up seeing the pressure it wants, so it's happy.

What it doesn't know then is that a couple cylinders are getting too much EGR with an elevated misfire risk, and the others are getting too little with an elevated detonation risk, and because the ECM is happy, it isn't doing anything protective with the timing to mitigate the risk.

 

That “may be subject…” would be more succinct as “will be subject…”?

I know, maybe not always, but that seems to be the tediously regular case, with cyl 1 being first to clog. And near invariably, the head gasket failure reports are cyl 1 or 2, typically in the zone between those two cylinders.

 

I have followed his advice and cleaned the intake manifold.
The vibrations have disappeared and I am measuring 19-20 kPa consistently.
Thanks for his advice and also to Mendel Leisk for commenting that it is not necessary to remove the cooling ducts from the throttle body.It was the final boost I needed !!

 

Thanks for the report!

So there can be cases where it is worthwhile to check and clean out the manifold passages even when the overall flow measurement looks very good. That's a pretty quick, easy job.

 

I used a refrigerator coil cleaning brush I got from Walmart to clean the main intake passage from the EGR. It was perfect, just long enough to go all the way through my 2011 Gen 3 intake manifold. It was hard to push through, but you can do it by using a "screwing/twisting" action.

In the picture with the brush laying across the manifold, you can see that the tip end half is brown. I too found that's where the most residue/buildup was in the main EGR intake passage.

I used undiluted Simple Green Pro HD and regular Simple Green to cut through all the oily/greasy gunk. I wasn't able to remove all of it, I can still feel an oily film on the surfaces of the passage. But I know it's basically opened up all the way.

I used nylon brushes for cleaning stainless steel drinking straws, about 1/2 inch diameter bristles to clean the small EGR passages at each port.

Posted via the PriusChat mobile app.

 

I believe from 2012 on the main egr "gallery" is somewhat different, doesn't go the full width of intake manifold. @NutzAboutBolts has a 2012, and he mentioned (in his intake cleaning video) that a cleaning brush only went in a few inches IIRC.

 

It makes sense. At the far end of the intake manifold, the passage was really dirty. When I flushed it with water, the water would come out of the small egr holes at the port on the far end first, then the second farthest, and so on. The EGR gases probably behaved similarly.

Toyota must've molded in baffling to more evenly distribute the EGR gases.

Posted via the PriusChat mobile app.

 

Changed it to a 'tournament' design. I think there's been an illustration posted somewhere.

 

I saw a very low-res picture, a cut-away view. The sense I got is that it was changed, from a full-width gallery going into four capillaries, to a partial-width gallery, going into two intermediate passages, and each of those split into two capillaries.

 

Turn the picture upside down, tape it on a wall, and write in four sports teams. Got yourself a tournament.

 

Or a corporate line of command diagram, family tree.

funny thing: dealerships and Toyota seemed to be touting the revised intake as a “cure” for a while, then seemed to drop it. Maybe very marginal improvement.

 

Ok, but I think 'tournament' design was actually their word, in some release that talked about it.



[Bonkers World]

 

Looks about right.

 

Saturday I've cleaned intake manifold, EGR pipe and changed PCV valve.
Today was the third day of monitoring that value and until now I'm back to 18.xx kPa.
I'll monitor this a couple of days more and someday I want to finish the job cleaning EGR cooler and valve.

But I have another question. In Torque I have a lot of sensors to monitor. MAP, MAF, EGR open in %, all kind of oxigen sensors and so on.
Could some of them corroborate with this EGR sensor which all we look at to get a better picture of airflow to EGR/intake manifold or something like that?
For example this morning I've take a look at MAP and MAF sensor on a very-very short trip (2 miles) but I don't know if it's fine/average/bad/whatever.



I'm curious if we can foresee EGR problems by monitoring and cross different sensors.

 

Well, the built-in EGR monitor isn't doing anything but opening the EGR valve a certain amount and watching how much the MAP value changes.

But I think the challenge with watching those same values in real time is that they're naturally all over the map under different driving conditions. The trick that's programmed into the EGR monitor is that it waits for very specific conditions when you are decelerating, the engine is spinning, and the fuel injection is cut, and it sneaks the EGR test into those known conditions, so it knows what to make of the readings.

I don't really see any practical way to improve on just letting it do that, and pulling up the result now and then to look at.

 

I have wondered if EGR step (the commanded opening level of the EGR valve) might give that kind of corroboration, when compared under similar-enough conditions at long intervals (like OCI time scale). It's purely a guess but I'd expect that as the cooler clogs, the ECM should ask for wider opening of the valve in order to achieve the same expected O2 level under the same engine load. It's sort of easy to keep an eye on the maximum commanded opening level of the valve, and it's fairly easy trigger that in ordinary driving patterns. (Maximum commanded step tends to happen near the top of the red part of the HSI, right before the ECM commands 0 EGR as it nears w.o.t.) It seems like those peak commanded openings would be valid for comparison so long as the ambient temperature and barometric pressure (elevation mostly) are similar enough on those months-apart dates.

So in theory, peak-observed EGR step should inversely track the EGR monitor. I think?

 

OK, after cleaning manifold and EGR pipe for three days it was in lower 18's.
Next four days was in upper 17's.
Today coming home from my brother in law 17 miles trip I read it on the road close to home and it was 14.94.

Fuel consumption for this trip was 61 mpg.


TBH I have no idea how it works.

 

I don't see anything wrong with gathering the data to test that hypothesis. Seems like it would take a decent-sized sample of cars and readings over a decent time period, and then somebody to do the fitting and model testing.

 

Plus in theory peak EGR valve step doesn't add information over what the EGR flow monitor might already provide more conveniently. (Nothing wrong with academic exercises.)

More down-to-earth, I've noticed my 2010 (EGR cleaned 35K-ish miles ago) sometimes has a jag of misfires which show up in OBD cylinder misfire counts, but are too intermittent to set the CEL. I can sometimes hear the misfiring, but not always. The misfire counts are automatically cleared and could easily go unnoticed.

Since we know that an unevenly clogged intake manifold can cause misfires: detected misfire counts might be a data-driven early warning of either clogged IM EGR passages or misbehaving EGR valve. In Torque this is labeled something like "[Prius]All Cylinders Misfire Count". (There are also PIDs for per-cylinder counts.)

Obviously once you can actually hear and recognize misfires, or the MIL is on with a misfire DTC, EGR blockage should be on the suspect list. But in terms of using data for an early warning of EGR blockage: the ECU detects intermittent misfires well before it decides to light the MIL, and before the EGR flow monitor notices anything amiss.

So practical advice could be to periodically (maybe 10K miles) drive a confirmation pattern by warming the car up to EGR operation, then pass slowly through lots of different RPM levels. Immediately afterwards check for misfires via OBD or Techstream. If misfires are detected, we know to suspect the intake manifold EGR passages and valve (along with all the other standard misfire suspects).