EGR cleaning benefits

I noticed an improvement in the car's EGR flow test results (from ten point something kPa to 21 point something).

Realistically, unless the obstruction before cleaning was severe enough to be making the engine run badly, the effect of cleaning might not be anything you're going to notice, except in the test result number. At least that way you can prove that you accomplished something.

 

Nicoj36, the first time I cleaned mine I was noticing a slight amount of roughness at low speed, high load conditions. When I removed the intake manifold I found several ports almost completely plugged. The ports that are plugged do not get the EGR they should and run a little better. The ports that are not plugged get all the EGR flow, which is more than they need. This causes poor combustion and possible misfires in the cylinders with clear ports. I was able to notice a smoother running engine after the cleaning of the intake manifold and EGR pipe.

 

That might be a bit of a lopsided way of putting it ... a multi-cylinder engine with combustion imbalances between cylinders is just running badly. The ones receiving too little EGR and the ones receiving too much both contribute to that.

The ones receiving too little EGR are at greater risk. The worst thing that can happen in the cylinders with too much EGR is they misfire, nothing happens on the power stroke. The worst thing that can happen in the cylinders with too little EGR is they detonate, which can do mechanical damage.

When the EGR is clogged overall and the ECM can detect it, it dials back engine parameters like ignition timing to avoid that risk. But when the manifold is unevenly clogged and the ECM can't detect it (because it can only check overall flow), then the ECM does not make those protective adjustments, and the cylinders receiving too little EGR are at detonation risk.

Moral: any "EGR cleaning" job has to include cleaning the manifold passages. Don't do the cooler and valve and other stuff but neglect the manifold. The manifold is the easiest part of the job anyway, so there's not much reason for neglecting it.

Conversely, it can be pretty reasonable to do a manifold-only job (easy peasy), and then just watch the ECM's flow test results to decide whether or when the more difficult upstream cleaning is called for. By dealing with the manifold, you deal with the chief cause of improper EGR delivery that the ECM can't detect and account for.

 

Not sure about that "inverse" relation, between plugging and problems. The EGR capillary passage in intake manifold at cylinder one usually plugs first, and the head gasket failures usually occur at cylinder one, and/or two.

I noticed no appreciable difference in performance. That said, I did my first cleaning very early, just over 70K kms. The real reward is not fragging your engine, around 150K miles.

 

Seems the biggest hit when the egr gets wonky is loss of fuel economy. This would Is especially notable when a car like the Prius has 50-plus MPG.
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That would be interesting to know about. Can you say roughly how many Prii that is based on, their odometer readings, their EGR flow before and after cleaning, and the confidence intervals on subsequent MPG change?

 

You have a pressure washer?

moto g power ?

 

One more data point for you: 2012 Prius, cleaned EGR valve / cooler / intake manifold and replaced PCV valve at 8.5 years / 113k miles. Car ran fine before cleaning, and no noticeably difference after. Off topic, the biggest improvement in MPG came after I replaced the air filter.

 

Any chance you jotted down the EGR flow test numbers before and after you did that?

 

I started off with brake cleaner; let it soak overnight, drained it, and was not too impressed. It was "cleaner", but still a lot of stuff coming out.

@mjoo recommended soaks with concentrated Oxi-Clean in hot water solution. I plugged one end, poured it in, wait about an hour (it'll bubble out carbon-flecked froth) till it subsides, rinse, and repeat. About 4 sessions thus, it looked like new.

 

If it also flows like new, you ought to see a flow test result somewhere around 21 kPa after cleaning and reassembly; at least that has been a typical after-cleaning test value from people who have reported theirs.

As always, it helps build our community's knowledge if you can report your own test numbers from before and after cleaning, and the odometer miles on the car at the time.

 

There's more at the link. The car measures how well the EGR is flowing, so you can ask it, and it tells you. We're collecting the info before cleaning and after from people who tackle the cleaning, so we eventually can answer threads like this one.