EGR vs NOX & Sufficient Diameter Piping for EGR?

[jmgtp]

LX9 swapped Grand Prix, 5 spd. OBD I ecm.

When the motor was on the stand I replaced the LIM gaskets. When it was in the car and started up, a pushrod slipped off a rocker arm on #4 intake valve - essentially causing it to run on 5 cylinders. Before I discovered the issue to the poor running motor I had to have it emissions tested. The car exceeded the NOX limit (with a brand new 3 way cat) by a few hundred parts per million over the threshold.

Now, after discovering the 'missing' pushrod and correcting the issue the engine runs incredibly well - though it still needs some ECM tuning.

Lets assume that the tune was spot on, should I be able to pass the NOX test without an EGR? How about without an EGR AND lean cruise enabled in the ecm?

My dilemma is that during my swap I decided I didn't need the egr and I welded closed the bung on the exhaust manifold. If I need an egr I believe the approach I will take is to weld a bung into the downpipe and run 3/8" brake tubing to the egr valve. Will the 3/8" tubing be sufficiently large enough for proper egr functionality?

That said - the old dohc motor passed emissions on a 2 way cat, with retarded exhaust cams (lope), no egr at all and lean cruise enabled. So I'm hoping a bone stock LX9 can do it, but I think I may just add the EGR and be 100% in compliance and not risk another failure.

[jmgtp]

Anyone? Is 3/8" tube too small for sufficient exhaust gas flow for the EGR?

[3400-95-Modified]

I have passed emissions with no cat and no EGR at one point in time (in CT)... Granted by the skin of my teeth but it still passed... I'm curious if you have an issue somewhere causing the NOX to be too high.

NOx is also produced due to the engine combustion temperature exceeding ~2500F which can be a result of a lean condition, so if you are running lean cruise at the time you could be contributing to the problem with that.

[jmgtp]

At the time of testing I had a major issue in that an intake valve wasnt opening - even then it was only a few hundred PPM over the limit on NOX (hydrocarbons and CO were a pass).

That valve issue has been corrected and with a proper tune, ya I think it will probably pass. But, I'm going for 100% compliance and a guaranteed pass, which means installing an EGR.

I guess I'm just going to give the 3/8" tube a shot, it won't flow quite as much as the standard size tube but some egr effect will be better than none.

[3400-95-Modified]

You should be able to pass without the EGR if the rest of the engine is running right... At least I would think so. I'm sure the other test was definitely a fluke since you weren't running right with that bad pushrod.

As for the EGR size, the ports on the intakes are very small and so is the passage in the valve so I'm sure 3/8" will be fine for a tube.

[Azrael]

The EGR only really operates at highway speeds. Unless they put your car on a rolling road and do the sniff test at speed, not having an EGR shouldn't be a problem unless they look for it visually. Which it sounds like they don't.

You can reduce the NOx with a slightly richer mixture but other emissions will read higher.

It's possible the dead cylinder could cause the elevated NOx. The intake valve will still open some due to the intense vacuum that will be created on the intake stroke. But it's just as possible that there's an underperforming fuel injector in one of the other cylinders.

[jmgtp]

In CT, for OBD I vehicles they don't do a visual inspection (they might peak under to ensure there is a cat) but they do run it on a dynamometer so it is as if the car is being driven on the street. They do measure NOX emissions and I failed.

I'm thinking 99% of the problem was the 'dead' cylinder. But, all said and done, an EGR is not detrimental to the motor and it is easy enough to hook up, so why not.