So, here's the situation in a nutshell: I have a cat with the tube for AIR injection, along with the AIR pump itself. The diverter valve does not work (no computer to control it, as I'm using an aftermarket EFI system).

From what I understand, I need the AIR injection to the cat or the lifespan will be significantly shorter. And it should be easy enough to set the diverter valve so it always allows the AIR pump to push air to the cat, while preventing it from pushing air to the AIR tubes on the headers (with aftermarket EFI this is a no-go anyway).

My question here is whether pushing air to the cat 100% of the time will cause any issues? I understand it will actually reduce the effectiveness of the cat while the exhaust warms up (because it keeps the cat cooler longer during startup) but will I have problems with overheating or similar from forcing air in all the time? Has anyone done something along these lines before?

Basically, I want the cat to work, I don't want the lifespan to be drastically shortened from not having AIR injection, but I also don't want the thing to catch on fire or explode or something. Any feedback would be appreciated!

 

A quick update - we do have emissions testing in this part of Colorado, and although a visual inspection isn't normally part of testing I would like to keep the appearance looking as close to stock as possible.

 

I don’t think you can modify the diverter valve but maybe applying accessory power to both solonoids would be the answer. The tune might need to be adjusted for the additional air into the air pipes. Stock the ecm adds 1mv to compensate for air into the pipes.
One solonid might do the air pipes and the other might go directly to the cat.
So powering up the one solonoid might work.

 

This is what I had in mind! Block the tubing that diverts air into the AIR tubes on the headers (the FiTech EFI I'm using can't be tuned for this, so injecting extra air into the exhaust before the O2 sensor would cause problems) and let the air pass to the cat freely. If the solenoids are closed with no power I can power the one that lets air run to the cat; if it's the other way around (open w/ no power) I'll power the other one. I think I have that side of things figured out.

My major concern is whether pumping air to the cat all the time will cause problems such as overheating the cat/exhaust. I'm not certain whether the factory ECM regulates the air going to the cat aside from when it does so at startup (to help the cat heat up faster). In other words, does the ECM wait for the coolant temp to hit X degrees, then let air flow to the cat freely? Or does it continue to regulate that airflow based on some other parameters after the engine/coolant is warm? And if it does, will it hurt if I don't have that additional regulation?

And I know it would probably be easier to swap in a cat w/o AIR and just pull the smog pump (and swap in some better headers while I'm at it) but again, I'd like to have a chance at passing a visual.

 

I’m not sure about the cat overheating I’d think the opposite running to cool and not functioning as well. Does the Fitch have a way to control nos. If it does that might be another way to control the diverted solonoid.

 

Just curious how are you running the egr ? Tvs

 

Good question - the unit I have does not have any way to control NOS (they do have it on a higher-tier model though). And that's what I'm hoping to hear regarding the cat! If I can get by with running air to it all the time without risking overheating, I'll just do that to keep things simple.

I'm planning on building my own controller for EGR to generate a pulse signal for the EGR solenoid (IIRC it accepts something like 0-60 pulses per second) based on throttle position, plus a cutoff to disable below a certain temp. I'm still figuring out how exactly I want to do this (I'm thinking about using an arduino, manifold temp sensor, and TVS/TPS). However, before I fool around with that I want to get the car running.

 

AIR is diverted under some normal operating conditions, and specifically under emission failure conditions. A rich condition with air injection to the converter can create excessive underfloor temperatures (allegedly), besides overheat and damage the converter.

 

Just delete the AIR and run a cat that doesnt require the fresh air tube. For that matter, the stock cat will probably never know the AIR is disconnected.

 

Correct me if I'm wrong, but you're saying that the overheating conditions would only take place if air injection was taking place and the engine was running rich?

 

This might be something I do in the future, if I ever move to a county that doesn't require emissions testing. Emissions will check for a smog pump and air tubes to the cat and headers/manifolds under certain circumstances.

 

At first glance I thought this was a typo on TPS, and since my original idea was to try to build my own EGR regulator with an arduino taking readings from a TPS I just rolled with it. Turns out I don't know nearly as much as I think I do, and I'm overthinking something simple.

So, using a TVS to only allow vacuum above a certain temperature and an EGR valve driven by ported vacuum could work too, right? Like the older 70's era solutions, similar to this diagram (first one I stumbled across and obviously not for a SBC, but you get the idea).

 

Exactly what I was thinking for the egr, you can find tvs under carb applications at RockAuto.com .

 

Awesome, thank you! I'll start exploring this option. Looks like I'll need a TVS and a negative backpressure EGR valve.

 

Correct, it would be hotter in general, but rich with air injection would create an over heat condition.

 

Some cars have been set on fire because the overheating converter ignited the grass underneath the car.


How strict are Colorado emissions employees? Can you get away with having certain systems look like they are operating, when in actuality they aren't? Example: air tube connected to cat converter, but no air actually being pumped.