I've been chasing a small problem on my 383 SuperRam with SLP Tri-Y headers. By all indications, the right side of the motor is running rich. I'm running a heated AC Delco 3 wire O2 sensor on the left bank of the motor, and I installed a WB O2 on the right bank. With the DIY tuning, the BLMs are looking very good, usually within 4-8 of 128, so all would appear to be fine. However, the WB O2 is typically reading an AFR of 12.5-13.0 at idle, and 13.25-13.75 at cruising. The only time I see the WB go over 14 is when accelerating.

The plugs look to be maybe a little rich, they have a little carbon around the ring but nothing on the electrodes. And all 8 appear about the same. None of them are wet, either.

In addition, I just barely passed my emissions test - NOx and HC were about midrange, but the CO was at the absolute limit at both 15 and 25 mph. Another .01 and I would have failed on the CO.

So I went looking at the A.I.R. pump, even though I put a new one on in May when we installed the 383. Checked that it is diverting to the cats while in closed loop, and it is. I was a little surprised at how little air is actually flowing out to the cats at idle, had to hold my finget in front of the hose to feel it at all. Is this normal? How much flow should there be, and how would I measure it?

Also, should I be feeling a slight vacuum like pulse on the A.I.R. pump side of the check valves? I do if I hold my finger over the end of the valve opposite the headers, and it's uite warm so it has to be exhaust pulse I'm feeling. Just trying to confirm this is "normal".

It doesn't look to me like the engine itself is really running as rich as the WB is implying, so I'm thinking maybe there is an air supply to the exhaust problem. Since the CO is so high, it almost sounds like there's not enough air flow into the exhaust, at least on the right bank.

Does any of this make sense? Hopefully I've explained it clearly.

What do you folks suggest could be the problem? I'm really pulling my hair out over this one! (and I didn't have any to spare!)

- Ye Old Almost Bald Phat Phart, Vern

 

It is my knowing that the AIR system is only operation during closed loop, to help the catalytic converter warm up -- thus being more environmentally friendly by burning off the waste gas faster.

Now I've never fiddled with my AIR pump while the car is running, closed or open loop, so I cant help there, sorry.

 

Thanks, I found that out as well, per the service manual and proven last night, under closed loop it is pumping air towards the cats only. And all 3 check valves do not flow back towards the pump.

Anyone else? Please?

How much air should be flowing towards the cats?

 

It doesn't flow a huge amout of air. I know some racers who use an A.I.R. pump as a crankcase vacuum pump, and it's barely adequate.

It is normal for there to be a vacuum pulse on the check valve. In fact, some systems have used that pulse to actually provide the A.I.R. flow without any pump (1980 Citation V6, for instance).

It isn't entirely accurate to say all A.I.R. flow is directed to the cat in closed loop operation. See the sticky at the top of the forum about eliminating A.I.R.

It also is not accurate to say the A.I.R. flow is directed to the manifolds during open loop to warm up the cat. It is up there because that is where the exhaust gases are going to be the warmest, and therefore provide the maximum benefit until the cat warms up. On my 1984 full sized van, there is no diverter valve, and the A.I.R. is only routed to the manifolds - and it does have a cat. Since it is a mechanical open-loop system, it doesn't have an O2 sensor to avoid (which is why the A.I.R. is routed to the cat in a closed loop system).

 

five7kid - thanks for the response. I read the sticky, as well as the thread it referenced.

Glad to know the vacuum pulses and low air flow amounts I see are pretty "normal". Thanks for eliminating those from my 'scope.

I'm going to burn a new chip as referenced from the sticky and set the divert enable temp to 151 using my Tunercat stuff. If I read it correctly, this makes the computer divert all output from the pump to atmosphere, is that correct? Thought I might just try that and see if there's any difference....

Again, THANKS!


- Vern

 

I'm not going to pretend to be a PROM expert. From what I can gather, though, the A.I.R. to the manifolds under certain operating conditions was done because they determined its effectiveness in emissions reduction was increased by putting it there under those conditions. Diverting to atmosphere I'm afraid I don't understand at all.