Hey,

Does anyone know exactly how the ACV directs air pump air across the RPM band? I've searched and I haven't found anything too definitive. I know it sends air to both cat and combustion chamber at idle, and I know the air pump shuts off altogether at a bit over 3K RPM. However, I saw someone post that it also fed air to the engine at low non-idle RPMs...is that correct?

My reasons for asking: My air pump is going bad, so I pulled the relay while I decide what to do about it. I know this causes idle to be poor due to running overly rich, and I am not too concerned about that. However, it also does not seem to run that smoothly driving around town either. There is a bit of a stumble transitioning between very light throttle and moderate throttle, like often occurs in light traffic. Right now this is with the stock ECU, until I get my Pettit ECU either fixed or replaced. I was thinking if idle were the only problem then I would just yank it, but if it affects around-town driveability, I'll get another one and put it back on.

One other thing...is there a check valve of some sort to prevent hot exhaust gasses from backing up into the air pump from the cat? I've had two air pumps go bad in relative short order, although the first was pretty old and the second was used. Still...if there is a valve there that has failed, that could certainly cause problems I would think.

jds

 

Yes. The stock cat has a steel check valve welded onto the hardpipe that comes out of it.

Sorry, can't help with your other problems.

 

Interesting that the check valve is welded into the stock cat...do the high-flow cats have this too?

jds

 

Not that I have seen. How big a problem that is I don't know. As long as the psi coming out of the pump is higher than the backpressure of the exhaust, the flow will always be towards the cat.

With the pump off at higher RPM though I imagine the pump could possibly become contaminated with exhaust gases over time?

 

Tisk tisk... The check valve is held on the to the pipe by two studs. You can remove it and transfer it to your high-flow cat (assuming the high-flow cat has the same two stud mounting plate). You can get under your car, remove it and test it if you need to.




I've heard this as well, but I don't believe it. Seriously, look at the secondary air injection system section of the FSM (details the ACV and it's operation, starts on page F-115). There are four ports on it: the airpump feed, the airpump blow-off (goes back the air box), the exhaust feed, and the main cat feed. There are no ports for feeding the engine fresh, combustable air.

Also, there is another check valve between the ACV and the LIM that might have gone bad. This check valve prevents exhaust gasses from getting into your ACV (and possibly your airpump.

Be sure to check out the FSM. It should tell you how to test some of that stuff.

 

Hmmm, good info...I'll go hunt that stuff down. But...none of my easily observable results make any sense if the air pump cannot feed air into the combustion chamber. I can see on my "worthless" AFR gauge that idle is much richer with the airpump off than on...I can see/hear/whatever my idle oscillate at cold temps and practically stall if I have the AC off. It never does this at all with the air pump functioning. It can't be the ECU not detecting the pump either...I'm not throwing an error code because all I've done is pull the relay. The pump itself is still connected.

jds