Air pump introducing false air?

[sgtpoliteness]

So, I've always had some decent fuel smell from my truck since the TBI conversion. You know, that 'too rich' smell? I paid it no mind until I was washing the dishes a few weeks ago and had a thought. Could my AIR pump be introducing enough addition oxygen before the HO2 to make the PCM think that the engine was on the lean side? I spoke with a couple other TBI-conversion buddies on FSJnetwork and they thought I was onto something.

Has anyone else run into this? Babywag, you mentioned disabling the system so it can continue to pass a visual, if need be. I don't believe I can tune in the additional air so I need to remove it. Thoughts? I've poked around with it and can't fine a good, safe way to pretty much open the diverter valve up all the time.

[Fast355]

So, I've always had some decent fuel smell from my truck since the TBI conversion. You know, that 'too rich' smell? I paid it no mind until I was washing the dishes a few weeks ago and had a thought. Could my AIR pump be introducing enough addition oxygen before the HO2 to make the PCM think that the engine was on the lean side? I spoke with a couple other TBI-conversion buddies on FSJnetwork and they thought I was onto something.

Has anyone else run into this? Babywag, you mentioned disabling the system so it can continue to pass a visual, if need be. I don't believe I can tune in the additional air so I need to remove it. Thoughts? I've poked around with it and can't fine a good, safe way to pretty much open the diverter valve up all the time.

Factory GM setups have a air selector valve and a bypass valve. The selector valve switches the air injection from the manifolds to the catalyst when the ECM enters closed loop. Air injected before the 02 sensor will cause the engine to run rich, this includes exhaust leaks.

[RobertISaar]

i've seen jammed/stuck/melted select/check valves cause some really goofy things to happen when AIR is involved, it really wouldn't surprise me if this were happening.

[1project2many]

Many years ago while I was just beginning to learn about computerized engine controls, I lost an engine to just this problem. The old CCC carburetor systems were very simple and a faulty diverter valve caused excess fuel to wash the cylinder walls and kill it. I also lost a couple of mufflers due to backfiring during downshifts.

[User Nameless]

So, I've always had some decent fuel smell from my truck since the TBI conversion. You know, that 'too rich' smell? I paid it no mind until I was washing the dishes a few weeks ago and had a thought. Could my AIR pump be introducing enough addition oxygen before the HO2 to make the PCM think that the engine was on the lean side? I spoke with a couple other TBI-conversion buddies on FSJnetwork and they thought I was onto something.

Has anyone else run into this? Babywag, you mentioned disabling the system so it can continue to pass a visual, if need be. I don't believe I can tune in the additional air so I need to remove it. Thoughts? I've poked around with it and can't fine a good, safe way to pretty much open the diverter valve up all the time.

I have the Air Pump assembly from a 2000 Impala 3.8 Series 2 L36 engine complete including EGR valve and exhaust manifold. The manifold is cracked due to a lean burn, but it is repairable as it is not the cast manifold from the LH side of the engine. If you are interested in any or all of the parts, let me know, I will sell cheap if you pay shipping.

[sgtpoliteness]

Wow, guys, thanks! I guess I should have been A LOT more specific though. I forgot I don't have a signature here.

I've got a '77 Cherokee 360/TH400/QT that I've converted over to TBI. No EGR control, disabled. The Jeep still has the working factory air pump, diverter valve and lines to pump air into the manifolds. Ideally, I'd like to leave the system intact for a visual inspection (which I don't think they really do in Colorado for pre-1982 cars) or in case I sell it and the next owner needs it. Obviously the truck didn't come factory with a cat either.

[lionelhutz]

The typical factory way the AIR system works is that the PCM will switch to open loop when running the pump. It's all tied into the PCM and co-ordinated so there isn't a problem and in fact watching the O2's measure a lean mixture is how the PCM monitors the AIR system. Obviously, if your system is a separate stand-alone setup from the PCM then it won't work that way. Having the AIR system is injecting air ahead of the O2 sensors while the PCM is closed loop is a bad idea.

[sgtpoliteness]

The typical factory way the AIR system works is that the PCM will switch to open loop when running the pump. It's all tied into the PCM and co-ordinated so there isn't a problem and in fact watching the O2's measure a lean mixture is how the PCM monitors the AIR system. Obviously, if your system is a separate stand-alone setup from the PCM then it won't work that way. Having the AIR system is injecting air ahead of the O2 sensors while the PCM is closed loop is a bad idea.

Yeah, if it was controlled by the PCM then the system would know when air was injected. But, since it's not, it's the factory Jeep system then the HO2 sensor has no idea that there's false air in the system.

[Tex WS6]

There is an old post on third gen.org/techboard/diy-prom about compensation for AIR when smog pump is removed. Post is by TRAXION in 12-12-2003. I have been researching my high idle problem and came across this information. I do not have the knowledge to comment further. Hope I am not violating any rules. TEXWS6

[JeepsAndGuns]

Wow, guys, thanks! I guess I should have been A LOT more specific though. I forgot I don't have a signature here.

I've got a '77 Cherokee 360/TH400/QT that I've converted over to TBI. No EGR control, disabled. The Jeep still has the working factory air pump, diverter valve and lines to pump air into the manifolds. Ideally, I'd like to leave the system intact for a visual inspection (which I don't think they really do in Colorado for pre-1982 cars) or in case I sell it and the next owner needs it. Obviously the truck didn't come factory with a cat either.

This is most definately your issue. The stock FSJ air pump injects air into the exhaust manifolds, way before the o2 sensor. This is giving a false reading. Disable the system and I bet it clears up. You will probably want to unhook the battery after you disable the air pump to let the ecm reset.

[1project2many]

Nope, not violating any rules by posting links to other sites. If you find good info elsewhere feel free to discuss.

[sgtpoliteness]

Fantastic! Thanks for everyone's help! I'm going to unplug the system this weekend and run a bunch of logs to re-set the fuel trims and try that.

[lionelhutz]

Yeah, if it was controlled by the PCM then the system would know when air was injected. But, since it's not, it's the factory Jeep system then the HO2 sensor has no idea that there's false air in the system.

Yes, the details of the system you didn't share in your first post are rather important. The stand alone AIR system injecting before the O2 sensors will make the engine run rich. You either need to disable that AIR system or run in open loop.

[billygraves]

It would help me if you could tell what you are referring to. 1989 7.4L 400 trans 4.10 axle.
I have seen the AIR valves STICK half way inducing air or extra O2 in the exhaust in the early 7.4L TBI trucks. This shifts the fuel system to the rich side. In some engine families (like the big block) the fuel running rich melts the cat converter and the beads fly out. In the early 7.4L TBI's the 3 way bead cat melts and forces the pellets into the PUP converter and when the beads can or IF they blow past the pup (the pup has a hole in the middle for this) and fills up the muffler. The engine runs as a plugged cat. If the AIR Valve is not caught and replaced it will happen again. IF you wanna, pull the AIR pump apart and remove the VANES and I would shift the stuck AIR Check valve and remove the elect plug and plug the vacuum line to the AIR Valve. Of course this would be only for a test...... Yea right.....
If you get in the big block cal in the early TBI's 1987-early 90's WITH THE BEAD TYPE CONVERTER REMOVED, there is extra fuel in PE and at WOT to cool the cat so it won't melt itself. you can pull some out but I suggest you do it very carefully and only if it has the cat removed. Lower the idle from 750 also when it's hot or warmed up. They run pretty good at 600 too. Even 550 rpm BUT you gotta get the blade opening right. I target 5 to 9 IAC counts in park warmed up for the low speed idles. Just my 2 1/2 cents worth.
YES I have seen the AIR valve stick and run the fuel Rich...

[ony]

if you are running a 7747 ecm raise the cts to max for the air deveter in the scalers.