t2d2

iTrader: (8)

I've got a new AEM Wideband collecting dust, waiting to be installed one of these days. Rather than getting a bung welded onto one of the exhaust headers, it occurred to me that I've got an easily accessible, unused and capped EGR pipe that it could go on. It would require twisting the pipe a bit to angle away from the back of the intake plenum (if installing the bung on the capped end, as opposed to somewhere along the side of the pipe), but the metal is soft enough, that should be doable.

Is that a brilliant or idiotic idea? Would there be enough exhaust airflow to it at the end of a dead end? And would stagnant air affect the accuracy of the readings? If nothing else, I'm thinking it would be slower to respond to AFR changes.

Now, if I could figure out how to get to the EGR pipe's mounting point on the exhaust header without pulling the engine and tranny, that would be an ideal place to mount the Wideband as part of a block-off plate. There aren't many mounting options pre-cat that are going to be easy to get to.

1997Soarer

iTrader: (1)

Bad idea. Wideband needs to be in the main exhaust stream where it gets exhaust from all 6 (or 8) cylinders

1997Soarer

iTrader: (1)

And yes, the stagnant exhaust in the egr area (now that it's plugged) would give inaccurate readings.

t2d2

iTrader: (8)

Kinda what I figured. But as for getting exhaust from all cylinders, that's a puzzler... It needs to be pre-cat, right? On the V8, that means it can only be on one bank. That's what got me brainstorming in the EGR pipe direction in the first place.

However, if my understanding was wrong and it can be post-cats, that would make bung access much, much easier, and I could perhaps replace one of the floorboard rubber plugs with a grommet to run the wire through to the cabin.

t2d2

iTrader: (8)

There was a brief break in the rain today, so I pulled some stuff off the parts car and realized I can see the EGR pipe's mount on top of the pass. side header with the ABS pump and A/C hard lines removed. One bolt will be easy to access, but the other may be challenging. I haven't attempted a line of sight/access on my car yet with those items still in place...

The AEM Wideband's sensor fits within the diameter of the EGR pipe with room to spare, so assuming I can get the pipe off the header, that looks like the perfect spot to mount the bung to a blockoff plate. Or maybe even cut the flange off the EGR pipe and have the bung welded to that. Assuming I can find where it's bolted to the back of the engine and remove it, of course. That way, the welding can be done off the car, eliminating tricky access points pre-cat.

t2d2

iTrader: (8)

Well, yesterday's nice weather was indeed a brief break, but curiosity got the better of me so I dug back in in 50 degree torrential rain (edit: and 25+ mph winds). Fun. I was able to get the rightmost bolt off the EGR-header bolt easily enough, but getting to the other one required removal of the header heat shield, which was fairly rusted on. Fortunately, the lower pipe's curvature is such that you can get on both bolts (nuts, actually) with a socket, unlike the upper attachment to the plenum that requires painstaking wrench work.

I still can't locate where the EGR pipe is attached to the back of the engine, so no luck fully removing it and showing a Wideband test fit in its mount. And, I'm pretty sure that, having done that on the parts car, access from above will be impossible with the A/C hard lines in place. It might be doable from below, though, now that I have the visual of what I'm trying to reach.

My big concern, though, is location. The AEM instructions say to mount the Wideband at least 18" from the exhaust port (to avoid heat damage), which I take to mean the furthest downstream port. The EGR mount is directly on top of the O2 mount, and if you know what the 1UZ headers look like, you know that's immediately after the last exhaust port... I just don't see any workaround to that. There's like an inch of space between the exhaust ports and the cat, and everyone says to not mount it after the cat because that will mess up Wideband readings.

What have other people done on the SC400?? Is the only alternative to move the cats downstream? I don't really want to do that, having just had custom exhaust work done.

Ali SC3

iTrader: (10)

just get a bung welded next to the factory o2 sensors. the spot where the factory main o2's are is safe, and you could even take one of those over but the stock ecu wouldn't be happy then.. and they should be before the cats otherwise the readings will be off by a few afr points and quick afr changes will be more averaged out due to the catalyst, I know cause the idiots who first tuned my car stuck their super expensive tailpipe sniffer wideband in the tail pipe assuming everyone in the world with a turbo does not run a catylitic converter, when I brought the car back and complained about the tune and the afr's they responded... "you have a cat?" some shops are pretty clueluess who doesnt look underneath before a tuning session especially when I had a wideband in the car.. they actually at first told me there was something wrong with my aem wideband cause they could not figure out why the read 2 different values, and decided to tune the car extra rich.. some people just love wasting time and they thought it was "good to go", I regret even paying them. egr pipe is probably not going to give the best reading and if a wideband doesn't have a good reading then it kinds defeats the purpose.

on a V you really need to run 2 sensors unless you are merging the banks together for a single turbo setup. most people probably just run 1 on one side and as long as all injectors and iginition are up to par the other side should be relatively close to the same values.

t2d2

iTrader: (8)

So, you wouldn't worry about AEM's 18" minimum distance recommendation? Here's what the pass. side header looks like, in case you aren't familiar with it:



EGR pipe on top (nuts removed from studs), O2 directly below it on bottom of tube.


My original question was about the feasibility of mounting the Wideband at the upper end of the EGR pipe, but the subsequent question was about using the lower mount to the header, since there's nothing far enough downstream possible without cat relocation. As you can see, the furthest downstream exhaust port is directly on top of the O2 location, which is pretty much squished up against the flange to the cat. 18" is a pipe dream, no pun intended. Are Wideband sensors more sensitive to heat than O2 sensors? If not, you're probably right that that location is okay.

The only negative I can see about using the EGR pipe's mounting location is the raised lip it sits on. I think the tip is long enough to extend that far down into the header, but I'll need to get the pipe off there for a test fit, which is much easier said than done.

Yeah, that idea consistently gets shot down.

Man, you really struck out with that tuner. They were either supremely incompetent or just looking for a sucker to take money from for doing nothing in return. Hopefully, your catching them red-handed put them on better behavior with subsequent customers.

You trying to ruin my day? I see your point about going blind as far as tuning balance between banks, but the other stuff I've been reading says just one sensor is fine. And let's face it, it's tough enough figuring out where to mount one, let alone two.

Ali SC3

iTrader: (10)

yeah I would go with one sensor as well it should be rather close side to side on the banks. I would not worry about putting it next to the stock o2 sensor, if it was too hot then the stock o2 would have failed the wideband isn't made that differently for it to go bad in the same spot. the 18" reccomendation is just a guide and they probably think you are sticking it after a turbo. I think I have mine like under 5" away from the back of the turbo, no issues for several years now.

t2d2

iTrader: (8)

That's more reassuring, thanks.

AEM actually says 36" from the exhaust port if running a turbo...

Ali SC3

iTrader: (10)

Yeah I never actually listen to anything that aem says.

t2d2

iTrader: (8)

Duly noted.

So, I finally got the EGR pipe off the parts car. That middle bolt on the back of the block is every bit as hard to get to as advertised. Yowsers. With it off the car, I cut the lower flange off to line things up. It may not be as clean of a solution as I was hoping for...



That's the best, lowest angle I could snap. The Wideband bung is ever so slightly bigger diameter than the EGR opening into the header. You can sort of see in the pic, that whole section is elevated about an inch from the header tube. If I open up the cut off EGR flange enough to slide the bung down flush with the header's mounting plate, the tip of the Wideband will be ~1/2" out of the direct flow of exhaust. Will that be a problem?

The alternative is to try and get down there with a round file and/or Dremel to open up the header's side of the flange slightly, but I would probably have to drop the cat and deal with seized, rusty bolts to avoid clogging it with metal shavings. Talk about a snowballing project.

There's also the concern of how close the Wideband's wires would be to the heat shield. Even if I insulate them, that's bound to be pretty warm. Then again, that's going to be the same issue on the driver's side, being the only other pre-cat place to mount it, so anyone who's installed a Wideband on a SC400 either manages with that heat proximity or moves the cats.

t2d2

iTrader: (8)

Just occurred to me, another thing I'll need to check on is whether I can get an O2 socket over the Wideband when the heat shield is in place. That could be pretty tight.