A/F wideband gauge after cat, useless?
 

I was looking around on scoobymods at a wideband gauge install and someone posted that if you have any catalytic converters that you will not get correct readings if the gauge is installed after them. Is this true?

Yes, but it can be corrected. Mostly by simply putting your wideband in front of the converter...

Tuners tune ith a WB in the tail pipe all the time, but it is not a great choice. WB belongs before any CAT. With some WBs, it is possible to put it in place of the OE NB and emulate the NB signal for the ECU.

Is a wideband gauge useless for me to have in a car unless I'm planning on tuning it? I was thinking about getting one, but I am not going to be doing any tuning of my own.

Mostly, yes. It is unlikely that you would look at it in a critical time to "save' your engine from some fueling issue, so unless you are tuning don't bother.

O.k. well that still leaves me with 2 empty holes in my triple gauge pod. Other then boost which I have, what other gauges should I get to fill the empty spaces. I see most everyone suggest an EGT but, like the wideband, I don't know if I "need" that one either. I guess I don't really "need" any gauges. Either way, what do you suggest for my other 2 gauges?

Oil pressure/temp are as good as any.

Here's my gauge importance order:

Boost, Oil Pressure, Oil Temp, EGT, Water Temp, A/F

Though, I'd bump EGT higher if you're going to be driving the car hard but not at the race track. The oil temp and pressure are more important if the car's seeing a lot of lateral G's, but EGT is a better indicator of an issue with the car running lean.

Tuners will tell you that boost is #1, closely followed by EGT. Third is a tie between oil temp and fuel pressure IMO, but after the first two it's kind of a toss up if you're not spending time at the track. I personally still have a set of Defis I've been hanging on to forever- EGT, Oil Pressure, Oil Temp. Someday I may or may not add a boost gauge when I add, like, boost or something. But A/F is not even very useful for tuning, and totally useless when you aren't except for bling factor.

anyway, back to the subject more or less- widebands can compensate for being behind cats, but they lose precision and accuracy to some degree. Doesn't anybody make an uppipe yet with a spare bung for temporary AFR use?

Vishnu used to, but that was their non-flex uppipe sold in 2001. :lol:

And I'm not sure why Fuel Pressure is all that important. No one tunes the FPR on these cars... you just need to make sure you've got a beefy pump and you're set. If the car runs lean due to a fuel pressure issue, you'll see it in the EGTs and AFRs.

Huh? WB is essential to tuning. Don't get tuned by anybody who says otherwise. Nothing else tells you what is happening as well in open loop. EGT is a lagging indicator and can lead you down the wrong path to a blown motor.

And in a turbo car, you don't want it in the up-pipe, as the temps are too high. Downpipe is the correct location for a WB.

Oh, and what Scott said.

I said a wideband gauge isn't a good tuning tool, not a wideband sensor. You need to be reading/logging it through tuning software for it to be useful. EGT lags slightly, buts it's a pretty consistent delay. As for fuel pressure, it's an indicator of potential problems you may not have been able to notice until it's too late, lik eoil pressure. If you have a VF34 on a Walbro, it's probably superfluous. But if you got a setup like Scott's that's on its third or fourth large turbo iteration, it's the only indicator you'll ever have that your fuel pump is not capable and/or goiong out. Story: Vishnu Stage 4 WRX tester made 376 wheel horses on Shiv's (at the time) low-reading dyno. But the funny thing is, the first 20 pulls or so maxed out between 325 and 330. But towards the end of the session, it sudenly started magically climbing. Shiv was rather perplexed. After various investigations, they found that the Walbro was failing, causing the car to get lean after boost. A fuel pressure gauge would have shown this the moment it started to happen. Anyway, fuel pressure isn't super vital, I just htink it's as viable as other fluid temp/pressure gauges.

A WB gauge would have shown it long before a FP gauge, as would an EGT. :P I use my WB gauge all the time, much more than my EGT.

EGTs can be high for a number of reasons, O2 levels only change for one reason, more/less O2!

Scott an I are agreeing Fp is low on the list, so you must be wrong Kevin... ;)





Or the world is ending. :)

No, the world ends when all 3 of us are in an argument and end up agreeing.

:manatee:

EGT and oil pressure (or temp).

I think I am going to get the oil temp and pressure. Which leads me to my next question. Should I buy the $65 sandwich adapter or go the cheaper route and use the galley plug with a T fitting?

I thought the sandwich was only like 30$

Scott's drilled out oil cooler sandwich method is probably way cheaper.

I've decided the best place for oil pressure is in the heads. There are already 1/8 NPT ports at the end of the galley for the cams. Which means no adapters are needed, and you're reading the oil pressure out at the furthest point of pressure from the oil pump. I put my oil pressure gauge on the driver's side heads. It's the same port that the turbo gets fed oil from on the passenger side heads.

In the past I had my oil pressure gauge in my remote oil filter block, and I always saw plenty of pressure, meanwhile I was starving the crank journals and eventually nuked a rod bearing. I'm hoping that with the sensor way out in the heads, now if there's any oil starvation I'll see it for sure on the gauge.

And for the oil temp, this time around I drilled and tapped the oil galley plug on the top of the block for the 1/8 NPT temp sender. I'm a little afraid the temp will be more like the "block temp" rather than the "oil temp", but lots of other folks have used this location without issue so I figure it'll be okay. I just wanted to get all the sensors out of the oil cooler loop.