paul_23

Just installed an Innovate Motorsport wideband and took it for a drive. The readings go wild on acceleration so I suspect the sensor is mounted in the wrong place.

The garage has fitted it in the stock O2 bung accessible from the left hand rear wheel arch - is this correct or is it better to put it further away and near the outlet?

Cheers

turboholic

the stock O2 bung is before the turbo, many say the O2 sensor should be after the turbo but not too close to it due to heat. My O2 sensor is also before the turbo but not in the stock location (I have different headers). It works there with no problems since 2 years. The readings are spot on, tested and compared on several dyno pulls (compared with post-turbo dynometer O2 sensor). what AFRs does your gauge show @ idle? what exactly at WOT?

JamesE

It is FACT that widebands are affected by the pressure induced by placing before the turbo. My original shop placed it before the turbo. I checked the difference between before and after and was material enough for me to change it. There is plenty of technical documentation on the effect include compensation curves if you choose to leave it before turbo.

turboholic

Ok, so how much was the difference? Is post-turbo richer or leaner? I have done 3 dynopulls and compared my pre-turbo AFR readings with the post-turbo AFR readings of the dynometer sensor. If there is any difference at all it is minimal. Many prefer to put the AFR sensor far away from the turbo on a colder spot, i.e. between cat and muffler. My sensor sits before the turbo and works perfect since 2 years, daily driver including high speeds on german Autobahn.

One pluspoint for post-turbo installation is that, if the sensor fails, there is no risk of damaging the turbo.

Geoffrey

As James says, it is important to install a wide band sensor after the turbo due to the backpressure which affects the readings. On some ECUs like MoTeC, you can build a compensation table to compensate for the back pressure and then install it pre turbo, but I don't think that is applicable here.

turboholic

I understand what you are saying, my own experience is that if there is any difference it is very small. It would also be interesting to know if pre-turbo shows richer or leaner compared to after turbo readings.

All 3 dynoplots from my car show the same AFR readings as my in-car pre-turbo AFR gauge (no EFI, CIS typical pig richness (high 10s) in midrange, high 11s from 4000rpm up to max rev @1bar).

paul_23

Thanks.. I thought this was the problem but wanted to check before I remove the end pipe and cut/weld etc.

On idle I was getting AFR at about 11-11.5. On hard acceleration it was going to 30 but on gentle acceleration it was about 12. The back pressure must have made it read incorrectly.

On a similar note, the CO mixture 3mm hex can adjust idle mixture but if the AFR is out higher up the rev band what can you do? Do you have to adjust by the adjustable WUR (I have Leask mod with stronger diaphragm).

My mechanic is saying he thinks my fuel distributor needs a refurb as it is still a bit rough on light throttle before the boost picks up and we have changed/cleaned everything else (injectors, WUR, fuel accumalator, filter, cleaned tank etc). What do you guys think as he says the springs and valves in the distributor can get tired and/or clogged over time.

Metal Guru

Do the cheap, easy checks first.
I'd check the spray patterns of the injectors, check for leaks in the intake track (especially the o-ring on the throttle body/intercooler interface) and have the wur rebuilt before I would crack into the fuel distributor.

paul_23

Injectors have been removed and cleaned at Bosch. Vac system also checked and can't find any probs but will recheck the o ring. WUR is rebuilt by Brian. Not sure what else to do as process of elimation.

turboholic

Your AFR sensor must be knackered. Find a shop where they can put a O2 sensor inside your right tailpipe, check the readings and adjust the mixture correctly via the 3mm hex. Avoid WOT until you havent done this.

paul_23

The mixture was set as normal with the 3mm hex and I am using the wide band to validate I am not too lean. It is brand new. It seems to work fine apart from under strong boost - as it is located before the turbo the back pressure must be affecting it.

turboholic

Well, if the mixture is adjusted you are fine. I have no experience with innovate sensors but I would surely try to install it after the turbo if you have problems with the readings. On the other hand the back pressure shouldnt affect the idle AFR readings and it shows far too rich readings @ idle.

Metal Guru

I know shops claim that those injectors can be cleaned but I don't see how that's possible, given the design of the screen in the injector. New injectors are cheap insurance, even at $100 each, against catastrophic engine failure, IMO.
Sounds like the wur can be eliminated.

Metal Guru

Go over to Pelicanparts and search fuel distributor. Some guys over there have successfully cracked into theirs and repaired them. It would be educational for you just to read the threads.
Some failures that I've heard about are broken diaphragms and rusty plungers. I'm sure there are other failure modes.

JamesE

The compensation curve is NOT linear and is also index by the actual AF ratio. You are probably using a chassis dyno which wont load the engine like street use will. Believe me I have been through all this crap at my expense. It would be real nice to have it before as you can run twin sensors on a single turbo. But without the compensation curves you might as well guess the reading. The better the accuracy of the reading, the more you can get out of your engine; or another way, if you are already close to the limit, the more likely you are to over-step it with dire consequences.....

Here are the details for working out the compensation:

A pressure change of the measured gas gives a deviation of the sensor output signal of:
IP(p) = Ip(p0) * p/(k+p) * (k+p0)/p0
The factor k is depending on operation conditions “rich” or “lean” and is for the measuring gas from LSU test bench:
klean gas = 0.47 bar krich gas = 0.39 bar