Bad AFR readings from sensor in muffler?

[sigchuck]

Hi guys, after many months of tinkering with my CIS, moving the o2 sensor for my innovate gauge, etc., I narrowed down my lean on boost “issue” to relying on the 930 boost gauge. The electric gauge was reading .2-.3 bar before a mechanical gauge registers any positive pressure. Problem solved, so I thought.

I’ve recently been commuting in the car and have noticed very lean readings while idling in traffic (16+ AFR). I don’t notice any pinging and the values are fine when the car is under load. I only notice this problem while sitting in traffic with the car fully warmed (right at the first notch on the temp gauge). It doesn’t occur instantly once the temp gauge hits, but maybe after 20-30 minutes of stop and go traffic in 90 degree weather.

I guess my question is with the o2 sensor in the short piece of exhaust between the very hot turbo and the muffler, is it possible that I am getting the safe effect as thermal reactors or a cat and the heat at idle is burning off hydrocarbons? If not, any thoughts?

[Jeff NJ]

My Bosch AFR sensor has died twice. They just don't last long, I guess. I'll probably replace it again at some point, but I know my motor well enough to know by sound and feel if something isn't right at this point, so I'm not in a rush.

[lite75]

Always run mine on the exit side of the muffler, no problems.

[quattrorunner]

I would not worry too much about 16/1 afr at idle if it's not running hot ie oil and egt temps. If it's keeping load afr safe 12-11afr and cruise 14 or so afr.

[mark houghton]

Originally Posted by lite75

Always run mine on the exit side of the muffler, no problems.

That's where I ran mine when I had one. The only possible downside of that location is ambient air creating a false lean reading at idle due to minimal exhaust velocity, though I never experienced that.

[Bucketlist]

Not solutions, just comments. I don't spend any time in stop and go traffic and run a zork but haven't replaced my O2 sensor in over 5 years. When I had a problem with high afr at idle I was able to cure it adjusting idle mixture.

[gsxrken]

Originally Posted by sigchuck

I’ve recently been commuting in the car and have noticed very lean readings while idling in traffic (16+ AFR). I don’t notice any pinging and the values are fine when the car is under load. I only notice this problem while sitting in traffic with the car fully warmed (right at the first notch on the temp gauge).

You might want to check around for some vacuum leaks, particularly the spacers under then intake to the cylinder head port, or the line to the power brakes. Getting some un-metered air in means more air without more fuel, and would lean out your idle, but probably not make enough of a difference to show up under higher RPM / normal driving conditions.

[bleucamaro]

I don't know if Innovate has made any revisions in the last 10-15 yrs, but I've had a lot of unreliable readings using the Digital Gauge (LC-1) including the following: reading lean, erratic readings, etc.

I also have the LM-2 hand-held, and it is infinitely better.

As far as bung placement in the muffler, that might be too cold. I recall the recommended location is in the down-pipe shortly after the turbo. I think they also like the sensor to be a couple feet from the end of the exhaust pipe.

Also, I've always placed the O2 sensor before any catalytic converter.

[sigchuck]

I read through a few posts from 15-20 years ago discussing Intercooler and WUR heat soak. I should have also mentioned that I have AC that I use, so there’s added heat from the tail condenser when in use.

Last weekend, I installed a small puller fan on the underside of the Intercooler, and stop and go afternoon traffic at 102 ambient I did see some slight reduction in idle AFR (15.5:1). Still no issue at all with AFR under load, so I’m pretty happy with the initial result from minimal effort. Happy to post more details on the fan if anyone is interested.

Yesterday I also added some 1/2” rubber isolators between the WUR and intake manifold to see if the air gap helps bring down idle AFR any more. There was a theory at one point that the bimetallic spring could heat soak in extreme temps and cause higher pressures/leaner mix. Will be interesting to see if this has any effect on the issue. Overall, pretty happy I can drive an aircooled Porsche in stop and go, 100 degree traffic with comfortable AC.

EDIT - should have also added that oil temp is and has been great. Throughout all the idling and traffic it sits at (or within one needle widths above) the first white line.

[Miguel Antonett]

16/1 at idle after warmup, no problem!