Creeping AFR indication - What's the cause?

[flightlead404]

My AFR creeps up.

I have the basic idle mixture set somewhere in the middle of won't idle too lean and won't idle too rich.

I *think* its somewhere around 14:1 when warm but can't tell.

As the engine starts to warm up the AFR indication creeps up - getting leaner and leaner. But here's the thing, the engine idles along just fine. Its not changing in sound, speed, or anything else. The AFRs creep up slowly into the 15-16 almost 17:1 range with no change in idle. So, that tells me its an indication problem, not a real mixture problem.

I've got two working controllers right now, a Spartan and an ALM. Both controllers exhibit the same issue, so I can't believe its a controller issue. I'm reading AFR from the Microsquirt they are connected to.

In my mind it has to be either the Microsquirt (I think that's a pretty low likelihood), or the sensor.

Has anyone experienced this and was it a bad sensor? This is the 3rd sensor I've had all genuine Bosch. First one failed outright, second one only worked in free air (internal grounding issue), now this one. Are these typically that high a failure rate?

[Bucketlist]

I am still running CIS, BLWur, euro fuel head, one 044 pump and monitoring with the old innovate lm2. My car loves to idle around 13.5 and runs good to about 14.5. When it is hot outside (around 100*) I sometimes have to tweek the wur to get more fuel and keep the numbers in that range. If my afrs get above 15 it will pop, sound lean and run rough. I installed 2 fuel control pressure gauges one in the dash and one at the wur running off one pressure sensor at the wur so I can easily verify control pressures with afrs. This also makes those wur adjustments easier.

[Rich76_911s]

Originally Posted by Hot Euro

I am still running CIS, BLWur, euro fuel head, one 044 pump and monitoring with the old innovate lm2. My car loves to idle around 13.5 and runs good to about 14.5. When it is hot outside (around 100*) I sometimes have to tweek the wur to get more fuel and keep the numbers in that range. If my afrs get above 15 it will pop, sound lean and run rough. I installed 2 fuel control pressure gauges one in the dash and one at the wur running off one pressure sensor at the wur so I can easily verify control pressures with afrs. This also makes those wur adjustments easier.

Steve any chance you could show how you plumbed in the fuel pressure sensor? I’ve wanted to do this too, but have been stumped on the proper way to plumb it in.


Flight I’ve had similar issues with AFR sensors. Where do you have yours mounted, and have you done anything to protect it from external heat?

Thanks
Rich

[356911930]

Hey Rich,

Here are two links that should help you!

Rahl


https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/902452-fuel-pressure-gauge-adapter-fittings.html

https://forums.pelicanparts.com/porsche-911-technical-forum/516270-dash-fuel-pressure-gauge-cis.html

[flightlead404]

Originally Posted by Rich76_911s

Flight I’ve had similar issues with AFR sensors. Where do you have yours mounted, and have you done anything to protect it from external heat?

Its mounted in front of the muffler right after the turbo. Probably 1-2" after. Its a RarlyL8 exhaust and I had zero problems with it there until my recent mods. I don't attribute the failures to the mods per se, only to messing with it

I've done nothing to protect the sensor itself, I expect that it is designed for high heat, perhaps I'm wrong.

[356911930]

AEM says that if you run the sensor with out being connected to the gauge it will destroy the sensor.
don't know if this is your problem but possibly.


Rahl

[flightlead404]

Originally Posted by 356911930

AEM says that if you run the sensor with out being connected to the gauge it will destroy the sensor.
don't know if this is your problem but possibly.


Rahl

Not to the gauge, but to the controller. No that's not the issue.

[dos531]

Honestly with CIS you're better off not looking at the afr too much. It will never be where you want it, but itll run ok. When I had CIS and an AFR gauge it would just stress me out looking at it all the time. Like you said, it'll idle anywhere from 13 to 16 depending on temp, but you'd never know it without the gauge.

[Bucketlist]

[QUOTE=Rich76_911s;10570124]Steve any chance you could show how you plumbed in the fuel pressure sensor? I’ve wanted to do this too, but have been stumped on the proper way to plumb it in.

Had Len (boxtergt) build a fitting for the sender and run the wires to the dash gauge marked with min and max ideal control pressure. Added a tee for the under hood gauge.

[flightlead404]

Originally Posted by dos531

Honestly with CIS you're better off not looking at the afr too much. It will never be where you want it, but itll run ok. When I had CIS and an AFR gauge it would just stress me out looking at it all the time. Like you said, it'll idle anywhere from 13 to 16 depending on temp, but you'd never know it without the gauge.

I need it to have the microsquirt calculate VE for me. It worked just fine 2 years ago, so I know it can work properly again.

[911nut]

If I drive my car, shut it off for a while and then start it up, my afr will be 15/1 to 17/1 at idle. This is because the bi-metallic lever in the wur moves during/after heat soak to lean out the setting. Idle drops 200 rpm so it's a nuisance, especially with the a/c on. When driving with the engine at constant speed, my afr is 14.5/1. The cool fuel passing through the wur cools the wur off and the idle wur returns to 14 to 14.5/1 eventually.
I've never had the afr steadily increase during constant speed. I'm thinking Flightlead may have a wur issue.

[xbmwguy]

Flight eventually you will end up getting rid of the cis stuff and go stand alone and your world will be a much happier place

[flightlead404]

Originally Posted by xbmwguy

Flight eventually you will end up getting rid of the cis stuff and go stand alone and your world will be a much happier place

Don't tempt me lol

[dos531]

Originally Posted by flightlead404

Don't tempt me lol

You're already like 80% of the way there!

[flightlead404]

Swapped in a brand new sensor, similar behavior. It seems to behave normally any other time, except at idle. I adjusted the idle mixture and the indication moved the correct direction, but it still creeps at idle from 13.5 to 16.5 over 10 mins or so which makes no sense at all.

[Bigtoe32067]

Small vacuum leak somewhere. I'd start checking anywhere I just recently touched since it wasn't doing it before your latest mods.

[flightlead404]

Originally Posted by Bigtoe32067

Small vacuum leak somewhere. I'd start checking anywhere I just recently touched since it wasn't doing it before your latest mods.

lol that's everwhere

but what's the mechanics that makes it creep, rather than just be a bit lean?

[smurfbus]

Possibly grounding issue?

[flightlead404]

Originally Posted by smurfbus

Possibly grounding issue?

I thought about that. I've quintuple checked all the electrical connections. I though, maybe if heat is affecting a weak ground and changing the resistance it might have that effect, but nope they are all good. I may not be able to do much, but building electrical harnesses is one thing I can do

[smurfbus]

I would try battery, block or even chassis just for test.