AFR Readings (LM-2) - Idle speed vs. Partial load

[Tom C.]

Just got my Innovate LM-2 up and running using a tail-pipe clamp for the o2 sensor. So I'm able to get AFR readings at various RPM's, however, I've seen some factory documentation for my motor (2.4 liter with MFI) that specify's AFR settings at Idle and then under Partial load.

So my questions is - Will AFR readings really be different when the motor is reving at 2-3k RPM with no load . . . vs. reving at 2-3k RPM under load?

BTW . . . no problems with my LM-2 . . . out of the box it is working exactly as I would expect.

Thanks,

[smurfbus]

Can you log rpms too?

I would say AF is not the same as the throttle is not the same.

[Tom C.]

smurfbus - Thanks for the reply.

No, I can't log RPM yet . . . only because I don't have the required analog cable. However I have a Tach so I can see what the RPM's are. And I can read the LM-2 so I know what the AFR is at a given RPM.

I'm just not comfortable driving the car down the roal with the tail-pipe clamp/02 sensor setup, because I don't believe the tail-pipe clamp was designed for road use.

Does anyone with a Innovate Gauge (Permanent Install) have some feedback on there experience?

[LJ851]

It is worth welding in some bungs closer to engine , much more accurate readings. When i dyno tune ducati motorcycles, there is aprprox. 1 point of AFR difference between an 02 sensor up near the exhaust port and one at the end near the muffler. As in 13 to 1 vs 14 to 1. It varies the most at idle and low speed. To test the quality of your fuel "map" you should put the engine through all of its operating conditions and verify AFR, ideally on a dyno but you can do it while driving as well just be careful.

[LJ851]

I have one mounted perm. in my 85 carrera. i love it.

[Tom C.]

LJ851 - thank you for your feedback. I sold my '97 916 four years ago and have regretted it ever since. So your saying the tail-pipe clamp will read lean vs. a reading that is closer to the exhaust port. I was afraid of that. So a permanent install (ie. welded in bung with guage) is really the way to go.

Any others with AFR tuning experience (Porsche specific) with feedback?

Thanks,

[T77911S]

when i have done tests with the LM2, i did not see any difference between 2500 rpm in the drive way and 2500 steady driving. do the test yourself, dont trust me

here is a thought, how did the factory measure the AFR and where did they measure it?

you can also look at this way. you can mount the O2 on one bank, but you are only getting 3 cylinders for the reading. you could put in 2 O2s, i think the LM2 will take 2 inputs, not sure if 2 O2's at once though. if you mount the O2, you have to take it out or buy another to use in another car. but the draw back to the tail pipe deal is, it can fall out.
you will find that the AFR data really needs to relate to an RPM.

here are some other fun tests to do.
see how timing effects AFR's, at idle, at mid rpm and at WOT.
see how and idle mixture change effects mid and WOT AFR.

[Tom C.]

T77911S - are you using a tail-pipe clamp for your reading?

[tobluforu]

Check post number 19 of this thread, this where I just had a bung welded on my Dansk.
LM-1 Installation in Early 911- MFI

Another good thread: AFR Measurements and the early 911

[smurfbus]

It will read more accurate when there is a lot of load but on idle there is some reverted air with the clamp.

I was curious of the rpm as I believe innovative has made some changes on their firmware so it would not freeze and that might make the rpm sampling slow. I have the dual LM-2 and it used to freeze frequently. The LM-1 did not freeze but it stopped receiving LMA-3 channels like rpm so I bought the LM-2.

I installed a diode and a condensator in the power line (straight from the battery) and it helped the stability a lot.

[Tom C.]

tobluforu - those are excellent posts. Thanks.

smurfbus - yes that makes sense too since the tail-pipe clamp is more exposed to clean air . . . any reading at that point could be leaner. Which is the same comment LJ851 made earlier. I'm also curious how easy it will be to get the LM-2 to read RPM's. That is my next project, after I figure out how to get better AFR readings.

So far, feedback received tells me the tail-pipe clamp is not ideal and so I'm considering two bung installs in the SSI's after the collector, or in the muffer at the input flange. I've also been told (with MFI) getting AFR readings with the motor under load is more accurate and will differ from simply reving the motor in my driveway. Also FWIW, I've read that for better performance I'm looking for AFR between 12.9 and 13.1 vs. 14.7 (stoichiometric ratio).

Alright . . . more work to do before I can start tuning.

Thanks for all the help . . . this forum is priceless.

[Jeff Higgins]

I've used the LM-1 setup for about two years now on my oddball 3.0 liter MFI motor. My SSI's have the O2 sensor bung already welded into the left bank, so that made it easy to hook it up. Unfortunately, even with their recommended heat sinks, I had a couple of sensors fail on me in relatively short order. So, when I ordered a third sensor, I also ordered the exhaust pipe mount. My thinking was that putting it further downstream from the heat would prolong its life, which it did.

Hearing all the talk about dilution when mounted in the tailpipe, I wasn't going to trust it without checking. I found that under any sort of load, from just cruising along to WOT, it read the same in either position. Trailing throttle did read lean with the tailpipe mount, but we don't really care about trailing throttle, now do we?

Funny thing with MFI, too - now that we can accurately read A/F ratios, it is a little bit surprising how much they vary. I have now used this thing on a pretty good sampling of different cars, initially thinking (when I first saw the A/F's on my weird 3.0) that its range of variation was due to the nature of my cobbled together setup. It turns out every MFI car I checked (carburated cars as well) varied every bit as much. This was certainly no Motronic or EFI in those days - no wonder they get such poor milage.

[brads911sc]

Jeff, What exactly did you do? I have been through 3 in 4 months and I suspect its the heat sink as well... Unless there are a bunch of bad Bosch 02 sensors out there...

[Jeff Higgins]

I bought one of these tailpipe mounts:

Pelican Parts.com - LM-1 Exhaust Clamp

[brads911sc]

Thanks

Originally Posted by Jeff Higgins

I bought one of these tailpipe mounts:

Pelican Parts.com - LM-1 Exhaust Clamp

[Tom C.]

Originally Posted by Jeff Higgins

I bought one of these tailpipe mounts:

Pelican Parts.com - LM-1 Exhaust Clamp

Hi Jeff . . . this is the tail-pipe clamp I am using too. You didn't have a problem with it shaking loose and falling out of the tail pipe?

BTW, your MFI thread gave me the confidence to try and dial my T MFI pump to play nice with my 2.7 (mod S) motor with help from Mark Jung.

[Jeff Higgins]

Yeah, unfortunately, the darn thing likes to shake loose and fall out. After the first time I just safety wired it with a long piece of wire up around one of the inlet pipes.

Mark is the man on this stuff. What he has added to our collective knowledge of MFI is just absolutely invaluable. My efforts were really no more than stumbling around blindly in the dark until Mark turned the light on. His input put me over the top, answering the remaining questions and finally pulling it all together so that it made sense. We owe him a great deal.

[mca]

Tom,

I just bought one as well and did some tests last weekend. Got tired of sharing with Ty and his brother Tim . By the way Ty ... my initial AFR was 13.0! Holy rich! I adjusted it to 13.7.

I figured out a great way to keep the clamp in the tail pipe.

Install it and screw the clamp on nice and tight. Then run the cord along the body into the driver's side window. Use PAINTERS TAPE to secure the cord along the bumper and the body of the car. If the clamp comes loose, the tape will keep it from banging up your car or hitting the ground.

Here is a graph of my AFRs. I only did one run because I ran out of time on Saturday. It took me half the day to update the firmware on the damn thing. What a pita.

My idle AFR was 13.7 ... not running O2 sensor. You can see that I get into the low 11s at WOT. You will see some very lean conditions off throttle. From what I've read, this is due to air rushing up into the tailpipe. I don't think a car could run at at AFR of 20. If you use the LM2 on a dyno you won't see this kind of bad data.

Oh, and the RPM clamp seems like a pain unless you are using it on a dyno. The cord is only like 4 feet long.

[Tom C.]

holy crap mca, you got all this from your first run with a new LM-2! Nice work. I'm still messing with trying to get accurate readings. I need to stare at this for a little bit and come up with some worthy questions for you. Thanks for posting this. It's great to know I will get this sort of data some time in the near future.

[smurfbus]

I always let the car start first and get some heat before I switch my widebands on. These engines run so rich and moist on startup it ruins a hot sensor fast if one lets the sensor heat before startup. But you need to switch the LM-1, LC-1 or LM-2 on because the WB sensor also needs to be powered on to survive. They won't die righ away without power but the lifespan is greatly redused.

E8 errors might also happen when you go WOT and lift the throttle suddenly. It helps if you install a long bung for the sensor. With LM-1 the earlier IIRC 1.10 firmware was more tolerant for errors and sensor aging.

I can use sensors that wont work anymore on my LC-1 or LM-2 in my LM-1!