on the scout i've got a closed loop system that uses an o2 sensor to trim fuel up to 15%, and prior to installing that i bought a air fuel ratio meter to test my mix. now that i'm using holley's proprietary o2 sensor i'm curious if i can tee into the signal line and run that signal back to my air fuel ratio meter.

teeing into it won't affect the readings returning to the computer, will it?

jason

Generally the O2 sensor signal goes back to the ECM so it can process the signal and change the fuel mixture of the FI or carb. The sensor sends out a voltage signal that fluctuates from .1 to .9 of a volt, that is when it is in Lambda and the mixture is "correct". You can check it with it disconnected with the engine idling and warm then adjust your air meter to get the voltage to start swinging back and forth. If you check it with it connected to the ECM then it may always swing back and forth while your changing the air meter since the ECM will be trying to keep the mixture at the correct spot. As far as you teeing into the O2 sensor wire and having it feedback to the air meter may or may not work, this may be one for "Cyberdine" Matt.

lol

for the fact that you work on vanos systems and v12's with three brains all day long, you sure are a hater! ;-)

i decided just to install another o2 sensor on the other bank to monitor the mix.

know much about egt gauges? how can i get a baseline for mine to figure out how to use it to determine lean/rich conditions? it currently fluctuates between 800 and 1200 degrees depending on load.

jason

Uhhh, hater? Of what? Isn't Matt(Phatmatt) the one with the tricked out mini-van?
Where is your EGT sensor mounted? I am just begining to learn about them on our Jr Dragster, the distance from the port can affect the readings along with the depth of the sensor into the manifold. My instructions say to mount about 1"-2" from the flange by the port.
Here is how it supposed to work on our dragster, at idle I want about 400-500 degrees and down track temp around 1000-1200 degrees. If it is too low at a idle I need to richen it up, more fuel-more power-more heat and also there is some flame travel into the port. Now for down track temps I've been told if the temp is too low I need to lean it out to raise it because there is too much fuel and it is "cooling" the probe down.
Here is what happened at our race this weekend, our exhaust temp down track was 1055 and the car ran a 13.39, then I richened it and it went a 13.03 and the temps came down to 980. So maybe for our car we need the temp closer to 900-1000 rather than 1100-1200. Each car will be different but you will see immediate changes by using a EGT rather than a "lazy" 02 sensor reading.

a hater of electronics!!! i'm just funnin with ya though, don't take me seriously!!

as for the egt shit...my truck runs hot egt no matter what. i think it has something to do with the restrictive ports, small valves, high torque and the the fact that it's got damn near cast steel heads. the shop i took it to is a 4x4 shop that does smog. they mentioned a few things:

1. 1200 degree egt's in a scout would most likely be very normal.

2. the heads & block on a scout are made out of something wierd. it's very low carbon content, very high nickel content and technically can't even be called 'cast iron.' it is rumored that you could drop a block off the empire state building onto a diamond and it'd bounce.

3. my egt is about 4" away from the downpipe to manifold flange. how could i be getting a hotter reading by putting the sensor too far downstream?

i'm going to call autometer as well...

thanks much for your help. it is greatly appreciated. hell, it's just nice to hear from someone who runs a pyrometer in the first place!!

what brand do you run? mine is an autometer procomp ultralite (only type i could get at the time, about $119 from kragan pricematched to summit racing)

jason

Small exhaust valves will definitly cause more EGT temp, that is what they used to do in the late70's on into the '80s to get cars to pass smog. More of the exhaust would stay in the combustion chamber creating more heat and burning off the residual fuel. The air injection would help also help with emissions along with cooling down the exhaust manifolds, that is why some motors ran worse after a while when people took the air injection off, too much heat now.
If you decide to go with bigger exhaust valves i would leave the port alone, just do the valves.
4" away sounds a bit far, but check with Autometer and see what they have to say.
We use a unit made by Digatron, it is also used on go-karts, but you could almost use it on anything. It has a 2 screen display for RPM,CHT, EGT, one screen has two modes for CHT and RPM and it records max readings on a run.

see, you're runnin a cht gauge too...shißevagen huh...

you think an aircooled cylinder has anything to do with egt's being lower than mine? what do your cht's run (range wise) from idle to wot under load? is the head aluminum or iron? sorry to ask so much but i'm just trying to understand this...

aside from the small valve size, i also thought it might have been due to restrictive exhaust manifold design. and last i checked, air injection functioned about like a blowtorch creating a superhot lean-type condition to help decrease hydrocarbons on exhaust valve opening. obviously i may be completely wrong on that. my experience with air injection is thermal reactors, and they're certainly different than the air injection on my scout. if you're knowledgable on this, enlighten me...seriously.

from what i hear, headers will do wonders to this engine, and drop the egt's quite a bit.. can't wait to buy a pair after i get this bitch either smogged our registerred in oregon.

i got the adjustible timing module installed for the msd today. works pretty well, but i've got to fine tune the timing so i know the numerical base equivalents of the chits on the potentiometer that allows the control from the cab. right now, full turn to the right is a little too much...that's all i know.

jason

oh and i seriously can't wait to use this rig as the tow vehicle for my coupe. i can't wait to see it. pooh brown scout decked out with a mild lift towing a flat black classic bimmer with waaay to much chrome and a 3" side exit exhaust!!!

also, i found out the holley 2d projeciton ecu i've got with its archaic potentiometer type controls can be upgraded to the 2di ecu with full computer programming & datalogging capability....once the bimmer's done.

jason

Almost as good as the scout being a ferrari tower

-Ben

Not sure if being aircooled is any different other than it isn't as efficient as watercooled, it still sucks the fuel in and sends out hot gas. The cylinder head is aluminum and my cylinder head temp is about 140-190 degrees at idle and finishes at 280-320. Something else to screw you up, we run the engine on alcohol.

The air injection puts fresh air into the system to thin out the mixture and may help complete the burn in the exhaust, but I'm not sure if it super heats the air any. When checking a '77 320i with air injection out the tail pipe, you disconnect the air injection and set the CO. You usually set it at 2-3% and when you hook up the air injection it drops to .2-.7% and the same things happens with HC's, they may be at 300-500 then drop below 100. A thermal reactor (early style cat converter)has plates in it that do get super heated to help burn off the excess emissions, but I'm not sure if the air injection helps with that part, unless it works like blow air onto hot ambers in a fire pit and you can get the fire going again. In fact when one of those is hot and you crank the engine with no spark the fuel will literally explode in the reactor. I'll some people at work and see if the have anything else to add.

very interesting. yeah my experience was with a '77 e12.

so i'm assuming 10ppm hydrocarbons is pretty clean? that's what my scout was running. nuts huh...

thanks again for the info. as for the alcohol, does it burn hotter or cooler than gasoline? i've now got my egt's down to 7-800 at idle and a max of about 1100 at 75mph (nearly 3900rpm - a TON of revs for this engine). additionally i connected the a/f ratio meter and it's on the first rich light all the time. perfect. funny thing is, every time i let off the gas above 2000rpm, it closes the throttle blades so much that it'll run superlean then flood rich and backfire. i need the decel solenoid to kick in a bit more. other than that, i think i've got it nearly perfect.

jason

I believe it will help the engine run cooler, the VW bug racers liked to use it since some dont run the normal cooling fan like on a bug motor and it would help it run cooler. But the overall EGT temps of our 1 cylinder Briggs motor are close to your Scout, so I'm not sure if the burn is any cooler, it may have more of an affect on the intake charge being cooler.
I asked a guy about the air injection and if you notice on the thermal reactor the air injection pipes are pointed towards the exhaust port, the air is being injected into the combustion chamber while the valve is open to help "flush" out the remaining exhaust gases. That also helps to explain that when you remove the air injection that more gases are trappped in the cylinder (with the small exhaust valve/port/manifold) and the engine begins to run poorly after a while from the heat build up, maybe even burning the exhaust seats.