Like the title says I'm trying to find an AFR vs Boost and/or AFR vs RPM table. I'd like one for my own knowledge but also to better understand my cars problem...

My 87 TII is running at ~12-13 AFR at idle (~1k rpm). If I apply the throttle just a little (~2k RPMs) it drops to about 10-11 AFR, then with a little more throttle (~3k RPMs) it goes to 14-15, then with a little more it drops to 10-11 AFR as it builds boost. I don't know if this is how it is supposed to run or not but it doesn't seem right to me. Does anyone know? I'm thinking it should be at 14 or so up until it starts to build boost at which point it goes more rich with boost level. Any help would be appreciated. Thanks in advance.

 

14/15 afr is too lean for any amount of boost. 3/4krpms is the staging point for the secondary injectors on the factory ecu, its not uncommon to see overly rich/lean spots before/during/after this area. Age I would imagine has something to do with this; dirty injectors/corroded wiring harnesses, etc..

Anyhow; 13.5:1 afr low vacuum tapering down to a 11:1 past 8psi is the most common afr tune. Its usually that simple to get started, but honestly its not that easy to just lay it out. Every motor is different, it takes experience to tune beyond the above.

 

Thanks for the reply. That's about what I expected to see... But that's not what my car is doing. And actually, I was a little unclear about my problem....

I have a hot start problem (which is what I'm trying to diagonse). I've replaced the injectors, adjusted and replaced the TPS, and reinstalled the BAC. None of these things change the AFRs I see.

I think the problem is that it is running way too rich at 0% throttle. If it is just sitting at idle it is running at 12-13 or even more rich sometimes. If I give just a little throttle (~5 or 10%) it goest to 14-15. Then with more throttle (~15% throttle on up) it begins to build boost and the AFR it drops like a stone to 10-11. I didn't expect it to drop so quickly but I can believe it.

Throttle position AFR
0% (idle) 11-13 (I don't think this is right)
5-10% 14-15
15% and up 10-11

I think the richness at 0% throttle floods my car as I'm trying to start it. Perhaps, when the engine is cold it has enough compression to overcome this... When it's hot it doesn't. But If I pull the EGR fuse and clear it out (after 3 seconds of cranking the afr shoots to 20) it starts right up. What do you think?

 

anyone? Bump

 

And on the first day GOD said: *the amount of fuel injected during START is dependent of the rpm, water thermo temp sensors output and the ECU seeing the START signal input on pin 3B***

On the second day he said: * the AFM plays NO part during the START

 

And on the first day GOD said: *the amount of fuel injected during START is dependent on the rpm, water thermo temp sensors output and the ECU seeing the START signal input on pin 3B***

On the second day he said: * the AFM plays NO part during the START cycle. None at all*.

On the third day he said: *the afr can be adjusted for IDLE and IDLE ONLY, using the Variable Resistor on a series four engine*. Turning that resistor will make the afr go up/down approx a full afr point i.e. from 13 to 12 or 13 to 14afr, as an example.

On the fourth day he said: a grand of rpm is not idle.

On the fifth day he said: Most difficult starting is due to low compression OR the water thermo sensors input signal to the ECU is not being shown therefore making the ECU default to a temp of 176 degrees F during START cycle resulting in not enough fuel being delivered during a cold engine start. A hot engine would start fine with the water thermo signal disconnected i.e. ECU defaulted to 176 degrees (normal temp).

Make a fuel cut switch and use it or rebuild using NEW ROTOR HOUSINGS and lapped side housings.

 

11-13 is normal for idle, any leaner and it will start stumbling, i leanest i set mine and still have decent idle is 12.3

 

Satan says to ignore GOD and simply try to fix your car by referencing various AFR numbers that you read on the internet. With this method you are assured to stay in Hell forever while in search of the elusive "True AFR" that will magically cure all woes. The AFR meter is the tool of Satan, so use it every chance you get, and maybe you too will become a tool.

PS: The AFR meter is also great for troubleshooting electrical problems, fixing paint blemishes and minor body damage, and it also makes thousands of julienne fries.

 

both my n/a and my turbo idle between 12 and 12.5:1 when fully warmed up.

remember too not to put too much stock in what the "throttle" is reading. s4's have a narrow-range TPS. It's going to read 100% with the pedal nowhere near the floor. when you are coming into boost it's going to go richer.

 

**** I'm thinking it should be at 14 or so up until it starts to build boost at which point it goes more rich with boost level.**********8

If you talking about actually driving the car (no idle talk here) then what you MIGHT see while at a constant speed, say 3000 rpm, and with the 02 narrow range sensor connected to the ECU, is afr in the 14-15 afr range as long as you don't fiddle with the gas pedal. It's in closed loop.

Now if you step lightly on the pedal, the ECU goes out of closed loop and you'll see a richer figure, all dependent on the LOAD being put on the engine. Seeing 12.-13afr would be normal.

If you floor the pedal while doing that steady 3000 rpm, then the afr will go much richer because of the LOAD and it depends on how large the load is. You might see figures in the 10afr if the load is high and as you start really boosting, the afr might and probably will get leaner than that 10afr. Like it will go from the 10afr range up to the 12.5 or so range on a stock ECU car as you hit full boost. At full boost, if the boost pressure starts dropping/bleeding off, the afr will start getting richer again..........because the LOAD is going down, even though the rpms might be still climbing.

If your talking idle.......the afr on a car with a non functional emissions system, might idle just fine at 13.5 afr, but if you turn the variable resistor to the LEAN range which causes the mixture to go into the 14 plus afr range, the idle might and probably will get shakier/rougher.

If you have a functional emissions system, at idle you'll see figures in the 14-15 afr range. That's because the ACV mixes air from the airpump with the exaust AT THE EXAUST PORTS. To prove your ACV is working, a simple test can be made by looking at the afr at idle, then pull the blue connector off the Relief solenoid and now the afr will go richer i.e. into the 13afr or so range. Because now no air will be going to the exaust ports to mix with the exaust.

You need to realize that the afr will change with the LOAD put on the engine. Even a light throttle input is a load. More load, the richer the afr will get.

If you floor the car while at say 3000rpm and the engine stutters, falls on it's face, take a look at the afr. It most likely will be in the under 10afr range. Too much fuel. A lot of people have this stutter and think its a LEAN problem when its really just toooooo much fuel for the conditions.

God says to drive your car for several weeks while observing your afr and you'll see how or figure out how the thing works all by yourself.

10 and under afrs are the devils work and are to be avoided at all costs. Too much fuel for anything.

Load seems to be a combination of the input from the afm, rpms and maybe a little boost/pressure sensor input.

 

*********I think the richness at 0% throttle floods my car as I'm trying to start it. Perhaps, when the engine is cold it has enough compression to overcome this... When it's hot it doesn't. But If I pull the EGR fuse and clear it out (after 3 seconds of cranking the afr shoots to 20) it starts right up. What do you think?**********

I think you need to buy a simple fuel cut switch for three bucks and install it. Either that or read a previous post I made on how to overcome this with a simple voltage switch kit that can be bought from JAYCAR and assymbled. It bypasses the START signal on pin 3B during HOT starts which means the ECU will now actually use the AFM instead of the ECU start map. That means fuel being injected during hot starts at a duration of 6ms instead of say 17ms which is too rich and causes flooding. That or buy a RTEK product that has an anti flooding function built into it. Talking series four........no series five talk here.

 

Thanks for all the replies... I've read all of them all and taken the time to understand them. Below are my thoughts and what it sounds like I need to do.

I have a fully charged and new 1000A/hr battery so I don't think cranking RPMs is a problem unless my starter is just that old and worn.

I don't have any reason to believe my AFM is bad.

I know 1k is not idle... My have my car set to idle at 700rpms. Which it does 90% of the time. But every once in a while it will idle at 1200rpms. I don't now why. One problem at a time... Maybe that problem is related though?

I have not been able to test the compression on my car with a mazda tester because no one has one for at least 150 miles from my home. I have read several conflicting things about testing with a piston type compression tester so I don't know what to believe. Mine with piston type tester with the check valve removed shows 90 to 95 psi on both the front and rear with equal jumps with the relief valve pressed. I have read that these numbers are on the low side to typical of a used engine... Atkins rotary said they were more than acceptable for a strong runner and that 70 psi is low.

Also, if compression were a problem why would it start up no problem when it is hot after I pull the EGI fuse and clear the chamber? I do believe I am clearing the chamber because I can see it on the AFR.



***If you talking about actually driving the car (no idle talk here) then what you MIGHT see while at a constant speed, say 3000 rpm, and with the 02 narrow range sensor connected to the ECU, is afr in the 14-15 afr range as long as you don't fiddle with the gas pedal. It's in closed loop.***

Yes, this is exactly what I see... I didn't think the dip with slight throttle increase was right but it sounds like it is. Thanks for expalining that. It make sense.



***If your talking idle.......the afr on a car with a non functional emissions system, might idle just fine at 13.5 afr, but if you turn the variable resistor to the LEAN range which causes the mixture to go into the 14 plus afr range, the idle might and probably will get shakier/rougher.***

Yes, the emissions has been removed. I am going to try the variable resistor first and adjust it to 13 or so. That would be great if it fixed the problem!



***I think you need to buy a simple fuel cut switch for three bucks and install it. Either that or read a previous post I made on how to overcome this with a simple voltage switch kit that can be bought from JAYCAR and assymbled. It bypasses the START signal on pin 3B during HOT starts which means the ECU will now actually use the AFM instead of the ECU start map. That means fuel being injected during hot starts at a duration of 6ms instead of say 17ms which is too rich and causes flooding. That or buy a RTEK product that has an anti flooding function built into it. Talking series four........no series five talk here.***

I did install a fuel cut (even though I hate half way fixes!). But I figued it would at least help me to diagnose the problem... The car does the exact same thing if I use the fuel cut or not. That's why I don't think it's the injectors (besides they are brand new too). If the problem persists your i'd feel comfortable about doing one of your other suggestions. Thanks for the advice.