What's stock afr under boost?

[bpu699]

Perfect stoichiometry is 14.7. Right? The o2 sensors sole job is to keep it there. I assume the o2 sensor is shooting for this value whether under boost or not.

Lots of folks on here are running 12.5 or so under boost. Is that the stock afr also? Or is that with the 02 disconnected and a modified wur?

Just trying to figure out what stock is... Are folks shooting for the lower afr as a safety measure, or is that how the stock system reacts?

Thanks

[Tippy]

On EFI, WOT disables O2 so you can run a safe AFR far fatter than stoch.

[Speedy Squirrel]

Nope. The stock '86 to '89 KE-jetronic disables closed loop above a certain engine speed and a certain throttle opening. It is open loop at WOT.

[bpu699]

So what is a stock afr under boost while accelerating? What's it supposed to be?

Now that I have an afr meter, I am just trying to figure out what I am supposed to be seeing...

Lean under boost is bad, that I understand. So, what is it supposed to be? Anything below 14.7?

Bo

[dos531]

I dont know what stock cars usually get, but you should shoot for around 12 under boost. Mine is around 11.5, but the gas in california is especially terrible so I feel more comfortable in that range.

[RarlyL8]

If your CIS is fresh and engine bone stock the AFR under boost ranges from 10:1 to 11:1 or so. The stock curve is most fat at the point full boost is reached, about 4200RPM and leans slightly to redline. With age the WUR drops pressure and the mixture becomes more rich. Power increasing mods are not compensated so curve becomes more lean.

[T77911S]

on the diagram it has 3k RPM above the speed relay for the O2 sensor cutout.

[RarlyL8]

WOT goes open loop.

[bpu699]

Thanks guys, that was extremely helpful. I haven't had a chance to drive much yet, but at least now I know what I am looking for.

Bo

[Ronnie's.930]

^^^ A couple of other things worth mentioning - 12.5 under full boost (number you mention in your first post) is approaching dangerously lean - 12 is typically considered the lean limit with K-jetronic; anything richer than 9.5 under boost typically results in full throttle misfiring (bogging down, cutting out) and by 9 you see major misfiring.

[bpu699]

Originally Posted by Ronnie's.930

^^^ A couple of other things worth mentioning - 12.5 under full boost (number you mention in your first post) is approaching dangerously lean - 12 is typically considered the lean limit with K-jetronic; anything richer than 9.5 under boost typically results in full throttle misfiring (bogging down, cutting out) and by 9 you see major misfiring.

Whats makes it run "richer" under boost?

Is the afr different at 5000 rpm at cruise (where boost is low), vs gunning it to 5000 rpm where boost is .7-1.0 bar? I presume the answer is yes?

Bo

[RarlyL8]

The control pressure regulator (WUR) has a vacuum port that allows boost pressure to act on a diaphragm which changes the control pressure reading to the fuel head. Lower CP enriches the mixture.

[bpu699]

Originally Posted by RarlyL8

The control pressure regulator (WUR) has a vacuum port that allows boost pressure to act on a diaphragm which changes the control pressure reading to the fuel head. Lower CP enriches the mixture.

Wow. Thanks!

Bo

[oilonly]

Here is a good thread on AFR's and adjustments that can be made.

Want to raise boost AFR - I have a WUR adjustment question

[JFairman]

Originally Posted by bpu699

Wow. Thanks!

Bo

and if you want to experiment and see how your car runs with a little richer mixture there's all kinds of expensive gadgets and other short lived stuff you can buy to do it with CIS, lol...

Once you've been driving for 15-20 minutes and the motor is at operating temperature open the engine lid and un plug the 12 volt supply plug on the control pressure/WUR and go back to driving.

Over a 10-15 minute period the CPR will cool off to engine heat ambient temperature and control pressure will slowly drop around 20 psi from where it was and it will let the air flow meter push the control plunger higher in the fuel head uncovering more of the fuel metering slits and then it will shoot more fuel to the injectors richening up the mixture.

If you have a wideband AFR gauge you'll quickly learn what AFR your motor runs at best.
Then stop and plug the 12 volt plug back into the CPR and control pressure will rise back up to where it was in 2-3 minutes leaning out the AFR as it does it.

Now if you're really crazy you can experiment with wire wound ceramic resistors or 8 ohm wire wound speaker L pad potentiometers in the 12 volt supply or the ground wire to the CPR to lower the current going through the heater element on the bimetallic spring inside the CPR and adjust how fast it warms up or how hot it gets. That will give you adjustable AFR with CIS from the driver seat.
CIS is 100% old school mechanical fuel injection and this is how you can easily adjust your AFR with it for less than 10 bucks.

[bpu699]

That sounds pretty wild... .

Thanks for the great info.

Bo

[krasuskyp]

not to threadjack, buuuuuuuuuuuut...

...I've got Bosch CIS gauges from fleabay awaiting my return from 2wks @ the beach in NH

never in my life have I been so eager to get the fukk home from vacation!! lol / d'oh!

sad / true

I finally figured out my AFR gauge's wonky readings after buying my 3rd Bosch WB02 sensor (don't ask)... and was dismayed to see my AFR's still hitting 13 to even 14 under WOT and over 5500 rpms... this is after I've installed dual 044's hoping that would solve the issue.

My BLWUR came shipped tuned to my basic previous mods, and I'd gauge'd my pressures years ago and things were in spec. My cruise AFR's are great @ 13-14ish, and my on-boost AFR's are really great... 11's to low 12's... until 5500 when the readings shoot too damn high.

This w/ my idle AFR current @ 10.2! Fuchme (and the poor eyewater'd bastids behind me!). And it idles @ 1100... w/ the idle air adjustment screw cranked nearly all the way in. WTF. Seems I can't lean it out any more w/o screaming the idle.

I'm verymuch looking forward to playing w/ my WUR and figuring this the FUKKOUT, and tuning things to my current setup (think I've added headers/turbo/cams/FP's since the BLWUR installed yearseses ago).

Odd thing, is the car runs like a banshee possessed... no sputtering or spitting or popping or pinging - nothing... just great power everywhere, and steady idle. But wonky readings and scenarios, certainly.

loving these threads and all the related links being shared - thanks much guys... beware: many questions to follow! 8-)

[Ronnie's.930]

Originally Posted by krasuskyp

never in my life have I been so eager to get the fukk home from vacation!! lol / d'oh!

sad / true

Paul, you might as well stop laying the BS on so thickly; everyone knows how much you like the steady view of d&*%s in Speedos!!!

About yer upper RPM leanout - have you tried drawing the full throttle enrichment disc out a couple of milimeters and see what happens (that is in the moreer richerer direction)?

Also, what happens to the high idle when you lean the idle afr out to 13.5 and/or 14.5? A high idle like that, with throttle bypass screw all the way in ( ha ha - ya' that's what I said) makes me think you have an air leak at some point after the throttle plate . . . typically that would be in the vacuum limiter valve (decel valve), but I know you have that removed . . .maybe check all of the vac ports you blocked off for that (maybe one of yer old pasties that you used now has a hole in it)?

[RarlyL8]

Extreme lean conditions under full boost (14:1 AFR) cause rappid backfire which is unmistakable. I would double check that your AFR reading is correct.

[T77911S]

my thorttle switch was causing my idle to hang sometimes. it would also make the idle return to different RPM's. i removed it.

timing can make the idle too high.

air leaks. water the engine down really good. around all the intake ports. it wont isolate a leak but it wil let you know if you have one. if wastegate is original, check it too. also all the IC connections/turbo.

i would fix the idle problem first. like me, if you have air leaks, doing all that testing of AFR's is meaningless if you have an air leak.

i have 2 sets of brand new gauges. they read .4bar different for system pressure. they read the same for control pressure. dont buy cheap gauges. (i did not think mine were cheap)