• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

240 How quickly should an O2 sensor adjust?

E

EivlEvo

Active member
Joined
Sep 11, 2012
1993 240+T

I had been having idle issues (long post about surging idle in performance) since adding 577cc/min injectors and an 012 AMM. After significant troubleshooting that had me second guessing ALL of my results, it ended up being a bad AMM. Replaced it and the idle and cruise is fine now.

However... when I go clutch in from any normal driving RPM, the car will struggle and not be able to react quickly enough, and die. This is not related to brake booster as it happens with or without brake application.

IF however, I leave the car in gear... decelerating around 1500RPM or so, you can sort of feel the car lurch forward as it switches into a different mode(?)... if I clutch in AFTER this happens, the car doesn't have toooo much issue and will stay running.

Through all of this my oil got soaked up with fuel, and I noticed that I'm getting some oil into the exhaust. My compression is good, my vac is GREAT, and the car is smooth (oil separator is clear and free).

I'm wondering if perhaps my O2 sensor has had enough of being caked with oil, fireballs, fuel soaked oil and has just gotten a bit lazy? If that makes sense...
 
Once up to operating temp the O2 sensor will operate quickly, really too quickly to see on anything other than a scope or it needs to be replaced.
 
I'm just trying to gauge if a weak/bad/slow O2 might be causing the car to be slow to respond with fuel/air corrections.
 
an O2 sensor sweeps between below lambda=1 and above lambda=1 all the time during idle and also during light cruise conditions. That's how they are supposed to work. The averidge A/F ratio will be 14.7:1

During decel (in-gear engine braking) the LH-ECU cuts fuel 100% until the revs fall below (if i remember correctly) 1250rpm. It's a fuel saving feature that is hard coded into the software of the ECU. At 1250rpm the ECU starts injecting idle fuel again. This can be felt through the driveline, specially when the car has a manual trans. It's normal.

Fuel in the oil and oil in the exhaust is never a normal situation.
IMO your engine has a different problem that is not related to the O2 sensor. I'm thinking leaking fuel pressure regulator or a leaking injector. (meaning 1 or more injector(s) not closed when it/they should be closed) or a leaking (blue) cold start injector (if it still has one.)

Injector size seems a bit big to me. Are they properly sized/matched to that 012 AMM?

The LH-jetronic ECU can only adapt upto a point. If it's operating on the edge of it's adaptive range (due to the use of big injectors) it only takes a small issue to cause A/F ratio's to go wrong.
 
Janspeed said:
an O2 sensor sweeps between below lambda=1 and above lambda=1 all the time during idle and also during light cruise conditions. That's how they are supposed to work. The averidge A/F ratio will be 14.7:1

During decel (in-gear engine braking) the LH-ECU cuts fuel 100% until the revs fall below (if i remember correctly) 1250rpm. It's a fuel saving feature that is hard coded into the software of the ECU. At 1250rpm the ECU starts injecting idle fuel again. This can be felt through the driveline, specially when the car has a manual trans. It's normal.

Fuel in the oil and oil in the exhaust is never a normal situation.
IMO your engine has a different problem that is not related to the O2 sensor. I'm thinking leaking fuel pressure regulator or a leaking injector. (meaning 1 or more injector(s) not closed when it/they should be closed) or a leaking (blue) cold start injector (if it still has one.)

Injector size seems a bit big to me. Are they properly sized/matched to that 012 AMM?

The LH-jetronic ECU can only adapt upto a point. If it's operating on the edge of it's adaptive range (due to the use of big injectors) it only takes a small issue to cause A/F ratio's to go wrong.
Click to expand...

This nice fuel cut feature...
My 245 got LH swapped 3 months ago..all is working great and i have WB installed.. so i can see whats going on in ,real time"..
I have noticed that the WB gauge went full lean on deceleration most of the time.. but one day maybe a month ago ive noticed that no such thing is happening.. so now im thinking about what could happen.. possible air leak?!
OP, sorry for threadjacking
 
12david34 said:
This nice fuel cut feature...
My 245 got LH swapped 3 months ago..all is working great and i have WB installed.. so i can see whats going on in ,real time"..
I have noticed that the WB gauge went full lean on deceleration most of the time.. but one day maybe a month ago ive noticed that no such thing is happening.. so now im thinking about what could happen.. possible air leak?!
OP, sorry for threadjacking
Click to expand...

I would suspect a vac leak first yes. It could also be a mis-adjusted TPS.

Janspeed said:
an O2 sensor sweeps between below lambda=1 and above lambda=1 all the time during idle and also during light cruise conditions. That's how they are supposed to work. The averidge A/F ratio will be 14.7:1

During decel (in-gear engine braking) the LH-ECU cuts fuel 100% until the revs fall below (if i remember correctly) 1250rpm. It's a fuel saving feature that is hard coded into the software of the ECU. At 1250rpm the ECU starts injecting idle fuel again. This can be felt through the driveline, specially when the car has a manual trans. It's normal.

Fuel in the oil and oil in the exhaust is never a normal situation.
IMO your engine has a different problem that is not related to the O2 sensor. I'm thinking leaking fuel pressure regulator or a leaking injector. (meaning 1 or more injector(s) not closed when it/they should be closed) or a leaking (blue) cold start injector (if it still has one.)

Injector size seems a bit big to me. Are they properly sized/matched to that 012 AMM?

The LH-jetronic ECU can only adapt upto a point. If it's operating on the edge of it's adaptive range (due to the use of big injectors) it only takes a small issue to cause A/F ratio's to go wrong.
Click to expand...

Yeah that 1250 is where it's catching itself fine... above that though and it's not quite able to hold on. I might run another tank of fuel through before I get hasty...

Those 577's are matched to the 012 AMM AND the TLAO chips. Mike did mention that 460's were probably "ideal" but had evidence to support trims up into the 600 range iirc. That said, there's no question that the size of these injectors is the problem.

My AFRs are quite good all around. Idles fine. Drives fine... it's just that above 1250 when it's leaned out that it struggles to catch itself in the transition.

This is why I'm (purely thinking out loud as I do) wondering if maybe my O2 sensor is soaked in oil/soot and not up to snuff?

*the oil is from turbo seals... I have a repair kit and 2 other turbos to pop on... just need to weld the downpipes up

*the fuel is from the early tuning process when there was a leak and bad AMM so it was running wonky. I said oil, but meant exhaust... though, that oil will probably be on it's way out this weekend. I have an oil cooler to splice in.
 
You must log in or register to reply here.
Back
Top