Euro (non-O2 sensor) air/fuel tuning
05-04-2004, 04:07 PM
#1
Rennlist Member
Thread Starter
Euro (non-O2 sensor) air/fuel tuning
I'm looking for better fuel tuning of my 928. I have the LH ECU w/ no O2 sensor (euro).
I'm considering a wideband O2 sensor (WBO2).
PLX-300 for a permanent setup, and simple function.
or
LM-1 for a handheld 'not-so-permanent' setup, w/ datalogger for PC analysis.
...haven't made up my mind, though price is similar.
But most importantly, will the WBO2 help get me to an optimal state of tune?
My two options for fuel tuning are adjusting CO level of the MAF, and fuel pressure (coupled w/an adjustable FPR)??
I recently installed a new MAF, but didn't adjust it at all, as it is already calibrated (?) It 'seems' to be running rich, even at idle. Also I have noticable 'flat spots' in the high RPM range before the WOT switch is activated.
Is there any way to add a narrow band signal to my ECU, and/or is it needed?
Thanks in advance!
I'm considering a wideband O2 sensor (WBO2).
PLX-300 for a permanent setup, and simple function.
or
LM-1 for a handheld 'not-so-permanent' setup, w/ datalogger for PC analysis.
...haven't made up my mind, though price is similar.
But most importantly, will the WBO2 help get me to an optimal state of tune?
My two options for fuel tuning are adjusting CO level of the MAF, and fuel pressure (coupled w/an adjustable FPR)??
I recently installed a new MAF, but didn't adjust it at all, as it is already calibrated (?) It 'seems' to be running rich, even at idle. Also I have noticable 'flat spots' in the high RPM range before the WOT switch is activated.
Is there any way to add a narrow band signal to my ECU, and/or is it needed?
Thanks in advance!
Last edited by Jadz928; 05-04-2004 at 04:47 PM.
05-04-2004, 04:51 PM
#2
Rennlist Member
Thread Starter
From John Speake at JDSPorsche.com FAQs
Q OK my car is non-cat, what now?
A. Because this system does not have a catalytic converter with an oxygen sensor, the LH computer and MAF operate as an "open loop system". That is to say, it does not have any type of automatic compensation for small errors in the MAF output. So if (for example) the MAF gives a lower output voltage than it should, the LH computer outputs fuel from the injectors corresponding to a lower airflow, and the mixture is weak. This will reduce power, and may cause hesitation when the throttle is opened quickly. These effects will gradually get worse with use over some time, due to hot wire erosion.
As well as a gradual weakening of the mixture due to wire erosion, other types of MAF failure have resulted in excess rich mixture, with lots of black smoke, a strong smell of petrol in the exhaust, black sooty spark plugs, and rough running. If the MAF output voltage eventually reaches a point well out of calibration, or for some reason the output suddenly jumps out of normal tolerances, the LH computer will ignore the MAF output voltages entirely, and should revert to a stored "limp home" programme. (see later)
So MAF failure often is a gradual degrading of performance, often first noticeable with "flat spots" causing hesitation during acceleration.
A. Because this system does not have a catalytic converter with an oxygen sensor, the LH computer and MAF operate as an "open loop system". That is to say, it does not have any type of automatic compensation for small errors in the MAF output. So if (for example) the MAF gives a lower output voltage than it should, the LH computer outputs fuel from the injectors corresponding to a lower airflow, and the mixture is weak. This will reduce power, and may cause hesitation when the throttle is opened quickly. These effects will gradually get worse with use over some time, due to hot wire erosion.
As well as a gradual weakening of the mixture due to wire erosion, other types of MAF failure have resulted in excess rich mixture, with lots of black smoke, a strong smell of petrol in the exhaust, black sooty spark plugs, and rough running. If the MAF output voltage eventually reaches a point well out of calibration, or for some reason the output suddenly jumps out of normal tolerances, the LH computer will ignore the MAF output voltages entirely, and should revert to a stored "limp home" programme. (see later)
So MAF failure often is a gradual degrading of performance, often first noticeable with "flat spots" causing hesitation during acceleration.
05-04-2004, 04:59 PM
#3
Rennlist Member
Hi Jim,
Assuming you have set the idle mixture pot for 1% CO at idle (aitrpump blanked off) then you shouldn't have a richness problem further up the scale. The Euro S2 tends always to run on the leanish side.
Have you checked the fuel pressure ? It is possible that someone has "adjusted" it to compensate for an aged MAF. A favourite method some people have used is to squeeze the casing of the FPR to increase the pressure. If it is done neatly, it is impossible to deect without measuring the fuel pressure.
Another thing to check is that all the injectors are flowing freely, and that non are leaking. This could explain unexpected running symptoms.
What you describe for your car is not typical of the Euro S2.
Your new MAF will be calibrated to within 0.5% (2.5% on mixture)
Regards
Assuming you have set the idle mixture pot for 1% CO at idle (aitrpump blanked off) then you shouldn't have a richness problem further up the scale. The Euro S2 tends always to run on the leanish side.
Have you checked the fuel pressure ? It is possible that someone has "adjusted" it to compensate for an aged MAF. A favourite method some people have used is to squeeze the casing of the FPR to increase the pressure. If it is done neatly, it is impossible to deect without measuring the fuel pressure.
Another thing to check is that all the injectors are flowing freely, and that non are leaking. This could explain unexpected running symptoms.
What you describe for your car is not typical of the Euro S2.
Your new MAF will be calibrated to within 0.5% (2.5% on mixture)
Regards
05-04-2004, 05:14 PM
#4
Rennlist Member
Thread Starter
Assuming you have set the idle mixture pot for 1% CO at idle (aitrpump blanked off) then you shouldn't have a richness problem further up the scale.
I didn't set this. Could you explain how to set it? Is it in the WSM?
I think I'm running rich at idle. I can smell much gas in the exhaust. I'm not sure if I'm running rich in the higher rpms.
I'm assuming an O2 sensor will do very little for my car? I thought it may help with tuning the MAF and fuel pressure.
I will check the fuel pressure.
05-05-2004, 10:04 AM
#5
Rennlist Member
Yes, it's in the manual, 24-123. Anti-clockwise for leaner mixture.
Are you sure the fuel pressure is OK ? Should be 30psi at idle, and 36psi, engine stopped and fuel pump relay bridged.
Are you sure the fuel pressure is OK ? Should be 30psi at idle, and 36psi, engine stopped and fuel pump relay bridged.
05-05-2004, 12:47 PM
#6
Burning Brakes
Join Date: Aug 2001
Posts: 784
Likes: 0
Received 0 Likes
on
0 Posts
I think the only reason the air mass meters have adjustment screws is because they are not all that accurate at low air flow rates - like at idle. So the screw is for the idle mix, but anything off idle and under load won't be affected by the adjustment on the air mass meter. L-Jet "Flapper Door" meters are like this too - the screw adjusts a tiny air bypass that routes a tiny amount of air past the door. But under any sort of load, the door opens so much that the air bypass is negligible.
If your engine has the air pump running (on the Euro 16V motor, it injects air into the exhaust ports in the head just outside the exhaust valves), it shouldn't smell rich at idle. The air gets pumped in there to finish burning any hydrocarbons that escape from the combustion chamber. I'm pretty sure this is purely an emissions thing because it shuts off under full throttle.
I've had success in setting my idle mixture by shutting off the air pump, leaning the mixture out at with the air mass meter screw until you start to get a lean misfire (this is all done with the car warmed up and idling). The engine will be running smoothly and then you get a little "pum.....pum..pum........pum" in the exhaust note. You have to listen for it carefully. Then enrich it until the miss goes away and you're back to all 8. Then enrich 1/4 turn more. The exhaust should smell pretty clean. Turn the air pump back on and the exhaust should smell very clean. This should be a good base state to start from.
Before you do this, make sure you've got a good air mass meter, no vacuum leaks, proper fuel pressure, good injector spray pattern, and no leaking/dripping injectors. You might want to send your injectors out for cleaning just as a matter of course. It made a big difference on my car.
I think the hot setup would be to put an O2 bung on each downpipe leading to the cat. Since the engine has two fuel pressure regulators, you can install two adjustable regulators and have separate fuel pressure control for each bank. If you can then use a wide band O2 on each bank and get them both at like 12:1, you'll have a pretty optimized setup and should get some real gains.
Anyhow, getting the engine to that well tuned, clean and smooth running base state should be task 1 before starting with mods. And it's all pretty easy stuff - igntion (wires and plugs - just stock stuff - made another big improvement in eliminating misses), air leaks, injectors, correct fuel pressure.
Bryan
If your engine has the air pump running (on the Euro 16V motor, it injects air into the exhaust ports in the head just outside the exhaust valves), it shouldn't smell rich at idle. The air gets pumped in there to finish burning any hydrocarbons that escape from the combustion chamber. I'm pretty sure this is purely an emissions thing because it shuts off under full throttle.
I've had success in setting my idle mixture by shutting off the air pump, leaning the mixture out at with the air mass meter screw until you start to get a lean misfire (this is all done with the car warmed up and idling). The engine will be running smoothly and then you get a little "pum.....pum..pum........pum" in the exhaust note. You have to listen for it carefully. Then enrich it until the miss goes away and you're back to all 8. Then enrich 1/4 turn more. The exhaust should smell pretty clean. Turn the air pump back on and the exhaust should smell very clean. This should be a good base state to start from.
Before you do this, make sure you've got a good air mass meter, no vacuum leaks, proper fuel pressure, good injector spray pattern, and no leaking/dripping injectors. You might want to send your injectors out for cleaning just as a matter of course. It made a big difference on my car.
I think the hot setup would be to put an O2 bung on each downpipe leading to the cat. Since the engine has two fuel pressure regulators, you can install two adjustable regulators and have separate fuel pressure control for each bank. If you can then use a wide band O2 on each bank and get them both at like 12:1, you'll have a pretty optimized setup and should get some real gains.
Anyhow, getting the engine to that well tuned, clean and smooth running base state should be task 1 before starting with mods. And it's all pretty easy stuff - igntion (wires and plugs - just stock stuff - made another big improvement in eliminating misses), air leaks, injectors, correct fuel pressure.
Bryan
05-05-2004, 12:54 PM
#7
Rennlist Member
Hi Bryan,
The Euro S2 has a Hot wire air mass meter, so is different to what you describe. the adjustment is electronic to the ECU, not an air bypass.
Regards,
The Euro S2 has a Hot wire air mass meter, so is different to what you describe. the adjustment is electronic to the ECU, not an air bypass.
Regards,
Trending Topics
05-05-2004, 01:52 PM
#8
Burning Brakes
Join Date: Aug 2001
Posts: 784
Likes: 0
Received 0 Likes
on
0 Posts
I realize that the hotwire air mass meter is physically different from the electromechanical L-Jet meter, but the principle is the same. At low air flow rates, the air mass meter isn't accurate for whatever reason - the thermodynamics of heat transfer or some such. Therefore, when the air mass drops to a certain point, the air mass meter just sends a fixed signal to the ECU. You can tune this signal with the adjustment on the air mass meter. So in practice, the adjustment is for idle mixture, not an offset in the response of the meter over its entire range.
Bryan
Bryan
05-05-2004, 03:10 PM
#9
Rennlist Member
"Therefore, when the air mass drops to a certain point, the air mass meter just sends a fixed signal to the ECU. You can tune this signal with the adjustment on the air mass meter. So in practice, the adjustment is for idle mixture, not an offset in the response of the meter over its entire range. "
Hi Bryan
I'm afraid I have to disagree on this one, I have test jigs for both the hot wire MAF, and the ECUs and know what a Hot wire MAF does. Although the idle mixture pot is mainly for idle mixture, on a non cat car, the idle mixture pot also has an effect across the whole fuelling range, although this is proprtionally less that at idle.
The Hot wire MAF is very accurate and senstive down to much lower flow levels than ever used in a 928 engine, well below idle airflow rates. It's output is constantly variable, it does not "limit out"
Hi Bryan
I'm afraid I have to disagree on this one, I have test jigs for both the hot wire MAF, and the ECUs and know what a Hot wire MAF does. Although the idle mixture pot is mainly for idle mixture, on a non cat car, the idle mixture pot also has an effect across the whole fuelling range, although this is proprtionally less that at idle.
The Hot wire MAF is very accurate and senstive down to much lower flow levels than ever used in a 928 engine, well below idle airflow rates. It's output is constantly variable, it does not "limit out"