AFR problems

[Marcin]

Hi,

I have dyno'd my 911 with stock 3.2 Motronic US engine with sport exhaust and stock chip.
There is one thing that makes me worry.
As you can see on the picture I have very unstable AFR from 3000rpm upwards.
The mixture is rather lean and I cannot adjust it.
O2 sensor is out of order so the mixture should be rich.
Air volume measurer adjusting screw is working but there is no reaction forr turning the screw.

What should I look for to make proper setup?

Here is a link to picture http://picasaweb.google.pl/peterjarvis18/Pulpit#5356367621945035026

Marcin

[equality72521]

Your picture is not showing up for me.

[scarceller]

No picture?

Have you set the base CO mixture according to spec and by the correct procedure?
Here is the correct procedure and setup:

CO = 0.8% or AFR=14.2

Setting base idle and CO mixture
1) Oil temp at 90C
2) All electrical consumers off (AC, heat, lights, ...)
3) O2 sensor unplugged
4) Adjust the CO screw on the AirFlowMeter for CO=0.8 or AFR=14.2 (clockwise=richer)
5) Now connect O2 sensor
6) Bypass idle speed stabilization by bridging B&C terminals on test port (left side near rear fuses)
7) Adjust idle speed with bypass screw on ThrottleBody, 84-85 cars are 800RPM 86-89 are 880RPM, set base idle 20to40RPM above target, if target is 880RPM set base at 900 or so.
8) remove jumper

If you follow this procedure and you find that turning the AirScrew on the AFM (not the ThrottleBody) does not cause the mixture to alter then something is wrong with the AFM.

Also keep in mind that lean mixtures are most commonly caused by air leaks into the system after the AFM (Downstream). Often failed gaskets where the intake runner(s) meet the head, these gaskets get sucked into the port. If you are seeing lean conditions above 3000RPM DO NOT put the engine under any LOAD! Lean conditions can and will eventually destroy these motors because they do not have knock sensors.

What are you seeing rich or lean above 3000?

Also, if you are dynoing I assume you are at WOT and you need to be sure the WideOpenThrottle switch is closing on the ThrottleBody, the TB has 2 switches, one comes closed when the throttle plate returns to idle this is the idle switch and MUST close when plate is closed. The other closes at about 80% throttle, this is the WOT switch and it MUST close for the WOT fuel and ignition maps to to activated in the Motronic box. The WOT switch often fails to close and if it does not you will be running in the Part Throttle maps instead of the WOT maps and the AFR will not be correct.

[Marcin]

Sorry, here is a link to picture http://picasaweb.google.pl/peterjarvis18/Pulpit#5356367621945035026

Thanks, Sal. I will go through the list with my mechanic later this day.
I wonder what you think seeing the graph.

Marcin

[ischmitz]

Here is the dyno chart for others to comment. I assume the dotted line that starts out above 20!! and then comes down to about 15 at 3000 RPM is the measured A/F ratio. It looks to me like the measurement is simply incorrect. Maybe their sensor is bad or completely out of calibration. I don't think the engine would even run with an A/F of 20.....

The torque and HP curve look more or less as expected. With the A/F ratios shown I don't think you would get that nice of a HP and torque response.

Ingo

[Marcin]

Yes the dotted line is the AFR. How should it look like to 3000 rpm? Should it be more or less straight line around 14 ?

[scarceller]

Those AFRs can't be right, you are way to lean! In the 3000-4000RPM range it shows AFRs above 14, no way, under full load with an AFR above 13.0 the engine will most certainly be in detonation range. I'm betting that AFR data is wrong, I don't think you could produce those HP numbers with that AFR.

What's the gray line at the bottom? That one would seem more appropriate, although a bit rich at the low RPM. The stock chips tend to run rich in the lo 12s.

I'd hope Steve Wong can chime in here?

[Marcin]

The grey line are HP losses (don't know what it means).
I will be back with the report when we go through your list and air leaks and switches checking.
Thanks
Marcin

[Steve W]

I have seen AFRs like this before, usually from engine transplants in early bodies. Did you:

a) plug the two loose pin 10 wires by the DME together?
b) transplant the full 3.2 fuel system too, including fuel pump?
c) check what position you fuel quality switch is in?
d) verify operation of your full throttle switch?

[Marcin]

Steve,

a) plug the two loose pin 10 wires by the DME together?
b) transplant the full 3.2 fuel system too, including fuel pump?
c) check what position you fuel quality switch is in?
d) verify operation of your full throttle switch?

a) will check
b) the fuel system is 75' except pump which is brand new Bosch unit correct for 3.2. Is there anything else that matters?
c) I ' ve checked it already but couldn't figure out what should be proper position for EURO 98 I'm using
d) my mechanic says it is ok

I ' ve checked Motronic unit and there is written by PO that it is EURO 231PS version. How to check it's proper for my engine? Can it influence AFR?

[Steve W]

fuel quality switch should be in full counterclockwise position.

the ROW/Euro DME lacks provision for an O2 sensor. So it's not that its out of order, but that the the DME and chip software does not recognize it and does not use it. ROW 84-86 DMEs commonly are 0.261.200.051 or 052, chip #s 1267355027, 1267355154, or 1267355099. 87-89 ROW DMEs are commonly 0.261.200.078 or 084 chip #s 1267355357, 1267355236, 1267355211, or 1267355301. It works fine and net power is not all that much different than if you used a U.S. DME and stock chip with your U.S. spec motor.

[Marcin]

I've checked DME and the number is 0261 200 082 and the chip is 1267355357 so this is ROW 87-89 one.

[Steve W]

Not necessarily. The 082 DME is a standard 87-89 unit. The 357 chip can be set up to run in either U.S. or ROW specification, depending on the external jumper configuration of the pin 10 wires, and the existence of the ROZ adapter. This adapter plugs in the harness between the DME and the altitude sensor. On U.S. cars this does not exist and it's just the altitude sensor plugging directly into the harness.

In either case, with or without the ROZ adapter, the motor should spec out to no more than 207 DIN hp with the 357 chip.

[Marcin]

I have dyno'd my car once again after followed your recommendations

a) plug the two loose pin 10 wires by the DME together? done
b) transplant the full 3.2 fuel system too, including fuel pump? done
c) check what position you fuel quality switch is in? full counterclockwise position
d) verify operation of your full throttle switch? strange behaviour

http://picasaweb.google.pl/peterjarvis18/DynoChartAfterChecking20091807?authkey=Gv1sRgCOe53 sPmsdPf6gE#5360170691043620402

The AFR seems to be better and more proper now. Nevertheless HP and torque is ca. 10% worse from previous dyno chart.

It seems that the mixture is going lean where it should be the richest 5500 rpm.
The strange thing is the AFR and results are better with Full Throttle Switch (FTS) diconnected (this chart). FTS was checked eletronically and it was sending the signal to DME.

I wonder if its out of order and how to make proper check.
As I can see AFR charts on Steve W site the AFR is straight line going down from 14-15 to 12- 13 at the highest rpm.

My AFM seems to be ok - the regulations works and we also tried with several options with the spring and plastic plate inside and this results are the best we could achieve.

Suggestions ?

[Steve W]

If those AFRs are correct, then you have a hardware issue that needs to be traced. The charts I have of stock AFRs on my site are more typical. You should check your fuel pressure, or it could be a clogged fuel filter, bad fuel injectors, condition and gapping of your spark plugs. Such lean mixtures can cause predetonation and break your rings and pistons. The curve is extremely non-linear, possibly indicating fuel starvation at higher flows.

With the WOT switch not activated, the AFRs will be a bit richer, as the DME is still referencing the part throttle maps which are mapped richer at the upper rpms vs full throttle.

[Marcin]

Thanks Steve. I think that this AFR chart we can trust now.
Tomorrow we we will check the hardware stuff. Just to be sure. The fuel pressure should be around 35 psi no matter of rpms?

[Steve W]

Fuel pressure should be 2.5 bar with the vacuum line disconnected from the fuel pressure regulator, regardless of rpms. If would say if you're seeing 38-40 psi, you are good.