Doc

I would like to pick some of your master tuner brains, if I could.

I have a 2002 S2000 with a Comptech SC/Aftercooler and VAFC. Otherwise the engine/ECU is stock.

The car ran perfectly, well tuned with the VAFC prior to installing the aftercooler.
Ever since installing my aftercooler, I had been getting a CEL off and on. When I would pull the code, it was:

P0170
P0171

Saying that I was running too lean. So I thought that since I am running cooler air, maybe it is messing it up a bit, so I zeroed out the VAFC to run stock, but still got the CEL.

I then had the car tuned with VAFC and WBO2 and seemed okay for a little bit. Now I am getting the same CEL codes again. I zeroed out the VAFC once more, and still got the CEL after driving the car 2-3 times after resetting the ECU.

I thought that maybe the tuner had leaned it out a bit too much on the Fuel Pressure Regulator from Comptech, so I increased the PSI to around 39 at idle with 20" Hg vaccuum. This is just slightly higher then stock settings according to Comptech. And I STILL GET THE CEL!!!!

The driving situations where it comes on are at simple cruising speed around 3-5k RPM. Not under WOT or heavy use, just cruising along the freeway for instance.

So now I am stuck. I am planning to remove the VAFC all together to see if the ECU is getting some strange reading from it, but my ESM is wired into the harness as well, so it will be a wiring nightmare to undo all that to return to stock. I have checked all the vaccuum hoses, and don't have any vaccuum loss according to my boost gauge.

Any ideas what could be giving me a "Too lean" code with fuel pressures above stock settings? Bad injectors? Bad plugs? I'm at a loss.

Thanks for any input!
JJ

smyroad

Have you taken it to a shop to determine to see if it is running lean?

If it is too lean:
1. Re-tune the VAFC using an A/F sensor
If that doesn't work
2. Map sensor problems can cause the ECU to lean the mixture too much. If the cel light is off, try idling the car at 2,000 rpm for 1-2 minutes and look to see if the cel light comes on.

If the A/F is good or too rich:
1. Check Cables/Replace the O2 sensor in the car.

Doc

Thanks.

1) that is why I got it tuned again, I was having the CEL prior to tuning with A/F, and the CEL went away for a short time but now it is back with a vengance!

2) It doesn't turn on right away when reset. I can drive the car normally 2 or 3 times before the CEL comes on again, so it isn't instantly on when I reset it, even at a long idle.

I may just have to take it to the dealer and check the diagnostics on it, but I was hoping to avoid that. I will remove the VAFC prior to that.

Any other thoughts?
JJ

smyroad

Was it actually running lean before it was re-tuned?

I have no idea how the VAFC interacts with the O2 sensor so take this with a grain of sand.

The only map sensor issue I've experience was in my integra. It seemed very random at first, sometimes taking several days repeat. The CEL wouldn't turn on idling at normal rpm or repeated WOT cycling. If I sat in the car and reved it to about 2,000 rpm within 60 seconds the cel light would go on every time.

The Map Sensor was broken causing the ECM to lean out the engine to the point that the O2 ssensor couldn't detect the A/F ratio. At that point the ECM would switch to pre-programmed mode. The A/F would then come back in normal range and the fault would disappear (Pre-OBDII days).

Slows2k

I'd would first check for any vacuum leaks underhood. A can of throttle plate cleaner works well, Spray the intake manifold, any suspicious vacuum lines. If you hear an increase in rpm you have found the leak. The next step is to monitor 02 sensor voltage, You will need a scan tool that reads data stream to do this. The HO2S1 voltage should rapidly change from 0-1V, and not stay at 1 voltage # for more than a second. If the volts don't switch, you have was is called a "lazy O2" Replace it. The next check is for the EVAP purge soleniod is holding vacuum, not leaking back through the intake. After that, check valve clearances. (The will have to be pretty tight to cause the DTC ) Your last cause of the DTC is clogged/ restricted injectors. This is all assuming the VAFC has nothing to do with your problem. If you are using a VAFC harness double check all of your connections. When the car was tuned did it run lean in any RPM range?

Doc

Great! I will try a few of these, although some of them are far too complicated for me to perform.

Here is what the final run came out as when I tuned the car last. (remember that all these settings have been zeroed and are now running stock - The second picture is Stock at the time in Red and Final in Blue)

Final A/F Readings with VAFC



Red is set at Zero, Blue is Final after tuning with VAFC.

So as of now, I am probably closer to the Red, since I have removed all settings on the VAFC.

Thanks for all the help.

JJ

Slows2k

Doc, Do you have the freeze data from your DTC's? The data is stored any time a DTC is set. It has all main engine operating conditions at time of DTC. I would be interested to see the MPH and RPM the DTC occured. Your A/F#'s don't look bad to me, But they also represent a WOT run, not part throtle cruise.

Doc

I am supposed to pick up a data logger this weekend. I will check that when I get back, I am curious what those readings are too.

JJ

fperra

I assume the AF ratios you posted are for open loop WOT. The CEL lights you are getting are for closed loop operations. You need a Wide band in the car to see what is happening under partial throttle operations. Your A/F ratio should be right around 14.7 under partial throttle conditions.

Gernby

I bet it is the MAP sensor.