AFR problems with MAFT pro

[7MGTEsup]

Hi and thankls for looking, right down to the trouble.

If I start my car from cold and drive it will run as I tuned it all day long. But if I key the car off and restart the engine it will run at 12:1 instead of the 14.6:1 that I tuned it for. Also when its running like this I can pull 20% fuel and it makes about 1 point difference on the AFR.

Any ideas because I'm stumped

 

[89turbotoy]

when you restart you will go into startup enrichment it runs richer for cold start wait a few minutes and it should go back to what you tuned for.

-Zac

 

[sneakypete]

could heat soak have anything to do with it?
ive noticed that after driving for a bit and then stopping somewhere to pick something up, that when i go to start the car back up i experience the same symptoms. i notice that the intake temps at idle are much higher than when ive been running the car.
if i start driving again for a while, and then come to a stop... my afr is ok.
i made the mistake of putting my iat sensor in the 3000 pipe
-pete

 

[7MGTEsup]

Its not heat soak, my IAT is on my ic pipe just near the head light and I never see temps above about 90.

Its not cold start enrichment because I can drive 30 miles and it will stay the same.

The thing that confuses me is I can pull 20% fuel and it will not lean the car out. Makes me think that the unit isn't comunicating with the ECU for some strange reason.

Also my MAFT reads 0.6 higher afr than my wideband, both are earthed with the same wire to the battery.

 

[CRE]

Double check your wiring. I've got the same problem with warm starts with the stock O2 sensor disconnected, but that probably doesn't help as I'm N/A.

I presume you're not getting any error codes either?

Here's the $3 million question.... If you pop/push start the car when it's warm does it run normally? Mine does... go figure.

 

[Jaguar_5]

Also my MAFT reads 0.6 higher afr than my wideband, both are earthed with the same wire to the battery.

What kind of wideband are you running?

If you're talking about the signal ground (purple from the maft iirc) that ONLY connects to the signal (sensor) ground from the wideband, they do not also go to a ground source

That's how mine is with the LC-1 at least

 

[DangoAZ]

Wideband reading different than your narrow band... Have you done a free air calibration with you WB recently? Is the WB really close to the turbo - WB's sometimes are finicky about being hot (close to the turbo).

Also, are you monitering Vf with your MAFT-Pro? When you're pulling/adding fuel in closed loop (computer adjusting off narrow-band signal), you can change it quite a bit on the Pro before it will max out your computer's ability to change the fuel trim to what it wants to see. You change it, and the computer changes it back - You could be fighting each other. If you don't follow what I mean, try some searching on MAFT and Vf - Like here:

http://www.supramania.com/forums/showthread.php?t=39712&page=3&highlight=vf

Anybody that knows a bit about narrow band sensors could chime in here, too: What is the failure mode of the NB? Could the WB be right, and the NB tracking his computer in closed loop to the wrong AFR (when he has driven around for a while and the sensors get really hot)?

 

[CRE]

Ideally, you want the ECU and the MAFT Pro and the Wideband on the same ground (on the head).

If you're using PTT you need to disable the stock O2 sensor.

If you're running with the stock O2 sensor turn off PTT, then check your wiring, make sure all of the connections are clean wire to clean wire and solid. If you've used the the supplied IDC (Insulation Displacement Connectors, the clamshell things) ditch them, they're unreliable, especially with old wiring.

If you've still got the offset, try recalibrating the WB, perhaps try another NB or stop by a local performance shop and ask if they can double check the AFR against your WB, don't even need to dyno so they might do it for free they may want $20.

A bad NB generally swings SEVERELY, although I could imagine one shifting a bit from heat... The ECU should compensate though and if it's not enough to cause a code 21 You wouldn't see a difference of more than a few decimals.

 

[7MGTEsup]

Sorry if it wasn't clear at the start this is running without the NB o2 sensor conected so its not a conflict with the ECU. I'm running an AEM wideband, all wires were soldered with good solid connections.

 

[CRE]

See the last line in my first post again. I'm curious about this.

Aside from that test the voltage at STA on the ECU when you crank the engine. It should be 12v or a little more, if not it can apparently cause issues. Push starting the car may cause an error code for the STA signal though, so if it shows up that's probably why.

Aside from that heat soak's about all I could think of, nut in my case if i plug a resistor in the ECU's coolant temp sensor harness connector to fool it into thinking it's a cold start the car runs fine... something odd and I just can't figure it out. You may also want to see if using a resistor to force a cold start gets things running right... don't leave it there though, it's not a fix, just for testing.

With the wideband if there's a sensor ground make sure it's connected to the right wire on the MAFT Pro. If there's not a sensor ground then you need to ground the MAFT Pro's sensor ground line to the same location as the WB's ground, you can't leave it disconnected though.