Suggestions on mechanic's report

[vdop69]

Alright, some of you may have read my previous threads in the past couple months about a lean code I was getting. Well, I finally decided to let the local mechanic take a look at the car to see what was causing the code. I get a call the same day as I dropped off the car and lets me know that there is nothing wrong with the car and that the code was probably tripped due to aftermarket intake/headers-back exhaust (more airflow).

1)Does this sound correct? Because last time I checked, there were other 5sfe's with aftermarket intake/exhausts that are not throwing codes.

2)Now I'm not too educated about fuel systems, but when the ecu sees the car running lean, do the injectors start to dump alot of fuel in as safety? Because that would explain why the car would be running overly rich, at times.

3)Would an afc solve this problem?

Thanks

[Curry]

do you have an intake/headers?

did you reset the ecu after installation?

[vdop69]

Originally Posted by Curry

do you have an intake/headers?

did you reset the ecu after installation?

Yes, I have a sri, and rippmod headers.

Pulled the EFI fuse to reset the ecu also.

[wiccanferret]

EFI fuse? You need to pull the ECU fuse.

[Curry]

Yep, or just pull the negative terminal of your battery and leave it for a few minutes.

EFI fuse wont do the trick.

[vdop69]

Originally Posted by Curry

Yep, or just pull the negative terminal of your battery and leave it for a few minutes.

EFI fuse wont do the trick.

Thanks for the reply.

Only recently have I been pulling the EFI fuse, since I thought that reset it also since it clears the CEL. But after the exhaust and intake was installed, and many times after trying to fix the problem, I have pulled the negative terminal off.

[Qslim]

Originally Posted by Curry

Yep, or just pull the negative terminal of your battery and leave it for a few minutes.

EFI fuse wont do the trick.

Yeah, it will. The EFI fuse removes power from the computer, resetting any codes and learned values. Same thing as disconnecting the negative battery terminal, but you don't lose memory in other components like the radio.

Now I'm not too educated about fuel systems, but when the ecu sees the car running lean, do the injectors start to dump alot of fuel in as safety? Because that would explain why the car would be running overly rich, at times.

When the computer sees the fuel trim show a lean condition, it will add fuel to get the mixture back to stoichiometric (14.7:1), but it will still set a code and turn on the MIL to let you know that it had to make an adjustment beyond what is normal to get the car to run normally. Now, if the engine is running correctly in the first place and the lean fuel trim #s are false, the adjustment the computer makes by adding fuel to correct a fake lean condition will really result in a rich condition. Hope this makes sense.

[vdop69]

Originally Posted by Qslim

Now, if the engine is running correctly in the first place and the lean fuel trim #s are false, the adjustment the computer makes by adding fuel to correct a fake lean condition will really result in a rich condition. Hope this makes sense.

This does sound like what is happening. What could cause a fake lean condition other than a bad o2 sensor?

[Qslim]

Originally Posted by vdop69

This does sound like what is happening. What could cause a fake lean condition other than a bad o2 sensor?

Coolant temp sensor, that's about it. When they start to go bad, they'll tell the computer that the coolant temp is below freezing, and the computer will subsequently jack up the fuel trim to warm the engine up. This will usually result in rough running, black smoke, and stalling.

[toyomoho]

The ECU receives a signal input from the A/F sensors to verify and aid in setting the mixture ratio. The ECU is programmed to know what the approx ratio should be given RPM, engine temp, TP, etc. If the ECU computes the sensor data is much differant then what it should be it trips a code.


If code 0171 is showing, the real air/fuel ratio is lean not rich as the code definition would lead one to believe.

When using headers, the new A/F sensor location may receive a greater variation of exhaust pulses (or fewer pulses) and as a result the voltage it generates may vary to a greater extent. The ECU may compute there is a problem with the sensor. This could be a reason the code may come and go.

[boombringer]

Originally Posted by Curry

do you have an intake/headers?

did you reset the ecu after installation?

What happens if you don't reset the ECU after putting on a intake? I still need to do mine.