When the MAF is disconnected..... - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

DMC · 01-31-2006, 11:11 AM

When the MAF is disconnected, does the motor stop using any other sensors? Like possibly the O2 sensor?

I hope someone knows this....THANKS

-David

DMC · 02-02-2006, 09:39 AM

please does anyone know this? it would really help me out SOOOO much!

SpeedMonkeyInc · 02-02-2006, 11:35 AM

I would guess no. What use is the o2 sensor when the ECU already knows its dumping fuel?
No maf = safe mode so sensor inputs are going to be way off normal readings

brokeAs240sx · 02-02-2006, 11:40 AM

not sure which engine you are referring to (or if engine even matters), but I believe for the ka's, disconnecting the maf puts the car into fail-safe mode, which only allows you to rev up to 2.5k.

Since it is in fail-safe mode, I don't THINK o2 sensor matters any more.

What are you trying to do?

DMC · 02-02-2006, 03:41 PM

my car runs fine when the maf is disconnected, but when it is connected it just stalls. I figured out today that i am missing my o2 sensor and i wasnt sure if that could be my issue.

Nizzan4u2nv · 02-02-2006, 09:20 PM

That doesnt really make much sense. The ecu cant use its regular timing and fuel maps with the maf disconnected and goes into limp mode when its failed or disconnected. Are you sure you arent talking about the TPS(throttle position sensor)? I assume you have an s14 going by your avatar, which means youre obd 2. Are you talking about the primary or secondary 02 sensor(exhaust manifold vs cat). Your car can run without the secondary, but I highly doubt it will run without the primary. How could you be missing the primary anyway, you would have a big hole in the exhaust manifold.

g6civcx · 02-02-2006, 09:53 PM

That means your MAFS is faulty somehow. When you unplug it, the engine can compensate and runs somewhat okay. If the MAFS is faulty and you plug it in, it will give faulty readings and the engine will run poorly. That is how you diagnose a bad MAFS.

Start with the MAFS and go on from there. Good luck.

DMC · 02-02-2006, 10:39 PM

sorry i should have givin more info, i have an s13 with a ka24de swapped in. I have replaced the MAF with one from the junkyard, maybe they are both bad! I also replaced the computer. I will try to borrow my friends maf and see what happens. Let me know if you guys have any other ideas PLEASE.

Thanks
David

outerheaven2k4 · 02-02-2006, 10:57 PM

That's odd..
when I disconnect the MAF on my 89 240...it just dies :P

sblack13 · 02-03-2006, 12:28 AM

Quote:

Originally Posted by outerheaven2k4

That's odd..
when I disconnect the MAF on my 89 240...it just dies :P

same thing happens to me. some cars do it some cars don't, weird...

DMC · 02-03-2006, 08:46 AM

I am pretty sure if you disconnect or connect the maf while the car is running, it will stall. But if you disconnect it and then start the car it will run on a preprogrammed map. And the ecu will not allow the motor to rev past 2500. But what exactly is limp mode? Is it what i just said where the car wont rev past 2500?

asiangento · 02-02-2006, 11:26 PM

hi... from my experiences, if everything on ur car is ok, and u pull the maf... it should run like shit and die. however, if other things are bad... like coolant temp or maybe o2 sensor, car goes into "limp home mode" which is just the ecu's preprogramed program. and when the car is in that mode it dosnt use any sensors.

so... i think with ur o2 not there, it's putting the ecu into limp dick mode.

g6civcx · 02-03-2006, 09:14 AM

The best bet is to get a MAFS tester. Your local mechanic should be able to do it for you. They hook up the tester to the MAFS harness and measure the MAFS reading. When air is coming through, the waveform should rise steadily, with no spikes or peaks. If there are abrupt changes, your ECU will not be able to adjust and the engine will run poorly.

It shouldn't cost you too much money to test it. May save you the trouble of buying a new MAFS.

Or you can try swapping in a known-good. MAFS fail all the time so make sure it is really a known-good.

DMC · 02-03-2006, 10:25 AM

Ok I just installed a good mafs from my friends running car, and the same thing happened

I am thinking I may not have something hooked up or grounded, but I have no idea!

outerheaven2k4 · 02-04-2006, 07:42 AM

Recently I removed my cat and while in the process of fabricating a straight pipe, I drove with just headers ^_^. I noticed while driving like that, around 2000-3000 rpm I had a huge power loss, roughness, after 3000, it smoothed out. After putting in the straight pipe, its still there, I just noticed it better without the pipe. My gas milage is TERRIBLE, like 9-10mpg. Idle is a little rough. Just wondering if this was the MAF causing all of this...sounds like it. I figure while we're on the subject of MAF I'd bring this up...I hate MAFs....

01-31-2006, 11:11 AM	#1
DMC Zilvia Addict Join Date: Jan 2003 Location: Chesapeake, Va Posts: 609 Trader Rating: (0) Feedback Score: 0 reviews	When the MAF is disconnected..... When the MAF is disconnected, does the motor stop using any other sensors? Like possibly the O2 sensor? I hope someone knows this....THANKS -David

02-02-2006, 09:20 PM	#6
Nizzan4u2nv Zilvia FREAK! Join Date: Oct 2003 Location: San Diego Age: 40 Posts: 1,226 Trader Rating: (3) Feedback Score: 3 reviews	That doesnt really make much sense. The ecu cant use its regular timing and fuel maps with the maf disconnected and goes into limp mode when its failed or disconnected. Are you sure you arent talking about the TPS(throttle position sensor)? I assume you have an s14 going by your avatar, which means youre obd 2. Are you talking about the primary or secondary 02 sensor(exhaust manifold vs cat). Your car can run without the secondary, but I highly doubt it will run without the primary. How could you be missing the primary anyway, you would have a big hole in the exhaust manifold. __________________

02-02-2006, 09:39 AM	#2
DMC Zilvia Addict Join Date: Jan 2003 Location: Chesapeake, Va Posts: 609 Trader Rating: (0) Feedback Score: 0 reviews	please does anyone know this? it would really help me out SOOOO much!

02-02-2006, 11:35 AM	#3
SpeedMonkeyInc Zilvia FREAK! Join Date: Apr 2003 Location: Oakland Age: 45 Posts: 1,271 Trader Rating: (0) Feedback Score: 0 reviews	I would guess no. What use is the o2 sensor when the ECU already knows its dumping fuel? No maf = safe mode so sensor inputs are going to be way off normal readings

02-02-2006, 11:40 AM	#4
brokeAs240sx Nissanaholic! Join Date: May 2004 Location: Southern California Posts: 1,917 Trader Rating: (40) Feedback Score: 40 reviews	not sure which engine you are referring to (or if engine even matters), but I believe for the ka's, disconnecting the maf puts the car into fail-safe mode, which only allows you to rev up to 2.5k. Since it is in fail-safe mode, I don't THINK o2 sensor matters any more. What are you trying to do?

02-02-2006, 03:41 PM	#5
DMC Zilvia Addict Join Date: Jan 2003 Location: Chesapeake, Va Posts: 609 Trader Rating: (0) Feedback Score: 0 reviews	my car runs fine when the maf is disconnected, but when it is connected it just stalls. I figured out today that i am missing my o2 sensor and i wasnt sure if that could be my issue.

02-02-2006, 09:53 PM	#7
g6civcx Post Whore! Join Date: Apr 2004 Location: Virginia, USA Posts: 5,764 Trader Rating: (5) Feedback Score: 5 reviews	That means your MAFS is faulty somehow. When you unplug it, the engine can compensate and runs somewhat okay. If the MAFS is faulty and you plug it in, it will give faulty readings and the engine will run poorly. That is how you diagnose a bad MAFS. Start with the MAFS and go on from there. Good luck.

02-02-2006, 10:39 PM	#8
DMC Zilvia Addict Join Date: Jan 2003 Location: Chesapeake, Va Posts: 609 Trader Rating: (0) Feedback Score: 0 reviews	sorry i should have givin more info, i have an s13 with a ka24de swapped in. I have replaced the MAF with one from the junkyard, maybe they are both bad! I also replaced the computer. I will try to borrow my friends maf and see what happens. Let me know if you guys have any other ideas PLEASE. Thanks David

02-02-2006, 10:57 PM	#9
outerheaven2k4 Join Date: Oct 2004 Location: Lexington Park MD Posts: 40 Trader Rating: (0) Feedback Score: 0 reviews	That's odd.. when I disconnect the MAF on my 89 240...it just dies :P

02-03-2006, 08:46 AM	#11
DMC Zilvia Addict Join Date: Jan 2003 Location: Chesapeake, Va Posts: 609 Trader Rating: (0) Feedback Score: 0 reviews	I am pretty sure if you disconnect or connect the maf while the car is running, it will stall. But if you disconnect it and then start the car it will run on a preprogrammed map. And the ecu will not allow the motor to rev past 2500. But what exactly is limp mode? Is it what i just said where the car wont rev past 2500?

02-02-2006, 11:26 PM	#12
asiangento Leaky Injector Join Date: Jun 2003 Location: Santa Ana Age: 40 Posts: 148 Trader Rating: (10) Feedback Score: 10 reviews	hi... from my experiences, if everything on ur car is ok, and u pull the maf... it should run like shit and die. however, if other things are bad... like coolant temp or maybe o2 sensor, car goes into "limp home mode" which is just the ecu's preprogramed program. and when the car is in that mode it dosnt use any sensors. so... i think with ur o2 not there, it's putting the ecu into limp dick mode.

02-03-2006, 09:14 AM	#13
g6civcx Post Whore! Join Date: Apr 2004 Location: Virginia, USA Posts: 5,764 Trader Rating: (5) Feedback Score: 5 reviews	The best bet is to get a MAFS tester. Your local mechanic should be able to do it for you. They hook up the tester to the MAFS harness and measure the MAFS reading. When air is coming through, the waveform should rise steadily, with no spikes or peaks. If there are abrupt changes, your ECU will not be able to adjust and the engine will run poorly. It shouldn't cost you too much money to test it. May save you the trouble of buying a new MAFS. Or you can try swapping in a known-good. MAFS fail all the time so make sure it is really a known-good.

02-03-2006, 10:25 AM	#14
DMC Zilvia Addict Join Date: Jan 2003 Location: Chesapeake, Va Posts: 609 Trader Rating: (0) Feedback Score: 0 reviews	Ok I just installed a good mafs from my friends running car, and the same thing happened I am thinking I may not have something hooked up or grounded, but I have no idea!

02-04-2006, 07:42 AM	#15
outerheaven2k4 Join Date: Oct 2004 Location: Lexington Park MD Posts: 40 Trader Rating: (0) Feedback Score: 0 reviews	Recently I removed my cat and while in the process of fabricating a straight pipe, I drove with just headers ^_^. I noticed while driving like that, around 2000-3000 rpm I had a huge power loss, roughness, after 3000, it smoothed out. After putting in the straight pipe, its still there, I just noticed it better without the pipe. My gas milage is TERRIBLE, like 9-10mpg. Idle is a little rough. Just wondering if this was the MAF causing all of this...sounds like it. I figure while we're on the subject of MAF I'd bring this up...I hate MAFs....