How is it that my car runs with no MAF?

[ranger2339]

So had the bucking issue with my 95 SC400, there were many options that might fix the issue, but only one for sure answer and that was unplug the MAF plug, I did that and it runs great now?
How does this work?

Josh

 

[Lextreme II]

Your engine will still run with the maf unplug but if you try to rev the engine it will die.

 

[gloverman]

It is quite common for EFI systems to run well when some sensors are unpluged.
The ecu will use a signal even if it is bad but if it does not receive a signal it goes to a Base type table which is often better. Cheers

 

[duza]

When I first did my conversion, I inadvertedly left the plug off the AFM. The motor ran great. Heaps of power and it did not die when revved. Drove around for a couple of days like that. Fuel consumption was a little high and there was obviously a fault code generated. The ECU reverts to a preset factory levels in the event the AFM fails. My motor was from a mid 90s Celsior, but I have heard that some models will not run properly without it.

 

[Jake Breyck]

im deffnatly gunna have to try this tommrow

 

[ranger2339]

Ya it runs great now,great idle,great power and bad gas milage because I have a heavy foot now. I love it! It will hold me over untill the manual swap. I might just make a custom cold air intake kit and delete the MAF for good.

Also my heater started blowing air now. I love when stuff fixes its self.

 

[crushu]

My LX470 wont go above idle with the MAF disconnected.

 

[Jem]

The ecu will revert to open loop, so will not use any engine sensors other than throttle position and engine revs to determine the amount of fuel to add and the ignition timing, just as it does when the engine is cold.

 

[LS400GUY]

When I first did my conversion, I inadvertedly left the plug off the AFM. The motor ran great. Heaps of power and it did not die when revved. Drove around for a couple of days like that. Fuel consumption was a little high and there was obviously a fault code generated. The ECU reverts to a preset factory levels in the event the AFM fails. My motor was from a mid 90s Celsior, but I have heard that some models will not run properly without it.

Now that you know the problem is MAF related, have you thought about replacing the MAF instead of keeping it unplugged?

LS400GUY

 

[LS400GUY]

It is quite common for EFI systems to run well when some sensors are unpluged.
The ecu will use a signal even if it is bad but if it does not receive a signal it goes to a Base type table which is often better. Cheers

glove..., do you think by running the engine with an extremely dirty air filter for 50,000 miles (maybe many more) could screw up the MAF? It seems to make sense to me that it would, it's a very sensitive component, is it not? TIA.

LS400GUY

 

[Nick M]

The ECU substitutes a known good value. Open and closed loop has nothing to do with it. In fact, closed loop would be better, as it gives the ECU an idea about how well it is controlling the engine.

When the airflow signal is lost, a base value is used, as pointed out. The engine speed and position sensor and airflow sensor are the two main inputs. All others are secondary. The engine speed and position can get you home, slowly.

 

[LS400GUY]

The ECU substitutes a known good value. Open and closed loop has nothing to do with it. In fact, closed loop would be better, as it gives the ECU an idea about how well it is controlling the engine.

When the airflow signal is lost, a base value is used, as pointed out. The engine speed and position sensor and airflow sensor are the two main inputs. All others are secondary. The engine speed and position can get you home, slowly.

Interesting, I pulled the plug on the MAP, and the engine started but died out quickly. I then reinserted the plug, the engine started as usual, but the "check engine" light came on for the first time since I've owned the car in over a year, also the "Traction Control" is now blinking. Any ideas what that means? Strange the "check engine" light would come on simply by disconnecting and reconnecting the MAP plug. The blinking traction control light really has me confused. Btw, the car still runs smoothly but sluggish on acceleration, never gets over 2000 rpms before it hits 70 mph. Any thoughts?

LS400GUY

 

[duza]

Now that you know the problem is MAF related, have you thought about replacing the MAF instead of keeping it unplugged?

LS400GUY

Unfortunately that is not so. I have replaced the MAF. Fault re-appears. This means that either there is a wiring problem between the MAF and the ECU, or one of the sensors that are ignored when the MAF is disconnected is playing up. Which one though? I hate faults like that, very hard to diagnose.
Ric

 

[Nick M]

Interesting, I pulled the plug on the MAP, and the engine started but died out quickly. I then reinserted the plug, the engine started as usual, but the "check engine" light came on for the first time since I've owned the car in over a year, also the "Traction Control" is now blinking. Any ideas what that means? Strange the "check engine" light would come on simply by disconnecting and reconnecting the MAP plug. The blinking traction control light really has me confused. Btw, the car still runs smoothly but sluggish on acceleration, never gets over 2000 rpms before it hits 70 mph. Any thoughts?

LS400GUY

Did you pull the EFI fuse for 30 seconds yet? What year is the car?

Traction control blinking means it has a problem also. Time to check all DTCs'.