MAF disconnect
 

I have read on this site that it is ok to disconnect the MAF for a while to see if the car runs better. If it does you would most likely have a bad MAF. My question is how long is it safe to leave it disconnected? Five miles? Twenty miles? As always thanks for your input in advance.

You'll know after a short jaunt (say 20 miles), if the sensor is bad. If the sensor is in fact bad, the vehicle should run noticeably better while disconnected . Are you getting a CEL ?

No i don't have a CEL. I used an Actron scanner and found no pending codes. I have a hesitation at full throttle over 5,000 RPM's. I had another thread on the site about it. I have changed the plugs, fuel filter and air filter. It has not improved. I figured it was free to disconnect the MAF to see if it made any improvements. I just don't want to leave it disconnected for too long and have it cause any damage to anything else. Cats, O2 sensors or anything.

Most will agree, that disconnecting the maf for a brief ride is a safe and effective way to rule out the sensor as being the culprit. Provided, however, that it is in fact the sensor that's causing the problem .

Well I'm at work. I disconnected it. I now have a 14 mile ride home. I guess i'll see if it helps or not. I'll post back when i hopefully arrive safely at home around 12am EST.

Well I left work a little early. My findings were: On the positive side dead solid idle. It fluctuated a little before. Pulls strong to 6,500 RPM full throttle.

On the negative side, I got a CEL with in the first mile after i started it.

So at this point i will hook it back up, read the code and then clear the code. I already had the MAF out of the car a few weeks ago. It looked brand new, but i cleaned it with CRC MAF cleaner anyway.

So what do you guys and gals think?

The CEL is likely the result of pulling the sensor. The code that will probably appear is P0102 . Many have reported having a failing maf sensor without it necessarily causing a CEL.

Tommy,
When you disconnect the MAF your DME will light a CEL and revert to default fuel trims. If the car runs better you know you have a failing MAF that was sending faulty info to the DME. If the car runs no better or worse, your test was inconclusive.

This is a simple test anyone can do that will not harm your car as long as you don't have something else seriously wrong. The process of elimination works.
:cheers:

If the car runs better without the MAF, clean it. If cleaning doesn't address the problem, then you'll have to replace the MAF.

The codes I had were P0102 and P0112. I cleared the codes and hooked the MAF back up. No codes on my way to work. I cleaned the MAF a few weeks ago, it didn't show any improvement. But it seemed to run quite a bit stronger with it disconnected. So i guess my next purchase will be a new MAF.

I thought so . :)

Check for air leaks, too. Unplugging the MAF will also effectively zap bad running due to leaks.

I ran my old BMW 328i with the MAF unplugged for four months including a track day with no ill effects, so I wouldn't worry too much - the ECO will just default to stored values that aren't too far off reality.

It will run a bit better with a good MAF plugged in, however.

Can you explain? Even when running on the default maps with the MAF disconnected, wouldn't an air leak cause the engine to get more air than the default map expects resulting in poor running? I would expect an air leak to result in poor running either with or without the MAF. Yes?

ecu uses maf to tell it how much air the car is getting. air volume and rpm are used to look-up the required fuel amounts on the programmed maps.

if the maf isn't working the car will use the throttle position to determine how much air is getting in. should be pretty accurate, but can't compensate for pressure differences, etc.

if there is an air leak after the maf (ie, the aos system is often a culprit - failing aos causes excessive vacuum in the crankcase which collapses and cracks the oil fill tube which then allows air to be drawn in post-maf but pre-throttle body) then the ecu will get thrown off. not so with the throttle position sensor.

I disagree with this. Unplugging the MAF removes it from the equation but does not affect intake air leaks. A significant air leak will be revealed in O2 sensor codes like 1128.

Well i don't have any codes besides the ones i had and cleared from unplugging the MAF. I did look at all of the tubing, everything seemed connected and sealed.

The AOS was replaced last year. I don't think it had a total failure, but i was seeing a little smoke here and there.

when they replaced your aos, did they replace the oil fill tube as well? perhaps check it for cracks, as a bad aos can collapse and crack it.

I replaced it and no i did not replace the oil fill tube. I'll take a look at it. Would the cracks be easy to spot with it still in the car? Is it a worse job replacing the fill tube or the AOS?

Update. The new MAF came in the mail today. All i can say is WOW!! It's like having a new car. It seems like it has 50 extra HP. Thanks everyone for your help.