Running a car bypassing the MAF

cadaliac · 04-04-2012 02:32PM #1

I am having problems with the Air flow meter and bought a replacement from ebay. The replacement isn't an original part and behaves the same as the old one, which is running rough and cutting out at idle.
The car is a '97 Merc E200.

The MAF was disconnected and therefore bypassed. The car runs perfectly well when like this. There is no engine light on when I bypass the MAF.

My question is: Will I do damage to the car (long journey over Easter) running it when the MAF is bypassed?
I can assume that the car will use more fuel, but that's something I will have to live with rather than pay €250 for an original Bosh MAF. Well, for now anyway.

Thanks in Advance.

Ronnie Beck · 04-04-2012 03:46PM

cadaliac wrote: »

I am having problems with the Air flow meter and bought a replacement from ebay. The replacement isn't an original part and behaves the same as the old one, which is running rough and cutting out at idle.
The car is a '97 Merc E200.

The MAF was disconnected and therefore bypassed. The car runs perfectly well when like this. There is no engine light on when I bypass the MAF.

My question is: Will I do damage to the car (long journey over Easter) running it when the MAF is bypassed?
I can assume that the car will use more fuel, but that's something I will have to live with rather than pay €250 for an original Bosh MAF. Well, for now anyway.

Thanks in Advance.

Is it a diesel?
I've been wondering the same thing from my VW t4. Runs alot smoother with the MAF unplugged. It only controls your air /fuel mix so shouldn't damage the engine... but I could be wrong.
I priced the bosch sensor without the housing at 100 euro the other day in the local motor factor. Micks garage etc. you will have to buy the whole unit ( sensor + housing pipe ) for 250 roughly. Do you still have your old bosch sensor?

I going to run VCDS/borrow a mates MAF

first before changing mine just to be sure it's sensor thats the problem.

cadaliac · 04-04-2012 04:03PM

Thanks Ronnie,
No, its petrol. There is an unbelievable difference with (stalls and misfires) and without (normal) the meter.
I bought the part which is small and fits between the air box and pipe. Unit is small enough. I'm confident its the MAF and was just wondering if I should proceed with a long journey or not.
Cheers.

Nissan doctor · 04-04-2012 04:10PM

It will be running very rich if its running with the MAF disconnected, on drive on any more then a few mins this will start damaging the cat/lambda sensors etc

Plug · 04-04-2012 06:05PM

As above what doc said.

Here are a few simple tests you can do:
1)Disconnect the MAF sensor and check do you have 12 volts at the red/blue wire(pin 2) with the ignition on.

2)Make sure you have an earth, brown wire(pin 4).

Two nice and easy tests that will take two minutes with a multimeter. Try them and let us know.

cadaliac · 04-04-2012 06:18PM

Nissan doctor wrote: »

It will be running very rich if its running with the MAF disconnected, on drive on any more then a few mins this will start damaging the cat/lambda sensors etc

Thanks ND,
So I guess a Cork to Donegal trip is out of he question.....
5 hours of solid driving each way? Would the sensors pack up that quickly? Car will be heading for the scraper when the NCT expires in a month or so anyway.

Nissan doctor · 04-04-2012 06:23PM

cadaliac wrote: »

Thanks ND,
So I guess a Cork to Donegal trip is out of he question.....
5 hours of solid driving each way? Would the sensors pack up that quickly? Car will be heading for the scraper when the NCT expires in a month or so anyway.

They defiantly would alright.....but if its going the scrapper soon then keep her lit:P

Couldn't guarantee you'll get there and back without issue though.

cadaliac · 04-04-2012 06:34PM

Plug wrote: »

As above what doc said.

Here are a few simple tests you can do:
1)Disconnect the MAF sensor and check do you have 12 volts at the red/blue wire(pin 2) with the ignition on.

2)Make sure you have an earth, brown wire(pin 4).

Two nice and easy tests that will take two minutes with a multimeter. Try them and let us know.

I'll get a hold of a multimeter tomorrow and test that thanks.
What is the test for? Is it to see if there is a correct, or any, message being sent to the ecu? I think the signal is being sent, due to the fact that the engine behaves so differently, which is running rich, I guess

Plug · 04-04-2012 06:41PM

cadaliac wrote: »

I'll get a hold of a multimeter tomorrow and test that thanks.
What is the test for? Is it to see if there is a correct, or any, message being sent to the ecu? I think the signal is being sent, due to the fact that the engine behaves so differently, which is running rich, I guess

The two other wires go off to the ECU. You should have 12 volts there, supposing you had 8 volts because of a damaged wire well thats not going to send back the correct signal to the ecu and maybe its having an effect on the engine management system. Worth a try.

cadaliac · 04-04-2012 06:46PM

Plug wrote: »

The two other wires go off to the ECU. You should have 12 volts there, supposing you had 8 volts because of a damaged wire well thats not going to send back the correct signal to the ecu and maybe its having an effect on the engine management system. Worth a try.

Ah, right. Yes indeed we'll worth a try.
Cheers.

cjt156 · 05-04-2012 10:35AM

Have to call you on this one, guys. I frequent another forum where reports of MAF failure on a particular model are a regular occurrence. There the diagnosis is to run without the MAF and see does the engine run smooth to the redline. Dead MAF will typically splutter over about 4k revs (on this model). The thinking is that the ECU reverts to standard fuelling ratios, rather than active ratios & the car drives fine - lumpy idle at worst.

I've done this myself, driven for a week without a MAF inline while waiting on a replacement. So have many others. None of us report an issue with failing Cats or lambda sensors. With 20k miles since the new MAF mine is running like a champ. I'd say you're more likely to do harm with the dead MAF in place.

Muckie · 05-04-2012 10:48AM

Had similar issue with a Subaru a few back.

Drove the car for a week with a faulty MAF. Didn't cause any long term

problems. Drank a bit more petrol that was about it.

(Maybe different cars have different set ups)

Check out a few Merc forums too.

cadaliac · 05-04-2012 07:58PM

cjt156 wrote: »

Have to call you on this one, guys. I frequent another forum where reports of MAF failure on a particular model are a regular occurrence. There the diagnosis is to run without the MAF and see does the engine run smooth to the redline. Dead MAF will typically splutter over about 4k revs (on this model). The thinking is that the ECU reverts to standard fuelling ratios, rather than active ratios & the car drives fine - lumpy idle at worst.

I've done this myself, driven for a week without a MAF inline while waiting on a replacement. So have many others. None of us report an issue with failing Cats or lambda sensors. With 20k miles since the new MAF mine is running like a champ. I'd say you're more likely to do harm with the dead MAF in place.

Jesus, I wish I saw this post earlier today. Anyway, as I mentioned before I have a Cork - donegal trip planned tomorrow and I could have called a merc man I know.
He would have known if the car would have damaged the cat and sensors or not. He works for a garage that specialises in merc/vw/Audi etc. they have the merc star diagnostic equipment too but I was too cheap to bring the car to him, as the car isn't worth spending too much money on.
Any hoot, I still can't take the chance that "this model" won't sh1t itself about 250 miles from home. It has done this to me already last Xmas. (the CPU sat down

) so I had to get a replacement CPU, steering lock, key and barrel set.
So I have been stung by this car before and the risk of it happening again has to be avoided.

I will however use it for the to and fro work thing and see if any lights show on the dash. My own mechanic recomeded that I just drive it away, as he had a similar issue with a BMW 3 series of the same vintage about a year ago.
While I would like to drive on, so to speak, in the merc, Mrs Cadaliac has to surrender her car for the journey tomorrow. Thanks for all the info people.

mickdw · 05-04-2012 09:53PM

I drove an alfa 166 around for a month or more with the MAF disconnected and it had no issues with the NCT later. It did drink fuel while disconnected but drove significantly better disconnected than with the bad part connected.
I guess I was lucky.

06-04-2012 11:46AM

Nissan doctor wrote: »

It will be running very rich if its running with the MAF disconnected, on drive on any more then a few mins this will start damaging the cat/lambda sensors etc

Sorry Nissan Doctor, that is not the case with this particular application. I had an E220 '93 with similar engine (M111) as OP. When the MAF went the motor was running really rich spewing out black smoke and hardly idled. With disconnected MAF it was running almost perfectly, just ever so slightly down power at full load. The engine management in Merc has both MAF and MAP, and once MAF is disconnected it fuels just about perfectly with MAP only.

Happened to me night before due taking a ferry to France. I ended up getting a MAF from a '97 E200 from breakers on the way to port that had the same part no. But as a backup plan I was going to go with the MAF disconnected as the car was driving great.

Running a car bypassing the MAF

Comments