kfriceman

Had a check engine light on and took it to the dealer (2 days ago) and the issue was a bad mass air flow meter/sensor. Had the MAF replaced and ever since this visit to the dealer(to the very day) when the ML is shifting from 1st to 2nd we get a dead spot or hesitation in engine power and have had the same problem with accelerating from a dead stop before the upshift. There have been times when the ML shifted and this event was slight or really pronounced to the point the car almost stops because of no power produced by the motor even with increased throttle input.

During this hesitation there have been no engine lights and the dealer could pull no codes. At this point I have no idea whether it is a engine managment or transmission problem.

Lastly, this is an intermittent problem that does not occur with every standing start or upshift.

Any input would be greatly appreciated,

-Kevin

pleubner

Intermittent? could be if the tansmission oil heats up the effect is different ..... try changing it!

AC_ML

Take a portable decent OBDII scanner and connect it to your ML and drive around.. There should be some problems reported on the scanner even though the problem lights may not turn on the dashboard. They will only turn on if they repeat at specified intervals.. In addition, you need to monitor the live MAF sensor readings to see if they are within working ranges. You can request this to be done, too,s on the other MB dealer and they can provide you a printout..


I would take it to another dealer and have them run a complete MB computer test to make sure all sensors and components are within range at different loads.

Don't they have to run an adaptation process on the computer once they change the MAF sensor..? If they didn't, your ML computer may not have the best parameters settings to work optimally..

Did they really install your MAF correctly or really change your MAF..? Below are some of the symptoms on MAF failure..

Have you tried driving with the MAF sensor disconnected..?

AC

Excerpts from a MAF article.. Not an ML but similar ...

Q What are the symptoms of MAF failure ?

A. This can vary, depending on whether your vehicle has a catalytic converters or not. But MAF failure can result in weak mixture, giving low power and hesitation under acceleration. Or at the other extreme, over rich mixture with black smoke, a strong smell of petrol in the exhaust, black sooty spark plugs, and a reluctance to run unless the throttle is opened.

So if (for example) the MAF gives a lower output voltage than it should, the LH computer outputs fuel from the injectors corresponding to a lower airflow, and the mixture is weak. This will reduce power, and may cause hesitation when the throttle is opened quickly. These effects will gradually get worse with use over some time, due to hot wire erosion

If the MAF output voltage eventually reaches a point well out of calibration, or for some reason the output suddenly jumps out of normal tolerances, the LH computer will ignore the MAF output voltages entirely, and should revert to a stored "limp home" programme

So MAF failure often is a gradual degrading of performance, often first noticeable with "flat spots" causing hesitation during acceleration.

An oxygen sensor which monitors the exhaust gases before the catalytic converter feeds a signal back to the LH computer, forming a closed loop system.- a "lambda control loop". This loop adjusts the amount of fuel injected, keeping the air/fuel ratio within the very narrow limits required in order to meet emissions standards. The cat can be contaminated by an incorrect fuel/air ratio, so this feedback loop is essential. So if the MAF drifts gradually from its correct calibration, the LH computer will adapt to these new settings and the car will run well. But when the MAF drifts too far, the LH computer will revert to the pre-set "limp home" programme, as for the non-cat cars. So MAF failure is often sudden, without warning.


Q. How do I tell if the MAF has failed, or my car has another fault ?
A. If the car runs much better, although not perfectly, with the 6-pin connector to the MAF disconnected, then MAF failure is a strong possibility.

Q. It doesn't run any better, or any differently, what now ?
A. This could be the case if the MAF failure is total e.g. a broken hot wire. The car would have already reverted to limp home mode.

Q Well, it runs much better, or differently, with the MAF disconnected, what now ?
A It is almost certain that the MAF is faulty. If MAF failure is not total, but due to the output being out of calibration, cat equipped cars will often run very rich, or not run at all, until the MAF is disconnected. Then they will run in limp home mode. Non-cat cars typically run with an increasingly weakening mixture over time, in limp home mode they will tend to run rich at small throttle openings.

kfriceman

With much research I found out the MAF part number should start with a 113 for the V8 engines the one the dealer installed starts with a 112 which is for the V6. I can't wait to call them in the morning so I can give them my bill!!!

-Kevin

Lemottee

hi Kevin was wondering if you ever found out what is causing that hesitation outta first ??, I also have it when it down gears into first , it almost had a buzz noise while doing it , only lasts about a second and sometimes shorter , sounds like exactly what you had going on any input would be greatly appreciated thanks in advance Jory

kfriceman

The dealer installed the wrong MAF, that is what caused my problems. See my post above yours.

-Kevin