MAF mod

[Dieselman]

When I fitted a new MAF to my car I took the voltage readings. I took another set of readings yesterday and compared. The MAF has a 3% drop in output voltage when the engine isn't under load, i.e. in neutral.

This made me think about bringing the output back to normal, or even a little better, so...
today I decided to fit a potentiometer to feedback some of the MAF input signal back into the output.
The ECU should see a higher output voltage so should add more fuel as it thinks there is more air available to burn. In turn this should give greater torque output from the engine.

Knowing the MAF monitors the EGR valve I needed to be careful to not allow the EGR to operate any differently, so fitted a vacuum gauge to monitor the valve.
I found that at idle the valve is closed but as soon as the revs rise over about 900RPM it's open.
I fitted the pot into the ECU loom by taking the 5v feed into one side, the MAF output signal into the pot and the return to the ECU from the centre wiper.
I then turned it up so that it just didn't interfere with the EGR valve operation.
I found the maximum idle voltage for this situation to be 2.25v, as opposed to 1.99v as the MAF was reporting.
I've plotted the readings the ECU now sees against the ones it saw before the mod.

This is just at the experimental stage at present and I'm going to monitor the feel and results of this mod, but so far my Butt dyno says there is a definite improvement in midrange torque.

The turquoise line is the brand new MAF in neutral against engine revs.
The brown line is the New MAF under full turbo boost.
The green line is the MAF now in neutral.
The purple line is the MAF after the mod.

I haven't tested it under load this time as that requires a helper to watch as you drive...err..rather quickly.

 

[stevesey]

Interesting.

For some real time monitoring how about a laptop and one of those PC Scope programs that use the line-in as the input (or just sound recorder and analyse the waveform later).

 

[Dieselman]

All the real time monitors I know of use the HT pickup, which isn't much use on a diesel..

I ought to measure the full load readings and acceleration from say 20-70. That would give a definitive figure, but it does feel 'meatier'.

 

[Bobby Dazzler]

Sounds interesting. So are you monitoring EGT?

 

[Dieselman]

Ha ha. Not got round to that yet.. But i do intend to.

This isn't the same as amplifying the signal to the fuel pump though, it's an ECU input as opposed to an output.

I'll get an EGT gauge as a test..

p.s. The intake manifold was a uniform 60c after a 5 mile drive..I've mailed about the spacers..

 

[Dieselman]

BTW, Bobby. It would be well worth you measuring the MAF output on your ML. Timskemp's was well down on his E270. He's going to post the results of that and a new one when he gets round to it...

 

[Bobby Dazzler]

Next time I see a clever bloke with all manner of electrickery filling his boot, I'll ask him to take a look!!

 

[Adam230K]

Very interesting. Trying my best not to sound like an idiot here, but are you fitting a different MAF to put a less restrictive air filter maybe? cuz as far as i know mercedes air filters cant be swapped for any other air filter because the MAF will cry later...

 

[Dieselman]

No filter mods. If you measure the pressure drop across a standard paper filter you will see it is negligable compared to the other induction losses.

When I get a suitable manometer I'll take some readings for you.

It's much more important to site the intake in a high pressure zone and to ensure the rest of the intake doesn't cause restrictions.

Phenolic manifold spacers are definately worth their money from what I read.