Advice on MAP and MAF please

[sanders7284]

So I got an engine management light, went to merc and they quoted me £3k in repairs for a blocked air manifold, stuck exhaust flap and a suggested EGR replacement. After some independent advice I tried some fuel system cleaner £40 and the light as gone, however I have bought a OBD reader and think the MAP and MAF readings do seem a little high, suggesting an air flow issue, but can't be 100%, so dose anyone know what these should be?

 

[supernoodle]

Why do think they are high?

That looks an awful OBD tool, that appears to be converting everything to US units, the module certainly doesn't report data in deg F or lb/min.
Also OBD tools should also query the module and determine which PIds (parameters> are supported and only display those, not just show N/A if it doesn't get a response.

If you see here, I showed how you can calculate approx MAF (in proper units)
What if you MAF reading in g/s?' https://forums.mercedesclub.org.uk/...if-you-maf-reading-in-g-s.192963/post-1979289

95kpa is just less than atmospheric pressure , so seems reasonable to me.

 

[mioba]

You get what you pay for scanners, 17 quid of amazon. It is just false economy if you plan on doing a degree of car DIY yourself. Don't get me wrong you get a scanner and come asking for help.

MB are shot gunning with the 3k bill. Did they even scan the car. With Star Xentry they will know exactly problem and fix but may well not tell you.

Blocked air manifold - easy take it off and check - unlikely unless you got a rat stuck in there and never changed your air filters.


Maf can be cleaned with contact cleaner.

A failed MAF will show on an erm decent scanner.

 

[sanders7284]

Why do think they are high?

That looks an awful OBD tool, that appears to be converting everything to US units, the module certainly doesn't report data in deg F or lb/min.
Also OBD tools should also query the module and determine which PIds (parameters> are supported and only display those, not just show N/A if it doesn't get a response.

If you see here, I showed how you can calculate approx MAF (in proper units)
What if you MAF reading in g/s?' https://forums.mercedesclub.org.uk/...if-you-maf-reading-in-g-s.192963/post-1979289

95kpa is just less than atmospheric pressure , so seems reasonable to me.

Thank you for the reply,

I know it's a cheap scanner just wanted something that would clear the codes while I tried the fuel cleaner out, see if they come back. The fact it read some data I thought I may as well look t6hese numbers up, just wonder if anyone here had any experience.

For the MAF - 1 LBS/Min is 7.56 g/s so it is measuring between 7.5 (850rpm) & 21.5 (2500rpm) g/s.

In terms of the MAP I know 100kpa is atmospheric pressure at sea level, but most google searches said a good diesel engine should read down in the 20 - 30kpa range, when sat idle.

I have taken the car on a 200 mile round trip this weekend and all seems well after the cleaner, running well and the codes have not returned.

Cheers Sanders

 

[sanders7284]

You get what you pay for scanners, 17 quid of amazon. It is just false economy if you plan on doing a degree of car DIY yourself. Don't get me wrong you get a scanner and come asking for help.

MB are shot gunning with the 3k bill. Did they even scan the car. With Star Xentry they will know exactly problem and fix but may well not tell you.

Blocked air manifold - easy take it off and check - unlikely unless you got a rat stuck in there and never changed your air filters.


Maf can be cleaned with contact cleaner.

A failed MAF will show on an erm decent scanner.

Thank you for the reply,

I know it's a cheap scanner just wanted something that would clear the codes while I tried the fuel cleaner out, see if they come back. The fact it read some data I thought I may as well look these numbers up, just wonder if anyone here had any experience. I am grateful for any help and advice.

I have had the air intake and filter off all look well, I agree with what you are saying which is why I thought they just in "main stealer" mode.

I have taken the car on a 200 mile round trip this weekend and all seems well after the cleaner, running well and the codes have not returned.

Cheers Sanders

 

[mioba]

If it aint broke dont fix it and dont overthink it.

 

[Frontstep]

Switch to a fuel with cleaners in it and try driving like you knicked it, where appropriate of course.

 

[supernoodle]

Thank you for the reply,

I know it's a cheap scanner just wanted something that would clear the codes while I tried the fuel cleaner out, see if they come back. The fact it read some data I thought I may as well look t6hese numbers up, just wonder if anyone here had any experience.

For the MAF - 1 LBS/Min is 7.56 g/s so it is measuring between 7.5 (850rpm) & 21.5 (2500rpm) g/s.

In terms of the MAP I know 100kpa is atmospheric pressure at sea level, but most google searches said a good diesel engine should read down in the 20 - 30kpa range, when sat idle.

I have taken the car on a 200 mile round trip this weekend and all seems well after the cleaner, running well and the codes have not returned.

Cheers Sanders

The MAP value reported via the Service $01 PID (that's what your tool uses) is absolute, so 95kpa is just under atmospheric. I'm not sure what the 20-30kpa you quote is, but it's too low to be absolute, as that would mean a big depression and Diesels don't throttle (ok, there are some circumstances). Assuming that's gauge that would have to mean it's boosting, which isn't normal at idle, there's not enough energy in the exhaust, especially when you're running high rates of EGR. Your air flow rates compared to my the calculated rates I showed suggest 50% EGR, which is high.
To be honest the 95kpa indicates a slight restriction, which may relate to the original diagnosis you had of blocked inlet manifold.
Other possibility is one of those special circumstances where throttle can be used, to increase EGR rate, but throttle is only ever so slightly closed, certainly not to the 20-30kpa extent you mention. I also don't even know if this is even done on your engine or any MB. It's just something that is used by some marques.

With a decent tool you can you change the EGR valve and the other actuators to better check such things, but you have to know what the numbers mean.

Obviously we don't know the back story as to why you got the diagnosis you did, so I'd just forget the data and just carry on.

 

[sanders7284]

Switch to a fuel with cleaners in it and try driving like you knicked it, where appropriate of

Switch to a fuel with cleaners in it and try driving like you knicked it, where appropriate of course.

That's what I have done, v power and a dose of cleaner for good measure.

 

[sanders7284]

The MAP value reported via the Service $01 PID (that's what your tool uses) is absolute, so 95kpa is just under atmospheric. I'm not sure what the 20-30kpa you quote is, but it's too low to be absolute, as that would mean a big depression and Diesels don't throttle (ok, there are some circumstances). Assuming that's gauge that would have to mean it's boosting, which isn't normal at idle, there's not enough energy in the exhaust, especially when you're running high rates of EGR. Your air flow rates compared to my the calculated rates I showed suggest 50% EGR, which is high.
To be honest the 95kpa indicates a slight restriction, which may relate to the original diagnosis you had of blocked inlet manifold.
Other possibility is one of those special circumstances where throttle can be used, to increase EGR rate, but throttle is only ever so slightly closed, certainly not to the 20-30kpa extent you mention. I also don't even know if this is even done on your engine or any MB. It's just something that is used by some marques.

With a decent tool you can you change the EGR valve and the other actuators to better check such things, but you have to know what the numbers mean.

Obviously we don't know the back story as to why you got the diagnosis you did, so I'd just forget the data and just carry on.

Thank you for the detailed response.

I will do!

Cheers Sanders

 

[Frontstep]

That's what I have done, v power and a dose of cleaner for good measure.

you could also try Terraclean some swear by it;

Engine Carbon Cleaning Latest News & Updates | TerraClean

Keep up to date with the latest news from TerraClean. Our blog provides updates on the latest engine carbon cleaning industry and tips and advice for looking after your car engine.

www.terraclean.co.uk

 

[sanders7284]

you could also try Terraclean some swear by it;

Engine Carbon Cleaning Latest News & Updates | TerraClean

Keep up to date with the latest news from TerraClean. Our blog provides updates on the latest engine carbon cleaning industry and tips and advice for looking after your car engine.

www.terraclean.co.uk

Been trying to locate and book, it's proving difficult.

Regards Sanders

 

[Frontstep]

Contact them direct?

 

[sanders7284]

Contact them direct?

Yeah filled in the form on their website on Friday, still no response, will ring them when I can.