Unplugging MAP sensor improves things!

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NikTheGeek

NikTheGeek

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Wigan
Still striving to improve my 16mpg. It was doing 16.4. I changed the thermostat and it now averages 16.7 - not as much change as I'd hoped for, but a lovely warm heater now! :) Anyway, the other week I unplugged the map and maf sensors and didn't notice any difference in performance. So... I unplugged just the map sensor and ran it for a while and made the following observations:

1. No noticeable difference in performance. It's still sluggish from cold and less sluggish when warm. Acceleration is the same, top speed is the same. I haven't towed yet though.

2. Fuel economy has improved from 16.7 to 19.0 - 2.3mpg!! Ok, not a lot you might say, but when you unplug it, shouldn't it default to an over-fueling map and be worse? But it's not, it's better.

I don't want to leave it unplugged so what are your thoughts? Duff sensor? The vacuum hose is fine, I've taken it off, plugged the end and tried to blow air through it. Something else? Would a duff sensor show up on diagnostics coz it's been on an Autologic and not shown any faults.

I await, intrigued, your collective thoughts, words of wisdom and advice :)

Nik
 
If the MAP sensor is giving erroneous readings, it would not go to default. If MPG has improved with it unplugged so it is running on default settings, then I'm sure the sensor must be knackered. It ought to be possible to test it with a DVM and I would have thought it should show on diagnostics as a pressure reading, can't remember.
They are always sluggish when cold.
 
Carnt see it being map senor what milage is it? worn injectors could give you a poor mpg does it smoke a bit when hot , bad timing worn engine could be a manor of things really
 
Datatek said:
Why would unplugging the MAP sensor improve the MPG if that were the case? No logic in your comment.
MAP sensors do fail.
Click to expand...

Becuase if it failed it would be terrible , if nick is relying on the computers mpg for a start that's a waste of time not sure how he is calculating it ?? I get 23 mpg the computer say 19 for instance most mpg decreases are due to leaks, injectors and worn engines
 
defender300td1 said:
Becuase if it failed it would be terrible , if nick is relying on the computers mpg for a start that's a waste of time not sure how he is calculating it ?? I get 23 mpg the computer say 19 for instance most mpg decreases are due to leaks, injectors and worn engines
Click to expand...
So tell me why his MPG improved with the MAP sensor unplugged?
 
I am using the onboard computer, but... I'm using it conistantly. ie 16.7 mpg over a week with the map plugged in and 19.0 mpg over a week with it unplugged.

Can't find a replacement either apart from ebay - and I'd rather not get one from there if I can help it....
 
NikTheGeek said:
I am using the onboard computer, but... I'm using it conistantly. ie 16.7 mpg over a week with the map plugged in and 19.0 mpg over a week with it unplugged.
Click to expand...

Fair enough but road conditions weather ect is not a good enough surely if its not working your car would feel really sluggish seeing as it uses the air pressure in the the manifold to tell ecu to add fuel and if you aint getting the correct fuel I can't see you burning excessive amounts just my opinion
 
Nick if you want to test it you need a multimeter set on 12v the reading is about 4volts the pipe that goes to the map from the manifold make up a connection from a foot pump or similar the more pressure in the pipe the lower the volts
 
defender300td1 said:
Fair enough but road conditions weather ect is not a good enough surely if its not working your car would feel really sluggish seeing as it uses the air pressure in the the manifold to tell ecu to add fuel and if you aint getting the correct fuel I can't see you burning excessive amounts just my opinion
Click to expand...

It's been sluggish and running at 16mpg since I got it in August so I don't have anything to compare it to you see. I've just been playing, doing things that should help (like replacing the stat) and experimenting (unplugging things like the maf and map). It's when unplugging the map didn't seem to make any difference, I thought I'd try it for a whole week.

But you are right, it isn't a fair test.

I'd risk a replacement for £30-£40 but I can't find any! :)

Nik
 
I had a map fault logged on mine replaced it with one from ebay and its been fine no fault logged. Mine according to computer is 16mpg but that is around town and no more than 40 mph most of it is 20 to 30 mph in winter in summer it is 20mpg round town 27 to 30 on a run mine is a auto and ive learned to live with it if u want a luxurious vehicle u deal with the running costs.

Today at work I priced up a disco 3 satnav reader at £2300 omg
 
It would be a good idea to get it checked on a diagnostic computer, I would think that if the MAP was disconnected it would run "open loop" so not a conclusive test.
 
Its been on an Autologic for a health check when I first got it and they gave it a clean bill of health apart from "failing blend motors". Not failed, but failing. No engine/ecu/eas/etc errors so I was quite pleased. (Of course the map sensor was connected for that and didn't show a fault - but I don't know if it would depending on how it fails) I'm going to get a Nanocom eventually, but I've got 4 air bags on order first. I might get a replacement map sensor just to see. It's less than the cost of a tank of fuel....

tnx all

Nik
 
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