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MAP sensor failure, part no please


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Well after completing the "Nightmare Challenge" in a minus 12* frost the other week and arriving home around midnight I decided to leave the motor on the trailer until Sunday, it had run like a dreamthe night before and never missed a beat, and hadn't got to wet, it was to cold for that.....

but blow me it would not keep running to save its life Sunday morning in the frost, anyway after a major challenge to get it off the trailer dead and into the garage, frozen on muddy brakes, frozen plasma ropes, full hydrosteer with cold fluid etc, all sorts of things not helping anyway today was the day to try again now its a bit warmer..........

One of my original thoughts was a frozen K&N that had got wet on the way home from spray on the motorway and then refused to let air through but that was proved against by removing the snorkel, so armed with laptop we tried again,,,hey ho there's no movement in the MAP reading......quick check of pipework confirmed that all should be OK so spare ECU was tried.......

Cough.....splurt.... and perfect, so it looks like a faulty MAP sensor.

Finally the question is...is it a mpx4250ap thats available from Farnel or RS or is it something similar???? an RS part number would be a godsend if somebody can supply one hint hint Mr Fridge.......

Thanks again lads:)

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Not a problem Nige, RS in Stockport Manchester is about 1/4 mile from my office and we have an account there, so it's easy peasy really,

I was really impressed by the fact that within about 10 minutes of opening the bonnet I had managed to break it down to component level to diagnose the reason it wouldn't run right.

I don't believe there are many systems that it is possible to achieve that, I know a spare ECU is a monsterous help but that was really for self satisfaction i.e. just to prove the point..

not unlike the wife does......

Thanks again boys and Merry Christmas

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Boothy, just a thought...

I've had a couple that had "MAP" problems and it was a firmware issue. When you pulled up the spark or VE table was the green indicator just running up and down the 1st column but NOT advancing across the map?

Also you said it was king cold so is it possible that some condensation has formed due to heat sink from the plenum and froze the MAP sensor?

I only ask as I'm bloomin nosey. rolleyes.gif


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Your probably bang on there, the competition was a full 7 hours in a real full on frost that was damp and misty, proper hard winters night, the motor was not turned off from start to finish, and like I posted earlier ran perfect, but on thinking about things, the air intake is via a snorkel up the front rollcage with a paper cone filter (K&N) fully exposed to the elements, this has never caused me any problems in the last 4 or 5 years except when I roll on that side in water or gunge, so I carry a spare filter at all times. The ECU sits where the heater was in sealed box, on the bulkhead.

But obviously this cold damp air is what gets drawn into the plenum chamber and down via the inlet manifold which is precisely where the MAP vacuum sensor pipe attaches, so it must at some time take a breath of cold damp air.

My machine has a rear mounted electrically pumped cooling system so under bonnet tempretures are unusually low.

It seems strange sometimes after a session at full chat you open the bonnet and its all nice and cool even though the gauges show it's running bang on, the rear with the fans going is like being stood in front of a jet engine billowing heat out, so it's obviously working a treat, but it doesn't get a lot of heat in the inlet air tract which is normally a good thing.

So yes like you say it's probably got a bit of damp air the MAP sensor then froze or just give up because of the damp, so I won't risk any repeats for a tenner,

I will replace the sensor and refit and leave it as it is, with the thought that if I ever do a event in similar conditions in the future that I may have to swap over ECU's if it fails again.

It is the first time in three or fours years since I've had squirt on its happened so I don't think I need to do any major changes (yet) but will be aware.


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You could put a small, clear fuel filter inline with the MAP tube, this would probably catch most of the moisture, and if not you should be able to see the moisture in the filter to prove/disprove it...?

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  • 3 weeks later...

Happy New Year people and just an update for you.

I've replaced the onboard MAP sensor and thanks to Nige for the supply from his stocks, anyway when I removed the old one from the board there was a small amount of rust under it, which sort of left me with the feeling that I was barking up the right tree, anyway all refitted and "bingo" she's up and running perfect again.

So in summary, the MAP sensor can be affected by large and long amounts of water OR damp (just bear in mind my machine has had this ECU for longer than 3 years and has undergone some very wet and damp Challenges all over the UK in fact its very well seasoned) it's the one pictured on Nige's website driving across the lake up to the bonnet again.

So it's one for the record of possible reasons of bad running and a small clear lawn mower type fuel filter has been added in the vacuum pipe as a visual aid of any future problems.

Thanks for all your help and advice and I hope this thread may be of help to somebody else one day.


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