How tough is a MAP sensor?
 

I had a CEL recently, the codes read "No voltage from MAP" and "MAP value Out of Range" (not exact wording)
So I reset the codes and after a few more drive cycles the CEL went out. I've been having some driveability issues at idle and on over-run so I reckoned it would be good idea to load the parts cannon. Ordered a replacement online because no-one holds Jeep parts in stock round here.

All fine so far but after a couple of weeks I started to wonder where the thing was. It's been snowy so maybe it had been delayed but still. Anway, our postman sometimes leaves stuff in the outhouse so as I slid my way over the sheet ice to check it I found the remains of a cardboard box marked Autodoc. Then the packing slip for a MAP sensor.

Yeah, the dogs got to it first. :hammer: :2guns: :hammer:

After a quick seach my wife found it half buried. So this thing has been sitting in snow for about a week. Physically it looks fine - but how sensitive are these things to water? I had to laugh at the static-proof bag sitting out on the snow with the end ripped off... luckily the plastic MAP didn't seem to be that interesting once the dogs had shredded all the packing.

I'll probably just fit the thing anyway, but am I risking anything?

It is exposed to mother nature when its under you hood. Id use It.

Let it dry, maybe give it a few shots with compressed air if you have some for your computer, and go for it.

A bad MAP sensor will have similar symptoms to a bad O2 sensor, in that it is part of the air/fuel measuring system. So if you can check your fuel trim levels after installing, that will help give you some assurance that it is functioning correctly. Your fuel trims should be near 0% (they move around a little, but ideally, they hover around zero).

Because a MAP uses a pressure/transducer, I think if you blow it out with compressed air (gently) it should be fine. If it was a MAS, exposure to water inside might not be so forgiving (I think they use a thin metal/wire element that is heated, so water might cause it to degrade/oxidize quickly and mess up measurements, but not sure).

Good luck!

OK, I'll give it a go. Thanks for the reassurance :)

I'll definitely check the fuel trims, I'm pretty sure it's been out of whack for a while but I couldn't see anything specific that was an issue - until the CEL showed up.

Hi Morat,

Good to see there's at least one other Brit on this forum ! Found your post after Googling my latest issue which may assist you.
My '96 was 'inherited' from a neighbour (UK spelling!) having stood in the open for 18 months - had no intention of running another car in London but when she fired up first turn with a new battery fitted I decided she deserved to have a new lease of life.
Usual XJ problems to work through, diagnose & then try and fix but that's been the satisfaction :thumbup1:
I won't bore you with the litany of issues encountered over the last three years, and resolved, but this forum and it's members has been very helpful so I do feel it's time to give something back ... or at least attempt to.
The XJ had been running beautifully until a few months ago when the CEL came up (first time) and using the x3 key trick got code 14 - MAP sensor problem. There were no noticable symptoms at this stage and as part of my regime of pre-emptive servicing I'd already replaced the MAP sensor with a MOPAR unit some 6 months prior. Therefore unlikely to be that and vacuum line and connectors all seem ok.
I read somewhere that a failing fuel pump can sometimes show itself as a MAP sensor 'fault' and this does seem a possibility here. I know my fuel pump has never been replaced so it's 22 years old and the mileage is over 150k (odometer works only occasionally so I'm guessing!) and on basis it should be replaced anyway I'm changing it to see if a 'faulty MAP sensor' is indeed a false flag. I'll do the job sometime in next week and report back.
The problem, this being a '96, has been finding the correct fuel module and their relative scarcity meaning they cost a lot (for an XJ spare).
Only other existing problem is heat soak in traffic (not over heating as coolant system is now 100%) but I have some Fancy Dan bonnet louvres to fit which should cure that annoyance.
Oh yes, I agree regarding the wet/canine damage to the MAP sensor - shouldn't be an issue considering where it lives under the bonnet (er, "hood" for colonial cousins :smartass: )
Cheers,