MAP Sensor Hose

[ant9000turbo]

Hi All

Am I correct that the vacume hose from the MAP sensor is a specific length, diameter??

If so, can it be replaced with aftermarket silicone hose from the likes of elkparts etc and if so what length / diameter??

Thanks all in advance

Anthony

[mark e]

The OEM MAP sensor hose is different from the regular vac hose in the engine bay. It's a lot stiffer, presumably to make sure it accurately transfers the manifold pressure to the sensor. I ran 4mm silicon tube without any probs for a while before I was worried by somebody saying it HAD to be a specific length and type, so I changed back to new OEM hose.

Since then I discovered that the length of hose varies between models anyway so it can't be really critical. Likewise the sidewall stiffness is perhaps not over-critical.

I'd say 4mm ID 2mm wall silicon hose is fine but if you wanted to play safe, the part number for the OEM hose is 44 41 495. My local dealer just gave me a bit for free whe I asked for some

[SteveN]

The OEM MAP sensor hose is different from the regular vac hose in the engine bay. It's a lot stiffer, presumably to make sure it accurately transfers the manifold pressure to the sensor. I ran 4mm silicon tube without any probs for a while before I was worried by somebody saying it HAD to be a specific length and type, so I changed back to new OEM hose.[/b]

I had exactly the same experience

[billj]

I was worried by somebody saying it HAD to be a specific length and type[/b]

Might that have been me? I know I read it somewhere authoritative (can't remember where now) and may have mentioned it. Still, if stiffness is the issue I'm sure the silicone rubber hose sold by Elk, Demon Tweeks, etc. will be stiff enough to transmit any pressure transients accurately.

There must be a reason why Saab don't use the same rubber hose as for the rest of the engine.

[Edit] Found it in the Saab Trionic documentation on the Townsend Imports site:
http://townsendimports.com/Web/Trionic/trionicpg4.htm

The relevant passage says "The MAP sensor is in communication with the intake manifold via a hose, the design of which is carefully adapted to ensure that pressure information is transferred correctly. The length of the hose, its positioning, the quality of the material it is made of and other factors are decisive for ensuring correct pressure measurement."

I believe this to have been scanned directly from the Saab Trionic documentation.

However, since the hose looks very like silicone vacuum hose anyway, I'd say you're unlikely to cause problems by replacing the original with that. Then again, this hose seldom seems to need replacing.

[ant9000turbo]

Thanks guys, that answers my question perfect!!

Ta

Ant

[mark e]

No, Bill, it wasn't just you

I think the desription goes over the top to reinforce(!) the point that you can't just use any old bit of hose you have lying about.

As for length- if you remember Bill I asked you to measure yours for me only to find that in my case, it was too short as the inlet manifold was a slightly different design between our cars and it was connected to a different nipple!

[billj]

As for length- if you remember Bill I asked you to measure yours for me only to find that in my case, it was too short as the inlet manifold was a slightly different design between our cars and it was connected to a different nipple![/b]

Indeed - the '94-on Trionic cars appear to have the nipple in a different place on the manifold.
I know Ylee posted elsewhere that he had trouble after fitting the wrong type of hose, fixed by fitting one of the correct dimensions. Whether that was directly down to the wrong hose or perhaps to consequential leaks isn't known.

[Kelvyn]

What effect would having the wrong hose have? When tinkering at the weekend I noticed that the hose on my car is simply a plastic hose. It looks like black washer pipe to me, quite soft and thin walled.
Its obviously been on there ever since I got the car(nearly 2 years ago), it seems to perform ok to me. Perhaps its less critical on the LPT cars?

[billj]

It looks like black washer pipe to me, quite soft and thin walled.[/b]

That sounds like the original hose.

[berkbs]

Did anybody here have problems due to unoriginal MAP sensor hose?

Is the MAP sensor used for calculating Air/Fuel mixture by the ECU, or only for preventing overboost? What would happen if the MAP sensor did not function properly on a 95' 9000?

How long should the hose be on a 2,3 LPT?

A few days ago I was replacing the vacuum pipes on my car with 4mm hose I got from Saab by the meter, and I changed the hose that runs between the manifold and the MAP sensor. The old hose looked kind of worn and I threw it away. The new and old hose are about same length, but could be of different material. The car now drives better, probably due to all the other vacuum hoses I replaced. No problems with drivability. I am wodering whether I should order the original MAP hose from Saab.

[paul anderson]

Guys,

On both my lpts and on the current Aero, I find that the hose is prone to drying up and splitting where it connects to the nipple, especially when pulling it off for maintenance ( head off ). I have always just snipped off the end 1/2 inch or so and reconnected. No change in performance so my experience is that it's not that critical.

Paul @ Kippen.