External MAP sensor in place of TPS?

Broke4speed · Post by **Broke4speed** » Wed Jun 17, 2009 10:45 am

First off: I love my MJLJ. It took my driveable car to a whole new level. It fires up so easily now, and no flatspots anywhere now

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Second: I'm currently on a TPS-based setup, which works very well for me, but I was daydreaming one day and wondered about something. Since a typical MAP sensor (say a 1bar GM sensor) is just a 5v sensor, could it be wired up in place of the TPS? The 5v out from the MJLJ could go into the sensor, and the signal out would go back into the ecu on the TPS input wire. I don't see why it wouldn't work, unless there is a firmware/software issue preventing it. The benefit of this would be the ability to flip back and forth from MAP to TPS with a switch mounted on the pedal, or even using the shift light output as a trigger for a relay. TPS at idle, and above a set RPM point, flip back to MAP.

Pardon me if I'm off base, or incorrect. Daydreams aren't always correct

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Post by **brentp** » Thu Jul 09, 2009 8:26 pm

Sorry I missed this post.

Yes, it's conceivable an external map sensor could be plumbed into the TPS input.

However, I'm not sure about the benefits of using a switch to flip between the MAP sensor and a TPS. If you're worried about idle stability, just box in that part of the map below, say 1500 RPMs, for whatever range of MAP readings you might have at idle.

Alex B · Post by **Alex B** » Fri Jul 10, 2009 9:38 pm

Interesting thread. I'm still a long way from installing a MJ, but I was wondering about installing an external MAP-sensor like I have on my Saab 9000 Turbo (compatibillity issues to be solved of course). It is connected to the inlet manifold by about 20cm of tube. If you have the MJ in the passenger compartment it is easier to have some electric cabels running than a tube that might have to take sharp corners and could be squeezed shut. Brent, is the MAP-sensor that comes with the MJ under-the-bonnet proof?

Alex

Post by **brentp** » Fri Jul 10, 2009 10:06 pm

Hi Alex,
It is not. it should be pretty easy to ensure (and verify) the tubing isn't squeezed under normal operations. Also, the tube length is not a concern- the delay would only be a few milliseconds for a long run of vacuum tubing (don't have the math handy..

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Broke4speed · Post by **Broke4speed** » Sat Jul 11, 2009 4:54 pm

Cool. I'm still enjoying my TPS-based system, and live in a very flat area, so no need to mount an external MAP outside of satisfying my own need to tinker, lol.

Alex B · Post by **Alex B** » Wed Jul 15, 2009 8:37 pm

The reason why I would like to use a MAP sensor under the bonnet is because with a Saab Sonett it isn't easy to get a vacuum tube from the engine to the passenger compartment without having to drill a hole in the fire wall, which I don't want to do. Besides, in front of the the firewall all space is pretty much in use. Three wires are much easier to get through. Interesting option to investigate

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Alex

Broke4speed · Post by **Broke4speed** » Thu Jul 16, 2009 4:34 pm

If I could find a three pin weatherpak connector for a spare GM 1bar MAP I have, I'd give this a try once I put the engine back in my car. I'm perfectly happy with the TPS setup though, so it would only be out of sheer curiosity...and sometimes I do more damage than good when motivated by that

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DannyP · Post by **DannyP** » Mon Jul 20, 2009 5:13 am

Alex, use some 1/8" I.D. nylon tubing, very resistant to crushing. Also, if you heat it with a heatgun it can bend pretty well.