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Username Post: Map sensor location        (Topic#179047)
JimMel 
Contributor
Posts: 339
JimMel
Age: 56
Loc: Yorkville, IL
Reg: 05-10-07
01-07-08 08:54 PM - Post#1337565    

Is their any real valid logical reason MAP sensors are usually inside the engine compartment, or are they there cause that's where the vacuum is?

I'm trying to set up my system with minimum underhood visual impact. I hate wires and hoses.

I have a vacuum gauge in my dash, so I have a vacuum hose. any reason not to put the map under the dash?
My new Camaro board http://www.firstgens.com
68 Camaro Vert, SS clone,383 & TKO 500, Holley c950 TBI
http://www.Jimragtop.com


 
Doug_F 
Holley Subject Matter Expert
Posts: 4718

Loc: Bowling Green, KY
Reg: 08-20-01
01-07-08 09:01 PM - Post#1337572    
    In response to JimMel

It is because of response time to the sensor. I can't give you any real numbers that say how long is bad, but under the dash is a lot. I'd try to keep it as short as possible and not have to worry about it.
Doug
1972 Nova
6.0L LSx, 80mm BorgWarner, 4L80E
9.51@143.8


 
DeltaT 
Frequent Contributor
Posts: 1023
DeltaT
Loc: San Jose area, CA, USA
Reg: 06-20-02
01-07-08 10:05 PM - Post#1337617    
    In response to Doug_F

Plus the possibility of other device(s) on the same line having a damping effect on what the MAP sees, like if a vacuum/pressure signal had to move a diaphram or anything.

If you could keep it separate and use a dedicated hard or stiffer (not soft rubber tubing) line I could see running it right behind the firewall.

Jim

 
BrianEsser 
BANNED
Posts: 7383

Age: 38
Loc: North Star, Ohio
Reg: 06-30-01
01-07-08 10:17 PM - Post#1337623    
    In response to DeltaT

You can run your map sensor 2 to 3 feet or so without an issue if you do like Delta suggests and use a steel line. Thats what I did with my Megasquirt since the Map sensor is located in the ecm itself.


 
ChevelleFan 
Contributor
Posts: 328
ChevelleFan
Loc: Cleveland, OH
Reg: 06-04-04
01-10-08 03:45 PM - Post#1339713    
    In response to BrianEsser

I remember this topic came up in the Megasquirt forums once. Eric Fahlgren posted he had done some testing and essentially concluded that it made virtually no difference, even with something like a 30ft hose, which seems to contradict what Doug wrote. Both Doug and Eric are pretty smart guys, so not sure who to believe here.

For what it's worth, my Megasquirt sat on the transmission tunnel of my Chevelle and it ran just fine (prob 3-4 feet of hose to the rear of my Stealthram's plenum). Megasquirt has the MAP sensor on the board instead of in the engine compartment.

Found the post here:
http://msefi.com/viewtopic.php?t=26904


-Dave

'70 Chevelle xxx/700r4/3.55 / Hotchkis A-arms / Hotchkis Springs / B-body 12" brakes / 1.25" F-body swaybar


 
DeltaT 
Frequent Contributor
Posts: 1023
DeltaT
Loc: San Jose area, CA, USA
Reg: 06-20-02
01-11-08 12:49 PM - Post#1340421    
    In response to ChevelleFan

Maybe on a NA motor it wouldn't make a big difference, but on a forced induction motor that signal lag could be enough to blow the motor during a fast accel run.

30ft. I could see on a thin, hard pipe, but not soft rubber hose. I think you would have too much damping. Now that I read the cited post, I think they bring up similar questions. Good reference, though.

Jim

 
Z-man 
Senior Member
Posts: 335
Z-man
Loc: Foxfield, CO
Reg: 12-30-03
01-12-08 01:58 AM - Post#1340870    
    In response to DeltaT

You're probably going to see very little effect on tube length with hard tubing. Doesn't the pressure propagate at the speed of sound in the gas? So 3ft. or 10ft. hardly makes a difference.

With a softer hose, the hose walls could theoretically flex slightly during pressure changes which would create a lag in pressure measurements, but it's got to be really tiny...

 
JimMel 
Contributor
Posts: 339
JimMel
Age: 56
Loc: Yorkville, IL
Reg: 05-10-07
01-13-08 11:32 AM - Post#1341855    
    In response to Z-man

I'm gonna go ahead and put it under the dash. Will probably use that skinny hard plastic hose with compression fittings, like they use for mech oil pressure gauges.

The only other thing on the line will be a vacuum gauge.
My new Camaro board http://www.firstgens.com
68 Camaro Vert, SS clone,383 & TKO 500, Holley c950 TBI
http://www.Jimragtop.com


 
esahc 
Member
Posts: 27

Reg: 01-16-07
01-14-08 12:57 PM - Post#1342611    
    In response to JimMel

If you are going to put it under the dash and use hard plastic with compression fittings why not just go ahead and use steel line? Brake/tranny line is pretty cheap by the foot at most auto parts stores. You would not have to worry about it collapsing under high vacumm, but more importantly it will not dry rot,crackor develop leaks due to vibration/rubbing on anything. With it being mounted under the dash and out of sight it would be far better to use steel in my humble opinion. I have personally had to change alot of the hard line gm uses for map sensors, particularly in full size/ s series trucks with throttle body injection. they typicly either develop crask due to age or become loose and develop holes due to laying on the manifold, some of them have almost looked melted due to this. On older vehicles it is hardly worth it to order the preformed hard plastic, and as mentioned above regular vacum line could collapse. I commonly replaced them with hard steel and just used a couple 2 inch lengths of neoprene rubber at the manifold/ map sensor to connect it. works much better, just as cheap as hard line and most likely will outlast the engine/vehicle.

just my $.02 hope it helps you.

 
JimMel 
Contributor
Posts: 339
JimMel
Age: 56
Loc: Yorkville, IL
Reg: 05-10-07
01-18-08 09:43 PM - Post#1346203    
    In response to esahc


I could use a metal line, we'll see how it goes when I get in there. The plastic line is all ready there for the autometer vacuum guage in the dash, all I'd have to do is move an existing Tee that used to serve the distributor vac can. Judging from the action of the vac gauge, that line ain't gonna collapse, and the gauge responce is instant always.

Wouldn't a metal line fatigue and crack from the movement of the engine on the mounts?
My new Camaro board http://www.firstgens.com
68 Camaro Vert, SS clone,383 & TKO 500, Holley c950 TBI
http://www.Jimragtop.com


 
Z-man 
Senior Member
Posts: 335
Z-man
Loc: Foxfield, CO
Reg: 12-30-03
01-19-08 12:54 AM - Post#1346254    
    In response to JimMel

I'd go with the plastic line since it is less prone to crack. I've got my original plastic line to the oil pressure gauge in mine and have seen no problems...

 
esahc 
Member
Posts: 27

Reg: 01-16-07
01-19-08 12:18 PM - Post#1346504    
    In response to JimMel

I didnt mean make the line completely metal, I meant use a 2-3 inch piece of rubber at each connecting end to allow it to move

 
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