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Running an 86 without the M.A.S. ???


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#1 patra_is_here

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Posted 10 April 2004 - 11:52 PM

hi all!

i just got an 86 starion and I've been digging around online for info and such (as well as tooling around on the starion)

I read that the 86 can run without the MAS so I took it off and tried it, and, well, IT WORKED.

I just don't understand HOW or WHY it worked.

can some one please post some details to this occurance and any benefit/downsides to not using the M.A.S.?

because if I dont really need it, i'm just gonna fab up some intake tubing/filter and be done with it.





#2 Metric-man

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Posted 11 April 2004 - 12:08 AM

My opinion is a few 86 were experimented with because of idle problems.
Either the ECU or the MAS it's self was allowed to function w/ out the air flow inputs.

With out metered air readings the ECU will not change the injector in regards to air flow but engine temp and 02 readings from the oxygen sensor this may allow for quicker response and allow for less errors in fuel air mixtures.
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#3 Too Deep

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Posted 11 April 2004 - 07:19 AM

many cars in the 80's did not use mas.
they used manifold pressure to determine  load. this along with tps are the main driveability inputs.
the 86 uses a pressure sensor(map sensor) along with the mas.
mass is better for throttle response and wot performance. its nice to have both, when the mass fails the car is still driveable.

#4 patra_is_here

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Posted 11 April 2004 - 11:41 AM

interesting. thanks guys.

#5 Metric-man

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Posted 11 April 2004 - 01:11 PM

I wish my 86 would work without the MAS.
I have a 6/85 (1986) LE ; It uses a Manifold Absolute Pressure (MAP) sensor.
I unplug my (MAS) Mass Airflow Sensor and the car just dies immediately it will crank but it won't start.
Plug the MAS back in and it will start right up.
I think GREENSTAR has a 86 ESI (intercooled) that is able to run w/out the MAS ?
Maybe the intercooled models for 86 were the only ones that are able to do this because the values in air temp or atmospheric pressure were too variable ?
mike_c would be a good person to add to this thread.........

patra_is_here is your vehicle an intercooled model ?
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#6 Indiana

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Posted 11 April 2004 - 03:46 PM

for those that try 86 MAS-less I would suggest a new o2 sensor be installed

#7 patra_is_here

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Posted 11 April 2004 - 04:38 PM

the build date is Dec 1985, making it a 1986 model year.

its an esir.

its black with red interior.

#8 GREENSTAR

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Posted 11 April 2004 - 05:37 PM

Well I guess I should put my two cents in here.  From what I have found, running w/out the MAS is a smoother idle but in first gear on initial take off there would be a small hiccup when you first take off and also when running, say down the freeway, and if you just mash the gas the air/fuel get's all screwed up and bucks and sputters.  You actually have to feather it and it won't do that.  As far as performance goes, I think it runs pretty good.  You get a lot of airflow but from what I am told, the 86's that can run without the MAS, the ECU goes into a set mode and that is why you can run without it.  The ECU reads that the MAS is not working or not there at all and goes into like a fail safe mode so you can still run.  But it is not really right.  Some people like running it like that but I prefer to use the 1G MAS.  In Engine Mods there is a post that I put in there on how to run the 1G MAS on the 86.  It has been working pretty good for me.  Not sure if anyone else has been succesfull with it yet but what a difference.  Also, I think it was the early 86's that could run w/out the MAS.  Mine is a Jan 86.  I have heard the the later 86's need to MAS to run.  Hope that helps!  Steve

#9 mikec

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Posted 11 April 2004 - 09:33 PM

Mitsu was constantly playing with the logic, equations, and curvefits (data tables) in StarQuest ECUs.  For most years, the injector pulses occur once every "X" MAS pulses, where X is based on all the other sensors.  The length of the pulse is also dependent on the other sensors.  Without the MAS, the ECU can only assume certain things based on RPMs and TPS position, and the boost pressure sensor on the 86-earlier cars.  In theory it has enough for a basic speed-density system but, until 86, Mitsu didn't really tune it much at all.  Before 86, the limp-home stuff was basically enough to literally limp home... not really enough for the car to run right.  In 86 Mitsu tried all sorts of stuff.  In 86, Mitsu apparently played around with a speed-density type of setup, at least as the MAS-inop limp-home mode.  That's why some 86s seem to run half-way decently without the MAS - it depends on what month a particular 86 ECU was built.  Few 86s without the MAS however run perfectly... hesitation on mashing the throttle, excess fuel during part-throttle cruise, etc.  In limp-home mode, Mitsu sacrifices fuel economy and emissions to some extent; the default limp-home mode is generally waayy rich for engine safety.  

Even in the later years Mitsu kept monkeying with ECUs; that's partly why some 88/89 cars boost cut at different RPMs. In 87, Mitsu deleted the boost pressure sensor completely so all the speed-density limp-home stuff ended up in the trash.  Note too that in the 85/86/87 timeframe Mitsu re-did several of their cars, including the Colts, to have a Starion-like throttle body injection system.  Engineers concentrated on making regular mode (i.e. not the limp-home) equations/curves/tables for all the other cars... as opposed to spending time fine-tuning limp home modes.

Since the MAS is the main input to the ECU, a dead MAS pretty much keeps the car from starting/running.  Except for some 86s.

mike c.

#10 smog

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Posted 05 May 2004 - 10:37 PM

I suppose I will throw my car info up. I own a 86 conquest tsi built in may 1986. I'm assuming this was one of the last months of production for the 86? I'm not familiar with how far into the year they made them, but may seems pretty far into the year.
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#11 Metric-man

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Posted 05 May 2004 - 11:05 PM

QUOTE
I suppose I will throw my car info up. I own a 86 conquest tsi built in may 1986. I'm assuming this was one of the last months of production for the 86? I'm not familiar with how far into the year they made them, but may seems pretty far into the year.


Not as much the year/month of production of the vehicle it's self as the negation of the MAS from the drivability/emissions acceptance equation.
June is generally accepted as the begining month of production for the following year models. There maybe some 6/86's out there that can operate minus the MAS ?
As well as 5/85's ?
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#12 fastquestMA

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Posted 10 May 2004 - 09:13 AM

;)My 3/86 TSi will not run without the MAS! This is what I did! Fuel cut defencer, Modified 1st gen airbox with HKS half dome air filter on end and removed the honey comb from the mas air, The air intake is tremendous! That box resinates like you wouldn't beleive, it growls! a definate performance upgrade in my book! Spools much quicker also! Just make sure if you go with HKS, change the filter every 7K or sooner! Good luck! wink.gif
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#13 MightyMaxGS-T

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Posted 29 May 2004 - 11:30 PM

i know that on the 88-89s you can run w/o a maf by putting a 12v signal on the sensor power wire.....i ran like that for about 4 months, even raced at the track like that........but then i got a 1g MAF........
Yes it is a Mighty Max, yes it is turbo!  I have the same motor as all of you, only I'm lighter...

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#14 SidewaySStarion

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Posted 21 November 2004 - 02:09 AM

i have an 85.5 ill have to try taking out the mas. ill post results.
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#15 frenzy757

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Posted 05 December 2004 - 03:15 PM

ok is the o2 sensor the one thats in the OVCP?  so if i use Kellys, i had to unplug it, and i cant take out my MAS right

#16 Metric-man

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Posted 05 December 2004 - 04:28 PM

QUOTE
ok is the o2 sensor the one thats in the OVCP?  so if i use Kellys, i had to unplug it, and i cant take out my MAS right


There is a large black canister that holds the air filter.
on that canister is a square shaped electrical plug.

Unplug that plug and if your car runs with out it plugged in then your good to go.

The 02 sensor is behind the turbo on the down pipe next to the fire wall just before the precat don't touch unless you have to.

Have you uploaded the 88 online service manual yet ?

It's at the top of the page in the FAQ section.
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#17 slydogg

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Posted 05 December 2004 - 07:12 PM

heat temp sensor is in top of the pre cat, air temp sensor is in the ovcp, i want one of kdm's ovcp pipes myself, not sure if he does the bung for air temp sensor for the 86 ovcp, i'll be askin' soon. i need chrome
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#18 Metric-man

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Posted 05 December 2004 - 08:20 PM

QUOTE
heat temp sensor is in top of the pre cat, air temp sensor is in the ovcp, i want one of kdm's ovcp pipes myself, not sure if he does the bung for air temp sensor for the 86 ovcp, i'll be askin' soon. i need chrome


The heat temp sensor... what ??  :smile.gif
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#19 edjee

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Posted 05 December 2004 - 08:59 PM

I have been wondering about this also.  I just got a OVCP, and thought I had to run the air sensor on the stock ovcp.  Did a little test run today with it unplugged, my car seemed to idle smoother and boost came up pretty well but first gear a few times bogged on me, not sure if it was me or the car ;D  But I just wanted to see if I can run without it plugged, now that it can imma hook up my ovcp and bov.  ;)

#20 slydogg

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Posted 06 December 2004 - 10:05 AM

sorry mm, oxygen sensor is the correct term, my 86 runs fine without these items and with the mass unplugged, however i'm just not convinced it's a good idea
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