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


patra_is_here
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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.

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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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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.

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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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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
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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.

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  • 4 weeks later...
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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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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;)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! ;)
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  • 3 weeks later...
  • 5 months later...
  • 2 weeks later...
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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heat temp sensor is in top of the pre cat, air temp sensor is in the ovcp, i want one of *DM'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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heat temp sensor is in top of the pre cat, air temp sensor is in the ovcp, i want one of *DM'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 ??  ::)

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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.  ;)
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  • 4 months later...

Will a Fuel Cut Defencer prevent the hiccup on take off with the MAS not hooked up? I thought someone said that above.....

 

Also, will an 85 Starion ES have the same characteristics as the MAS-less 86?  Will it run without or not?  I have a project 85 starion right now and im wondering if I can play "Monkey See, Monkey Do" with the 86's.  Thanks.

 

CoKe

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  • 1 month later...

for those interested, this is what my 86 i/c is running now:

 

ngk plugs at 42

dsm bov

new 4 wire 02, same as used in a 90 na dsm 2.0

stock timing adjustment

3" exhaust

no MAS, it was even removed from the can

autometer a/f and boost gauges

turbo timer, I think it's a HKS clone

19C

stock fuel system but with one "J" injector replaced with a "L" (87-89 primary) and these injectors all were just cleaned and flow tested last week

Tim Cs monster banshee cam

roller rockers

schneider valve springs

masterblaster 2 coil

stock boost

and this is on the mid grade gas, NOT premium :D

 

side effects: little delay until it runs for a couple minutes on the hesitation part when pushing the gas pedal but that's about it but this is primarily a stop to first gear roll and goes away after you shift from 1st, it is not noticed at all after you are rolling.

 

Pushing 30mpg on the highway. the hesitation goes away after the car is warmed up except unless you purposely floor it from idle but you can mash pretty quick without the hesitation you just have to get used to it, runs one bar into lean sometimes to middle stoich on cruising and goes two bars into rich under boost all the way to 9.5-10psi and doesn't hit any fuel cut -what that is I don't know will find that out soon. If both the "J" injectors are left in, the car runs 3 to 4 bars rich (green) under boost and cruises in the rich state as well (this is bad). Swapping out one injector for a smaller primary solved that problem, the side effect to this is a harder start especially when warm, might have to roll over say 10 times compared to 2 on a cold start. An A/F gauge should be used when playing with an 86 doing this, you might feel "ok" running this same setup with the 2 "j"s but with one "J" and one "L" there is a significant power gain when you aren't pouring the gas in and the car pulls into 6500rpms without any misses, have yet to try to go further that is enough (for me). This is on the 89 engine with apx. 105k miles all stock internals from the cnm car and this is the car that previously had the 16G with 3" exhaust that the dyno run is posted somewhere on here. By the way, that car after the injectors were cleaned, the 02 connected (cause cnm had used the wrong wire and the 02 wasn't even doing anything) it ran much better than when he did that dyno run and I did confirm it did have a 16G as I had been told by Tim Brooks that it was only a 14G but I had paid for a 16G, this is just another example of the lies/errors that came from what was called CNM Motorsports. Changing the spark plug gap from 35 to 42 also helped, we tried 38 but still had a miss but that was with the two "J" injectors. Car still not tried with >10psi, on a few times when it did feel like a fuel cut with the 16G, most times it would just hickup and pull right through it and just keep going but this was with what we think was a dead wastegate, a new wastegate went on today and that problem went bye bye. Since the A/F ratio is good, about perfect imo at this point I can't see trying a 1G mas and the wiring mod at least on this ecu. If it is running into stoich when we up the boost then we can just put the other "J" injector back in.

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