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Who gots a rumored 83's with no factory boost cut?


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#1 83stariontravis

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Posted 22 January 2015 - 01:15 PM

I've got a hunch the factory fuel cut is in the MAP sensor.  After reverse engineering the digi cluster I took a look inside the factory MAP sensor and found a few things to try.  Nothing has worked yet but it almost looks like there are provisions for alternate circuitry in the sensor.  Just a guess but I'm thinking there might be a mod that can easily be done for the 83 to remove the factory fuel cut.  So anyone who has an 83 they think does not have factory fuel cut... I know I've talked to a couple people before.. but speak up and if you can post the part number on your map sensor that would be great for starters.  Mine shows X5T20471 on the case but X5T20177 on the circuit board.
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#2 importwarrior

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Posted 22 January 2015 - 01:52 PM

http://www.rojgonz.com/mr2/zener.htm

google: fuel cut diode

more good read

http://soarercentral...875/232321.html

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#3 Tim_C.

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Posted 22 January 2015 - 04:04 PM

The CBRII car does not have fuel cut. It has that funky factory harness adapter that attaches to the ECU. I think it was Shelby that told me it is a harness modification for the injection system, and that the cars that have it, can boost to 20 PSI with the stock injectors and have enough fuel.
My DD '83 does not have it, but it is not intercooled, so I don't take the boost up more than about 5 PSI on it. I'm driving it today, so I went out and checked it. It is the X5T20471 one. Not sure if it has the boost cut or not.
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#4 83stariontravis

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Posted 26 January 2015 - 03:29 AM

Can you post a pic of the harness you are talking about?

Same as this?
http://www.starquest...howtopic=145097

Ok so when tracing the boost sensor signal into the ecu it doesn't seem to go very far.  Looks like it goes to an ~80k ohm resistor to sensor ground and in parallel with the resistor there is also a diode to ground with the anode facing ground.  I am unable to find any other places the boost signal goes inside the ecu at all...  I would take a guess and say when the diode voltage is exceeded it shorts to ground killing anything that is relying on the sensor ground.  If the diode was removed would I need to keep the resistor for any reason?  And if this is the only place this goes in the ecu how about just cut the wire...?

Edited by 83stariontravis, 26 January 2015 - 03:36 AM.

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Black 83 Starion Daily Driver, LSD, TDO5H
Red 83 Starion LSD 5 lug swap, 7s and 8s, motor out

#5 83stariontravis

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Posted 26 January 2015 - 05:21 AM

So I started thinking and the 83 fuel system for sure compensates for altitude by switching a solenoid when the key goes to the on position and letting ambient air instead of intake source.  Started to think I must be wrong and that the signal must go beyond my current findings into the ecu but now I am thinking that the map sensor must self calibrate at the same time as the solenoid is switched upon receiving power.  So this compensation would happen outside of the ecu...(in the map sensor.)
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Red 83 Starion LSD 5 lug swap, 7s and 8s, motor out

#6 twojayzeestarion

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Posted 06 May 2015 - 01:14 AM

I have a 83 ecu with the jumper harness that has no fuel cut
, but the 83 maf will still cut at 17psi, swapping to a 89 maf eliminates that, but yea its like a piggy back harness plug it into ecu and eh plugs into it
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#7 twojayzeestarion

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Posted 06 May 2015 - 01:44 AM

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#8 twojayzeestarion

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Posted 06 May 2015 - 01:47 AM

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1.87 black conquest: committed suicide
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3.86 red starion: stolen by scrappers
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11.88 black conquest: parting out need parts?
12.89 red conquest: currently own
13.89 Orange conquest shp: 2jz single turbo daily driver
14.88 fiji blue conquest: currently own
15.89 silver conquest: currently own
16,88 Palemero grey starion (ulrichwolfs chariot): currently own
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#9 83stariontravis

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Posted 23 May 2015 - 07:15 PM

What are u smoking?!?!  I removed diode because I found one of those tsb harness and I get fuel cut 9psi...
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#10 twojayzeestarion

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Posted 25 May 2015 - 02:34 AM

hm wel maybe its somthing else with my 83, mine would boost 20 psi no cuts
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14.88 fiji blue conquest: currently own
15.89 silver conquest: currently own
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#11 JohnnyWadd

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Posted 25 May 2015 - 12:45 PM

Travis have you tried clamping the MAP and see what happens?

#12 StarquestRescue

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Posted 25 May 2015 - 06:38 PM

Perhaps it is not really fuel cut, but is the fuel pressure dropping at high load causing the engine to cut out. or pig rich causing a rich misfire. A wide band gauge will give you valuable clues. If it is dropping fuel pressure, a fuel pressure gauge will show the issues a little sooner then the wideband.
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#13 ucw458

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Posted 25 May 2015 - 08:32 PM

View Posttwojayzeestarion, on 25 May 2015 - 02:34 AM, said:

hm wel maybe its somthing else with my 83, mine would boost 20 psi no cuts

Maybe because you put an 89 fuel system in your 83.
My 87
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#14 twojayzeestarion

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Posted 26 May 2015 - 07:39 AM

View Postucw458, on 25 May 2015 - 08:32 PM, said:

Maybe because you put an 89 fuel system in your 83.

im speaking of before i did all that, it didnt fuel cut then
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1.87 black conquest: committed suicide
2.87 silver starion: sold
3.86 red starion: stolen by scrappers
4.88 red starion: sold
5.87 black starion: given to friend
6.87 black starion: sold
8.83 silver starion: currently own
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10.87 black starion: given to brother for Christmas as first car
11.88 black conquest: parting out need parts?
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14.88 fiji blue conquest: currently own
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16,88 Palemero grey starion (ulrichwolfs chariot): currently own
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#15 JohnnyWadd

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Posted 26 May 2015 - 04:40 PM

View Post83stariontravis, on 23 May 2015 - 07:15 PM, said:

What are u smoking?!?!

His tires LOL

#16 83stariontravis

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Posted 30 May 2015 - 04:14 PM

fuel pressure stays up at 50psi and adding the diode back in removes fuel cut...
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Red 83 Starion LSD 5 lug swap, 7s and 8s, motor out

#17 mooser83

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Posted 11 June 2015 - 10:27 PM

I had an all original 83 before the engine died and it always cut around 9-10 PSI. I tried removing the map entirely (causing the in dash boost gauge to stop working)

I got another 83 that had some modifications to it. I ran it at 18PSI briefly as a test, but I kept it at 11-12 psi. Its has the stock 83 TB and injectors, but it was converted to run an intercooler.  It also has what appears to be a rising rate fuel pressure regulator (i think)

If you want me to take a look at anything on the car let me know. I just can't drive it yet, I just started working on it to get it back on the road recently after sitting for 3 years. It needed a power steering pump and brakes when I decided to put it in storage. About a mile before getting there it started spewing oil under the hood onto the windshield (yey) When I went to take it out the old battery dead was and won't take a charge. I jumped it to see where the oil leak was and the radiator puked all over the ground and no oil came out of anywhere so it will be a few weeks until I have it all sorted out.
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#18 Metric-man

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Posted 14 June 2015 - 08:43 AM

boost cut and fuel cut are two different things
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#19 83TechMaster

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Posted 03 January 2016 - 11:32 AM

Fuel Cut? What is this fuel cut you speak of?
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#20 1rst Gear

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Posted 10 January 2016 - 12:35 PM

Well, I know on some cars the boost cut drops ignition momentarily to help control temp spikes in the combustion chamber during overboost, where as the fuel cut may be used as a rev limiter. Not that all cars are programmed this way or that this is the case with the 83' configuration.  

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