1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

air fuel tuning

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Old Jul 31, 2007 | 06:16 PM
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From: clarksville tn
air fuel tuning

i have an 85 gs that has a 13b out of an 85 se i can figure out how to get the air fuel mixture right. its running so rich it jerks when im accelerating or when im cruising. its kind of embarrassing to be driving and for no reason you car starts being funny on you. can anyone help me out. also do i have to have the variable resistor plugged in for the engine to run right
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Old Jul 31, 2007 | 07:41 PM
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im thinking it might be the tps not sure. but i barely put my foot on the throttle and it surges between like within 500 rpm up and down. then when i let off it goes back to the high idle.
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Old Aug 1, 2007 | 06:38 AM
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Are you using the whole SE fuel inj system?
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Old Aug 1, 2007 | 11:29 AM
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From: clarksville tn
yes im using everything but the stock air box because i didnt want to cut any holes so i have an after market air filter but thats it
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Old Aug 1, 2007 | 12:00 PM
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It could be a scratchy TPS. As I understand it, the GSL-SE had a touchy TPS. Then again, wasn't it just a switch back then? Like an idle postion and a WOT position? No variable resistance like the later ones?
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Old Aug 1, 2007 | 12:15 PM
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should i find a new one or something or get a used one off of some other car or something that works better
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Old Aug 1, 2007 | 12:25 PM
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Dude I couldn't tell you. A GSL-SE guru probably could. I've only ever messed with the variable type, and didn't really understand it at first because the pinout was different blah blah blah.
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Old Aug 1, 2007 | 08:37 PM
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Unplug the TPS and take it for a test drive.

The variable resistor is just for A/F mixture at idle.
I'm suspecting a vacuum leak.
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Old Aug 1, 2007 | 10:01 PM
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From: clarksville tn
that should make it better?
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Old Aug 1, 2007 | 10:06 PM
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If the TPS is malfunctioning, then yes.
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Old Aug 1, 2007 | 10:27 PM
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From: clarksville tn
i guess ill go for a joy ride after work then
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Old Aug 1, 2007 | 10:39 PM
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SE amd S4 engines have a tough time telling you how they feel since there is no check engine light or stored trouble codes in the ECU.They can definately run rough if the TPS is bad or even a touch out of whack.

I would not be looking at mixture being the problem.That is to say,its not a matter of the fuel delivery needing to be tuned or altered......rather the ECU is having trouble delivering stock fuel amounts due to an electrical/sensor issue.Get all the electrical underhood items you should have,including the variable resistor.If the GSL-SE has an underhood injector resistor pack,like the S4's then youll need that too.The low impedance SE injectors will fry the ECU in short order if you dont get the total resisitance up to about 12-13 ohms.The variable resistor screw is just for trimming the idle mixture,but you should still have it.Dont worry about the stock airbox,that shoudlnt change things.But make sure every electrical connection on the engine/EFI is hooked up and present before you blame anything else.

Are you running a baffled fuel tank, or do you have the tank FULL to the top right now?
Is the AFM level.....you cant tilt or rotate the flapper door style AFM's,gravity will affect their output signal.

There are actually trouble codes for the GSL-SE and the S4 engines,despite the lack of a check engine light or memory system.If its anything like the S4,you can access the trouble codes by hooking up a simple 2 LED light system to the diagnostic port of the ECU.You have to watch the codes read out as you drive,since the older systems dont keep them stored,but its easy to have the passenger do that.On the S4,there is a large green plug under the hood for diagnostics,Im not sure about the SE though.As was stated before,an SE guru will likely chime in soon with more specifics,but for now,since you have a swap (which presents MANY more possible variables) make sure that everything under the hood is in good shape,from tuneup to vacuum leaks.
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Old Aug 1, 2007 | 11:05 PM
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I am that SE Guru,:-)

I have instructed him before to do a pin test at the ECU to verify all values are correct including ground inputs. Also to do a test at the AFM.
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Old Aug 1, 2007 | 11:45 PM
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From: clarksville tn
i did do a pin check everything that i can find is close if not exactly what it should be on the ecu but ill try to get that stupid variable resistor soon speedo comes first though i think i spun it?
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Old Aug 2, 2007 | 12:14 AM
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The variable resistor is only for idle mixture. That you should not attempt to adjust without it being on a gas analyzer. Unless the AFM has been tampered with there will be no reason at this time to tamper with it.

I would however recommend testing the AFM per the FSM. It is also possible that the AFM is way out of calibration causing these symptons. But in order to correct it, you have to crack open the top and adjust at the potentiometer arm. This should also be done on a gas analyzer so you can see what the A/F ratio is going to.

As far as your speedometer not working. First check at the back of the instrument cluster to verify that the cable has not detached it's self. If that is ok then you can detach the cable at the trans and insert the end into a drill and see if the speedo works. If it does then it is in the gear that is in the tailshaft housing.
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Old Aug 2, 2007 | 06:17 PM
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From: clarksville tn
unhooked the tps it runs great no hesitation or anything. she runs so strong. where can i get a good working tps? do i need one? and as for the speedo i will check that a little later. my old car that didnt work so its not that big of a deal but would probably get one here soon. the variable resistor, i dont have one, will this hurt the car or it doesnt matter?
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Old Aug 2, 2007 | 09:36 PM
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Originally Posted by bugman1973
unhooked the tps it runs great no hesitation or anything. she runs so strong. where can i get a good working tps? do i need one? and as for the speedo i will check that a little later. my old car that didnt work so its not that big of a deal but would probably get one here soon. the variable resistor, i dont have one, will this hurt the car or it doesnt matter?

Post up a WTB in the classified section for the TPS. Yes, yo need to have the TPS in there to keep the fuel system working like it was intended to.

The variable resistor I would also round up. I can't tell you if there would be any adverse long term effect or not.
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