85 Supra wont start and has strange issue

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  1. #1
    CelicaSupra.com Member
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    85 Supra wont start and has strange issue

    So I picked up a 85 Supra and it sat for a while, So I hooked up my battery pack to boost it and it starts cranking strong to the point it even almost caught and started, But while doing this not everything lights up on the digital dash and nothing like power windows works..

    So I pull up my car to boost it as I figure the battery pack is weak, anyway same thing cranks but no starting,so I start checking fuses everything that I can see is good, I then pull the EFI relay to swap it with the one beside it that's the same taillights? once I do this everything powers up on the dash and everything works sunroof lights ect…

    but then there is no cranking when I try to start it? so I swap the relays back and again full power but no cranking... so I leave the car start looking for bad grounds or anything after like 10 mins I said let me try once more as it was getting late, the car starts to crank with full power then again no more cranking?

    anyone have any ideas? The car does have a aftermarket alarm but I don't have the key fob thing for it, Do you think maybe that has something to do with it? As the battery was dead so maybe this thing cuts off power somewhere?


    Any help is appreciated,

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  3. #2
    CelicaSupra.com Member 4SFED's Avatar
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    Quote Originally Posted by BILLY_GTS View Post
    So I picked up a 85 Supra and it sat for a while,
    How long a while? Long enough for the old gas in the tank to turn into turpentine? Was it running ok before it sat for a while? If it wasn't running before then it won't suddenly start now after it sat without troubleshooting and fixing first.

    Quote Originally Posted by BILLY_GTS View Post
    So I hooked up my battery pack to boost it and it starts cranking strong to the point it even almost caught and started,
    Almost caught what? Are you getting spark? Fuel? Two easy things to check while you're doing what you're doing. Speaking of shooting trouble - playing around with fuses and relays won't get you far unless you know what you're looking for. What were you looking for? Check that you're getting a spark and check that the fuel pump is pumping fuel to the rail.

    To check for spark, pull a plugwire off and put a screwdriver in the end of the wire and let it sit next to a metal surface (engine, head, manifold, etc) and see if the spark jumps the gap between the screwdriver and metal surface when you crank the engine over.

    To check if the fuelpump is working you have to fool the car into thinking that the engine is running - there are a couple ways - either pull off the air filter and reach up in there and prop open the flapper door of the afm with a screwdriver so that it appears you have air flowing into the engine OR jumper that check connector right there by the afm and it will supply the electrical power to the fuel pump. Then turn the key to on - no need to start - you should be able to hear the pump running and hear the fuel returning to the tank too. You can squeeze the rubber fuel line by the intake manifold and feel it too.

    These cars have a built-in safety feature where if the engine isn't turning then there is no electrical power being supplied to the fuel pump. Imagine being in an accident where you've smacked in the front end and the car dies, but because the key is on the fuel pump continues pumping away and feeding fuel to your non-running engine and a busted fuel line is spraying that fuel all over the hot engine and... It could ruin your whole day. So, Toyota put a little switch on the flapperdoor of the afm. When the flapperdoor is open (air is being sucked into your running engine) that little switch supplies power to the fuelpump. When the afm flapperdoor is closed (engine is not running and no air being sucked in) that little switch stops supplying power to your fuel pump.

    If there is no spark and/or the fuelpump isn't running then there are a couple fuses, relays, and wires you can check, but we'll burn that bridge when we get to it. First, run the checks for spark and fuel.
    Dave Harrison

    current lineup and year acquired:

    '85 white Mark2 7mgte 5sp 1988
    '85 white Mark2 7mgte Auto 2009
    '84 maroon Mark2 6mge 5sp 2013
    '86 red Mark2 7mgte 5sp 2016
    '85 black Mark2 6m Frankenmotor 5sp 2017

  4. #3
    CelicaSupra.com Member
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    Quote Originally Posted by 4SFED View Post
    How long a while? Long enough for the old gas in the tank to turn into turpentine? Was it running ok before it sat for a while? If it wasn't running before then it won't suddenly start now after it sat without troubleshooting and fixing first.

    Almost caught what? Are you getting spark? Fuel? Two easy things to check while you're doing what you're doing. Speaking of shooting trouble - playing around with fuses and relays won't get you far unless you know what you're looking for. What were you looking for? Check that you're getting a spark and check that the fuel pump is pumping fuel to the rail.

    To check for spark, pull a plugwire off and put a screwdriver in the end of the wire and let it sit next to a metal surface (engine, head, manifold, etc) and see if the spark jumps the gap between the screwdriver and metal surface when you crank the engine over.

    To check if the fuelpump is working you have to fool the car into thinking that the engine is running - there are a couple ways - either pull off the air filter and reach up in there and prop open the flapper door of the afm with a screwdriver so that it appears you have air flowing into the engine OR jumper that check connector right there by the afm and it will supply the electrical power to the fuel pump. Then turn the key to on - no need to start - you should be able to hear the pump running and hear the fuel returning to the tank too. You can squeeze the rubber fuel line by the intake manifold and feel it too.

    These cars have a built-in safety feature where if the engine isn't turning then there is no electrical power being supplied to the fuel pump. Imagine being in an accident where you've smacked in the front end and the car dies, but because the key is on the fuel pump continues pumping away and feeding fuel to your non-running engine and a busted fuel line is spraying that fuel all over the hot engine and... It could ruin your whole day. So, Toyota put a little switch on the flapperdoor of the afm. When the flapperdoor is open (air is being sucked into your running engine) that little switch supplies power to the fuelpump. When the afm flapperdoor is closed (engine is not running and no air being sucked in) that little switch stops supplying power to your fuel pump.

    If there is no spark and/or the fuelpump isn't running then there are a couple fuses, relays, and wires you can check, but we'll burn that bridge when we get to it. First, run the checks for spark and fuel.
    So I had some time to mess with the Supra and I got it started!!! so I kept hearing a click under the dash, So I said let me check the fuses under the kick panel,

    Well I had my booster connected with the ignition on and the 1st fuse I pull the click stops? well it was the gauges fuse... so I turn the key and the car fires up but the digidash does not light up with the exception of the lower box lights... so no spedo or temp ect…


    I put the fuse back in try to start it nothing... so I pull the fuse start the car and then put the fuse back and the car stays running but still no digi dash, I take it for a drive and the digi dash comes on lol...


    so I start taking the lower dash apart to see what the clicking is, So I see some ghetto wiring right off the bat and I found the clicking, its coming from what looks to be a late 80s early 90s Alpine alarm, I am going to start trying to put the wires back to stock via colors remove alarm but any ideas on any certain areas I should look at?


    Also would the digidash work at all if the guy previously just threw it in and the car was analog prior? he told me it was a digidash version but I really don't know if i believe everything he said...

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  6. #4
    CelicaSupra.com Member RedP85's Avatar
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    Clicking under the dash, somewhere behind radio, is the automatic climate control, slide the setpoint to fully cold, that may keep it quiet for a while.
    -Jocelyn,
    P85-6MGE SDR(HKS kit c/w IC and F-Con in a box) 225KKm, NAL seats, 2.5 Brullen, ACT clutch, LJM, SS lines, Trip Computer. EuroH4
    P85-5MGE SDR had 439KKm (for 17 years my daily driver, RIP...), 2002 E39 ///M5 LMB Hidden Content
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