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Discussion Starter · #1 ·
Hi all,
I know it's not easy (or impossible) to accurately diagnose problems without being there in person....just hoping someone can point me in the right direction.
So.....my '83 Supra will turn over, has good spark (now) but will only "run" for a few seconds if I spray starter fluid into the air intake. The fuel pump is running, (I can hear and feel it). No idea if it's producing enough pressure (is there a Schrader valve somewhere to be able to connect a pressure guage to test that?). I have siphoned out about a gallon of fuel into a clean white bucket. The fuel doesn't look or smell old or bad. No "trash" or water droplets noted in it.
This is basically where I'm at so far. If I let the fuel pump run for a few minutes, the engine will shudder and kinda attempt to start on the first crank. Then just spins over. With the starting fluid, it will run (very rough) for a few precious seconds. Basically, it appears to be starved for fuel to me......
Any help would be greatly appreciated!!


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Have you done some work to it? I once had the two connectors on the thermostat reversed and it would not start. I switch them and it fired right up.
 

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Discussion Starter · #3 ·
Have you done some work to it? I once had the two connectors on the thermostat reversed and it would not start. I switch them and it fired right up.
Wow, that's nuts that a thermostat issue would have kept the car from running! I've only had it for a couple weeks so, still looking it over, etc. It's a project car and needs a good bit of work. Like a lot of old cars, it's had a lot of "modifications" done by previous owners!

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I just got a Supra that had sat for years, and eventually it started just by cranking. Even with old gas. I've read that the Cold Start Injector and the water temp time switch are common culprits behind difficulty starting.

My car will start if I spend a min or two cranking with the throttle cracked open a tiny bit. Crank 2 - 3 seconds at a time, then let the starter rest.
 

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I had similar symptoms until I went through and "back-fed" all my injectors with 12v pulses with the fuel pump running (there is a 2 prong round plug near the MAF that will keep it running if jumped).

I have an old bosch injector connector with like 3 feet of wire on it and just slid it on to each injector (tricky to get the old harness off but small picks are your friend). Then made a circuit from each battery post and clicked one wire (doesn't matter which and polarity doesn't matter) on and off the terminal until I could hear the injector clicking. This method should work for the cold start injector as well.

Also worth checking the fuel filter under the intake, mine was ok after 10 years of sitting, but the old gas had varnished the injectors and fuel pump closed, while the vapors in the tank got it nice and rusty so the pickup sock in the tank would suck shut after any effort from the fuel pump.
 

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Discussion Starter · #6 ·
Appreciate the info from all! Gives me a good starting point. Also, I forgot to mention the previous owner ran a hot wire (12v) to a switch and to the fuel pump. Obviously to try and go around a problem and force the car to run. Didn't work. I plan on putting it back the correct way. Anyone think that might be contributing to the problem? Does the ECU need to "know" that the fuel pump is running in order to activate other things that would allow the engine to get fuel to the injectors etc?

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Appreciate the info from all! Gives me a good starting point. Also, I forgot to mention the previous owner ran a hot wire (12v) to a switch and to the fuel pump. Obviously to try and go around a problem and force the car to run. Didn't work. I plan on putting it back the correct way. Anyone think that might be contributing to the problem? Does the ECU need to "know" that the fuel pump is running in order to activate other things that would allow the engine to get fuel to the injectors etc?

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Intake tube leaks will bypass the afm and cause low or no fueling from the computer. It also needs VR trigger output from the ICM. The ICM may spark while cranking regardless of connection to the computer if only some wires are damaged.
 

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Appreciate the info from all! Gives me a good starting point. Also, I forgot to mention the previous owner ran a hot wire (12v) to a switch and to the fuel pump. Obviously to try and go around a problem and force the car to run. Didn't work. I plan on putting it back the correct way. Anyone think that might be contributing to the problem? Does the ECU need to "know" that the fuel pump is running in order to activate other things that would allow the engine to get fuel to the injectors etc?
It operates other way around. ECU must see:

  • engine is spinning
  • airflow is opening AFM

THEN it turns on fuel-pump. Everything is controlled by ECU. If you feed it incorrect sensor signals, car won't run. Best bet here is to restore all wiring back to stock configuration.
 

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On 85, there is 2 coils for the Fuel Pump relay (called COR :circuit opening relay) .
The ECU controls one coil, and the AFM the other, as long as the engine is pumping air through it by having the flapper open., and when the starter is triggered.
 

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Discussion Starter · #10 ·
Appreciate the help!
So.....if the guy hot-wired the fuel pump, then the ECU isn't turning it on, which may cause a lot of other things to not work correctly? I'm gonna track everything down, and try to systematically track down the problems....with the help of a few cold ones, of course!

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Technically the 5M ECU does control the fuel pump when you are starting the car. You can bypass all these questions just shorting the check connector to power the fuel pump so there is fuel pressure. If you have a car that has been sitting a long time the fuel pump is a likely suspect. For like $80 for a Denso pump it seem like a smart thing to change for peace of mind IMO.
 
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Also measure voltage at fuel-pump connector itself when cranking. Old crispy wiring and connectors are often problem themselves.
 

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Discussion Starter · #14 ·
Thanks again for all the help! I'll keep y'all posted. (I'm from the South....lol)

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Discussion Starter · #16 ·
Ok.....little update. Messed with the car today. Boy does it want to run, but not quite there! I found out the previous owner installed an inline fuel pump (I think in the place of one of the inline fuel filters near the back of the car). Ugh! And as I said before, he wired it to a switch on the dash. So.....do you guys think the car will run at all with this setup?? Please understand I fully intend to put it back correctly, but I would love to hear the car run first! Also, I hear fuel flowing though the lines near the engine. Didn't really want to spend money on a fuel pressure gauge that I may only use once in a blue moon. But I will if necessary. Is anyone getting a vibe on what could be going on with my car?? It tries to start, but still will only run for a few seconds if I spray starter fluid in the intake.
Thanks!

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82 and 83 have external fuel pumps in the back. Fuel filter in front on drivers side of engine.
Tank has filter sock and pump on suction side had a small filter.
17193
 

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Discussion Starter · #18 ·
Thanks 82TURBOSUPRA. Feeling kinda dumb! I thought someone didn't feel like dropping the tank to change a bad FP, and got creative. Hopefully they left the original wiring harness down there. Still learning about these cars, my first one. This forum has been amazing, great community here!

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No, don't use that manual fuel-pump switch. Unless they wired in isolation diode, you'll end up powering an ECU circuit that should be grounded or off. Thus risking damage to ECU. It may already be too late and ECU's fuel-pump activation circuit may already be fried.

Fastest way to get car running is to remove all non-factory wiring and restore every wire back to stock. Ignore everything else as they're not problem. Ignore pump, ignore filter, ignore fuel-lines, ignore fuel-rail, ignore FPR, ignore injectors, ignore ECU, ignore all sensors and AFM.

Only thing you need to do is verify every wire from ECU is connected to proper component on other end. That's it.
 

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Discussion Starter · #20 ·
No, don't use that manual fuel-pump switch. Unless they wired in isolation diode, you'll end up powering an ECU circuit that should be grounded or off. Thus risking damage to ECU. It may already
be too late and ECU's fuel-pump activation circuit may already be fried.

Fastest way to get car running is to remove all non-factory wiring and restore every wire back to stock. Ignore everything else as they're not problem. Ignore pump, ignore filter, ignore fuel-lines, ignore fuel-rail, ignore FPR, ignore injectors, ignore ECU, ignore all sensors and AFM.

Only thing you need to do is verify every wire from ECU is connected to proper component on other end. That's it.
Wow! That's some tough advice! Lol. I'll post back in 3-6 months when I have all that sorted out!
Jokes aside, I get where you're coming from. If someone "rigged" something to work, there was a reason, usually because they don't understand how it was supposed to work, or didn't feel like fixing it the right way. That responsibility has now fallen on me (like a ton of bricks)
I'm expecting a Toyota Electrician Wiring Diagram book soon, so that will definitely help me iron things out! Thanks for the "tough love"!

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