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Gas Tank Pressure needed?!?

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Old 07-23-14, 07:57 AM   #1
sc400aaron
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Unhappy Gas Tank Pressure needed?!?

Hello everyone,

My car recently died and I figured out the fuel pump/FPCU was bad, I replaced the FP and bypassed the FPCU. But my car still wont fire off at all when turning over, if I spray starting fluid in the intake I can get it to start momentarily but still not getting gas...

My Question: Does the Fuel tank HAVE to be sealed/pressurized for the Fuel pump to be able to send enough pressure through the lines? since I rewired the Fuel pump straight to a switch (after trying it the normal way and still failing to have my FP engage/turn on) I haven't yet sealed things up yet because I wanted to be able to get it going for sure so I dont have to take it all apart and mess with it more... its going to take some caulking to get a really good seal on there...

ALSO. does anyone know what that little black box/relay thing is inside the tank on the fuel pump assembly and what it does/is it needed? since that is also bypassed.

Thanks for your help guys.
-92 SC400
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Old 07-23-14, 09:25 AM   #2
mecheng10
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you don't want your fuel tank to get pressurized. that's why the charcoal canister has a vent.
gas tanks are suppose to have a slight vacuum.

are you sure you are getting power to the fuel pump?
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Old 07-23-14, 09:41 AM   #3
sc400aaron
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Yes. I wired the fuel pump directly to a switch. when I flip the switch, fuel pump turns on. I'm getting pressure to the fuel lines/fuel rails under the hood but for some reason it is almost like there is something preventing the fuel injectors from injecting fuel

really stumped on this at the moment. any tips appreciated

Thanks!
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Old 07-23-14, 10:53 AM   #4
mecheng10
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have you checked your fuel filter?
have you checked your fuel pressure with a guage?
have you checked your injectors? are they getting voltages?

actually lets take a few steps back.
how did you diagnosis that the FP was bad? how did you car die to begin with?
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Besides lag is just a JZ owners version of FOREPLAY!!!!!!!!!!!!!
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Old 07-23-14, 01:18 PM   #5
sc400aaron
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Fuel filter is new.

With the fuel pump on you can hear /feel the gas circulating around and through the fuel rails and feel the pressure in the line.

I however do not have the necessary tools to get a Fuel Pressure reading but I assume that everything would check out in that department, if I squeeze the fuel line in the engine bay the pulsation damper screw rises showing that there is atleast some pressure..

I am almost 99% certain it has to do with the injectors not getting necessary voltage to engage in spraying of the gas into the cylinders. while I am mechanically inclined to do most maintenance on both mine and my womans cars this subject is foreign to me.

so would someone be able to give me a hand and let me know what troubleshooting steps I would take to make sure there is the necessary voltage/ohms to the injectors? and what has to be done to restore proper voltage back to the injectors?


getting back to your original question I will post a link to another thread with more info. right now I have compression, Spark, and gas* new fuel pump. but its not getting into the cylinders due to reasons unknown to me

My buddy has a voltage tester I'm going to go steal from him when he gets off work at 5 and I'll pull of an injector and test the voltage they are getting if any, does anyone have a good reference manual to what the readings should be?

Thanks for your help!
P.S if someone can help me get my car going I'd be down to paypal a few bucks on payday for your troubles!

Last edited by sc400aaron; 07-23-14 at 01:27 PM..
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Old 07-23-14, 01:23 PM   #6
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---Previous post/ more info-----


"I got a 1992 SC400 that just died on me driving the other day and would not start back up, or fire off at all, just turn over.. since this happened I sprayed some starting fluid in the intake and came to the conclusion it was the fuel pump... replaced that, and hooked everything up the way it was and it was still not getting fuel or the fuel pump was not engaging/turning on.. well I bypassed the FpECU, tried the FP to B+ diagnostic bridge and nothing, so I wired the pump directly to a toggle switch mounted to the right of my drivers side seat. now the fuel pump turns on and that is no longer a problem.

BUT.. I still am getting no sort of engine firing at all.. again, sprayed starting fluid in the intake and the car was able to pop off and very briefly start for me, I had 8 new NGK platinum plugs I had bought to put in so while my car is sitting on the side of the road and I took off work today to work on it I put all those in, not a bad job only took 1/2 hour or so. STILL NOT STARTING, turns over great. but no fuel

I know I am getting fuel to the rails because while I have my fuel pump on I can feel the fuel lines pulsating and if I squeeze the fuel line the screw on the pulsation damper rises a bit, I also ******ed with that screw a bit as a last resort thing and loosened/tightened it in case maybe it would allow fuel to get to the engine, but it was a no-go.

I put both octane booster and a bottle of HEET in the tank in case it was a problem of bad gas. also failure.


So what in the world could be causing it to get gas to the rails but no gas to be fired/ignited?could it be the fuel pressure regulator?? (Checked it since this post and it appears to be clean and dry)
Could it be that the injectors aren't working? I pulled the 30amp INJ. fuse in the box by the battery but it looks good,

any help would be greatly appreciated
Thanks!
-Aaron
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Old 07-23-14, 01:23 PM
 
 
 
 
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