Help! Supra doesn't run right

[3p141592654]

Great, now we can compare.

At idle, your Bat to B+ drop at 0.9V is twice mine (0.46V). Your FP to pump drop at 0.45V is 3 times higher than mine (0.14V). Even though your battery voltage starts out higher, your pump voltage at 9V is 1V lower.

Jumpered, your Bat to B+ drop at 1.54V is 3x mine (0.46V). Your FP to pump drop at 1.48V (factoring in your lower pump current 4.3 vs 4.9A) is 1.5x higher than mine.

The main culprit seems to be the B+ to battery wiring, which is 3x more resistance than mine. You should take a look at the EFI fuse and the EFI Main relay. Maybe check them for corrosion or other issues.

To rule out the wiring, you could temporarily run your pump off of a 12 V power supply or battery directly connected at the pump connector and see if the problem goes away.

 

[Abe's 1987]

Ok so EFI fuse and relay pins looks good. I will have to test the relay out. With the car on engine not running, I'm getting a 0.12 volt drop to the EFI fuse vs battery volts.

Edit: ok so with the ignition on battery at 12.36 volts I'm getting 12.16 volts to the +B on the check connector, 12.07 volts to the +B on the ecu, and EFI fuse is getting 12.25 volts. I hear the efi relay clicking when tested.

Car seems to drop volt when ignition is on position but gose back up to 12.6 volt when off.

Could I possibly need new terminals?

 

[3p141592654]

Your numbers seem ok, but that's with no fuel pump load since engine is off. What I would suggest is you repeat measurements with FP B+ jumpered. That when your B+ seems to take a big hit 14.53 to 12.99V.

But really, the best test would be to run 12V straight to the pump from the battery, bypass all the car wiring. Then start it up and see if you can maintain fuel pressure.

 

[Abe's 1987]

If I run straight from the battery to the pump wouldn't it put 14 volts to the pump constantly when running? Could that mess anything up?

And could someone get me their volts to the fpr vsv at idle? Need to know if I'm getting the correct volts to that as well.

 

[3p141592654]

Don't worry, the pump can handle more than 14V.

The FPR VSV should have 12 Volts on BOTH terminals under all conditions except a hot start. For a hot start the Red-Blue wire will be 0V. The Black-Red wire is effectively B+, so is always 12V.

You can check for correct VSV operation as shown here.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=116

 

[Abe's 1987]

Might be the reason why some of the systems are not functioning right due to insufficient power getting to the system. I will check the volts to the vsv and connect battery straight to the fuel pump and test it out then. Will have to test the resistance of my complete EFI wiring.

I've also tested the vsv and it is testing good. Will test the power input on it.

 

[3p141592654]

I would expect the ECUand VSVs to work fine with a lower voltage, I have tested the ECU and it works normally with only 9V. The fuel pump, being a high energy device, could be impacted, but not so much the other things. The injectors have a cal table in the ECU that goes down to 7 or 8V as I recall so it will run just fine at anything above 8-9V.

 

[Abe's 1987]

So if the volts getting to the ecu drops, the volt output to let's say for instance the injectors would stay the same? Like a 1 volt drop to the ecu would not have a 1 volt drop to the injectors?

 

[Piratetip]

Its a correction factor so the injectors will still flow the same amount of fuel even if the voltage is lower.
This is due to the delay in response of the coil in the injector.
This requires the ms of requested opening time of the injector to be increased to compensate.

If the voltage to the ECU is lower, the voltage to the injectors will also be lower, along with every other component in the system.
Unless the electrical system has some serious isolated issues like high resistance somewhere due to bad connections or corrosion.

 

[Abe's 1987]

Its a correction factor so the injectors will still flow the same amount of fuel even if the voltage is lower.
This is due to the delay in response of the coil in the injector.
This requires the ms of requested opening time of the injector to be increased to compensate.

If the voltage to the ECU is lower, the voltage to the injectors will also be lower, along with every other component in the system.
Unless the electrical system has some serious isolated issues like high resistance somewhere due to bad connections or corrosion.

Got you. So like the +B, if it where corroded it would cause a lower volt to reach the ecu, therefore the ecu would have a lower output to the other systems aka fuel pump, vsv's, ect....... which in theory would be causing my fuel pressure to drop at higher load due to lower volts right?

 

[Piratetip]

I am not saying you have a wiring issue from the battery to the ECU or injectors, I was just expanding on what Pi said above.

A multitude of things can cause lower voltage, I was just explaining how the ECU handles firing the injectors under different voltages.

Right now I would focus on your voltage drop issues related specifically to the fuel pump.
Get that all sorted out and determine if there is also a fuel line restriction anywhere as well.

 

[3p141592654]

First thing is to run 12V direct to the pump and test if it fixes the problem. That will tell us if low voltage is the culprit. .

 

[Abe's 1987]

Will do tomorrow and will let you guys know the outcome. Hopefully this works!

 

[Abe's 1987]

Ok so I straight jumped battery to pump. Still 8 psi drop at snap throttle and drops to 10 psi full throttle.

That's with battery at 14.5 volts. The wire I jump reads at 14.5 volts before i jump the pump then reads at 13.3 volts after I jump the pump.

I also guess the check valve in the pump is bad as it doesn't hold pressure after engine is shut off.

Fuel pump is reading at 0.9 ohms for resistance.

 

[3p141592654]

Ok, good. Although your electrical seems to have some issues, it is not enough to be the source of your problem. You can forget about further electrical diagnosis for now.

So now its down to either a bad pump, FPR, or restriction somewhere in the line. The pressure drop after shut off can be the pump check valve, or the FPR. If either cannot hold pressure then it will bleed off.

You might want to try pulling the return line off the FPR before the J-connector. and see how much flow you get and if it affects the rail pressure.

Also if blocking the return line cause the pressure to hold after shutoff, then the FPR is bad.

Stock pump is around 150 Lph.

 

[Abe's 1987]

Got all these in my cart. I might as well go with all new. Not to expensive and it'll save me headaches down the road.

 

[Abe's 1987]

Ok after watching a vid on YouTube and taking Pi advice I figured my fpr is not the reason for the pressure drop after the car is turned off. I clamped the return line off near the fpr and jumped +B to Fp. Built up pressure the once I removed the jumper, pressure dropped fast. The YouTube was explaining it will always be one of three things: fuel pump check valve bad, fpr bad, or fuel injector stuck open. I ruled out fpr. Tomorrow I will pull the rail out to see if one of the fuel injector is stuck open. Then all problems point to the pump if rest test good.

 

[Abe's 1987]

What would be the economical (cheaper) version of our denso fuel pump? If I decide to go with a higher flow pump (let's say walbro 255), would it be ok to use on a completely stock setup? I'm seeing 255, 320, 340, and 380 lph kits on ebay like 1/4 the price to same in price of stock denso. Any thoughts on those?

 

[3p141592654]

255 Walbro is a common mod for supporting 550cc injectors. Some say it is noisy, and beware of counterfeit. Personally, I went with the denso MkiV turbo fuel pump. Any pump mod means you will need to drill out the restriction in the J-tube return line. Plenty of threads on how to do that. Also, given your voltage issues, you'll need to check all that with the higher current draw from these pumps.

 

[plaaya69]

What would be the economical (cheaper) version of our denso fuel pump? If I decide to go with a higher flow pump (let's say walbro 255), would it be ok to use on a completely stock setup? I'm seeing 255, 320, 340, and 380 lph kits on ebay like 1/4 the price to same in price of stock denso. Any thoughts on those?

Keep in mind those cheaper Chinese made fuel pumps usually fail quite fast. Personally if I were you I would want to plan a power goal for the vehicle. If you want the OEM power levels then the standard Denso fuel pump will do nicely. You want more boost then a Walbro 255 will be good with supporting mods such as adjustable fuel pressure regulator, j-tube bypass, 550cc injectors, Lexus AFM housing, ect...


You can run a Walbro 255 on a stock set up (this is actually what came out of my stock turbo Supra I parted out last year) just as a replacement and that is what I would recommend so if later you want to do some mods, you can have the fuel pump already done. I am running the walbro 450 and it is quite as they went back to plastic fins on the impeller instead of metal to keep the noise down but noise was one complaint with the 255 fuel pump.