Is my fuel pump DEAD?

[ForcedTorque]

I have just completed a wiring harness swap in my car, and now I can't get a thing out of my fuel pump. Prior to the swap it ran fine, but I have had to wiggle some of the wires before to get the pump going. I suspect that is where my problem is now, but not sure since it no longer helps. Could the problem be in my relay? I tested voltages, and I only get 12 Volts out of 1 post, and nothing over .5 out of any of the others. I didn't have any help, so I couldn't test the other posts with the car cranking, only with the key in the on position. I also tried jumping Fp and B+ in the diagnostic block, and got nothing. This is with a Walbro pump and 12 Volt mod. So I have reason to question the pump, the wiring, and the relay. It's easy to say my brain only uses about 4 volts, so I would appreciate any of the brighter opinions on the site.

 

[suprra_girl]

It all depends on how the new pump was wired in.

My car, I still use the factory fuel/relay system so in the event of an accident my fuel system will still turn off but I bypassed the resister in the engine bay and connected another relay further down the body in the car to supply 12v but excited by the stock relay system.

If you jumper fp and b+ and nothing happens either there is no b+ at the check connector or your pump is no longer connected to the fp circuit. Do some continuity tests via the tewd to determine how the pump has been wired in http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=47

 

[Dan_Gyoba]

What I see there indicates a wiring fault.

The one terminal that you tested in the picture appears to be one of the two relay control terminals (85/86). The one exactly opposite it should go to ground, and when it has +12V the relay should switch on.

The top terminal appears to be the N.O. terminal, which should go to the fuel pump. When the relay is powered, it should switch the terminal on the bottom (30/Common) to that top pin (87, Normally Open) Pin 30 really should also have +12V from a relatively direct circuit, though it would work if the pin 30 and 87 were reversed. one of the pair REALLY ought to have +12V as well as the one pictured.

Looking at the relay (There is NO way that I would ever wire it up like this myself, by the way...)

Taking the pins 30 (common), 87 (Normally Open), 85 (Coil+) and 86 (Coil-) and the wire L-B (Fuel pump +) I believe that the intent was as follows:

Pin 30 to some constant positive power source. Possibly a power distribution block for an audio system, or another wire with +12V run to the back of the car. Presumably this would be a better power source than the main EFI fuse, which is wired through the fuel pump relay to the L-B wire.

Pin 87 to the L-B wire on the fuel pump side.

Pin 85 (or 86, it doesn't actually matter) to the L-B wire on the chassis harness side, to take the fuel pump power as a signal to turn on the relay

Pin 86 (or 85, see above) to that crappy ground screw above the fuel hangar opening.

If it were my car, I'd remove the crappy 20A relay, remove the ground screw, and all the red wire, then re-connect the two ends of the L-B wire and watch fuel pressure return

 

[ForcedTorque]

OK, I am finally off of 12 hour nights, and able to look at this.

The first thing I did was look up the how-to Walbro install with pics that I wrote years ago with the wiring help from Shaeff ( http://www.supramania.com/forums/co...all-with-12VRelay-all-in-one-thread-with-Pics ) to see what I did then. That was in a previous car and then transferred to this one. The power wire comes directly from the battery on a switched wire BTW.

I wrote this long explanation of everything I did, and why it didn't help. Then it hit me.....the power wire was fused and I had never checked it to see if the fuse was OK. The fuse was blown, and when replaced, all was well! IT WORKS!

Thank you all!

Dan, I did write that how-to years ago with the help of Shaeff. I know nothing really about wiring. Your post got me searching for my old post to clarify all that you wrote. Can you look that over and still recommend ditching it. I'm sure there are hundreds of cars on this site that have used that thread when installing their Walbros.

 

[Dan_Gyoba]

Yes, I would still remove the relay in the hatch, and just connect the L-B wire together again.

The wire that you're using isn't any heavier than the factory wiring is, and won't carry any more current. The only part of that that I would keep is the bypass of the resistor under the hood, but I'd get rid of the relay in the back.

My only concern would be for the EFI main fuse, which is 15A. The factory system runs the fuel pump off of the EFI main relay, which it would still do with just the bypass of the resistor. The Walbro fuel pump specs list the 255lph pump as drawing 12A at 70 PSI/13.5VDC. Assume that you've set your base fuel pressure for 40 PSI, and are running 30 PSI boost, this is where the pump is going to run. I'm quite sure that nobody is going to use a single Walbro at 30 PSI manifold, nor would they use the factory wiring at that point. As such, I think it serves as a "worst case" and I believe that the fuse should be okay under normal circumstances.

I was recently looking into the load on the EFI main fuse, and had determined that the fuel pump is the largest current draw in the circuit. If you're running piggybacks installed on the ECU harness like they want, then 12A is too much draw. 10A (20 PSI boost) is pushing it more than I'd like. I've been given figures as high as 4A for a wideband controller, for example. Most estimates are still closer to 1A, in which case the 10A draw is acceptable. The TCCS itself is very low current draw on the +B and +B1 lines.

I believe that Toyota knew exactly what they were doing in powering the fuel pump off of the EFI main circuit. In the event that something goes wrong with the fuel pump, such that it blows a fuse, this will also shut down the TCCS. That means that the TCCS isn't going to lean out the car by assuming that there is fuel pressure when it opens the injectors. This is a safety feature that I don't want to defeat.