tbone heller

In a Mustang, the fuel pump relay is located under the front seat, & the inertia switch is in the trunk/hatch area. These two items are not part of the engine harness. I incorporated these into my wiring harness to keep the electronics all Ford. I did not like the Mazda "jumper wire" for the fuel pump or the puny wires going to the pump. It is pretty easy to wire in. Just follow the diagram I sent you.

V8MiataMike

I think maybe on the newer Fox body harness (90's?) the FP relay may be near the EEC relay. But regardless, If you have a gauge, I would put it on the fuel rail schrader valve to see if there is fuel pressure and how much. That burned looking one could be the A/C bypass relay.

Lateralgeez

0 psi at schrader valve.

It worked before I fixed the starter wire. The wire that was melted through and shorting to the cylinder head - 18 gauge yellow. Voltage sensor regulator? Shots in the dark I'm afraid.

I'm going to test all the fuses just in case. None are broken but that doesn't mean they aren't blown.

Lateralgeez

Latest heroic achievements

Located fuel pump relay.
11.9 volts at blue/red wire on fuel filler assembly (fuel pump power).
The new Walbro must be toast.

Grounds at filler assembly 0 ohms. Verified with 12 volt power source direct to connector, same bad noise.

Are there any other possible problems or is it time to swap a new pump and hope for the best?

I'm having a hard time understanding how the pump went from working to crap when all I did was fix the melted wire resting against head. Been parked the whole time.

Lateralgeez

0 ohms resistance from positive battery terminal also.

I cut the blue/red power wire and measured amps - 13.4

Lateralgeez

Found this on miata.net

(oem pump) "8-9A deadheaded (70-80 psi, 0 flow), at 13.5V;

FWIW, a Walbro 190/HP, or 255/HP will draw 16-17A deadheaded, (135 psi, 0 flow) at 13.5V this is well beyond the OEM wiring capacity;

They need 12-14A at 100 psi (120 lph or so, over 1200 psi the outputs of the 190 and 255 lph pumps are very similar)--this is about the upper limit for the OEM fuel pump wiring, adding an auxiliary relay will help if you need to run the pressure this high.

Make sure it's a sealed relay or put it somewhere other than right next to the tank (just in case!!!)"

http://http://forum.miata.net/vb/sho...d.php?t=155438

MRM331

Is the fuel pump relay wired to work with the ecu? Its pretty easy to wire it in. Get a ford type relay and base pigtail and wire it as follows:
Power to relay- pull from 12 volt constant wires in ford harness (yellow or black/orange)
Power from relay-run to pin 19 on the ecu (ecu's monitor) and to the fuel pump
Ground Signal to relay coil (one of the two small terminals)- connect to ecu pin 22
Power to relay coil (other small terminal)- connect to and solid red wire in the ford harness (keyed hot).

Note that the relay base will have three large terminals. You may need to switch the large ones around so they are configured just like the main ecc relay.

-Jason

MRM331

Reading what you just added I'd pull the power to the relay from its own source with a heavy gauge wire and its own 30 amp fuse. Use the same wire to run the other side of the relay to pin 19 and the pump itself. Pull the power directly from the miata fuse box main power in (a 10mm bolt) and locate the fuse before the relay.

-Jason

Lateralgeez

Thanks Jason you make it simple! I have 12 gauge wire and a 12v20amp 4 pin relay. If I can't fix it I'll do as you suggested.

The miata relay is getting 12 volts so I was wrong earlier.

However, the light green (ground?) shows no connection to any grounds including battery terminal regardless of key on or off. It runs to the Mustang ecu. Why does the ecu need a direct connection to the fuel pump relay? Is it for diagnostics or does it control pump rate? And if it's a ground why doesn't the multimeter show it.

More confusing, how does it show 12v at fuel pump with the pump relay removed?

I located the mustang ecu relay directly below the ecu itself. Possibly it has blown also.

MRM331

The wire from the relay to the pump should have a connected wire running back to ecu pin 19. This connection is used by the ecu to monitor the relay (it looks for power) and the pump (it looks for voltage fluxuations). If it sees an issue with one of those it triggers MIL and shuts down the ground connection to pin 22 (fuel pump trigger).

-Jason

cvx_20

I looked thru this post and didn't see any reference to this phenomenon that occurs often enough that it comes up on a google search, and that is the meltdown of the connector inside the tank. This connector was snipped off the wire from the fuel pump to the inside of the bulkhead connector that's located on the plate that supports the pump and sending unit inside the tank. It amazed me when I took the thing apart and found this total meltdown happening in the airspace at the very top of the fuel tank. The mating bulkhead connector was similarly destroyed. How can it not be exploding?? Not enough air??

The failure mode was: one day it ran fine, the next day it tried to start, then no fuel.

Mike

Lateralgeez

I'm glad you're alive! Do you know what caused it?

Getting a new pump since I haven't discovered anything else for certain.

Lateralgeez

New fuel pump makes loud noise just like the walbro did when it worked. However, still zero psi at Schrader on fuel line.

I'm at a loss.

tbone heller

Maybe the filter is clogged.

Lateralgeez

Tbone I was just thinking the same thing! It will be the third filter to date. I'm going to pick one up today.

Logically, the blown main relay could have been caused by the pump straining to push fuel through a clogged filter.

Fuel pickup strainer - when I removed the old pump, it held fuel inside. Like it was holding fuel by suction. When I separated the strainer from the pump, the fuel suddenly drained out the strainer.

Odd.

Lateralgeez

New fuel filter - nope
New fuel relay - nope

The Schrader valve for fuel pressure is on the return line. No pressure at all.

However, I loosened a clamp on the feed line and it immediately sprayed fuel - very high pressure. (I had just tried to start it)

Wtf. The only thing between feed and return is the pressure regulator. This is basically new, I replaced it and the filter after the busted pickup strainer episode last year and only been able to drive a few miles since.

Losing interest.

Lateralgeez

Ok maybe the injectors aren't opening. I'll rent a node light kit and see.

MX-Brad

Why is your schrader valve on the return? I wouldn't expect you'd have ALOT of fp on the return? Do you have the feed and return reversed at the Miata fuel lines?

Lateralgeez

Oh no I think you're right. I'm in a whole new class of retarded.

MX-Brad

lol, BTDT, got the T-shirt.

Lateralgeez

Thanks Brad! Finally runs again for the first time in months.

MX-Brad

Yay, glad you got it running. Beers all around.

Lateralgeez

I can drink to that! Thank you everyone for all the suggestions and advise. Here's some pix for the ceremony.





And this small block chevy powered Beetle from the Friday meet. Rebar welded directly to radiator.

Lateralgeez

In a fast curve the oil pressure drops...
It has an appetite for oil. Running 10w30 synthetic.
Warm idle - 13 psi
Max - 25 psi
It never goes above 25 when warm, regardless of rpm!

Is this just the high volume pump?
I think the rear main is leaking or the rear of the pan has broken seal due to front impact. However, it doesn't leave a puddle when parked.

It does smoke a bit but only under heavy acceleration and compression is good.
The pan has been cut slightly to clear the subframe so I'm not comfortable running more oil.

Leak down time.

Lateralgeez

Something is causing the main relay to fail, again. Last time it was wires melting against the cylinder head. It's probably some wiring I've screwed up along the way.

Before gutting every wire I'll check the battery to chassis ground. I replaced this for some reason long forgotten. Or it could be the chopped abs computer harness - another fail for the list.

*edit - duh it's probably the fuel pump like ya'll said. If I wire directly to a dash switch instead of the ecu, does it still need a relay?