94 B2300 wont start

[daltond]

I have a 94 B2300,, auto trans, no a/c. Cranks but wont start. I have spark but not getting fuel. Replaced fuel pump and filter, cleaned fuel lines.
Checked inertia switch, it wasn't tripped, so I tipped it and reset it, and still no fuel. The fuel pump is not running at all. fuel pump relay appears to be working, ( clicks when key is turned on, but fuel pump doesn't run. I took the bed off for easy access, and still cant hear the pump run,, even with a stethoscope. Checked all fuses no problem evident there. I''m at a loss as to what to check next, so I'm looking for advice or diagnostic tips. I thought about straight wiring the pump, but am not sure if thats a good idea, as I am not certain if the pump operates on a full 12 volts , and I don't want to damage it.
Any thoughts or advice would be appreciated,,
Daltond

 

[RonD]

yes, pump uses 12v, yes you can "hot wire" it to test, but don't run it this way.

Pump needs 12v from the inertia switch and it also needs a Ground.
If "hot wire doesn't work then could be the ground or if its a discount pump then it could be bad out of the box, this has happened before.

Power for the pump is only on for a few seconds when key is turned on, so you have to cycle the key on and off while listening for the pump, it is loud enough to hear from inside the cab.

Fuel pump relay is activated by the computer to get this 12v for a few seconds.
The 12v runs from the relay to the inertia switch and then to the fuel pump.

The computer then activates the relay while engine is running based on RPM and speed.

The EEC relay powers the Fuel pump relay, so two relays need to "click" with key on, and they are usually located right next to each other.

 

[daltond]

The pump is Napa, top of their line, a complete assembly, no part swapping from old pump required. Does the fuel pump relay switch 12 volts or is it a switched neutral, or ground? If It is 12 volts and I have lost my ground somewhere in th wiring, can I straight wire a new ground for the pump?
Daltond

 

[RonD]

This is a good reference for power in Rangers/Mazdas
http://www.therangerstation.com/tech_library/EDiagrams/index.htm

This one shows the fuel pump wiring
http://www.therangerstation.com/tec...les/Diagram_ElectronicEngControls2_3_1of3.JPG

The fuel pump should have 4 wires at the tank
Yellow/white for fuel gauge power
Pink/black for Fuel pump power(12v)

Orange for gauge ground
Black for fuel pump ground


Yes, you can set up a new ground for the tank.


The computer grounds the fuel pump relay to activate it.
The EEC relay comes on with the key, this powers several things, including the fuel relay(not the pump, that's on a separate fuse).
The Fuel pump relay will have 12v on 2 of the 4 connections.
1 is 12v from a fuse, this should have 12v 24/7 (black/yellow)
1 is 12v from the EEC relay, only 12v when key is on (red)

1 will be from the computer, this will be a ground for a few seconds after key is turned on.(light blue/orange)
1 goes to the inertia switch (dark grey/yellow)

 

[daltond]

I replace both fuel pump and eec relays, and now I have power to the pump when I turn the key on.
It only stays on a few seconds, then cuts off. I don't seem to be getting voltage to the pump when I am cranking it though. What do you think?
Daltond

 

[PanamaExpat]

Once it pressurizes the rail the pump wont activate again until the engine fires. Have you checked pressure on the fuel rail yet? Depress the Schrader valve (looks like a tire valve) and see if fuel comes out in a big spurt. Also... When I did my tank drain and clean it took a few prime cycles to get fuel up to the rail... Lot of air in the system.

Otherwise you will need to see if the injectors are getting a pulse to fire them. I don't know if your meter will be fast enough to catch it. You may need a scope with waveform freeze capability to catch the pulse.

 

[daltond]

I have a voltmeter that might catch an injector pulse signal, it's the top of Fluke's line. But I am feeling that that is not the most likely problem. As I said in my last post, the pump runs for a few seconds when the key is turned on, but does not run when the engine is being cranked. I am wondering what to check next to determine the cause of this lack of voltage. I would consult websited for wiring diagrams and diagostic procedures, but I am limited to a smart phone for web access, and reading wiring diagrams or fine print is impossible on my phones small screen.
Daltond

 

[RonD]

+1 ^^
Fuel pump will not run when engine is cranking, that is normal.
Fuel pump is primed when key is turned on, 1 or 2 seconds, then remains off until engine starts and RPM is detected, it will then cycle on and off as computer determines engine load/requirements.
Cycling the key on and off a few times will build up max pressure(assuming pump is coming on), which is approx. 35psi at the rail.

You should be able to hear injectors clicking with your stethoscope, while cranking.
All injectors should have 12v power when key is on, the computer fires them by grounding them.
If you pull out a spark plug it will tell you if fuel is getting into the cylinder, wet plug means gas is present.

You have spark but is it sparking at the correct time?
Distributors can be 180deg out since crank rotates twice for each 1 rotation of the distributor, so TDC line up could be 180 out.
If you remove spark plug on #1 cylinder and then manually turn over the engine, in it's normal direction of spin, you will feel the compression stroke via the #1 spark plug hole, air will be forced out of the hole, this will indicate the #1 cylinder will be firing once piston gets to TDC, the distributor rotor should just be coming up to #1 position on the cap.
If its not the spark timing is off.
A timing light can show normal spark at TDC, but not if its the correct TDC, for #1 cylinder.

 

[daltond]

My truck is equipped with DIS, so there is no distributor. I checked pressure at the schrader valve on the fuel rail and it seems to be correct after the key has been cycled on and off a few times. I probably won't be able to go any further with it today as it has started pouring rain. I just ried it one last time,, and it started, ran for 5 second and shut off. went back over the electrical, and found the 30 amp fuse for eec power was blown. This was a brand new fuse. I replaced it and it did exactly the same thing again. Started, ran 5 seconds, then shut down, and the fuse was blown once more. Any suggestions as to where I should look next for the cause of this? Also, Thanks for All your advice up to this point.
Daltond

 

[daltond]

Where is the ECM located on my 94 Mazda B-2300.? It is not behind the drivers side kick panel, as I have been told in the past.
Daltond

 

[Andy D]

If you're popping 30 amp fuses , that is a dead short some place.

 

[RonD]

The EEC relay powers several things directly so I would guess a shorted wire as well.
Each fuel injector wire,
Several PCM wires,
NSS(neutral safety switch), this is on the trans, by the shift linkage, and can get a short
MAF sensor
WOT(wide open throttle) relay
Fuel pump relay

The PCM, engine computer, would be last on the list since truck started, I doubt it would start even for a short time if that had a short, a wire going to it could be shorted.

 

[daltond]

I have removed the fuse box from its mount under the hood. Removed bottom of box to access wiring. there are two yellow wires for the EEC power fuse. One has a constant 12 volts and the other shows an open cicuit with the key off, and 17.2 ohms with the key on. I don't know if either of these resistance readings are normal,, or way off from what I should be seeing. I am a little hesitant to just start tearing into the wiring harness witout a better idea of what I'm looking for. In a perfect world, I'd take it to auto electric shop, but that is not feasible for me at this time. My wife died 6 weeks ago, and two weeks later,
I was laid off from work, so funds are tight. I live in rural Georgis, and the closest job prospects are roughly 25 to 30 miles away, so I really need to fix this truck, so I can find another job. Any help doing so would be greatly appreciated..
Daltond

 

[RonD]

The wire without 12v on the fuse socket is the "load" wire, it will go to the EEC relay socket.

Battery----fuse-----EEC relay-------(Your Short)

Your short will be on the "other side" of the EEC relay, otherwise the fuse would just blow whether key was on or off.
You said fuse blows when key is on.

So when EEC relay activates fuse blows.

0 ohms = straight connection, good wire or shorted wire if there should be no connection
High ohms(3,000+ depending on the scale you are using) means no connection.

17ohms is pretty low, I assume you are measuring ohms from ground to fuse socket.

What I would do is to keep ohm meter hooked up that way, key on, with 17 ohms showing, and then move around wires, always checking that 17 ohms, when you move that shorted wire Ohms will go up, no short.

You could also unplug the Fuel pump relay, and WOT relay, see if ohms go up.
And any of the other devices listed above.

 

[daltond]

As best I can tell,, there is no WOT relay on my truck, or if there is is is in a separate location, as it isn't in the fuse box under the hood. Tracing wires I see the output wire from the EEC relay goes to a diode, whose function I don't know, and from there enters a wiring harness going toward the front of the truck., where it turns and crosses toward the passenger side. When I put the ohmeter on it it reads .9 with the meter set on the 2kohm scale. I dont know if this is a good indicator of a short or not. I guess I have a tough job ahead of me with this. But I have to get it done. I suppose I can bjumper across the neutral start switch and see if that changes anything. I'm at a loss as far as checking the MAF sensor, as I have no idea what normal resistance readings should be, or what purpose each of the wires to it serves. I appreciate all the helpful advice, and if you think of any other tips, I would love to hear them.
Daltond