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normanahoyt, ASE Master Tech
Category: Mazda
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Experience:  I am a Mazda Master Tech
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94 b4000: intermittent..the fuel pump dosent come on..few second

Resolved Question:

I am having an intermittent start problem with my 94 b4000. Sometimes when I turn the switch on the fuel pump dosent come on. Sometimes if I wait a few second it will come on, other times I have to turn the switch on and off to get it to come on. I replaced the fuel pump relay but still having the same problem
Submitted: 6 years ago.
Category: Mazda
Expert:  normanahoyt replied 6 years ago.

normanahoyt :

Hello, my name is XXXXX XXXXX I am here to assist you.

normanahoyt :

You replaced the fuel pump relay, which is good, however you probably need a PCM relay instead. Can you check and see if you have spark when the problem occurs?

normanahoyt :

Here are the tests that you should perform....or simply replace the PCM relay and see if the problem happens again.

normanahoyt :

Vehicle Application:

1994 Mazda B4000 4.0L

Customer Concern:
No start. No power to the fuel pump. No spark and no injector pulse either.

1. Turn the key on. Check for 5v on the Brown/White (BR/WH) wire at the Throttle Position Sensor (TPS).

2. If the voltage is not 5v, go to the Red wire at the MAF sensor or the Idle Air Control Valve (IACV) and check for battery voltage.

3. If battery voltage is not present, check fuse #4 30A and fuse #1 60A in the engine compartment fuse box.

4. If the fuses are OK, remove the Powertrain Control Module (PCM) power relay. With the key on, check for battery voltage on terminal 30 and terminal 86 (or 85). If battery voltage is present on both terminals, check for a ground on terminal 85 (or 86 if 85 is the ignition power feed).

5. If all powers and grounds are OK, swap the A/C Wide Open Throttle (WOT) relay with the PCM power relay and recheck for battery voltage on the Red wire at the IACV.

Potential Causes:
Powertrain Control Module (PCM) Power Relay

normanahoyt :

Thanks for the question.

normanahoyt :

Please let me know your results.

normanahoyt :

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normanahoyt :

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