1996 Toyota Tacoma - Fuel Pressure

[LMORRIS249]

This vehicle starts but within 5 seconds it starts running rough, the fuel pressure begins dropping and it will either cut off or just run really rough. It had a new fuel pump installed in march, we have tested the fuel pressure regulator and it's fine, but we replaced the VSV because it tested bad. Open to suggestions.

[ricmorin]

Have you checked the filter? Did a new filter get installed with the new pump in March? (hint: always replace filter with pump).

You can also temporarily block the return line to see if the pump can make pressure. Also, check voltage and grounds to the pump.

If all else is ok, you need a pump. What brand did you use?

[steven kiser]

agree with ric. i hope an oem was used and a new skirt was installed on pump intake.

[ricmorin]

Another method I like to use when looking at a suspect pump is amperage analysis. I'll even go one step further and scope the amperage waveform. You can tell so much more with amperage than you can ever with volts. Start by looking at some known good pumps. The amperage waveform will look like an alternator voltage ripple, except we're talking amps. Bad pumps can have one 'hump' higher than the others.

[steven kiser]

something that i do and i know that there are pro's and con's on this. i'll either place my hand on the relay and see if it's abnormally warm or pull the relay, run a test light across the battery terminals, with key on jump power to pump wire. if the test light dims significantly you have a large amp pull. the battery should be full charged. i use these to give me a direction not a solid diagnosis. the amp meter is the primary test but if some tech had cut and spliced somewhere in the harness with an improper gauge wire it may be a bit difficult.