Jump to content
SAU Community

Recommended Posts

could someone in geek speak, more or less explain to me how the fuel pump circuit works ? Is the relay meant to energize when the ignition is ON? see diag.

Im chasing a no start, no prime with a voltage seen on the relay. Relay is good, clicks when pulled to ground. Shorting pins 3 and 5 on the relay does nothing.

post-110427-0-62379600-1369746224_thumb.jpg

Link to comment
https://www.sau.com.au/forums/topic/426043-fuel-pump-circuit/
Share on other sites

Pretty sure on a stock cicuit (i.e not hard wired or aftermarket pump) the Fuel Pump wont prime until the key is turned to "start".

I figured that much out. Whats does the initial priming the relay or the FPCM ? Cause the relay does not energize when i tun the key ON.

Check the FPCM (Fuel Pump Control Module)

That's next...

So is there power at those pins? If so, is the earth on the other end of the pump good?

Yep. All earths are good. At this stage Prob is either the pump or fpcm unless theres something else im missing.

Edited by vifer

update. Changed the fuel pump and while it now starts. It still doenst prime. So im thinking if i ever leave the car sitting for a day and the fuel in the rail evaps, its only a matter of time before it wont start again. Is my thinking right?

Why not hard wire the new pump (assuming walbro or bosch?) with a relay?

That way as soon as you get reds, you get power to the pump before starting.

The FPCM is there for a reason so I dont want to particularly bypass it unless its an absolute last resort. I believe the pump is meant to step down ( quiet down) when the car is idling not work its titz off.

I pity the next bloke who buys your cars finding these extra wires , relays, parallel circuits with no diagram to troubleshoot when things dont werk. lol

I pity the next bloke who buys your cars finding these extra wires , relays, parallel circuits with no diagram to troubleshoot when things dont werk. lol

I think he would be quite impressed knowing that a simple fault (if there was one) can be traced through a couple of wires and a relay, rather then jumping on a forum and asking for peoples help ;)

Do a search on hard wiring a fuel pump and maybe you'll understand when you start to make more then stock power you'll appreciate constant 12v power.

I think he would be quite impressed knowing that a simple fault (if there was one) can be traced through a couple of wires and a relay, rather then jumping on a forum and asking for peoples help ;)

As opposed to resounding a theory, (albeit proven within the right context) and not having a clue as to why they;re doing it? :rolleyes:

So now I have to search for hardwiring a fuel pump to appreciate the constant 12v power when i start making more than stock power. ic. :no:

note: I;ve solved the issue with the priming circuit and modified the FPCM to provide a good idle duty cycle without affecting power on transition. cheers for the responses.

Which pump did you install? Most aftermarket pumps will do similar things when supplied with the lower voltage the FPCM supplies at idle and cruise. They may also fail down the track (DC motors don't like being loaded up at low voltage as they burn out) which is why most of us have hardwired the power with a relay switched by the FPCM output.

If you want to run the FPCM for some reason, you will need to run either a stock pump or a Nismo/tomei.

Theory or not, modifying the FPCM sounds interesting, shame you gave us absolutely no information on what you modified... :rolleyes:

When chasing a no start issue, if u suspect a lack of fuel supply, spray some aero start (or wd40) for 2 seconds into the intake throug a vacuum hose, then crank. If it starts it has spark etc. if it doesnt u have no spark.

Diagnosing from here, check All fuses and power at ecu, CAS etc

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Hi, i’m making a rb25det coil loom for Vag short coil. Can anybody tell me which Ecu signal wire belong to coil number 1 and 2,3,4,5,6? The connecting switch in above pic is 8 wire i think white is for +12v and black for earth.
    • Was there ever a model of the Stagea m35 that didnt have a badge on the grill? I thought I saw that somewhere, some aero edition or something? I cant find it again? davemoto
    • Its a 2002 vr-x four VQ25DET, silver. Coil overs, lowered, polished alloys and sport exhaust. Bit of a project, was sitting in a shed for a while but runs and drives great.
    • I wasn’t able to replicate the sound anymore. It was a one time sound so maybe it was just coincidence but it was like small pebbles being dropped in a coke can.   should I try cleaning the MAF? It could be it’s functioning but dirty? I don’t know.
    • Update 4: Hi all. The car drives again! Haven't driven for long, only to store it in the garage again, but the test drive was successful. The coolant and oil leaks seem to be fixed for now. Temps on the engine were also very good, while moving I never even saw 80C water during the approx. 30 minute drive. Ate up all the coolant in the reservoir though so will have to fill that even more when I go to the car next time. One thing that pisses me off is that the RPM gauge is still f**ked, I even resoldered the board twice and used copper paste on the silly screws that are used as connections. Next time I take it out I'll take apart the board and fit new components, I'll see if I can get a replacement IC for it.  I have an appointment set for 22nd of September for the engine tune to 370hp. Alignment also still needs to be done. My hope is that I can get all the legal stuff over with by the end of this season. Anyone of you have advice regarding intercoolers? Currently there is an APEXI core fitted, one of those weird hybrid ones, 600x270x76. I don't think it's bad but it's not new and now I still have the chance to change it now to legally include it in the paperwork. Only issue is that the only options that would arrive in time are a HKS Type R intercooler or generic Ebay spec intercoolers comparable to a JustJap one. Ideally I'd order a Plazmaman but it takes over a month to receive which would mean making the car legal has to wait until next season. Would love to hear some input on this. Same story for my injectors, the previous owner was a nunce and put ID 1050x on the engine. They work but are obviously not ideal at "normal" power levels. But I don't see a reason to change them unless the tuner says it's necessary. I read online before buying a different exhaust that the top secret style rear diffusers won't fit due to the size of the rear resonators. My buddy and I made it work by slightly "adjusting the shape" of the mounting bracket and making some spacers out of 3d print for the mounting bolts. Fits like a charm. Just putting this here in case someone has this problem. Even the hefty HKS Silent Hi Power rear can fits without hitting anything.
×
×
  • Create New...