rx7dreams

iTrader: (1)

I've searched the forum, but I only found that the voltage at idle is 12V at the fuel pump? What is the voltage if the engine isn't running?

My car cranks, but doesn't start. There is spark, but there is no fuel pressure measured after the fuel filter. There is 9V measured at the blue wire at the fuel pump connector with the check connector jumped. Is 9V too low? Would this cause 0 fuel pressure?

RotaryRocket88

iTrader: (7)

Year/model?

If your car has a fuel pump resistor/relay, voltage will be 9V at times and 12V+ at other times. You can find this info in the FSM.

rx7dreams

iTrader: (1)

1988 gxl

satch

iTrader: (1)

Check the ground wire as well. Jumper a ground wire to it if need be.

Nick_d_TII

iTrader: (6)

With the engine off and the key off the voltage should be 0V.

Either you have a weak pump that won't spin on 9V or fuel pressure regulator is wack causing 0 psi.

You can bypass the resistor which gets you a straight shot from the Main relay to the pump and constant +12v. Fixed my problem.
https://www.rx7club.com/showthread.p...pressure+issue

Good luck!

j9fd3s

iTrader: (3)

all rx7's newer than 1983 should see 0v at the fuel pump with the engine off.

engine running on an 84-88 non turbo is 12v*. the 89-95's and 86-88 turbo should be 9v*

*the actual number will vary a bit, depending on alternator voltage and the voltage drop in the circuit. higher is better though

rx7dreams

iTrader: (1)

Just checked the black wire at the fuel pump connector. It has a good ground. Also tried jumping to the negative battery terminal with no luck. I can't even hear the fuel pump priming up.

Nick_d_TII: I'll try your suggestion tomorrow to get the constant 12V. After that, I'm gonna replace the fuel pump.

Is it usually the case that the fuel pump would die completely like that? I figure it should give at least some pressure.

rx7dreams

iTrader: (1)

Nick_d_TII: I guess the N/As should have 12V to the fuel pump like j9fd3s said. In the wiring diagram, it shows that N/As do no have the relay and resistor to bring it down to 9V.

I wonder why mine is at 9V. If my fuel pump is good, I should still get some fuel pressure at 9V right?

RotaryRocket88

iTrader: (7)

Yes, S4 NAs do not have the fuel pump resistor/relay, so 9V at the pump means a poor connection somewhere along the wiring. You should still get pressure with low voltage; just not much.

misterstyx69

iTrader: (142)

Have you verified that there is Fuel after the Filter?..Before the Filter?...after the secondary rail?

rx7dreams

iTrader: (1)

There is no fuel after the filter, not even a little. Therefore, there shouldn't be fuel after the secondary rail, right? I haven't checked for fuel before the filter, but since I don't hear the fuel pump priming, I figured there wouldn't be fuel there either.

satch

iTrader: (1)

A troubled voltage wire could deliver voltage but not the proper amount of amps. If the wire had a single strand left to it for example, the voltage would still pass through but not enough amps to power up the pump. If you did measure for voltage the proper place to choose from would be the fuel pump side of the harness and not the rear side of the harness.

rx7dreams

iTrader: (1)

I'm shopping around for used fuel pumps on the forum as we speak. Is it likely that I'm not getting enough amps through the fuel pump and the voltage readings are misleading? If so, I will hold off buying a pump until I can get an amp reading. As for checking for voltage, shouldn't it be the same voltage on the fuel pump side as the rear side of the harness as long as there is continuity through the harness? By harness, do you mean the connector?

satch

iTrader: (1)

The connector joins the rear harness and the pump pigtail. The connector could be problematic such that the voltage barely passes through the connector. And bringing a 12 volt source to the pump as stated earlier is a good idea to check the condition of the pump. You could also take the voltage reading on the Blue wire further up stream at the Circuit Opening relay located under the dash and just to the right of the steering wheel. The relay, yellow in color, houses the Blue wire in the top right position of the plug. With the fuel check connector jumpered and the key to on, the Blue wire at the relay should read 12 volts.