1990 Mazda RX7 1990 RX7 won't start

  • 1990 MAZDA RX7
Engine Performance problem
1990 Mazda RX7 Two Wheel Drive Manual 144000 miles

My 1990 rx7 will not start - It had a thermostat housing leak - tried to repair it - broke off one of the bolts holding the housing and then broke the ezout too. Tried to drill it out but kept burning out the bits. So it sat idle in the garage for 5 years. Finally found a special real hard steel bit and got it out and back together.
Now it won't start. Replaced the fuel filter and pump because the pump wasn't working, could not get any volume from the fuel line or hear it whirring. Also noticed the fuel guage showed empty. (I did put 4 gals of gas in and it still did not register.) When I removed the pump assembly from the tank, it was crudded up -- looks like the rubber gasket holding the electrical pump to the assembly dissolved into a tar-like sticky goo. I cleaned the tank as best I could with a wooden scraper. Mostly the crud was inside the fuel tank baffle.
The new fuel pump works and I get fuel going through the system, but the fuel guage still shows empty. Jumpered the yellow pump check relay connector to check flow and noticed that the pump never shuts off, even after 5 minutes. I can feel the fuel flowing in the large fuel rail for the time that it's jumpered. It feels like the pressure regulator is not working. Maybe the crud got to it too and clogged it up.
Questions: Since the requlator is not replaceable by itself (its part of the rail itself) and the whole rail must be replaced (And there are 2 and quite costly), is there some kind of test I can do that would definitely point to the reg as the problem?

When jumpering the yellow connector, what should make the fuel pump shut off?

If I take out the spark plugs and put a little gas in the opening and then replace them, should the engine fire a little thus saying that maybe the injectors are bad or there is too little fuel pressure?

Btw. I have good spark. Checked that the usual way. When I checked the spark plugs, they were pretty fouled and had to be cleaned. I also replaced the fuel pump with part # n370 while the original was an N351.
Do you
have the same problem?
Monday, August 23rd, 2010 AT 4:46 AM

2 Replies


Ok, Yes it is possible that the injector may need Cleaning or Replaced. If set for 5 years they are most likely gummed up from very old gas setting in them.

Here is some testing you can do.

Relieve fuel system pressure by starting engine with fuel pump relay (circuit open relay) disconnected and let run until engine dies. Then slowly and carefully remove hose on outlet side of fuel filter. Cover with a clean rag while removing hose, to avoid spraying fuel in your face.

Checking Fuel System Pressure

Using an extra piece of fuel injection hose and a fuel "tee" fitting, connect fuel pressure gauge between fuel filter and primary fuel rail.

Jumping Fuel Pump Test Connector

Energize fuel pump by bridging the terminals of the yellow fuel pump test connector (connector EM-30, located on the right side of the engine compartment, near the McPherson strut tower) and turn the ignition "ON".

Pinch the fuel hose closed, between where the gauge is tee'd into the fuel line and the primary fuel rail, using a pinch clamp.

Observe fuel pressure on gauge (this will be the maximum fuel pressure available from the fuel pump).

71 - 92 psi (490 - 637 kPa)

If pressure is higher than the maximum specified, replace fuel pump. If pressure is lower than the minimum specified, check fuel filter. If filter is OK, replace pump.

Turn ignition "OFF", wait 5 minutes, and observe fuel pump residual pressure. After the specified off time, the fuel pump pressure relief valve should retain a minimum fuel pressure as listed below.

57 psi (392 kPa)

If not, replace pump.

Remove pinch clamp from hose between gauge and pulsation damper.

Start engine and let idle.

Observe fuel pressure on gauge (this is the system operating pressure).

27 - 33 psi (186 - 226 kPa)

If pressure is higher than the maximum specified, check fuel return line for kinks or restriction. If pressure is lower than the minimum specified, check fuel filter. If filter and return line are OK and pressure is still not within the specified range, replace pressure regulator.

Disconnect vacuum hose from fuel pressure regulator with engine idling.

Fuel pressure should increase when vacuum hose is removed.

34 - 40 psi (235 - 275 kPa)

If not, replace pressure regulator.

Shut engine "OFF" and wait 5 minutes, then observe residual system pressure on gauge. After the specified off time, the pressure regulator should retain a minimum fuel system pressure as listed below.

Minimum 18 psi (128 kPa)

If not, check for leaking fuel injector(s). If injectors are not leaking, replace pressure regulator.

If all test results are OK, fuel pump and pressure regulator are OK.
Was this
Monday, August 23rd, 2010 AT 2:11 PM
Hi Wayne,

You could still check the fuel pressure even if the vehicle won't start.

I take it since you said the fuel pump works fine, that when you turn the key to the on position the pump comes on, just won't shut off.

The can pinch off the return line so that the system will pressurize then the pump should shut off.

FYI - When you use the jumper the pump will not shut off till you d/c the jumper.

To test the Injectors you will need a special tool. You can check your local rental store, ask for a Fuel Injector Test Kit.

You can check the Injector Harness with what is called a Noid Light.

The Injectors are most likely Gummed Up. To attempt to clean them you will need to remove them and soak the tips in carb cleaner for a while, and then there is no guarrantee it will work. I have done this 2 times and it worked ok on one (ended up replacing them 3 months later) and not at all on the other.

As for the Fuel Gauge check the wiring for brakes. If able to check resistance.

Was this
Wednesday, August 25th, 2010 AT 1:40 PM

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