My 87 NA RX7 has been suffering from what feels like a spontaneous fuel cut anywhere from 2,500-4,000 RPMs. I figured it was fuel delivery, possibly the secondary injectors dying. But before I rip into the intake manifold I want to make sure all the possible cheap/easy fixes are looked at first.

I was reading a thread about how the alternator can cause electromagnetic crosstalk if its not grounded properly. Causing the CAS to give the ECU wrong signals.. I discovered a single ground wire that I thought plugged into my alternator but upon trying to plug it in I noticed there's a hole in the back of the alternator that looks like where it should go there but there isn't any connector inside...

A little long winded but in short, this hiccup is really starting to drive me crazy and this unplugged ground wire is making me scratch me head more and more each day. Attached is a photo. Thanks in advance!

 

Alternator grounds through its mounting to the engine so that should not be an issue.

The grounds on an S4 would be Black thus the wire you documented is not a ground.

Secondary injectors come online at 3800 rpm.

An S4 alternator has one plug on the rear for two wires to plug into the alternator and the plug is in the shape of the letter "T". Black/White wire goes on top and the White/Black wire goes on the bottom.

 

Okay........ I already know the secondaries kick in at 3,800....

My alternator works fine. And you can see in the pic that the "T" connector is plugged in.

My question is, What is this MYSTERIOUS wire? Now knowing its not a ground and doesn't plug into the alternator...

And furthermore, if its not a injector problem causing a bad RANDOM hiccup/fuel cut between 2,500-4,000, then what is it?

When the engine cuts out and hiccups, the tach has a tendency to flicker faster than the motor is reving up or down.

 

That plug is for an optional temperature sensor that is installed in the water pump neck. You can see the casting for it in your picture. All the wire harnesses have the plug while only some cars had the sensor.

Could also be plugs, wires, fuel filters. How long have those things been on the car?

 

I think that plug is for the auxiliary fan that some AC equipped cars came with.

 

Brand new NGK Platinum plugs, Brand new NGK Wires, Brand new Fuel Filter. no difference from doing that tune up. Have yet to check the filter attached to the pump.

Ran two tanks with fuel cleaner and 101 octane, no difference.

 

If the wire is Green/Black then it is for a Temp Switch located by the thermostat housing that is part of the electric auxiliary fan found on autos and some turbos.

Might want to test the TPS and perhaps measure the voltage at the fuel pump when the problem occurs and compare the readings to when the car is acting normally.

 

Cool, so its useless. Phew.

I was really hoping it was going to be a miracle fix for my hiccups. Damn.

 

Coils or plug wires maybe?

 

The newest thing in my car is NGK Japan plug wires.