1975 280Z rough idling

[shadesh]

I have a 1975 280z with stock fuel injected engine. It starts up fine but idles rough and when it give it gas it is rough as well. I put a screwdriver to each injector and the #4 injector is not clicking. I also pulled the plug wires one by one with the engine on and on #4, there was no change.

I cannot figure out where the problem would be?

Is it

a. bad injector, ?

b. stuck valve, ?

c.bad spark plug, ?

c.bad ignition?

What can I do to pinpoint the problem?

Please help.. I don't know where to start...

[sblake01]

I would lean toward a. with an explaination. A stuck vavle, bad spark plug, or bad ignition wouldn't cause the injector not to click. Either the injector itself is bad, or somewhere in the connection to it is bad, either the connector itself or somewhere along the path of the two wires that run to it. With a device like a noid light (I made my own) you can plug into the connector and check for a signal. I also have another easy to make device that can be plugged onto the injector to check it's functionality. My tools may look kind of crude but they work. These were actually my 'prototypes' the finished ones look much better. These tools or something like them would be what you'd need:

Edited August 27, 2008 by sblake01

[MEZZZ]

Nice work Stephen. I picked up a set of noid lights at my local Auto Zone, 5-6 lights in the set but they have the one you need for the Bosch setup on our cars. $19.99. There is a guy that sells the one we need on Ebay for around $20 or so. List the ones on ebay that you dont need and who who knows, maybe you can even make a few bucks.

[shadesh]

Thanks Stephen, Can I use a test light to see if the injector wire is working.? I would touch one end of the test light to one pin on the injector wire and touch the other end to the second pin on the injector wire. Will that work?

[sblake01]

That should work except that the light will be very dim if your tester has an regular bulb rather than a LED bulb. That's one of the changes I had to make on my test light.

[shadesh]

Excellent! Thanks Stephen. I will test it with test light as soon as I get out of work.... man.. got a long way to go.

[shadesh]

Stephen,.. Last night I tested the connection to the #4 injector using my test light to see if there was a pulse. The injector is getting power because the test light was flicking.

Could the injector itself be bad or clogged?

Stephen, you mentioned that you have "another easy to make device that can be plugged onto the injector to check it's functionality" .. How can I test the injectors functionality?

If I find that I have a clogged injector, how can I clean?

If I have a bad injector, can it be fixed or repaired? or just replace?

Thanks.

[shadesh]

ok.. maybe I shouldn't have directed question to just Stephen.. does anyone have any thoughts... I could really use some advise here.. I appreciate it. (:

[sblake01]

Do you have a way of listening to it? Like a mechanic's stethoscope? You should be able to hear an audible 'click' from the injector when the car is running. If you don't hear a click, and the pulse is good, then the injector is bad. The tester on the left in my picture is just a 9 volt battery, an injector connector, and a momentary switch. I can test them with that one off the car or on the car without it running. It can be repaired but it's probably easier to replace it especially if the electronics are bad in it.

[shadesh]

Do you have a way of listening to it? Like a mechanic's stethoscope? You should be able to hear an audible 'click' from the injector when the car is running. If you don't hear a click, and the pulse is good, then the injector is bad. The tester on the left in my picture is just a 9 volt battery, an injector connector, and a momentary switch. I can test them with that one off the car or on the car without it running. It can be repaired but it's probably easier to replace it especially if the electronics are bad in it.

I finally got a chance to toy with the z again. I ended up pouring a third of seafoam in the gas tank and also through the vaccum line on the intake manifold... lots of smoke too.

.. then I put a screwdriver to each injector and they were all clicking. I also pulled the spark plug wire from each plug with the car running and I could hear the engine idling rough and when I plugged the wire back, it would idle fine. That tells me that the cyclinders are firing as it is getting gas from the injector.

Stephen, I do smell a little bit of gas in the oil though. Could it be that one of the injectors are not spraying the fuel but is just leaking?

Also, can you give me the specs on what I would need to build me an injector tester? I am talking about the picture on the left. I went to a parts store and I was asked several questions..

1. what type of battery? and how many volts? 9 volts. how many amps?

2. what type of charger for the battery? how many amps?

Thanks for your insight. Its appreciated.

[sblake01]

I don't really care for the screwdriver test. I prefer to use a stetescope because it isolates the sound better than a screwdriver. If you hear a click from each injector, and you're certain that the problem is with the injectors and not the ignition system, then one them could be either leaking or clogged. Look at your spark plugs. If one is wet with fuel, the injector on that cylinder is leaking. You can use a standard 9 volt battery or a rechargable 9 volt battery, it doesn't really matter. The amperage of the charger isn't really important as long as it's designed to charge 9 volt batteries. Other than that, the tester is just an old injector connector, a 9 volt battery holder from Radio Shack, and a push button momentary switch which completes the circuit when pushed.

Edited September 11, 2008 by sblake01

[sblake01]

Are you saying that the car ran fine after the Seafoam treatment? If so, change the oil and check again for the fuel smell in the oil in about a week. It's likely that the fuel smell in the oil was already there before the Seafoam treatment. The only way to really check an injector for leaking is off the car with a pressurized fuel injector cannister cleaner, a container to catch the fuel, and the tester on the left in post #7.