Your car has 162,000 miles on it. If one injector has failed, they all have the same wear on them. Unless you are going to do the labor yourself. change them all.

Testing the resistance across the injector is only one way to test an injector. Wakon, or Hickok sells an injector pulse tester for around $100. You touch the probe end of it to the injector. If it is firing, the pulse from it will cause the light in it to flash. In this fashion it tests the electrical and the mechanical parts of the injector.

If I were you, I would start with the basics. Compression test. Check the plugs, wires, distributer, if it has one and fuel pressure and flow. Don't just throw parts at it. Test before you buy.

Check compression first. Use compression gauge first. To followup, you can use a leakdown tester.

At 162000 miles, possibility of burned/damaged valve, blown head gasket, or other leak path bleeding off compression.

Park in a dark spot at night and without the under hood light watch as engine runs, look for flashes of light indicating shorting electrical wiring; bad insulation etc..

You say that you have spark from the plug wire? How much of a gap will the spark jump? If this engine needs at least 25K volt spark to just the plug gap when starting. This is the spark jumping a 3/8" gap, a 1/2" gap is better. Buy far the best way to test injectors is with a lab scope & a current probe. Grab a current trace & voltage trace from the negative side of the injector coil. This way you can see the working resistance of the injector, and you can also verify the pintle movement in the injector solenoid. My routine for a problem like this would be, do a relative compression test by using a scope & high amp current probe hooked to a battery cable. Disable the fuel, and crank the engine for 10 seconds watching the current waveform for compression drop outs. Scope the secondary ignition, watching for misfires, both from lack of fuel, & lack of spark. If need be, then scope the current & voltage of the injectors.

GA. I have not had a scope for use in 20+ years. I had never heard about doing a relative compression test until you posted. It sure saves a lot of work. Thank you for your excellent posts.

Thanks guys, great info and appreciate the comments about doing other testing first. I almost gave in to just buying a full set of injectors without further checking. And if I do find there is a faulty injector I will change em all.

Weird thing happened yesterday though. Left work for home and #3 cylinder was still dead from lunch time, about 5 miles down the road it starts to fire again and has run fine since. Do injectors typically work sometimes and not others or do they just completely fail. Something weird electrically is going on here maybe not totally injector problems. I turned on my AC on the way home and it would start to get misfires, turn it off and engine would smooth out again? What the heck?

Based on what you are saying in this post, I am inclined to believe that you have a bad spark signal at a spark plug, most likely #3. The higher load placed on the engine to run the compressor may be sufficient to allow the spark signal for that cylinder to jump to ground. As stated in a previous post check under the hood at night, with the A/C on high.

We have no way of knowing how comfortable you are with the testing procedures we are throwing at you. Absolutely the scope tests that were posted will show where your problem is. While paying to have these tests done will not repair your car, it will be money well spent if you can pinpoint the exact parts that need replacement, and eliminate throwing parts at a problem. On the other hand, if you do not have access to testing equipment, or just want to do it your self, there are some very experienced people that will walk you through this. Good luck.

Thanks Bob C,

I have very limited test equipment so the detailed test procedures are not something I can do myself. But I do have some trouble shooting skills but just using what I have.

I too am not inclined to believe I have a spark problem. What made me think this is when I did pull the plug wire there was arcing inside of the spark plug well to the insluated grommet on the wire, at least I think there was. I didn't think much of that yesterday when I was checking for spark because it did indicate I had spark at least to the wire, but there shouldn't really have been spark jumping from that grommet sheild to ground. The plug wire design is the type that fits down into the head, so there is an insulated cylinder on the end of the wire that slips over the plug if it's arcing in there it will be impossible to see. Thinking about it, for that arc to jump from the plug connector up in the grommet and all the way out to ground would be quit far, more than an arc usually jumps in an ignition system. So I will look a bit closer and see if it's not not a plug wire that is wearing me out. The car is probably due for a new set of wires, distributor cap and rotor anyway but will see if I can tell for sure if there is a problem with that #3 wire.

When the engine is running well, on all cylinders, use a spray bottle to spray some water on the plug end of #3. You can isolate the exact location that gets wet this way. If the engine changes from it's smooth pattern, You get to yell BINGO.

May well yell when replacing that wet wire on a running engine too

Please be sure to lean the front of your hips against the car while you are removing that wire from the spark plug.

Swap two injectors, see if the problem stays with the injector or the cylinder.

Then check compression for each cylinder. Then check again after injection motor oil into that cylinder, if there is a big difference, the bore is worn or the piston rings are out!

No difference but low pressure(s), then valves are not sealing, cylinder head needs renovating.

Follow all the good advise , but geeze man , since you didnt say when was the last time you changed the plugs and wires , i would think its about time at 162000 miles .?

Your spark energy sounds good but i suspect its leaking to everything else before it gets to the plug. Do the spray bottle thing at night and you will probably see quite a light show .

Let us know how it goes.

Thanks,

Just Changed plugs a week ago. Wires, cap and rotor are about 2 years old. Bad thing, now it's running perfectly even with the AC and lights on. If it whats bad would just go bad and stay bad it would be much easier to trouble shoot. Still haven't had a chance to spray some water on it, will likely check that out tomorrow. Did take a quick look at it this evening after work and see that #3 injector has something on the wire that the others don't have, will see where that is coming from and see is there is a way something is shorting it out somehow. I really want to keep this car going. I just rebuilt the whole front end and pulled the tranny and had it rebuilt a few years back can't let it die now.

If it whats bad would just go bad and stay bad it would be much easier to trouble shoot.

If it was easy, everyone would want to be a mechanic.

Sounds like you simply needed a minor tune up with new plugs , wires etc.

That extra wire on # 3 is probably a signal wire to your computer to deal with timing etc.

Your car has a few years on it , Nissans have a lot of wiring etc. I suggest you take some time and do the " pull test " on all the connections you can find . This is simply a pull on each and every wire you can find to ensure the wires are not corroded inside the connector blocks. I have seen many instances where wires look fine but a little tug at the connectors and they pull out with little effort. You will see green corrosion on the wire end. Replace connectors as needed. Use needle nose pliers to make this procedure a little easier and dont tug to hard.

She is nearly 20 years old and needs a bit of TLC.

Did the spray test on under the hood and no porblem or arcing so not a plug wire problem. Like you say probably a connector, will have to do some connector pulling.

Thanks,