Dead Injectors?

[z_ya]

1978 280Z all stock. Ran fine this morning just driving around, then I pulled into work to check a few things maybe took 20 minutes then I came back out started it up, and it just sputtered and was really just running rough it sounded as though it was missing. It would pop at every rpm and every gear and shakes horribly. I ran through the FSM and the connection test tells me I have no volts going to my injectors 2 and 3 but when I listen to them they sound fine. I went ahead and ordered new injectors for the car. I have no other idea what it could be. Any suggestions or ideas?

[Zed Head]

Is the tachometer needle pretty steady and following engine RPM or is it jumping around? If it's jumping around and/or reading high it might be the ignition module.

[ZCurves]

Installing new injectors for your z will definately help, but Iam thinking that there is something else going on. I would eliminate issues with the wiring harness, ECU, dropping resistors, etc. You can use an meter or an idot light to check the injector connectors- it would'nt hurt to replace the connectors when you replace the injectors. Check ALL of the ignition components to make sure that is not a problem. Check it out and let us know what you find out.

[z_ya]

See when i checked the ECU test with the meter there was just 0 for voltage to the injectors but when it was running I could hear them fire. It's my daily driver and I don't tear around town in it I will give it some gas from time to time but only after it has been warmed up. Uhm the injectors don't come in till like Thursday tomorrow when it's light out me and a friend are gonna run through it and check things out just to do another look an get another idea from someone. The timing will be checked as well as all the wiring connections. I greatly appreciate the help guys. I'll report back tomorrow with the findings and then HOPEFULLY we can go from there.

[z_ya]

And at Zed Head if i can remember correctly the rpm gauge stays right where I put it. It just runs like **** now to be honest with you. The RPM doesn't jump about everything is normal for the most part just the popping and stuttering of the engine through every gear and rpm.

[rcb280z]

How's your fuel pressure?

[siteunseen]

Check that vane under the black square cover on the side of AFM, they get stuck sometimes. It has a counter weight on it and should move freely when you touch the weight.

[z_ya]

After further investigating all of this, it is acting as if it has skipped time. I'm starting to think that my crank pulley has slipped as that seems to be a common problem. My guess is when I parked it and upon the start up that is when it slipped. It's going to a shop Wednesday to get the timing checked and fixed. The AFM is less than 2 weeks old and if i pop that cover off the warranty is void, I guess i could smack it around a bit to see if that is the problem though although I am doubting it.

[siteunseen]

Don't go smacking on a new AFM, knowing that I doubt it too.

[z_ya]

Yeah I can hear my AFM working so I know that vane isn't stuck. At this point I really don't know, I guess I'll have to wait until Wednesday to find out if it is the crank pulley that had slipped and caused a jump in timing. Thanks for all the replies guys, The new injectors should be in Thursday or Friday which is good because 4 5 and 6 are barely audible.

[Zed Head]

78 doesn't use a crank sensor. If your damper slipped the timing mark would move, giving an erroneous reading, but the timing would not change.

[Captain Obvious]

The new injectors should be in Thursday or Friday which is good because 4 5 and 6 are barely audible.

That's interesting because 4, 5, and 6 are all driven from the same transistor inside the ECU. It would be very unlikely for all three of those injectors to spontaneously fail at the same time. If 4, 5, and 6 have all stopped working, it would be much more likely that there's an ECU problem.

And if injectors do hard fail, it's almost always that they burned open. You can check for that by pulling the connector off the injector and measuring the resistance of the coil inside the injector.

[Zachary Lawson]

That's interesting because 4, 5, and 6 are all driven from the same transistor inside the ECU. It would be very unlikely for all three of those injectors to spontaneously fail at the same time. If 4, 5, and 6 have all stopped working, it would be much more likely that there's an ECU problem.

And if injectors do hard fail, it's almost always that they burned open. You can check for that by pulling the connector off the injector and measuring the resistance of the coil inside the injector.

I would check into the ECU. My Z recently was doing something close to what your describing. I bought a used ECU for $50 dollars from eBay and it cured it.

[Zed Head]

was really just running rough it sounded as though it was missing. It would pop at every rpm and every gear and shakes horribly.

"Popping" usually comes from a lean mix. Maybe your fuel pump is failing or your regulator has gone bad. Or your AFM plug fell off. Have you checked fuel pressure.

A lot of money can be saved with the right measurements, and confirming what you think. Have you restarted the engine since the problem occurred to be sure that the tach is not jumping around? Have you tried removing the #2 and # injectors while the engine is running to confirm that they work? There's a lot of noise up there to be sure that you can hear them. You said that you can hear the AFM working. That is incredible, as in I can't really believe it. You may have heard air passing through it but the vane would only make a noise when the throttle blade is shut quickly, otherwise there is no noise to hear.

The methodical and thorough approach is the best method on the EFI engines.

[rcb280z]

Hence why I asked earlier....has he checked fuel pressure. No response on that one yet.