78 280Z - no injector pulse

[Virto]

I'll see about pulling the plugs. The engine will start on starting fluid. The initial sputter I'm getting now seems to be fuel from the cold start injector - not sure how that's tied into the fuel system, really. Unless I'm totally wrong, it's basically another injector that dumps some extra fuel where, past the maf?

I suppose it could be bad gas. Back before I knew about how gas will varnish it had run on fuel that was probably 3 years old. It had half a tank of same-day gas when I dropped it off last July. It had last run sometime in November, I believe, when we made the call to have the head sent out for work. I'll mention draining the fuel. Water, have to drain it to be sure - it was kept both inside and outside at various points as it was shuffled around to make room for other cars. It has certainly been exposed to weather, hence the rust growth.

[FastWoman]

In general, old/bad gas can be deadly for a flat tappet, OHC, interference engine. If it's bad enough, varnish goo will form on the valve stems, and then it will solidify when the engine cools. When you go to start it again, your valves are stuck in place and collide with the pistons, while your rockers come loose. It makes a delightful, snappy-klink-klink sound. DAMHIK

Anyway, I wouldn't do any serious diagnostic work without some known good gas. in the system.

[Zed Head]

I threw the gas idea out there on the assumption that the ECU and injectors are actually working correctly. A big problem here is that nobody really knows if the garage owner knows how to test that the injectors are getting grounded or not. Since it runs on starting fluid, seems like there are two feasible possibilities - the injectors aren't opening or they are opening but they're squirting bad gas. Hard to say which is more likely. But the fact that it does run with starting fluid is significant, since it means that the plugs aren't fouled. Overall, it's still looking like the ECU is not properly grounding the injectors.

There is a test that you can do that will tell pretty surely if the circuit to the ECU is correct and if the injectors are opening. Connect a jumper wire to the negative post of the coil, leaving one end free. Turn the key On. Tap the free end of the jumper to ground quickly. Every three taps the injectors should click, all six of them. With no engine cranking and no extra noise, it will be easy to hear the injectors. If you get a spark at the wire on every tap, which you should, but no noise from the injectors, then something is wrong. At least you'll be back to a focus on the ECU and the Pin 1 circuit.

[Virto]

He did mention that he thinks it's a ground problem, and that's why he wanted a copy of the EFI wiring diagram. I'll drop it off tomorrow and mention everything we've discussed so far.

Thanks much, seriously. It means a lot.

[Captain Obvious]

The initial sputter I'm getting now seems to be fuel from the cold start injector - not sure how that's tied into the fuel system, really. Unless I'm totally wrong, it's basically another injector that dumps some extra fuel where, past the maf?

Yes, it's basically another injector that dumps fuel in, and it's located just behind the throttle body. You should be able to find it by following the fuel lines. The fuel line that shoots over towards the throttle body goes to the cold start injector.

The cold start injector is not under the control of the fuel injection ECU in any way other than it's connected to the same fuel source. If there's fuel pressure, the cold start injector should spray even if the fuel injection ECU has been completely removed from the car.

Assuming it's cold enough to warrant needing the cold start injector, the cold start injector should spray when the engine is CRANKING, and it won't do that forever. There's a temperature controlled switch (known as the thermotime switch) that will cut off the cold start injector after a few seconds of spraying regardless if the engine has started or not.

Take a look in the FI literature about the thermotime switch. That's what controls the cold start injector. The ECU has nothing to do with it.

[FastWoman]

I'll just mention that another tool in your diagnostic arsenal could be to unplug the coolant temp sensor (injector-styled connector going to the SMALLER sensor in the thermostat housing). That should result in the delivery of LOTS more fuel, as though you were trying to start the car during the winter in Antarctica.

However, try triggering the ECU manually without cranking, the way Zed and I suggested (posts 12 and 39). I bet your ECU is really working.

[Zed Head]

Sorry FW I thought that you had mentioned the "grounding the negative post" test but I couldn't find it when I looked back. It doesn't seem very sophisticated, creating sparks and ozone, but it does test a big chunk of the system, in series and connected. Seems like it should be an FSM test.

[Virto]

I dropped off a copy of the wiring diagram, the pinout for the ECU connector and instructions on how to ground the coil to test the injectors. He was out driving a customer car, so I'll have to call him later today and give him the details.

So, if we do this test and the injectors don't click, we're looking at some kind of issue between the ECU pin 1 and the coil, be it the drop resistors or the wiring, or perhaps the ECU itself?

Alternatively, if we test and the injectors DO click, what's the next logical step?

[FastWoman]

No problem, Zed! Yes, it's a very easy test. I've never had occasion to use it, but it seems a great way to confirm that the ECU is awake, is being triggered, and is sending out injector pulses.

Kelly, if the injectors don't click, then it's either a triggering problem (e.g. wiring to the #1, weak ignition), a problem with the power (which you say you have), the drop resistors and/or injector wiring, or a dead ECU. You can rule out the drop resistors and injector wiring by grounding the individual injectors at the ECU plug. You should be able to make them click.

If the injectors do click, then your EFI is functioning, and you have some sort of fuel or fuel/air ratio issue -- bad fuel, clogged injectors, clogged rail, wrong fuel pressure, massive vacuum leaks, or whatever.

[Zed Head]

That's a good point on the vacuum leak. An old-timey mechanic might have the oil filler cap off to listen for noise or something, not realizing that that would be a massive vacuum leak. Everything needs to be buttoned up tight. Too bad the garage owner's not on the forum.

[Virto]

, I can say for sure that the oil filler cap is on tightly.

I went over the vacuum lines yesterday, since I've had some vacuum leaks in the past. It would have to be fairly major to prevent it from starting. Even when I had a large enough leak that the transmission wouldn't shift, it would turn over and start very easily.

The real issue is that he's got a lot of needy customers that take priority over the guy with the old rustbucket that doesn't need it to live day to day. There's a possibility that he won't have time to get to it until the weekend, at which point I'll try to spend an hour or so at the garage working on it at the same time, like yesterday.

Wonder if it might be worth pulling an injector and seeing if there's any flow through it at all. If it was home in my garage I could run out there more frequently, but because of the layout of my driveway, I probably can't even have it towed. If it comes down it to, I'll see what I can do.

[Zed Head]

Listen for the clicks first. With no sounds but the tap of that jumper wire, either grounding the injectors directly, or grounding the coil you'll hear if the injectors are even opening. I would do both tests, first ground the pins at the ECU as FW originally suggested to verify that the injectors have power and will work, then ground the coil - to see if the ECU can do the same job.

A jumper wire, the key, a charged battery (don't forget that), and you'll know much more.