Fuel Pump Grounding

[FairAbrocoma]

I have recently taken ownership of a 1978 280z, original motor and everything. But, I am having a power issue with the fuel pump wiring. At the relay, I am getting 12V into the relay (the green/blue wire), but only about 3.4 volts out through the other green blue wire. My question is, is this a simple grounding issue, if so, where it the ground for the fuel pump exactly? I have looked at the wiring diagram still my eyes crossed and I have determined that the fuel pump is grounded inside of the ICM with a few other electrical items. So would my best option be to just cut the grounding off before it splits and just screw it onto the chassis for a ground? Would love your guy's help with this. Also, I jumped the fuel pump just to determine if it would work with 12V and it does so at least that works. 

[Zed Head]

The operation of the pump and its relays is described in great detail in the FSM.  There's a flaw in the design that lets you test the pump and relays, by pulling the oil pressure sender plug off and turning the key to Run.  The pump should run then.

Why do you think that you have a problem, besides the 3.4 volt measurement?  Not sure that your understanding of the wiring is 100% correct.

[FairAbrocoma]

I will try the oil pressure trick as soon as I get off work. 

I believe I have a problem because the car obviously wont start, it turns over and I have spark going to the plugs, but no dice.  And when I turn the key to the ON position, the fuel pump is not priming. Not even turning on. I figured it was grounding issue because 12V are intended for the pump at the relay, which means that the oil pump check, as well as the alternator signal, are allowing 12V to be sent through for the running and priming of the fuel pump. 

[Zed Head]

You should download the FSM from the Downloads section of the forum.  Read the Engine Fuel chapter.  The fuel pump does not prime on the 280Z, or turn on with the key.  It only gets power during Start or engine running.  Thinking that the pump should get power when the key is on is a common 280Z error.

The Engine Fuel chapter has an extensive list of tests that you can run.  Many things have to be right for the engine to start and run.

It might be that you have fuel pressure but no injection.  Or that you have fuel pressure but the fuel lines are full of water.  Or bad gas.  Lots of ways to test these things.  Welcome and good luck.

https://www.classiczcars.com/files/category/13-280z/

[FairAbrocoma]

A bit of an update. Turns out my pump is fine and it does actually run at start like you said. When I disconnected the cold start valve harness ( a little too easily I might add ) and the starter motor I could hear the fuel pump pumping gas. But still with no start and presumably gas, no start. I did all the electrical fuel tests at the ECM and everything checked out ok. I will start things by testing the cold start valve and testing the fuel injectors. I did find resistance for the those at the ECM which means continuity but I will check for functionality as well. If those check out, I will check the fuel filter and flush out the fuel system to get any water and or bad gas out of the system, also to see if gas is even getting the engine I just put in new gas already but it may have mixed with the old. What do you all think?

17 hours ago, Zed Head said:

The fuel pump does not prime on the 280Z, or turn on with the key.  It only gets power during Start or engine running.

 

[Zed Head]

Many different ways to get the engine to run.  Like many you've said that you "ran the tests" but didn't list them out with results.

Here are a few things that you could do just to learn more.

- Let the pump run for a while.  this will flush old fule out and get new fuel close to the injectors.  Of course, if you have water or old gas in your lines it will also contaminate your new fuel.

- Remove the cold start valve and run the pump.  Or just remove it and place the nozzle in to a container and give it power.  See what comes out.  It might be old dead gasoline.

- Test the injectors using a "noid" light or one of the various test methods described in the forum.  Make sure that the injectors are getting the proper circuit to open and close.

- Use a screwdriver or stethoscope on the injector bodies to see if they click when the engine is turning over, like they are supposed to.

- Connect a jumper wire to the coil's negative post and tap it to ground with the key at Run.  Every third tap should cause all of the injectors to click.  This might be the quickest, easiest way to confirm the injector operation.  It's quiet and it's a one-man operation, in the engine bay.  If the injectors aren't clicking they're not opening, if they're not opening there's no fuel.

- Use starting fluid in the intake manifold to make sure the engine will actually run with fuel.

[Zed Head]

But, of course, the history of the engine might be most important.  If the cylinders are dry they might not generate enough compression to fire a gasoline mixture.  Squirting oil in to the cylinders can help that.  Maybe the car was parked because it quit running.  You haven't given any history or much about how you prepared the engine to start.  You might be about to suck a bunch of old crud and fuel in to the cylinders.

The best is assumed, but maybe you should stop and rethink.

[FairAbrocoma]

I have not done much in preparation to start it. The only thing that I've done to start is putting new gas in it and buying it a new battery because the seller did not provide one. Other than that I have replaced most of the ignition systems. I have replaced the ignition coil, distributor and cap, new sparkplugs (which have yet to be put in), new sparkplug wires, and a new ignition control module. 

The testing I was referring to was the testing procedure in the FSM about an engine not starting, in the fuel section on page EF-22. 

In that section it says to check certain item numbers in case the engine doesn't start. In this case the items are:

1 - 3,5,6,7,8

2 - 1,2,3

3 - 1,3

 

In the first string of tests it asks to check for continuity at certain pins on the ECU. I set the multimeter I have to the OHM setting and got continuity readings for all of the test items for Test 1, which were things like the ground and the thermontine switch. They all had continuity and checked out OK.

For test 2 it asks to check for voltage at the these pins, which correspond to each of the injectors, the power line, and the revolution trigger signal. These checked out as I had battery voltage for all of these. 

For test 3 it is the same thing and it tests out the starter signal, and the cold start valve and thermotime switch. This checked out ok as well. 

As for the history of the engine, I have no clue. I asked the PO if it ran and he said it did a while ago and the only thing that was wrong was that the car was that it "shifted weird". Likely a new clutch. Will update with the cold start valve test though and injectors. 

[Zed Head]

12 minutes ago, FairAbrocoma said:

a while ago

That could be twenty years.

I would see what's in the cold start valve line.  Looks like the electrical checks out.  The same fuel is probably in the injectors since they are branches off of the fuel rail loop.  The new fuel will pass by those branches but there's no driving force to replace it besides the few squirts while trying to start.

[Patcon]

I might go back to the "waking the sleeping beast" thread too, based on unknown history. I wonder if there's oil at the valve train. Lots of other little things to check too.

[FairAbrocoma]

Gotcha. 

I pulled the cold start valve, and look and behold it works. But life caught up to me and I cannot test the injectors at this moment. But the valve is definitely getting the signal from the thermometer to inject gas. 

[Zed Head]

6 minutes ago, FairAbrocoma said:

Gotcha. 

I pulled the cold start valve, and look and behold it works. But life caught up to me and I cannot test the injectors at this moment. But the valve is definitely getting the signal from the thermometer to inject gas. 

Does it smell like good clean gasoline, or turpentine?  That's what I was wondering.  If it squirted then fuel is in the intake manifold.  Why isn't it lighting up, is the question.

I don't think the "life delayed me" wordage is allowed unless it's over a few months.