Noobie here needs Fuel pump help!

[FastWoman]

Well... If there is discontinuity between 72 and GND, it should read +12, and grounding 72 would result in current flow. But perhaps we're talking about a lot more current flow than normal.

I think Lenny's theory about the red GND wire is plausible. I was shaking my head about that color code in the color schematic.

[Zed Head]

has been to 3 other shops with no help, so I volunteered..How hard could it be right?

On to the problem. He had a no start, no spark condition when I got it. Figured I needed spark first. Found a bad distributor, Great! Got a new one from Z car source. Now I have great spark, Still no fuel pump.

Who knows what the other three shops did but it seems like the ground connection at the battery would be okay since the electrical system is right enough to give spark. And he has a good starter now. Looks like he's down to the fairly typical problems of no injector activity and problems making the fuel pump run.

The ECU grounds the injectors base on the discharging of the coil with voltage pulses transmitted through the wire from the negative post of the coil to Pin 1 of the ECU through the blue wire. The tachometer and its in-line resistor need to be in place for the ECU to do that correctly (in case you have some things torn apart).

Of course, the other half of that relay is the EFI relay. Have you measured voltage at the injector connectors with the key on? You should have 12 volts on both sides. Which I see that you have in Post 11. Check the circuit from the coil negative to Pin 1 at the ECU. You should have continuity.

[JRSGTS]

JR,

Something definitely not right here. P72 should be connected to GND already in the harness. If you are seeing +12V there, we have an issue already. P72 is the ground side of both coils in the relay. This would also explain why (12V to p36=no pump.) as the coil gets +12V from you on p36 via jumper wire, but the other side of the coil isn't grounded. The following tests would be of no use until we figure out why P72 is showing power.

This same ground is the ground for the ECU as well, so that might also explain why the ECU is not firing injectors.

One thing I might bring up is that Datsun did some crazy color schemes on the FI harness power supply. Such as the ground wire (The same one I'm talking about) where it connects to the battery is a large 8awg or so "RED" wire. Sometimes its Black, but I have seen them RED. Where it connects to the battery is just a big spade connector (stock) but might have been changed over the years, but someone could have mistook it for a power connection and have it connected to +12V instead of gnd. It runs right up to the battery & looks like it should be tied to +12V because its' red.

To find out, pull the connector off the ECU and measure the voltage at pin 35. It should be GND. Actually pins 35,17,16 & 5 at the ECU connector are all tied directly to GND. If one of these is gnd all should be.

Lenny

THAT"S IT LENNY!!!!! Has to be! Brilliant! I hadn't got a good look at the wiring diagram yet because I couldn't print it. Even at my inlaws on there PC, I could only print small hard to read pieces...OK my only question now is Which 8awg. wire is it? I have 2, both run to the Battery+ One still is in a big stock spade connector. The other has been spliced to the lead on a replacement battery cable. The wire must change colors before the ECU because there is no red wire there. Definitely the problem. NONE of the grounds you or Sarah listed are grounds right now. I hope no ECU damage has been done. Oh yeah, P1 does have cont. to -coil.

Funny how the owner says it just wouldn't start one day...Someone had to mess with the battery leads first... That's why I take customers descriptions of problems with a grain of salt. Going out to see if I can figure which wire..I'll report back soon. THANK YOU!!!

[JRSGTS]

Couldn't wait...Ran out and switched the ground. Suddenly I have FP when I test in run position, I can fire it with the AFM flap, I even have inj. pulse!!! Bad news is it won't even try to start...Think I have wasted plugs, I know I still need one of the temp. switches. I thought it would try harder... I'll have more time later to mess with it, but you have definitely fixed my big issue!! Thank you, Thank you thank you!!

[JRSGTS]

Oh yeah..we be all kinds of flooded, But it's going to work! Awesome Lenny! Of course now I go back and look at the wiring and see the big gang of them heading for ground! Then look at my car and see the link headed for + and not see The problem! Always clearer looking backwards with someone else's eyes...

I will go tomorrow and get plugs, FF. Fresh oil and filter(Heavily contaminated, so I really don't want to run it today anyway) Cap, rotor, wires, look fine. I do need the "Water temp. switch" The one with the eyelet ground wire. Which corroded enough to break the bolt. I'll rerun that some where. The blue lead was broke off. I can't find it on the wiring diagram. See all the other sensors...(Thermotime, AAR, water temp,CSV) But not a temp. "switch" Any hints..?

Any way, I'm really confident That you found it for me and this problem is Kicked in the butt! Winner, Winner I always say! Now I can sell him on the rest of what this car needs! But for now it's time to enjoy a Sunday and watch some Football!! :)

Sarah,Lenny, Zed, Thank you very much. This place is way cool, cool! I'll be sure to post some up and running shots.

JR.

[JRSGTS]

OK Last comment! Found the temp switch on the diagram finally..(Old eyes!) Np there. I'll get a switch or at least rewire this one before I try to refire.

NOW, On to couch potatoe / football land!

[Zed Head]

Glad you found a solution although I have to say it doesn't make sense to me. The small gauge wire from the positive post is the EFI power supply. I can see how not having that connected would allow everything to work except the EFI components. But connecting the EFI power directly to the small gauge ground spade should have caused a short. I think.

Maybe that is the EFI ground only and its isolated from the others. Or maybe yours is not connected to anything and you got lucky. The diagram shows it as connected to body earth so there should have been big sparks as soon as the small gauge positive was connected to it, shorting back through the large negative cable.

Anyway, good luck and carry on.

[superlen]

JR,

Glad you're on the right track now. I don't think you harmed the ECU. It's possible, but it was wired with +12V on both the supply and ground on the ECU, it wasn't reversed so I think it will be fine. No other parts on that gnd circuit would be damaged by the miswiring. Just check for injector pulses. If you are getting any at all the ECU should be good enough shape to get you started.

Lenny

[FastWoman]

Wow, fantastic! You're not out of the tunnel yet, but at least you can see some light. And yes, a red ground wire.... Hmmmm.... What could go wrong?

Giving the PO the benefit of the doubt, perhaps something besides the ground miswiring kept the engine from starting/running after setting up. Then one of the other three mechanics screwed up the wiring -- probably the first one.

Anyway, it sounds like you'll have it running in short order. Now we're beyond the weird modifications made by gremlins, and it's just a matter of trading down component failures.

[Zed Head]

I feel compelled to emphasize for any future readers of this thread, do not switch the positive and negative small gauge wires at the battery in an attempt to fix a "no injector pulse" or "no fuel pump power" problem. Bad things might happen. This thread is a special case of lucky.

There must either be a mistake in the wring diagram or the car in this case has a ground wire that is not actually grounded. I have a 76 and will check that ground wire when I get a chance to see what's what, but the solution here is not quite right. It bugs me.

[JRSGTS]

Good to have a disclaimer. Just to clarify. The car had BOTH the Pos. And the Neg. ECU leads on the Bat.+ I took a guess at which was which and got lucky. Now I have proper FP activation, and injector fire.

Now here's the update: Typical Monday, couldn't get new plugs till 11:30 unless I wanted Autolite's. No, waited for the NGK's Did try it with the old plugs now that they dried out...Barely tried. I did rewire my temp. switch, changed the oil and filter, Buttoned up all the wiring, Double checked inj. pulse on #1 and #6, good fire, but the bulb is quite bright...? Wish I could read Data on the coolant sensor to see what it thinks it is..I have a feeling it's out of range. Plugs getting very wet very fast. Got my new plugs, but they only sent 4...Figures. Tried them a couple times but didn't want to foul them. No luck. The fuel is definitely old. I've run cars on worse smelling, but I'm going to eliminate the variable and drain the tank and lines. Kill time till the other plugs get here. I did try to start it without the CSV in case it is flooding. Might have seemed like it helped a little but still no start. I'll go get fuel smelly and report back later...

JR.

[superlen]

+1 on what Zed said. This is definitely a special case. And JR...eeks on guessing 50/50. Had you been wrong you would have reverse biased the ECU. I'm not sure if that will kill it or not, but its not a great idea. I'll have to try with one I have lying around. I hope at least it was an educated guess.

Zed.

One thing that I have noticed on all of the FI harness' that I have looked at is that this ground wire is not connected to the frame anywhere. It is only connected to the battery (-). In the FSM it shows a star ground where all the wires connect, but I think that is just referring to the splice in the harness not an actual physical star ground to the frame. I think Bosch was trying to isolate this circuit from everything else in the car. The ECU case gets grounded to the frame when it's bolted in, but the case isn't connected to the gnd on the circuit boards inside.

The schematic I'm referring to is the one in the '77 FSM & the Z EFI theory/troubleshooting.. I haven't checked others, they may show it as a star gnd to frame. And the one in the FSM could certainly be interpreted as a frame grounding point. I've just never seen the frame gnd in the wild.

Len