Noobie here needs Fuel pump help!

[JRSGTS]

Hi Folks, Love the site. Great info! Did a lot of searching so not to waste anyones time...but. No luck yet.

My Name's JR. I am actually working on this 1976 280Z for a customer of mine. I own a shop that does mechanical resto work on classic cars here in upstate NY. I do love the Z cars and this guy 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. Jumpered pump, (Newer replacement) works fine. Downloaded FSM, started troubleshooting. Actually I took a stab and bought a FI relay. Didn't fix the problem:finger: I know better but fixed a lot of problems with just a relay before... Ayway, so I went to the relay testing. 3 tests in FSM. 1st one is testing pin 4 (ECU) to ground in start position. Should have Batt. voltage,Check. 3rd test is for air reg. and FP circuit. Pin 34 to ground= 85.3 Ohms, says should have continuity. Is that number high? The #2 test is for FP relay. Pin 20 to ground, should have cont. I have none with either relay. Says fault is either relay or wiring. If I provide ground to pin 20 with the original relay, I get full time FP running. With the new one nothing. So I did affect a change , just don't know what's wrong.

Sorry this is so long! Starting to pull some hair out...Could it be my ECU? Or do I need to start opening wiring harnesses?

Thanks in advance for any and all help! JR.

[FastWoman]

I don't know the '76 that well. Each year was a little different, with different safety mechanisms used to shut off the fuel pump if the engine stopped running. I believe the '76 still used a switch inside the airflow meter. When the engine draws air, the vane opens, and the fuel pump switch closes. Then of course there's the main fuel pump relay.

The most common electrical problem these cars have is crusty connections. For starters, I'd recommend pulling off all the connectors, cleaning them up, dabbing with a bit of dielectric grease, and reassembling. Then I'd focus in on the connectors that might be problematic with the fuel pump system. Check the big connector to the airflow meter and the one to the fuel pump relay. As you're checking out the FP relay connector, keep in mind that you can short across two of the connectors to deliver power to the fuel pump. I don't know whether the color codes are different on the '76 (re the '78, which is the year I have), but the wires feeding the pump are blue/green. If you short these connectors and the fuel pump fires up, you either have a bad relay or a crusty relay connection. If the pump doesn't fire up, then you've got a connection problem elsewhere. Of course confirm that you've really got +12 on one of the connectors you're shorting!

If you've got 12V to the relay and no joy with the short, then I'd say check the following:

1. There are two huge connectors for the wiring harness just inside the passenger firewall, at least on my '78. The FP circuit runs through one of the connectors. Make certain the connector isn't crusty/burnt. Mine was burnt (really an inadequate contact for the circuit), so I snipped it out and used a bullet connector.

2. Check the integrity of the contacts on the pump.

3. Check the integrity of the ground, which runs back through the floor to somewhere in the hatch area -- in the toolboxes, I think.

[JRSGTS]

Thanks "Fast"! You are correct, research tells me the 76 is different than all the later years. Similar in some cases to 75-77.

Anyhow, yes there is FP activation through the AFM. I should be able to activate it by opening the flap...Doesn't work. The only connectors I haven't checked /cleaned are the dropout resistors. I did try a new FP relay to no avail. however, with the old relay installed I can jumper 1 pin to ground and the pump will activate. No injector fire though. With the new relay, jumping the same pin gets me nothing.. Since the ECU provides the grounds for the injectors I am suspect of that...Maybe I had a bad FI relay AND a bad ECU? Hate to buy one without being sure though. Heading to the shop to check dropping resistors and any other connection I can find. Any other help would be greatly appreciated! JR.

[FastWoman]

I think you're getting ahead of yourself. I thought you had replaced the fuel injection relay (that powers the ECU), not the fuel pump relay (that powers the fuel pump). A running fuel pump vs. an operating ECU are separate issues. Unlike with many EFI systems, the ECU does NOT control the fuel pump in any way. So you need to trace fuel pressure issues separately.

I wonder whether you bought the right type of relay. If the old relay will actuate the fuel pump, then it's almost certainly working properly. Furthermore, you would have no other wiring issues. Perhaps you plugged a fuel injection relay into the fuel pump relay connector? (I don't know whether the plug configuration looks similar. It's very different on the '78.)

In diagnosing the system, remember that the fuel pump should only run with the key in the START position, not the RUN position, unless the engine is actually running. If you prop the AFM's vane open and turn the key to ON, I believe the pump should run.

Diagnosing the EFI is a completely different ball of yarn. To verify injector pulses, pull out a miniature Xmas light bulb ('tis the season!), and plug it into an injector connector. It should flash dimly as you crank the engine -- once per engine rotation. If you unplug the coolant temp sensor, it should flash longer/brighter. To diagnose the EFI, you should download the "Fuel Injection Bible" for the 280Z.

[JRSGTS]

Wow fast responses! I love it! I did replace the FI relay, but it is a 2 relay box. On the 76 they are together. The connections are correct, believe me I tried to do it other ways. Even tried connecting one plug to the old relay and one to the new. I did buy it from Z car source out west. They seemed to think I was on the right track, but they admitted limited tech help. Took me a while to learn the pump operation only when running, but I got it now. Opening the flap on the AFM gets me nothing. Going to try the home made NOID light trick now too. Didn't have enough battery last night (just got it in the shop late last night). Interesting that the ECU has nothing to do with FP operation...Seems my theory just fell to the ground... I'll go do some checks and check back later. THANKS AGAIN!!! JR.

[Zed Head]

Anyhow, yes there is FP activation through the AFM. I should be able to activate it by opening the flap...Doesn't work.

There might be a misunderstanding here on the details. The contact switch in the AFM closes (makes contact) when the AFM vane (flap) is opened. This allows power to the relay which then powers the pump, assuming that the initial power sources are correct. If you take the black cover off of the side of the AFM you can see the mechanism. I've had the AFM contacts get contaminated (on a "new" MSA AFM) to where they look like they're touching but they're not really making electrical contact. I had to give them a buffing with a match box strike pad to get them back in order. You can check that the contacts are closing by testing for continuity at the AFM with it removed or at the EFI relay plug (it takes some study to figure out which wires go to the AFM contacts).

I would check those AFM contacts before going too much further.

[JRSGTS]

Thanks Zed. Just double triple checked those...Even checked for voltage, NP. Have voltage coming out of the AFM as soon as the door starts to open. So here's what else I've tried. Did the Christmas light test on 2 injectors. Tho I'm skeptical of not having an actual noid light, no fire...I double checked the relays under the pass. side. I believe the only one I hear clicking is the starter relay. Double checked connections at fusible links. (Links are brand new) I did find one of the temp sensors not hooked up(the one with the eyelet to ground) I know I need this to run good, but my first concern is getting it to start. I decided to go back to square one. I had done a compression test (190-195 all) but not checked firing order. I was lazy when I installed the distributor and never set for tdc. OK..thats on me... Now that that's right, I even could static time it now. The first time I hit the key it sounded like it wanted to start...But didn't. Though I didn't hear the pump, and still have no pump activation or clicking at the relay. NOW...everytime I hit the key, The starter gives half a crank and the solenoid kicks free!! I can't even get a full engine revolution out of it!!! Hair pulling time! Before I set the timing it would crank all day long...UGH...Doesn't seem logical that the solenoid just died now. Or does it?? The times that I manually powered the pump, I still had no injectors. Didn't try it yet with the timing fixed. I'll also double check the ground wire at the pump. This starter thing has me head scratching good though!

Thanks for the input! I have to be missing something stupid. If I can get pump and injectors I can then go after all the driveability problems. JR.

[FastWoman]

Sounds like the battery is weak, so your cranking voltage is probably pretty low. I don't know that you can draw too many conclusions without normal voltage.

Anyway, if you're not getting a full engine rotation per crank, the injectors are unlikely to fire. The ECU counts sparks from the ignition, firing the injectors on every third spark.

Here's an alternative test: Connect up a wire to the (-) post of the coil, and leave the other end hanging. Plug in the Xmas tree lights. Turn the key to "ON." Now tap the wire to ground. Every three taps should give you a flash of the Xmas tree lights.

[JRSGTS]

No battery voltage was fine. I had the charger on it all night before., and the charger was on while cranking. Had over 13.0V during testing. The starter isn't kicking out slowly, It tries to spin the motor and instantly goes to a free spin. I get that it needs to spin to fire the injectors, but I should be able to manually run the FP. Car also has a fussy ign. switch that sometimes doesn't crank the motor. Someone installed a starter button. Same result with either starting method. I also checked power at the start terminal on the starter. Solid battery voltage with key in start position. I checked it to see if it was maintaining power and not dropping out causing my starter problem. NP here. Another thing I did was run a ground direct to the black wire on the FP to the battery negative to rule out a bad ground. Still no change. Starter problem or not, I should be able to disconnect the starter wire, the CSV, and hold the key on start to hear the pump run. Or open the AFM flap. Neither gives me a fuel pump!! Getting a bit frustrated.... Thanks for your patience! What about the fact that I have no continuity to ground on pin 20 of the ECU? as per testing the relays in the FI bible? I think I'm going to strip the wiring harness open and trace the wire...Oh yeah, before I fixed my timing issue ( when the motor cranked over like crazy) I had no injector fire then either... Sorry to run on, just thought I'd put as much info as I could out there...

Thanks again for the input! At least I'm not just standing there staring at it!

[FastWoman]

Before you start stripping apart the wiring harness, be warned that half/most of the wires are black -- with tiny little yellow numbers here and there! There are a few internal bullet connections that could be checked, and of course any modifications should be readily apparent. However, I doubt there's much you'll see.

I think you missed the alternative test for the ECU I mentioned in my last post. It doesn't require cranking the engine.

Starter issue: You might have an issue with bad switches (even the button that was added) or crusty connections. This is a somewhat common issue in the Z. It might be good to test the starter by jumping the solenoid's spade straight to the + post of the battery.

I can't help you with pin 20 of the ECU. That pin is not used/connected in the '78. (It's probably not used in the '76 either.) On the '78, I see pins 35, 17, and 16 are the main ECU grounds. Although there are minor modifications between years, I suspect the same pins provide the ground in '76.

[JRSGTS]

Hi again Fast, No I didn't miss the test. Just forgot to mention that I tried it... So many words to type...a lot for 2 fingers . I definately had no flash of the Christmas bulb. Still curious as to how that works on a bulb that is not 12V. I checked with my voltmeter across the inj. connector and there is Battery voltage on both terminals...Is this normal? I am going to get a correct Noid light to confirm. However, I'm fairly sure they are not opening. No clicking from them on any attempt I've made to start this thing.

There definitely is a bunch of differences between the 78 and the 76. All or most my ECU wiring is white with little tiny numbers on them. The #20 pin at my ECU definitely goes to the FP relay. Found it in the bible, and it is part of the relay testing procedure. Oddly, it says I should have continuity to ground. I do not, with either the old or the new relay installed. BUT with the old relay installed and I introduce ground to the circuit, I get full time fuel pump run. With the new relay....Nuttin...UGH!

Here is what else I have done. I've been through every connector I can find and cleaned , checked and confirmed continuity through them. I pulled the whole wiring harness down on the pass. side and checked every connector, plug and relay. Even though the bible shows all fuel related components on the drivers side. Cleaned and checked wiring at the dropping resistors. Checked wiring to ignition switch. Everything has been basically clean, I am an ASE certified tech. I know all about bad connections and such. The whole car looks fairly unmolested. The real kicker now is that with the timing and dist. set right the car won't turn over more than 1 revolution without the solenoid disengaging! And yes I've jumpered the start terminal directly. The only thing I can figure is it was a weak starter and when the timing was wrong there wasn't much compression to fight against so it would crank freely. Now that it has comp. the solenoid is too weak...Good news is my local Advance auto lists one at only $29.95 my cost, bad news, won't see it till Sat.!

Guess I could just walk away till after the holiday. Speaking of that...Happy Thanksgiving To you. One of the many things I'm thankful for is the nice people like you folks who have been so helpful!! JR.

[FastWoman]

JR, the Xmas bulbs are normally strung in a long series. They typically glow with maybe 3V across them. They definitely work, but I admit they're not as refined as real "noids."

When the key is in the ON/IGN position, the fuel injection relay should connect from +12 to the common sides of the two gangs of drop resistors. The other side of each drop resistor leads to one side of each injector. The ECU grounds the other side to deliver a pulse of fuel. When an injector isn't grounded, you should read 12V across both leads of the injector.

Regarding the fuel pump relay vs. the ECU: Yes, '76 appears to be different. I'm looking at a color schematic for the '76 at this link: http://www.4moores.com/280z/files/test_76_280z_wiring%20copy.jpg

It seems the fuel pump relay is part of the electronic fuel injection relay in that year (hence my confusion). There's indeed an input to this relay from pin20 of the ECU. HOWEVER, this input is internal to the relay and would appear to play some role in "keeping" the contact after it is initially "made" via input from 76 (+12 "START"). Pins 20 and 10 are the +12 supply to the ECU. Pin 43 feeds +12 to the drop resistors. So although there is connectivity between the fuel pump relay and the ECU, it's only because the fuel pump relay is part of the EFI relay. In other words, the "logic" of the ECU isn't responsible for actuating the pump, if that makes sense.

It's interesting you say that you get a running fuel pump when you introduce ground to the circuit. Are you saying it's when you ground 72 of the relay? If so, that would indicate you have an open ground. To be clear, the relay should be actuated when you introduce +12 to 47 ("START"). The ground should be continuous.