Fuel pump not running / not getting power

[charliekwin]

Took the Z to work and back on Tuesday with no problems; Wednesday it won't start.  Pulled the starter solenoid wire and hear nothing from the fuel pump.  Working my way through troubleshooting so far: there's no voltage across the fuel pump terminals with the key in the start position.  Fuel pump relay clicks with the key in start.  All the voltage and continuity checks in the EFI Bible are fine.  Negative side has continuity with ground, but the fuel pump runs if I give it 12V straight off the battery, so I guess there's an open circuit somewhere on the hot side.  Tomorrow I'm planning on working my way through all the wiring, but are there any fuses or anything obvious I'm missing?

[siteunseen]

There's one of those 4 fusible links that can cut power to them I think?  Some have a cut off in the AFM when the flap is closed, others have it in the oil pressure sender.  Kills the pump when you have an accident, no air or no oil pressure.  Look at Blue's picture and find the other stuff for EFI.  Good luck. 

   

[charliekwin]

As mysteriously as the problem starts, it resolves.  I checked both of the green wires on the fuel pump relay harness and they both had continuity with the fuel pump (am I wrong in thinking that's odd?).  Reconnected the relay again and everything works.  So I have no idea.

[Zed Head]

78 has the system that uses a control relay and a pump power relay.  The control relay uses either current flow from the alternator OR current through the oil pressure switch to actuate the pump power relay.  Relay powers relay.  There's a whole thing about how it works and testing on EF-35.  

One way people test their pumps with 78's is to disconnect the oil pressure gauge/switch and turn the key to On.  I'd guess that your control relay is sticking, and that won't work for you.

[charliekwin]

Thanks for helping point me in the right direction, Zed.  Electronics and circuit diagrams are something I have a hard time groking, and this is right around the level where I start getting shaky, so I sure do appreciate it when people indulge my questions.

Anyway, I think I was misunderstanding how the fuel pump control relay works.  I had thought the fuel pump relay would close when starting the engine, which once running, closed the control relay via the alternator and oil pressure switches.  With that line of thinking, I wasn't concerned about the control relay since I couldn't get it to start in the first place.  Sounds like I've got it wrong.  I just found this link (for future visitors who may come across this thread) http://atlanticz.ca/zclub/techtips/fuelpump/moreinfo.htm  and after reading through it a couple times, it's starting to make some more sense.

Guess I have a control relay to look at.  I'll bet it's expensive!

[charliekwin]

Tested both the fuel pump and control relays and both checked out fine.  The control relay looked like someone opened it once upon a time and I could hear something rattling around in there, so I cracked it open and this gasket-type material came out.

My theory is that by pure dumb luck, a piece of that got stuck between one of the relay contacts and wasn't allowing it to close.  Anyone else think that sounds like A Thing That Could Happen?  Because I'm planning on taking the car out tomorrow and would prefer not to get stranded.

[Zed Head]

I had a fine hair or thread or piece of dust stop my AFM fuel pump relay contact switch from closing.  Never did find the actual thing, I cleaned the contacts with a matchbook striker and it's been fine ever since.  So I'd say yes that can happen.

I saw a post recently about an EFI relay that stopped working because the internal ground connection broke.  I think that yours might ground through the case.  You might confirm and check your grounds.

And don't overlook a bad ignition relay.  Can't remember what exactly it powers but I think that the starter circuit might have its own power, independent of it.  Just checked and the manual trans. cars have a direct wire to the starter solenoid.  So the engine can spin with a bad ignition relay.  My ignition relay was full of rust.  One of the Z car vendors out there actually borrowed a pciture I posted of it to help sell his own parts.  They're in a damp location.

[S30Driver]

Where did you tap in for power to the new sound systems, did that system include a high powered amplifier?

Oops, I meant this post for the No EFI power thread .... sorry, one too many beverages tonight.

Edited April 24, 2016 by S30Driver

[siteunseen]

6 hours ago, S30Driver said:

 one too many beverages tonight.

No such thing IMHO.

Purple Rain had one too many Percocets though.

[charliekwin]

I can imagine the conversation with my wife:  "The Z isn't running again."  "Oh, what happened to is this time?"  "Some dust got in it."

And then back to the garage to get a beverage from the fridge.