our964

None of my searches have resolved this issue or my questions below.

Conditions and Measurements:
- ECU showing Code 22 for fuel pump circuit.
- Battery reference at 12.63V.
- Good crank, good spark.
- Car starts, runs fine if fuel pump circuit is bypassed and powered directly.

From FSM EF/EC 62-63:

Step A: Check power source from fuel pump car harness terminal “a” to ground. Result = 11.71V

Step B checks OK.

Step C checks OK. Result=.7Ohms

Step D: Check ECU output signal at terminal 108 of ECU harness to ground. Result = 10.66V five seconds after key is switched to on. Comment: I’ve seen an intermittent 12+V from 108, but now cannot duplicate. I wiggled every harness wire connection.

Step E checks OK.

Step F checks OK.

Questions:

1. Why only 10.66V from ECU signal? Do I have an ECU ground voltage drop issue? Where to look? I don’t want to blame the ECU until I’m certain that all grounds are good.

2. What does the fuel pump relay do? I can see it grounds from a signal from ECU terminal 20, but from the schematic on EF/EC 62, it looks like the pump already has the path to ground from ECU 108 and the fuel pump harness terminal.

Thanks in advance for your help.

Mike
'87 300ZX, NA, Manual

rogerz

just for a start have you load checked the battery? Free most places. z's don't like low voltage all sorts of gremlins from marginal battery will ensue. battery cable terminals tight and free of corrosion - both ends. battery system is the heart be sure that is A one shape before looking for exotic reasons.

duowing

I'm trying to understand the wiring for that as well. My 280Z Turbo uses a Z31 ECU, but my fuel pump wiring is a little different. The guide I originally followed mentioned that he couldn't seem to get the fuel pump to work by wiring it up like the FSM and had to wire it slightly differently. Pin 20 became just wiring in to a switched 12v. My ECU gives me an error code for 22 as well, but that doesn't seem to affect the pump. When you turn the key to On, are you hearing the fuel pump kick on and hum for the 5 or so seconds? Maybe you have a relay that's going bad and just becoming intermittent.

our964

Thank you for your input.

- Yes, the battery has just been load tested and was fine. The Battery connections are good (just resolved from different thread issue).
- No, I don't hear the pump run when the key is turned on. It does, however, run and the engine starts fine if I power the pump with 12V directly.

I just found the tables on EF/EC 25 and see now how the relay operates so forget my question #2 on my original post. All of my conditions act as they should according to the tables, except for the low voltage output from ECU 108 and 20.

- ECU 108: 0V for 5 seconds after key On, then = 10.66V.
- ECU 20: Key On = 11.71V, then 0V after 5 seconds.

Any additional help is appreciated.

Thanks,

Mike
'87 300ZX, NA, Manual

duowing

I'm definitely thinking it's your fuel pump relay. You shouldn't be seeing a drop on voltage across that wire. Basically I think I mentioned it, pin 20 is the ECU sending the positive signal to the fuel pump relay and it's grounding it back through the 108 wire. At least that's my understanding of how it works. If you're seeing the voltage for 5 seconds when the key is turned to on that indicates to me that your ECU is working properly. It's sending that 5 second prime signal to the Fuel Pump Relay, but apparently there's a poor connection and something is getting lost. The 11.71v sounds fine to me as well, I had it explained that even though you may have 12v at the battery there will be a bit of a voltage drop by the time it gets to the ECU. I'd say see if you can get a new relay and that I would think be your problem. Could just simply be that the relay is getting old and worn out, and is beginning to build too much resistance, hence the drop?

our964

Good info, thanks again for your continued help. Please bear with me as I believe I’m getting closer.

Things I’ve tried:

- Swapped the FP relay with other blue relays. Still no fuel pump start.

- On bench, applied 12V to relay. It closes and there’s continuity with .5 Ohms resistance between pins 3 and 5. Relay is good.

- On bench, applied battery +12V to FP relay male pin 2 (ref. L/W harness wire), and out male pin 1 (ref. Y/B harness wire) to ECU 20 (Y/B wire). Relay closes. (On duowing’s last post, and on others I’ve seen on various Z31 forums, the ECU is identified as +12V. From my review of the schematic on EF/EC 62, I believe it to be -12V, with the +12V signal coming from the fuse block (L/W wire) to close the relay. I may be way off, however, and anxious to learn.) So my relay will close if attached directly to battery +12V and ECU 20, so the ECU can control the relay, but there’s something wrong with the signal from the fuse block to the relay.

- I measured voltage between the battery side of the FP fuse at block and ground, and get 12V with key on or off. Good.

- I measured between the FP relay harness female for pin 2 (L/W wire from fuse block) and the battery ground, and only get 3.6V. This with key on or off. I should see 12V with key on or off.

- I get no continuity between after FP fuse at block and FP relay harness female for pin 2 (L/W wire from fuse block). Continuity should exist, as this is a straight path to the FP relay connector, and since it doesn’t, where is the phantom 3.6V coming from!

- From my first post, (FSM EF/EC 62-63: Step A: Check power source from fuel pump car harness terminal “a” to ground. Result = 11.71V). This is the same circuit (L/W wire) from the fuse block to the FP relay and FP. So, the L/W signal goes to the FP but not the relay.

So it looks like I may have a problem in this L/W wire to the FP relay. I need to dig into it further tomorrow, and look for an issue with this L/W wire where it splices from the L/W wire going to the FP. Worst case, I should be able to jump between the FP L/W and the FP relay L/W wire (near the connector).

I know that this is impossible to follow without the EF/EC-62 schematic in front of you, but when I get this resolved, it may help someone else by having documented my steps here.

Thanks for your attention and continued patience.

Mike
’87 300ZX, NA, Manual

our964

Found it!

Today I bypassed the L/W wire from the fuse block and tied it directly to both the FP harness and FP relay harness near the connectors. This is the same path as the factory L/W wire. The FP, FP relay, and timing of the two from the ECU all worked as per spec. The car fired and ran fine. Great!

OK, two choices: 1. Replace the L/W wire run with new wires of the appropriate gauge, with proper splices. 2. Follow the factory L/W wire and find the problem!

I got lucky, and found the problem in a spot where the harness was not buried too deep. Behind the passenger seat (LHD, 2-seater), and below the storage bin, I removed some factory tape from the harness that runs from the rear of the car, only to find the L/W wire from the FP wrapped in more factory tape. There was one heavy gauge wire from the FP in, and two out, one heavy and one light. I unwrapped the factory tape and the three wires fell apart.

The wires checked as follows: One heavy from the fuse block with +12V, one light to the FP relay, and one heavy back to the FP. It appears that there was a crimped splice under that tape that corroded through (see attached pic). From the pic, you can see some surface rust at the low spot where the harness runs, from a rear window seal issue left unresolved for too long from some time ago… my fault. So this time bomb has been ticking for some time, and finally caused an issue that has been driving me crazy.

I will repair this splice, and everything should work just fine.

If you happen to be under that bin for some reason, take a look for yourself to see if you may have a similar crimped splice, and a potential issue brewing.

Thanks,

Mike
’87 300ZX, NA, Manual

duowing

Glad to see you found the issue. This reminds me of the similar issue that nismopick pointed out with the 280ZXT. They had 2 ground wires coming from the ECU which were then in just a metal crimp connector to a much bigger wire that ran out to the engine bay. It's just wrapped in electrical tape and left. Over time as with your issue, the thing would corrode and start causing issues. Looks like a pretty easy fix. If there's enough length, just cut the wires down a little so you have clean wire, twist them all together nicely and solder away.