Miata Mailing List: September 1999, Message #162

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The saga continues... but hopefully not much longer...

When last we hear from poor Jezebelle, she had been startless for a week with few
prospects for returning to the road. Thanks to Bill, Brad, Jac and other sympathetic
listers we at least now have a plan of action, though little time to execute it. I
did brake down and get a Miata Shop Manual Monday, though. Thanks to procedures from
listers and the manual I have traced the non-functioning fuel system all the way to
the fuel pump itself. I find it hard to believe that a fuel pump should fail after
28K, but I suppose I cannot argue with the facts. Thats the good news.

Suspecting that it might be said fuel pump, I casually asked the Parts guy at
Roebuck Mazda how much a new one was. When he answered $403 I chuckled and asked how
much for the one thats not gold-plated. He didn't laugh. Turns out he was quoting
the "fuel pump assembly" with contains the tank level sensor and various plumbing
and wiring along with the actual fuel pump. I have not called back, but my hopes are
that the pump itself is a separate item and less precious than the entire assembly.
The manual has procedures for replacing it separately from the assembly, so I hope
they stock it separately and I just happened to get a less knowledgeable parts guy
(it was lunch time...).  I'll know tomorrow. If they are overly proud of their pump,
I suppose I'd consider and after-market replacement if anyone has any positive
comments or suggestions.

I'd like to thank the various folks who responded with insightful ideas and
encouragement to my problem. I owe you one, guys.

Cheers,

Terry James & "Jezebelle"
95 White & Tan Leather PEP

Bob Schnider wrote:

> > One other question, though. I'm still trying to reconcile the symptoms I was
> > having with the starting before. If the circuit opening relay was flaky
> > before, that would explain having periodic problems that occurred irregularly.
> > I could also believe that once it had closed, it might remain close reliably
> > until another start attempt (which would explain why things run fine once it
> > starts). The bypass of the relay, however, did not get the fuel pump going,
> > though, which I would have expected to happen. If the fuel pump itself is bad,
> > it would not explain why I was only affected at start time. I can't argue with
> > the logic of your diagnosis and I's be willing to replace both the relay and
> > the fuel pump, but somehow I still feel like it doesn't add up.
> >
> > Maybe I'm misunderstanding the purpose of the relay. Does it normally cycle
> > based on fuel demand, or does it start the fuel pump at crank time and stop
> > when the ignition stops? Based on the name "circuit opening relay" I might
> > think also that the fuel pump normally runs all the time the engine does and
> > the relay is used only to shut it off in the even of  an abnormal engine
> > condition (monitored by the ECU). In such a case, I'd like to know how the
> > diagnostic connector is wired and what shorting the FP and GND leads does. Its
> > entirely possible it just interrupts the ECU override and that a bad relay
> > could still be in between power and the fuel pump. Just speculation. I've GOT
> > to get a wiring diagram and some general layout information.
>
> the circuit opening relay (also referred to by some as the fuel pump relay)
> simply shuts off power to the fuel pump when the ignition is switched off.
> if the relay is defective then the fp receives no power and can't function.
> if the relay is the only bad component then shorting across fp and gnd will
> allow the car to start.
>
> shorting out the relay delivers power to the fuel pump.  if the pump is
> working you should be able to hear it... you have to listen closely.  you
> many even have to open the filler cap and listen at the opening to hear it.
>
> if you can't hear the fuel pump running check for voltage at the supply
> terminal on the top of the tank (behind the driver's seat under the carpet..
> . it's the larger of the two covers behind the parcel shelf cover).  not
> sure on the 95 but on the 90 fuel pump connector measure the voltage at the
> bottom left (L/R) terminal with the ignition switch on.  you should get
> battery voltage here. check for continuity between the bottom right (B)
> terminal and ground using an ohmmeter.  if you have both voltage and
> continuity then the fuel pump is almost certainly bad.  more likely you have
> to repair the ground circuit between the B terminal and the fuel pump.
>
> --
> Bob Schnider & Tango
> 90A Red, eh... #1598
> MCA, Sea to Sky Chapter
> Deja Vu Racing
> http://doc.schdist42.bc.ca/bob/