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Old 09-15-2010, 08:24 PM   #1
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Default Circuit Opening Relay

Guys, need some help (obviously).

Have a '91 with an intermittent no-start condition.

It has good voltage, I think it's a fuel issue.

******* around under the dash (quick check to make sure all fuses were OK, etc) got it to start, once.

Looking more, the Circuit Opening Relay was just hanging there, not fastened to anything with its tab. My question is; does this tab provide a ground?

I know its a super easy thing to test, and I will be going back out and testing it (car is stranded 5 miles away @ a Walmart), just didn't have any tools in the car and wanted to know any other things to check out if that wasn't needing to be grounded/the mount wasn't a ground.

EDIT - good voltage, meaning; gauge shows 12.1ish v, 14.2ish when it ran. On cables it shows 13.5, no start either way. The dash light saying "charge" is on though...odd.

Last edited by BradC; 09-15-2010 at 08:44 PM.
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Old 09-15-2010, 08:47 PM   #2
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Quote:
Originally Posted by BradC View Post
My question is; does this tab provide a ground?
My answer is: No, it does not. A constant ground for coil #1 is provided on the black wire (used only during cranking) with the primary (coil 2) switched ground going out on the light green wire.

I'm not aware of any relays in the Miata which are tab-grounded.

Open up the diagnostic box under the hood and jam a wire between F/P and GND. That will force the pump to run anytime the key is on. Open the fuel cap and stick your ear down there. Hear the pump running? If not, you've got problems in the fuel pump system. If so, try starting. Still no start? Problem ain't fuel-pump-related.
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Old 09-15-2010, 09:03 PM   #3
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Thank you Joe. I saw that the relay was grounded via its harness and assumed the tab did nothing, but thought it was the obvious thing to ask, with it just chilling there and all.

Thanks for the other tips, will do ASAP.
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Old 09-15-2010, 09:04 PM   #4
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Peace be with you.
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Old 09-16-2010, 02:04 PM   #5
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Got it to run to get it home by jumping out ground and FP on the diagnostic box, thank you.

The relay housing itself has a crack in the plastic, so it's going to get replaced regardless, but the intermittent nature of this problem is driving me nuts.

When I got to my car today, it cranked but would not catch, as yesterday. Jumped out the FP/GND, fired up, drove her home. Got home, removed the jumper, fired right up, a few times.

As a side note, the CEL was not lit (key in on position, engine not running) until I jumped out the FP/GND.

Took the relay out, checked the resistance and operation as per the FSM, all checks out ok when bench testing.

My confusion lies in the function of jumping the FP and GND pins. Does this take the relay completely out of the loop, or does it only take the AFM flapper door section out of the loop? Searching at m.net did not get me a firm answer.

The area under the master cylinder where the multiple grounds terminate is clean and fresh, with no loose wires.

Am I right in leaning towards an intermittent problem with my AFM, or can/do relays also fail intermittently?
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Old 09-16-2010, 02:13 PM   #6
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Two maintenace items that might help:

Open the AFM, clean the wiped contacts and either move the wiper assembly down or bend the wiper to get firmer contact. Check the FP contacts at the same time.


Pull the back of your ignition switch out, disassemble, clean the contacts, reassemble with dielectric grease.
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Old 09-16-2010, 02:38 PM   #7
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Good ideas, will do.
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Old 09-16-2010, 03:56 PM   #8
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Might be a stretch.... but if you have the ability to check the fuel pressure, might be a good idea, just to see if you have pressure in the lines when you try to start. It could be the relay, not enabling the FP... or I wonder if the stock FPR is not building pressure.

However, it's probably electric. <G>

Dave,
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Old 09-16-2010, 10:15 PM   #9
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Quick inspection before the rains came revealed a very, very slightly loose AFM connector. One side of it (furthest from the filter) didn't have the small wire spring lock fastened and it was very slightly askew.

Once it's dry again I'll drive it around and see if that was the issue.

Come to think of it, a few weeks ago I remember the car hiccuping on a rough section of road...
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