# 1990 MIATA FUEL



## baxtazz (May 27, 2011)

Hey Everyone,
After the timing belt fiasco,My Miata ran great for a week!But I parked it at night,went out the next morning,and it wouldn't start,turns over, won't start.Got some either gave it a sniff and boom it ran, so it's a fuel problem.I got a new pump, and relay installed them and it still didn't start.Went to Lowe's bought a meter and determined theres no power at the tank pump plug, the relay under the hood clicks when I turn the key and I have 12 volts at the diagnostic port.But for some reason I lost power to the pump!!!! I really have no idea what to do now,I have a Chilton's schematic,but it might as well be in CHINESE LOL no clue.
You guys have any ideas??????


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## octaneman (May 13, 2009)

Baxtazz

Look for a broken ground wire at the fuel pump's molex connector. Also since you already established you have power to the relay, test for power going to the switching side when it turns on. If power is there you will need to do a continuity test on the harness and the fuel pump assembly to locate the broken connection.


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## baxtazz (May 27, 2011)

Thanks OTM, I'm going to where I have the car I'll give that a shot,although I'm not sure how I'll check for power at the relay.I'll try removing it from the fender well so I can get under it with my meter probe.I'll be back!


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## octaneman (May 13, 2009)

Baxtaz 


I found a diagram for your vehicle and studied it. I've traced the wires on the relay side with red, if the diagram is the same like the one you got then it should be easy to follow. Looking at the diagram, the main relay energizes a circuit relay which activates the pump. When you turn the key on, the main relay gives power to the crank sensor (marked in red) and the circuit relay. If you look carefully the circuit relay also has a built in start capacitor, the capacitor gets its signal from the mass airflow during cold start. When the engine spins the computer gives the signal to the mass airflow to turn the fuel switch on, this in turn sends another signal (light green) to the circuit relay keeping the pump constantly on in run position. Keep in mind that the moment the computer sends the signal to the mass air flow (light green) the coil side of circuit relay will switch the fuel pump on.



Note: Bax , if the diagram is not the same please post the one you got and we'll take it from there.


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## baxtazz (May 27, 2011)

Hey OTM,Thanks for your direction,Found a ground down by the fuel filter cleaned it up and it started!!!!! I don't really feel confident this was the problem,because that is the ground for the battery and it seems to me if that ground was bad the car wouldn't have been turning over at all. But anyway it's running,O bye the way the schematic you found was a much better drawing than the one I had.I printed it out to save,thinking I'm not out of the woods yet.
THANK AGAIN OTM!


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## octaneman (May 13, 2009)

*Re: [SOLVED] 1990 MIATA FUEL*

Good job !



This thread will be marked solved.


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## baxtazz (May 27, 2011)

*1990 MAZDA FUEL*

HEY OTM,
Well as you see I'm back,my Mazda ran beautiful for two days! Start and stop no issues.Came out of a store yesterday and it wont start!!!!!!!!!!!! So I am at the here I go again stage. I don't have power to the pump,it's a new relay on the passengers side wheel well.and a new pump. So I pop the cover off the relay to expose the solder connections.So it should be simple,I test one side there's power on the other side no power.So I pop out the relay to find the 4 prongs,it seemed to me if I use a jumper to complete the circuit there would be power to the pump,well when I did this it blew the air bag fuse.I'm like OK the air bag is related to the fuel pump relay,this is going to be fun.And now, I can't find power at the diagnostic port.I have a yellow wire at the pump and a yellow wire at the diagnostic port so I'm assuming the power comes in on the yellow even tho it doesn't correspond with the schematic.Could this problem be in anyway related to the timing belt installation??
Any thoughts


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## Midnight Tech (Dec 31, 2001)

*Re: 1990 MAZDA FUEL*

Are they LARGE yellow wires? If so, DO NOT mess with those! Those are air bag circuits and you may get an expensive, unpleasant suprise!

Edit: Threads merged.


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## baxtazz (May 27, 2011)

Thanks for that heads up!! No there is a yellow wire on the fuel pump,and a blue red on the fuel pump,and I read that a jumper can be used in the diagnostic block to activate the fuel pump,I'm guessing it bypasses the relay. The air bag fuse is in the same location as the relay for the fuel pump when I removed the relay and went to jump across the points is when the air bag fuse blew


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## octaneman (May 13, 2009)

Bax 

First check out all the fuses with a test light light to see that none are burned. Relay circuits carry their own fuse when you turn on the ignition, so the first step is to determine the state of the ECM fuse because you got no power going to the diagnostic connector. When your satisfied that all fuses are good, test the ALDL connector by extracting the codes at the same time listen for the pump. If the pump activates then you know the connection to that side of the circuit is OK. 


Midnite Tech made an excellent point of the yellow wires, please do not poke them or use jumpers if you don't know what they do because you risk accidental deployment of the air bag. What you need to do is focus on the relay, you already mentioned you get power to it, which tells me that the coil side is OK but the trigger side is not. Since you already tried jumping the relay and it blew the fuse, It tells me one of two things; 1) That there may be a short circuit on the ignition relay side. Or 2) The fuel pump relay trigger pin is triggering on the negative side instead of the positive to activate the fuel pump. To verify that it is on the negative side, re-test the relay only this time place your test light alligator clip on battery positive and the test light tip on the relay pin when you turn ignition on. ..Does the test light turn on for 3 seconds ? 


post back your findings.


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## baxtazz (May 27, 2011)

Hey OTM,
I'm just getting in,and just reading your post.Here's where I'm at with the ole Mazda.I got away from all the relays up under the hood and started diagnosing from the tank.I took a hot wire right from the battery and put it to the molex at the tank,and I couldn't get the pump to spin doing that.So I pulled the pump back out(it's a brand new pump now) there is a six inch lead coming from the pump that goes to the fuel sending unit housing,and one side of the fitting(the side that plugs into the sending unit housing,male end) was all black and melted! Any way I put 12 volts to the pump and it still works.Altho the wire is not part of the plug anymore I can still stick it into the receiving end to make the connection.I just need to know if there is any type of epoxy out there I can use to fill around it so it stays in place,again this connection is in the tank so the epoxy can't be effected by the gas.
I'll start with all the other testing in the morning.
Thanks Again for all the help you guys


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## baxtazz (May 27, 2011)

One more thing,in the fuel pump kit I bought they supplied a new plug end fitting, but it was for the pump side.I just found that interesting,like they have had problems with melted plugs before.
And another thing if anyone is looking to by a replacement fuel pump for your Mazda,I first went to Napa they sold me a pump for $126.00 and recommended I buy the filter sock so I did for $42.00.Well I ended up at Car Quest,just a random stop, and for the heck of it got a price from them.For the price of$123.00 I got the pump,the new filter sock new Orings,and a plastic bushing that goes in the fuel pump tower! Plus the new plug end that I didn't use and two but connectors! Unbelievable So make the phone calls people I can't believe how much the prices can vary!!
Thats it for now


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## Basementgeek (Feb 7, 2005)

Remember not all parts are created equal.

BG


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## baxtazz (May 27, 2011)

Good point, But I'm thinking a pump is a pump.It'll probaly kick me in the but,but after all this I'll sure know how to fix them!! LOL


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## octaneman (May 13, 2009)

Bax

Use JB Weld it works great because its fuel resistant, but don't use the quick weld.


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## baxtazz (May 27, 2011)

Ok thanks OTM


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## baxtazz (May 27, 2011)

Hey OTM,
Yesterday proved to be unfruitful,ya know I don't even know were the ecm fuse is,is it under the dash?This is what I know,the crank sensor (actually on the passengers side cam, right),the mass air flow sensor the diagnostic block, the main fuse panel under the hood,O and the fuse that blew had a air bag clip over it,it looks more like a relay in that it's big but I noticed later that on the cover it was marked, INJ so that would explain why it blew when I tryed to jump connections in the pump relay port,and the last is the fuse panel under the dash that just has a fuse marked engine. I did get a test light and tryed testing the pump relay under the hood,and although its new, it doesn't seem to be getting power on both sides so i figured I ruined it messing around,the new one I am getting will be in this morning. So thats it I,m hoping with the new pump relay it'll fire right up!!!!!! I'll check back


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## baxtazz (May 27, 2011)

Hey Otm,
Put in the new relay no go,so it's either the crank angle sensor or the mass air sensor right at some point I'll run out of things to replace and I'll be done! LOL


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## octaneman (May 13, 2009)

Before you go out and spend money on a crank sensor test it first. But you have to be careful because there is an O-ring seal that prevents oil from leaking, if its not installed right the engine will leak oil. If you decide to take it off there are 2 things: 1) There is an air gap from the magnet to the plate, if the gap is too far the engine wont fire. 2) To test the sensor hook your meter to the signal pin and ground if you pass a screw driver passed the magnet the meter readings will fluctuate. If it does the sensor is good.


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