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JoMo

626 V6 Cranks But Won't Start

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Hi,

My Australian 94 626 V6 cranks but won't start. It was like that for 24 hours and then suddenly I could easily start it over the course of the next two days. After that two-day period it again would crank but not start and I haven't been able to start it since.

I put the engine in dignostic mode by jumping pins TEN and GND on the diagnostic connector, but the CEL does not illuminate.

I removed a spark plug from the engine, reconnected the spark plug lead, earthed it to the engine and cranked the engine > I saw it spark.

When I turn the ignition to ON, I do not hear the fuel pump come on for a few seconds. So I jumped pins FP and GND and then heard the fuel pump continuously operate. However, the car still would crank but not start.

Any suggestions for the next step?

Thanks.

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A cheap place to start would be a new fuel pump relay.

Thanks hominid7,

I can't see how the fuel pump relay is implicated, because the pump does run when I jumper the FP and GND pins on the diagnostic connector (I assume the relay is required when the pump is forced-on via this method?)

Can you please tell me which relay in the fusebox controls the fuel pump?

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This thread might be useful: http://www.mazda626.net/index.php?showtopi...fuel+pump+relay . I can't tell if the fuel pump relay is the EGI main relay, or the "circuit" relay beside iot. It might vary with model year. Also note the link to the fuel pump circuit diagram in that thread.

But first, I would check to see if you are getting fuel (with and without the F/P and GND jumpered). Loosen the banjo bolt a little (the one where the main fuel feed connects to the fuel injector rails) and see if there's any petrol there.

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A cheap place to start would be a new fuel pump relay.

I found the fuel pump relay and tested it > it's fine.

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You mentioned you're in Australia...well, the Oz models don't have the diagnostic code readout mec'd to the check engine light. You need to plug an LED and/or lightbulb into the diagnostic connector to retrieve your codes.

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This thread might be useful: http://www.mazda626.net/index.php?showtopi...fuel+pump+relay . I can't tell if the fuel pump relay is the EGI main relay, or the "circuit" relay beside iot. It might vary with model year. Also note the link to the fuel pump circuit diagram in that thread.

Thanks NickR, but that info related to a 98 model; mine is a 94.

I bought a Haynes workshop manual and identified the fuel pump relay by the colour of the wires. On 93-95 V6s, the fuel pump relay is called the "Circuit" relay (not the "EGI" relay).

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You mentioned you're in Australia...well, the Oz models don't have the diagnostic code readout mec'd to the check engine light. You need to plug an LED and/or lightbulb into the diagnostic connector to retrieve your codes.

Ah-hah!

Thanks Snailman, you've cleared-up something that's been frustrating me for weeks.

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But first, I would check to see if you are getting fuel (with and without the F/P and GND jumpered). Loosen the banjo bolt a little (the one where the main fuel feed connects to the fuel injector rails) and see if there's any petrol there.

I loosened the banjo bolt and cranked the engine - there is fuel there (although I guess now I have to check if the fuel pressure is too high or too low).

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Now this is weird: when I first insert the key and turn it to ON, I do not hear the fuel pump operate for a few seconds like it's supposed to. I then attempt to start the engine - it cranks but does not start. But I've just noticed that immediately after this cranking stops, the fuel pump is heard to operate for about one second.

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Now this is weird: when I first insert the key and turn it to ON, I do not hear the fuel pump operate for a few seconds like it's supposed to. I then attempt to start the engine - it cranks but does not start. But I've just noticed that immediately after this cranking stops, the fuel pump is heard to operate for about one second.

It's possible your ignition switch is shot, only running the fuel pump in the "START" position.

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Now this is weird: when I first insert the key and turn it to ON, I do not hear the fuel pump operate for a few seconds like it's supposed to. I then attempt to start the engine - it cranks but does not start. But I've just noticed that immediately after this cranking stops, the fuel pump is heard to operate for about one second.

It's possible your ignition switch is shot, only running the fuel pump in the "START" position.

No, because the fuel pump is heard to operate for one second when the key is returned to the "ON" position from the "START" position (i.e. after cranking).

Yet the fuel pump is not heard to ooerate when the key is first turned to "ON" prior to attempting to crank the engine.

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Now this is weird: when I first insert the key and turn it to ON, I do not hear the fuel pump operate for a few seconds like it's supposed to. I then attempt to start the engine - it cranks but does not start. But I've just noticed that immediately after this cranking stops, the fuel pump is heard to operate for about one second.

It's possible your ignition switch is shot, only running the fuel pump in the "START" position.

No, because the fuel pump is heard to operate for one second when the key is returned to the "ON" position from the "START" position (i.e. after cranking).

Yet the fuel pump is not heard to ooerate when the key is first turned to "ON" prior to attempting to crank the engine.

Relays take finite time to disengage. It's just a thought anyway.

It's also possible your fuel pressure regulator is jammed open.

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It's also possible your fuel pressure regulator is jammed open.

I disconnected the fuel line that runs from the fuel pressure regulator back to the fuel tank. In its place I temporarily connected a short hose that was blocked at one end - this meant the fuel pressure regulator now couldn't release pressure from the fuel rail back to the fuel tank. I cranked the engine but it still wouldn't start.

So this suggests that the fuel pressure regulator is not stuck open.

I know that my fuel pump is pumping fuel to the fuel rail but maybe it's not supplying enough fuel pressure > fuel pressure test is next....

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It's also possible your fuel pressure regulator is jammed open.

I disconnected the fuel line that runs from the fuel pressure regulator back to the fuel tank. In its place I temporarily connected a short hose that was blocked at one end - this meant the fuel pressure regulator now couldn't release pressure from the fuel rail back to the fuel tank. I cranked the engine but it still wouldn't start.

So this suggests that the fuel pressure regulator is not stuck open.

I know that my fuel pump is pumping fuel to the fuel rail but maybe it's not supplying enough fuel pressure > fuel pressure test is next....

Do a compression test and post your results.

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You sure the ECU is getting power?

No, I'm not sure if ECU is receiving power - how can I test for that?

When I put the engine in "diagnostic mode" and then place a test light probe on the STO pin (it's an Australian 626, so no CEL on dash), I don't see any illumination at all of the test light (i.e. no codes). Does that suggest a ECU power problem?

I am seeing all the spark plugs firing and the voltage signals are arriving at the fuel injectors - can those things occur if there's no power to the ECU?

Thanks

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You sure the ECU is getting power?

No, I'm not sure if ECU is receiving power - how can I test for that?

When I put the engine in "diagnostic mode" and then place a test light probe on the STO pin (it's an Australian 626, so no CEL on dash), I don't see any illumination at all of the test light (i.e. no codes). Does that suggest a ECU power problem?

I am seeing all the spark plugs firing and the voltage signals are arriving at the fuel injectors - can those things occur if there's no power to the ECU?

Thanks

Since you have spark and you did try starting fluid, then better check compression. Could be that the timing belt slipped and there is not enough compression to start the engine.

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Since you have spark and you did try starting fluid, then better check compression. Could be that the timing belt slipped and there is not enough compression to start the engine.

OK, I'll buy a compression tester.

But I wish I could resolve the problem of no CEL codes displaying at the diagnostic connector (does that indicate an issue with the ECU?)

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A slipped timing belt could cause it not to start, but it would not explain a failure to display CEL codes. However, I (like most on this board) am not familiar with the difficulties of checking codes on an Australian model.

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Just because you had spark with the plug removed doesn't mean that the spark is strong enough to ignite the fuel mix under compression. This same thing baffled me on my '93 626 v6. I learned that igniter and coil failure are common on '93 and '94 models, primarily because of them being inside the distributor.

What the presence of a spark tells is that the igniter is working to send a signal to the coil. I changed the coil only in mine and the car fired right up. I've since performed the mod to a coil and igniter outside of the distributor.

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Just because you had spark with the plug removed doesn't mean that the spark is strong enough to ignite the fuel mix under compression. This same thing baffled me on my '93 626 v6. I learned that igniter and coil failure are common on '93 and '94 models, primarily because of them being inside the distributor.

What the presence of a spark tells is that the igniter is working to send a signal to the coil. I changed the coil only in mine and the car fired right up. I've since performed the mod to a coil and igniter outside of the distributor.

Hmmm...that's interesting.

I tested my plugs by removing them, then reconnecting the cables, earthing them to the engine and then cranking the engine. Although I saw them all firing, they produced a yellow spark rather than a blue spark.

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What the presence of a spark tells is that the igniter is working to send a signal to the coil. I changed the coil only in mine and the car fired right up. I've since performed the mod to a coil and igniter outside of the distributor.

Is there any way to perform a test of the coil? (I don't want to spend money on a replacement if it's unnecessary).

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I don't know how to test the coil, but here's one way to test JimII's interesting theory: buy a spark tester (it looks a bit like a fuse, that you connect in-line to the spark plug lead), and test for spark without removing the spark plug. I think spark testers are cheap.

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Just because you had spark with the plug removed doesn't mean that the spark is strong enough to ignite the fuel mix under compression. This same thing baffled me on my '93 626 v6. I learned that igniter and coil failure are common on '93 and '94 models, primarily because of them being inside the distributor.

What the presence of a spark tells is that the igniter is working to send a signal to the coil. I changed the coil only in mine and the car fired right up. I've since performed the mod to a coil and igniter outside of the distributor.

Hmmm...that's interesting.

I tested my plugs by removing them, then reconnecting the cables, earthing them to the engine and then cranking the engine. Although I saw them all firing, they produced a yellow spark rather than a blue spark.

Yellow spark means your ignitor is fried.

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