Good fuel pressure, good spark, won't start...

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Mar 24, 2015 | 11:13 AM

Ajvaz

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Good fuel pressure, good spark, won't start...

It's a 2000 mercury mountaineer with a 5.0. I recently changed it's fuel pump and it works fine. But there is something wrong with its relay switch or something! I changed it, it started, next day it wouldn't! Could it be a bad RAP module? If so, could it not start but still work the locks and stuff?

Mar 25, 2015 | 12:03 AM

Mikeman

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From: PNW

A little more information and someone here can help. Won't start = the engine won't turn over? Or won't start = engine turns over but won't light off?

Mar 26, 2015 | 10:35 AM

Ajvaz

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Engine turns over but won't light off. It lights off with starter fluid so it's clearly a gas problem. I checked an ingecter and it gave off 13 ohms of resistance and checked the voltage on the cable and it gave off 12 volts. I don't know if that means that the injecter is open or closed. I sent the computer for a check up and everything turned out ok. It really has me stumped...

Mar 27, 2015 | 10:03 PM

impish

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Starts on fluid eliminates quite a few possibilities. I would check fuel pressure at the Shrader valve. EFI fuel pressure gauges are available at all parts stores, not all that costly, if you consider the price of someone else looking into the trouble. impish

Mar 28, 2015 | 02:01 PM

aquanaut20

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From: BC Canada

Have you checked injector pulse, NOID or Lab Scope...

Yes use a fuel pressure set and check pump, FPR, Inj bleed, Inj pulsing

... Philip

Mar 28, 2015 | 09:48 PM

shorod

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Joined: Jun 2009

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From: Cedar Rapids, IA

A noid light or backprobing with with an oscilloscope as mentioned above will help, especially if you measure good fuel pressure prior to that. The fuel injectors are supplied with battery voltage and have a switched ground connection via the ECM. So measuring 12V with a high impedance multimeter indicates the fuel is likely good but does not indicate that either the circuit can handle the load of a fuel injector or that the injector is being triggered by the ECM.

If you find that a noid light does not flash yet you have good 12V to the injectors my first suspect would be the crankshaft position (CKP) sensor.

-Rod