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Matt
Matt, Engineer
Category: Jeep
Satisfied Customers: 20595
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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I have a 2002 Jeep liberty. It turns over but won't start. I

Customer Question

I have a 2002 Jeep liberty. It turns over but won't start. I have 50 PSI fuel pressure. I replace the cam and crank sensors. Put in a new programmed PCM. new coil packs and plugs , also new battery and checked all of the fuses
JA: Does the battery look like it's leaking? And does it have a strong smell -- like sulfur?
Customer: what ? no it is a new battery
JA: Are you fixing your Liberty yourself? What have you tried so far?
Customer: I just sent that to you
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 2 months ago.
Category: Jeep
Customer: replied 2 months ago.
no battery is new , not leaking
Customer: replied 2 months ago.
I am fixing my self
Customer: replied 2 months ago.
again I have replaced the cam and crank sensors, new battery, new programmed PCM, new plugs and coil packs , checked all of the fuses.. No spark, fuel pressure 50 PSI
Expert:  Matt replied 2 months ago.

Hello

1st check for spark by removing one of the spark plugs and plug it back into its lead and rest it on the metal of the engine ( DO NOT hold it on place by hand) then have your assistant turn the engine over whilst you watch the plug. It should give a fat blue spark at regular intervals.

If not then check that there's power to the coil pack (at the other end of the plug lead) using a meter. If there’s 12V at the pack but no spark then check the ECU power supply (fuse and relay) and also the connections to the crankshaft speed sensor.

If there is a spark and its still not starting then its likely that the ECU isn't opening the fuel injectors, if the injectors are working you can hear them click - its difficult to hear them with background noise so use a long screwdriver like a stethoscope, placing the handle end in your ear and the metal tip against the body of the injector whilst your assistant turns the engine over.

If you can't hear anything check the ECU power is present by measuring voltage at the fusebox and on its relay socket if OK then check the connections to the crank speed sensor and consider replacing this sensor if the wiring / connections look OK

If the car will start using a squirt of quick/ easi start into the intake then this confirms the problem is lack of fuel

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If you remove the filler cap to the fuel tank and listen inside while your assistant flicks the ignition you should hear it clearly

If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V.

You should be getting around 3 bar measured at the injector rail check to see if the plugs are getting wet indicating fuel is flowing – if not and the injectors are opening then there’s a problem with the pump or the filter or even the pressure regulator

Could also be incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will never add the 'cold start' extra fuel required if the car starts OK when warm then I 'd look into changing the sensor.

Expert:  Matt replied 2 months ago.

Hi

do you still need help?

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