Jeep Liberty #5 misfire valbe job tune up

Tiny
MRSTAYLOR
  • MEMBER
  • 2004 JEEP LIBERTY
  • 0.6L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 111,800 MILES
I got a valve cover job done with a tune up because the check engine light said misfire cylinder #5. The car use to shake. Now that the mechanic did the valve job and the tune up. The jeep is not starting up. The jeep sounds like it wants to start but its not. What the problem?
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Thursday, March 5th, 2015 AT 9:06 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
There's dozens of things that can cause a failure to start but given the recent service, (thank you for including that), and your description of the symptoms, the first suspect is a huge one and a very common one.

When major work like this is done it is almost certain the battery had to be disconnected. That causes the Engine Computer to lose it mind. A number of things are going to be relearned as you drive without you even noticing, but there is one exception. That is "minimum throttle". Your vehicle might be too new for this to apply, but when minimum throttle has not been learned, you will not get the nice "idle flare-up" to 1500 rpm when you start the engine, it will tend to stall when you approach a stop sign, and the engine may not start unless you hold the accelerator pedal down 1/4".

If holding the accelerator pedal down just a little gets the engine started, the fix is real involved! Drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals. That will meet all the conditions to trigger the relearn. From then on the computer will know when it has to be in control of idle speed.
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Friday, March 6th, 2015 AT 12:27 AM
Tiny
MRSTAYLOR
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How do you Test a Crankshaft and Camshaft Sensor? Its a 2004 Jeep Liberty
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Friday, March 6th, 2015 AT 1:33 AM
Tiny
CARADIODOC
  • EXPERT
The only practical way is with a scanner. I use Chrysler's DRB3 scanner. During cranking it will list each sensor as "no" or "present". The only other partial test you can do is back-probe through the rubber seals where the wires go into the connectors and find if there's 5.0 volts on one wire for each sensor. If it's missing at both of them, one sensor could be shorted. To identify which one, you have to unplug one, then turn the ignition switch off and back on to reset that power supply. When there's a shorted sensor, which is not common, the Engine Computer will shut the 5.0 volt supply down to protect it. You have to cycle the ignition switch off and back on to reset it.

Have you checked fuel pressure and spark? You won't have spark if one of these sensors fails.
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Friday, March 6th, 2015 AT 1:51 AM
Tiny
MRSTAYLOR
  • MEMBER
It got fuel pressure but No Spark
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+1
Friday, March 6th, 2015 AT 2:07 AM
Tiny
CARADIODOC
  • EXPERT
Fuel pressure is misleading. The fuel pump will run for one second after turning on the ignition switch to insure pressure is up for starting in case it bled down overnight. The pump will not turn on again until the Engine Computer receives pulses from those two sensors indicating the engine is rotating, (cranking or running). When one of those signals is missing, there won't be spark AND the fuel pump won't resume running during cranking. In effect, you don't really have fuel pressure. It's misleading because what you have is just residual pressure from that initial one-second burst at key-on.

When spark is missing you won't have injector pulses either so that residual fuel pressure won't bleed down. That adds to the confusion telling you there is fuel pressure.

All of these things are turned on through the automatic shutdown (ASD) relay which is turned on by the computer. You can watch if that is occurring by monitoring the voltage on the wire that feeds all those circuits. On most models that is a dark green / orange wire at the coil pack and every injector. If yours is different, look at every injector to see which wire color is the same at each one. It's best to use a test light to get a quick visual indication if that circuit is working. Most digital voltmeters don't respond fast enough to catch it. You'll see the test light turn on for one second when you turn on the ignition switch, then it will go off. It should turn on again during cranking. If it doesn't, suspect one of those sensors first.
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Friday, March 6th, 2015 AT 2:26 AM

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