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Truck wont start

(1999 Lincoln Navigator)
in Novi, MI on October 15, 2010
The timing chain guides broke in the motor, and I replaced them along with both chains in the front of the motor, afterwards the truck was still running rough, so I tuned it up. I used a " hand held code reader" which indicated to change the O2 sensors 1 upstream and 1 downstream and crank sensor. Changed all sensors. The truck still wont start. Any idea what may be causing this problem?
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Popular Answer
on October 15, 2010
Just to advise -- no code reaader can tell you to change any sensors. Codes are provided to give clues as to what systems are not operating as they should. You then have to diagnose the cause of those codes, and ultimately y our concern.

The oxygen and catalyst monitor sensors will not cause a no-start situation. The crankshaft position sensor could cause an issue, and you could have a wiring issue there too.

The truck did run after your repairs, correct? After the tune up it stopped starting?

Are you certain the engine timing is correct? These are not simple to time when you are replacing the chains. Further issues may have occured in the meantime.
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on October 16, 2010
Yes, the truck did run afterwards, it ran rough but it did start. In the meantime I took the cover back off to make sure the chains are tight and in tact. Even if the timing was off wouldnt the truck still start? Maybe causing a backfire noise or something? when I Replaced the chains and guides, can that throw it out of timing?
on October 16, 2010
You have to follow procedure to set the timing and put the chains in the right positions for the cam phasers to operate properly. You could have it 180 degrees in the wrong direction on one bank, compared to the other. I know highly skilled Ford technicians that have been working on engines for 20 years that consider it difficult to replace chains on a DOHC 5.4L engine. I'm only saying that unless you have replaced many before and are an expert at it, and have the special service tools to do the job, and the shop manual to follow to the letter, you are risking issues. No offense directly to you as I don't know what your skill level or experience is, by any means. You certainly completed a major undertaking by replacing the guides and chains on this engine.

It is definitely possible to cause a no-start by being out of time. Unless you diagnose it with the proper diagnostic equipment, you may never know for sure.
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