Ford taurus no start

1999 ford taurus will not start. it has a new battery and spark plugs, new fuel filter and fuel pressure regulator, new coil pack. it has had checked and verified good the alternator, cam position sensor and throttle position sensor. it is getting fuel and it is sparking but it will turn over and run, only an occasional backfire. any help please would be appreciated.

Your post is confusing, how can it turn over and run, without starting?

If you have tested the actual fuel pressure and it is ok, and you have spark, providing the gas is good, think I’d be looking at the timing belt or chain whatever it uses.

thanks I will suggest this to the mechanic. the cover was off the timing chain when it was replaced, could this have anything to do with it?

HOW does it backfire? Out the exhaust pipe, or back through the intake? If it is backfiring through the intake, the ignition timing, or an intake valve hanging open could cause that.
Timing can be off from several causes. The timing belt could have jumped a tooth, or two. The signal from the cam or crankshaft position sensor could be erratic. If it has spark plug wires, they could be cross-firing.
I’m not sure you have the right mechanic. Does he just change parts, or does he troubleshoot?

It sounds to me like you need a new mechanic - he’s just throwing parts at it without diagnosing the problem properly.

As for the timing issue, this car uses a chain - and if it is equipped with the OHV Vulcan that most Tauruses had, the chain is extremely short, has no tensioners (or need for them) and is extraordinarily unlikely to skip a tooth. It also should never have needed replacement, at least not this early. They should last at least 200,000 miles… likely more.

it is backfiring thru the intake. I am not sure how much he is troubleshooting now to tell you the truth and how much of it is just swapping parts till it works. he did check the cam position sensor but not the crankshaft position sensor, he has said he has cecked the plug wires and I saw him change out the plugs and put the wires back on and he did them one at a time. the no start condition started before he did all the gasket work and it did start up right after that. but running rough.