My buick verano has had a engine "rebuild" . Now, when I started this morning (first morning after rebuild) the engine stared then quits after about 20 seconds. It did that for a few times and I kept RPM'* up to 1500. Check engine light went on for low fuel rail pressure and says on dash "reduced power!". After a while the engine ran fine. I cleared the code and no code now. The mechanic tells me that the fuel rail pressure sensor needs replacing. This was not problem until the engine was redone..could this happen as he has not done anything to the sensor and he says that it does't have anything to the work he has done(he did put in new cylinder head). He also said that another car he overhauled with similar engine did the same. Yesterday I drove 100km with no code and this morning at startup the code returned. Also the coolant level went down until the reservoir emptied and I have driven the car only 100km (mostly from mechanic to home) ..he said that it must have been air bubbles and I should refill so that'* what I have done. Any ideas why my car is behaving this way? Is is just a coincidance sensor problem happened at this point or is there something else going on..Does the lower coolant level have anything to do with this problem/concern ?

And can this leave me stranded on the road? Someone told me you just have to turn off and restart a few times.

Coincidence on the failure. You can live with it but it'* not worth it.

Could "stale" gas cause problems in the sensor reading . My car was not used since last Christmas and gas was sitting in the tank for 10 months. I just added 10 L of Chevron gas 89 Octane to boost up the fuel. 10 L was all the space I had in the tank.

Darn, The car doesn't want to start and my son has job interview out of town early tomorrow and needs a car. The car just makes a click sound but doesn't start.

and no check engine light so far.

Need to know what the fuel pressure is while this is happening.

Your mechanic should have purged all of the air pockets out of it as part of installing it. I'm not sure how much you were referring to when you said the coolant reservoir got emptied, but that seems like a lot.

Fuel wouldn't be stale enough to cause this issue within a year, especially since it was over 83% full during that period. Since you added fresh fuel until full and there are no changes reported, I do not believe fuel is the problem.

I'm curious: With the stalling issue and possible air-pocket issue, did the mechanic not test drive it after putting it back together?

Seems likely that it would. It'* not reliable until it is reliable.

Isn't this where we started on this car?

Coolant issue, stalling issue, non-start on newish battery/starter/fuse. I have to wonder what your mechanic tested before handing it back to you. Seems incomplete to me. After this much time and work, they should have taken it through a couple of warm-up cycles and driven it around for a while, like 50 miles or something. How much did they test? Are they willing to look at the current issues?

I'm not sure what happened in this case, but it seems like the mechanic tightened the last bolt, slammed the hood, and let you start it and do the test driving. With the same symptom as before, I'd start troubleshooting the starting issue with Post #2 of this thread.

coolant was full to start. I drove 100km and coolant in reservoir was almost empty (reservoir seems to be about 1 L) ,I refilled it to full and now it is almost finished again. I think there is some air pressure in the reservoir when I open the lid.