Pontiac Repair: Problem to start when engine is warm, fuel pressure regulator, rich mixture

Question
QUESTION: Hi, my montana 2004 runs perfect, it starts perfect on cold engine but if it runs and engine get warm and I stop the engine, it won't start until it gets cold again.  When I try to start it an the engine is warm, the engine choke.

I suspect there in a problem with the choke. Is there a temperature sensor for the choke? I suppose there is one and it is faulty so that the choke close at each start, cold or warm causing the problem.

Does someone knows how to find the source of my problem.

Many Thanks, Eric

ANSWER: Hi Eric:

what happens when you tryto start it does it chuck and buck? start and stall start and billow black smoke? any service engine soon lamp on? This van has no choke fuel injection doesn't require a choke. if the service engine soon lamp has been on have the van scanned for codes at one of the big box auto parts stores they do it for free and see what if any codes are stored that could be a starting point.


---------- FOLLOW-UP ----------

QUESTION: Hi, thank you so much for your reply,

As I said it start perfectly when engine is cold or just a little warm (after 10 minutes drive, stop and restart). However after 30 minutes rive, when not only the antifreeze but the engine is completly warm (normal temperature according to the gauge) then if I stop and restart the engine after 5 minutes it will start, stay at low rev (500-800 rev)  choke and buck without going over 1000 rpm and the stall (like a too rich mixture of gaz). after 30-40 minutes it will start again no problem. No service engine lamp lights up (and I am sure it is functionnal) and I did not see black smoke.

Thanks in advance, Eric

Answer
This is odd. Have you noticed a drop in fuel economy since this started? It could be a few things it could be fuel injectors leaking down when the engine is hot and it has a apor lock in the fuel rail. Of a fuel pressure regulator that is leaking and the same issue happens. 1 way to check this is with a fuel gauge. put it on the fuel rail and monitor it after the engine is hot and sitting. The fuel system should hold pressure and not drop. warm the engine up and shut it off wait 1 minute then just turn the key to run that will prime the fuel system and then mnitior the pressure it it rapidly drops off in say 10 -15 minutes you are have a vapor lock issue going on.