Cadillac Repair/1997 seville
Misses only after it gets warm but there is no overheating. Cleaned mass flow throttle body had rails worked on and replaced both coils that show indifference still misses and surges and dies at intersections when it gets real warm in summer months in phoenix
Did you ever get problem corrected?
Your parameters as to getting real warm in Phoenix make a diagnoses over the Internet make it virtually impossible to give you a valid answer.
I understand the warmth as you are espousing, living n Texas with temperatures in triple digits. In order to diagnose though, the problem has to be able to be duplicated, with electronic test equipment attached such as the GM tech II scanner, which many service centers carry, so you are not stuck going to the "parts replacement kings"-the dealers.
Without doing such, you will end up with the same results as you have tried for a fix already with no success.
This does not sound like a fuel related issue and more an electronic issue.
Years ago, when we had heat related issues such as this on various makes and models, we would through ice cold water on the engine control module (common on Fords) and instantly, the engine would run fine.
This could be a BCM failure under the dash in your vehicle. You are dealing with an 18 year old vehicle that has been subject to wide temperature variations, dust and ambient elements. When dealing with electronics, you are dealing with plastic circuit boards that crack and decompose. Heat causes expansion, which could separate a soldered connection temporarily. As temperatures cool, the board may go back together.
I have run across many of these situations over the years. The problem is finding the exact cause and without diagnostic equipment connected at that time, you are never going to find it!
Even if you have the same exact symptoms in 2 vehicles under the same conditions, the correction could be totally different.
I would say, if you know you can duplicate the problem on a specific day, have an appointment made with a tech that has a Tech II scanner. Bring the vehicle in for diagnostics when the problem is present and have the diagnostic scanner hooked up. The potential for finding exactly what is giving you trouble rises significantly. This way, you are not changing all sorts of components on a guess, in which the failure can be located under the hood or under the dash, in a variety of sensors and computers.
This exact problem as it pertains to your specific vehicle, may not even be addressed in a factory service manual. There are so many factors that can be applied to an 18 year old vehicle. Was it ever in a collision? This may have broken something or jarred a connection loose from the impact.
What do you know about the car's history? You are searching for a cause to a problem now, but did this problem exist last summer? What brought this problem on? Did it just appear, or indications of it last year?
When is the last time the plugs or wires were changed?
I had a vehicle that ran perfect and all of a sudden on hot summer days would develop a miss and would run fine when temperatures cooled off. I pulled a spark plug and found the electrode was virtually non existent. I pulled another. The same! Best as I could tell, these were the original spark plugs from 190,000 miles before! Replaced the plugs and problem was gone!
This is why you need to duplicate this problem and put the vehicle on a scanner. If nothing shows up as problematic, you have ruled out the computers and sensors and go to something else.
I also find it interesting that you state the engine was not overheating. Overheating in the aluminum engine rarely causes a miss or to stall (unless it locks up and will not start again). These engines just melt at more than 225 degrees f causing the first thing to go are the head gaskets and further consequential damage seconds later. These aluminum engines simply cannot be overheated, because if they are, you might as well consider junking the vehicle, because the used engines in the junk yards are junk as well.
I hope you try my suggestions because it will become very costly and frustrating using guesswork for diagnostics.
Let me know when you find out the problem.