89 4.5 deville no start problem

All cars are sensitive to cold .it being a new car you can turn on the ignition for say 30sec to a min before cranking to allow the oxygen sensor heater to warm so it can read properly and will help in these conditions .also a new set of spark plugs can help too.

fuel pump

Try what Wyatt says ..put key in ignition . turn to on position for about 15 min. Turn ignition to off (not lock). then turn on and start. This will override the theft ignition system , and maybe allow the system to reset itself. let the car run for about 10 min

Think about what you just said. Only does this in times of higher temps out BUT never in winters cold. Doesn't that seem strange to you. Well I guess it does, huh. Anyway, know these systems helps. When engine is started, the temp sensor tells the computer it needs to place the engine to cold start mode. It does this and extra fuel is put into the cylinders to keep it running like a choke on the carbureted engines. But those you can turn the choke off or it does this automatically from the warmer engine. If in fact the temp sensor is not telling the computer it's warm enough to be taken out of cold start mode, it keeps dumping excessive fuel into the cylinders an flooding the engine causing it to surge and then die, because it's flooded. Therefore, the temperature sensor is faulty and needs replaced. Do that and drive on.

it could be your alternator or you cynloid went bad i would check them first

the problem must be with the batteries. check the voltage levels of the battery using a voltmeter. if it goes lower that 10v and fast dying, then replace them. and also check the alternator charging the battery for any charging problem.

I would look to see if you got a broken ground wire!!! witch are a big thing on todays computered cars. I know you have dumped a lot of money in your lawn ornament but one unhooked or dirty ground wire not making a connection can reak havick with everything, I would chk.for ground issues like around the fuel tank and where they hook to engine to body to frame or k-member.

when you overheat an engine. certain parts expand more than usual. like pistons, crankshaft and camshaft bearings. im afraid its time to overhaul the engine. inspect for cracks etc...
check the oil on the dipstick...if it looks like a milkshake...you cracked something...head or block......sorry dude for the bad news. good luck

I had a similar problem and it turned out to be the rubber fuel lines being old and cracked. The hoses would warm up and fuel would squirt out of the cracks. I had to replace three fuel line hoses and it has been running great ever since. Good luck.

the first one is your security light on?