engine stall

[1984transam]

Hi folks, i'm new to this site, can someone possibly shed some light on my problem. my car is a 5.0 v8 trans am and the engine has been rebuilt, the car never starts on the first turn of the key from cold, when it is running it runs fine for about 25 minutes then the ideling goes irratic and then dies on me .............any thoughts

[PontiacRegistry.com]

We gotta get a little more info here.
First, how does it finally start? Lots of cranking? Lots of gas pumping?
Second, when it dies, is it after just sitting and idling for 25 minutes?
Third, have you run it out on the road, and if so, does it keep running?
Fourth, does it restart, and if so when? After sitting? Immediately?
Baring some small elf whose feet get hot and pulls out your coil wire, this has got to be fuel related, or at least intake, carb, vacuum leak related. Don't look for an "exotic" problem, it's usually just the basics.
Send some more information so we can chew on it a bit

[1984transam]

hi again,
well, it takes 4 or 5 turns of the key to start, and fuel pumping, i dont take on the road cus im still rebuilding the car, so it hasnt been on a descent run since engine was reconditioned and reinstalled over 6 months ago, so the car is always idling, it does sound more like fuel starvation,but why does it take 25 mins to effect it, which would lean torwards the vacume leak idea, up until that point it runs just like a v8 should. ...... when it stops running after the 25 mins it will NOT start again until completly cold...

[Larry]

OK, if it restarts again and sounds like it should, you definately know that whatever condition was created was only a temporary one. So we know it is a simple problem.... although elusive, nonetheless. Let's start with the simplist.
Once upon a time I had a Ford...... I was young and foolish. It started starving out and dying. I could travel pretty much normal distances (work and such), but it was spitting and sputtering if out for longer periods. One time as it was about to stall out again, I decided to check the gas with the old sniffer to see if it smelled funny (old myth of "Ya got some bad gas, son!"). Well, I couldn't even get the cap to turn. It took a huge channel lock to turn ther cap..... whoosh! In shot the air and the engine perked right up. Bottom line, the gas tank vent had clogged up and the fuel pump was sucking a vacuum into the tank until it couldn't any more and then starving out. What I thought was a "cool down" period until restart was actually a "leak down" period.
Let's check that and then we'll move on if all checks out OK. Either run it with the gas cap on until it dies and then check the cap. Or, remove the cap and run it to see if it goes longer than 25 minutes. We can always work our way to the more complicated.

[1984transam]

taking the fuel cap was one of my friends idea, tried that last week and it is the only thing i have tried, good idea though, start with the most simplist thing, did exactly the same

[Larry]

Drat!
OK, let's check another thing that will tell us something. You say it takes a lot of pumping and cranking the next time you go to start. So, the next time you run it and it quits. Check that the carb is dry of gas.
Because it sounds like it might just be "running out of fuel" the carb should be dry if that is actually what is happening. Let it cool down a bit and carefull look down the primaries while pumping the accellerator pump to see if it squirts fuel. If it does not, that is because there is no fuel to pump. That would put us one step closer to the problem, while probably also eliminating some other possibilities.
Check the attached cartoon-- one of my favorites. We ain't that bad yet!

[1984transam]

I like the cartoon, lets hope that it doesn't happen!
i'll try what you have suggested, i'll let you know in a couple of days, ps thanks for the help 'n advice

[1984transam]

Hi me again, had the car running today, and exactly the same, but took some notes....
Firstly, againa died after twenty to twenty five minites
Secondly it over heated,water boiled and spilled out of
header tank, fan was on constantly,
thirdly i noticed oil pressure was dropping until it reached
just under forty and started idling eraticallly until it
eventually died,
as for starting, i removed air filter and there was fuel squirting into the carb, so starting issues is not down to fuel starvation,

i have made up my mind now to put interior back in get wiring looked at and get my american car garage to sort it out, cus' i ain't got a clue.

[1984transam]

No i didn.t check carb after it died , but it wouldn't start again, and had to wait for the water to stop boiling out of the header tank

[Larry]

Got a bit of a chicken or egg thing going on here. Although the overheating would really have to be severe to be causing the dying problem (though not impossible).
You have to get that solved, so why not yank out the thermostat if you have one in. I assume it didn't overheat before the engine rebuild (so let's hope the radiator is doing its thing properly for now). Also, just keep the radiator cap to the "first notch" for now just in case you need to burp some air out of the system. Turn your heater on to circulate water through the entire system.
This is kind of like trying to explain to someone how to tie their shoes over the phone, but we'll eventually get it.
If we can stop the overheating, we can concentrate on the stalling problem again. Let's hope the overheating is one of these simple things.