I have a 89 IROC with the 350 tpi. It has the Holley stealth ram intake larger fuel injectors larger fuel rail hooker competition headers. 370 gears in the rearmed. 3” exhaust with Flowmaster 80 series American thunder muffler. 700r4. 3 core aluminum race radiator with dual electric fans not toe factory ones. I’ve owned the car about 3 years now and here’s what has went on
when I first got the car it was cold out and it ran fine. Then comes summer and when it got over 80 degrees outside it would fall on its face like it’s not getting fuel. This is after driving it all day many miles with no problem. So first I notice excessive pressure from fuel tank when taking the cap off. After investigating I notice the vapor line to the charcoal canister has been unhooked and has a bolt stuck in it. So I remove canister take bolt out of vapor line add a small filter. Now it will run a little longer. Does it again. So I change fuel pressure regulator, and coil. Mind you it also has an MSD ignition. It runs a little lol longer now but still does it after a while of driving in outside temps over 80. During all of this the engine temp doesn’t go up. So drive it one day about 30 miles with outside temps hovering close to 80. It runs like a brand new one. However after spending probably a couple hours at my destination I head back the 30 miles halfway back I notice the engine temp starts to climb but nowhere near critical then it does it again. Falls flat like it’s not getting fuel. So as in sitting on the side of the road trying to get it to start. I notice that when o turn the key on the fans aren’t coming on which they should because car is up to temp maybe a little high and the fuel pump isn’t kicking. Pop the hood and the relays for each are so hot you can’t touch them. So now I’m thinking under hood temps are really high because of the unwrapped headers. Causing relays to cut out. Maybe first the fan relay goes which causes temps to rise even more then fuel pump relay goes. So last couple weeks I pulled header wrapped then. Wrapped the y pipe halfway back down the car. Also I took some auto floor insulation and wrapped both of those relays. Didn’t fix it. Still did it yesterday when outside temps got over 80. But fan relay didn’t kick. Fans were still working. Please somebody tell me you have the answer to this problem. Next hint I’m gonna do is pull the fuel tank and check to see if maybe it has rust in it and it’s pulling it around the filter and chocking the pump. And replace fuel pump. Please help!!!

Check fuel pressure cold, and when it's acting up. Get datalog. Maybe replace the relays but I wouldn't start there. Could be the MSD ignition acting a fool.

I agree with Komet on what he said. Also, when the car is acting up, place a timing light on a spark plug wire. You should see consistent flashes. The flashes will change, faster and slower, as the rpm drops and goes up, but If the timing light is flashing intermittently then there could be an issue with the ignition system. I no longer use MSD stuff on my engine. I had issues with their cap and rotor. For the ignition system on my street driven car, I use GM parts. Some from their performance parts catalog.

You described multiple individual potential problems. Fix the known issues first. You described an intermittent overheating problem so I would focus on that first, especially since your primary issue (engine stopping) seems heat related.

BTW, this is the reason I am now a huge advocate of leaving cars in generally stock condition. Someone has clearly created a high maintenance problem machine with all the aftermarket crap on it. No going back for you now, but for all you rednecks out there wanting to "mod" your car this is its future.