We have an 86 with the 5.0 tbi I believe. It starts up great and idles good for 10 seconds or so. But then the tachometer cuts out and it dies. With the ignition still in the “run” position and try to crank it over, it will not start and there is no response from tachometer while cranking. But if I turn the key to the off position and then back to crank, there is tachometer response and it starts right up. But then after roughly 10 seconds the tachometer cuts out and then the engine dies again.

 

Disconnect the tach at the hei drivers side. See if that makes it run better. A shorted out tach circuit can cause running issues. Just curious has fuel pressure been checked the tach issue could be unrelated.

 

I haven’t checked fuel pressure. It starts right up and I can press the throttle it’s very responsive and doesn’t shorten the amount of time that it will stay running. I will check tomorrow with someone and see if I can see the injectors still spraying fuel when it cuts out. And I also can check fuel pressure.
Maybe I’m not on a good path with the tachometer, it’s just that the rpm’s stop reading on the tachometer about a second before it starts to die.