Have an 88 K5 Blazer, 5.3 with EFI from 2008 Tahoe donor. Been running quite well for the last 8 months until last week.

Started truck for work one morning in garage - backed it up in the driveway (small incline) and it died after 3 minutes and would not restart. It died very quietly like turning the key off - no rough dieseling. From there it was a no-start with a crank. No codes as well.

Tried restarting it later that night - still no-start with a crank. Pushed it back into garage, and after a few goes, it started again, ran for maybe 2 minutes and died quietly again. Waited, tried again, and it started and would not die. Still no codes. Did some troubleshooting:

• pump primes and works at keyturn (55psi to rail)
• Fuel Relay Works and Fuse is fine
• Air is not blocked - it has healthy compression at turnover
• ignition under steering column is good - tapped everything while it was running - nothing dies
• Wire to pump and negative are good - wiggle tested everything while it ran

I decided to drive it to work the next day. Got to work fine, but it died on me in rush hour on the way home at 45mph (nice and quietly). It eventually restarted and got me home.

I suppose it could be IAC, but if it was, wouldn't it run rough and throw a code when it killed out?

If it was a bad injector coil, that would throw a code as well, right?

I'm pretty stumped at this point. I haven't yet tested every injector coil with a noid light, but the fact that it's starting and running makes me thing it's probably not that.