I have an 85 lb9 tpi with an 86 computer and harness running the 89 prom. Just installed bosch 3 injectors and a new fuel pressure regulator from Southbay, new fuel filter and since I had the plenum off I changed the mat sensor since it was giving me some crazy readings.
The change in the way the engine runs is amazing. It idles rock solid and smooth. The only problem that I have is that it is a little harder starting then it was. It has to turn over several times before it starts and when cold it stumbles and seems like it wants to stall. If you give it the gas when cold it bogs. It never did this before. Also, the fuel pressure drops when you turn it off pretty quickly from 43.5 to 30 and then slows down. I have pinched off the return line and the pressure spiked to 65. Should I be concerned about the dropoff in pressure even though it has never run this well before??

 

check the pulsator on the in-tank sending unit attaching the fuel pump to the hardline, they are notorious for leaking, remove it and replace with a rubber hose

 

But why would that all of a sudden go bad right after he changes injectors?

Stepside, I have the same issue going on a few posts down from this one. Same year car same engine and same Bosch 3 injectors. I'm ready to swap my old injectors back in. Long cranking gets embarrassing. Ill Be following this thread too.

 

I have an external fuel pump..My TPI is in a truck.

I'm thinking it has to be the regulator, it's an adjustible from Southbay with a new diaphram as well.