You have to test the voltage with it turning over? I didn't know that. But since that is connected directly to a separate battery it would have to have nothing but 12 v if that battery is good. But I could still test the wires from the car and not have to drop the tank for the wires are out sitting in the back seat area.

Could this be an injector problem or not? It was likely caused in the first place by long periods of sitting as it is only used once a year for a short time. Parked it ran good, started up 10 months later started having this problem.

I didn't read through all these replies. You still have a fuel pressure issue, Correct? You have a pump with 12V and yet the pressure drops, correct?

You ran 12v from a spare (good) battery, but did you also run a good clean ground to the pump from that same battery? The injectors would have nothing to do with a low voltage problem at the pump.

Did I run a separate ground from the battery negative terminal? I do believe I did try running a separate wire from the ground wire to the door of the car and it did nothing to improve the fuel pressure from dropping. So I removed that extra wire. But I could be wrong. I could try it again when I get back in a few weeks.

But the injectors could cause the pressure psi to drop over a short time yes? That is what I have seen in multiple sites stating as one possible problem.

I would give 10 to 1 odds your wiring is problematic.

If you lose pressure through the injectors leaking it causes hard starts and you can usually smell fuel when it turns over or starts. They will not be so bad that it will cause fuel pressure problems on a running engine. They can't get that bad.

I don't intend to pile on, however:

You are here for advice. We tend to be okay at this stuff, even from the far side of the Internet without ever seeing your car in person. Do any of us need to fully explain every possible way it can be less than 12V in order to get you to check? If so, I expect you'll be disappointed.

We are now at 76 posts for a simple voltage drop in a known span of circuits. This type of thing is usually a 15-post kind of thing.

Next steps:

1. 12V on one end. Measure with a good volt meter to be sure.
2. Check at every possible point along the way with a meter.
3. Note each test point, and the readings, all the way to the pump.
4. Where does voltage drop? Is it little by little along the way? Is it 12V, 12V, 11.9V, 11.8V, 9V, 8.8V, 8.7V, etc.? Test from each end (11.8V and 9V) toward the center (problem). What is between the 11.8V and the 9V?
5. Fix.

It would be great if we could just tell you, and we'd love few things more. Sometimes we get lucky like that. In your case, the troubleshooting required that things get tested that we can't help you with because we are not there. If we go around in circles justifying why we ask you to do something that is a simple and reasonable part of troubleshooting the issue, we'll likely see 176 posts before this gets sorted out.