Guys - I'm troubleshooting my new engine and TPI setup, struggling to get it to run. Currently getting idle fluctuations (750-1000) and vacuum between 12-15. Dialing in the spark and fuel maps, which is helping.

One thing I'm trying to resolve is a wildly bouncing fuel pressure gauge at idle. Attached is a short video clip, but the needle bounces back and forth constantly. This is with the vacuum hose disconnected. The first few times the engine was running, fuel pressure was pretty steady. Last couple times, though, it has been erratic.

With key-on, engines off, gauge rock steady at 43psi.

Parts involved:
Fuel Pump - Deaschwerks DW200 (New)
Fuel Filter - AC Delco (forget part number, but new)
AFPR - SouthBay with new diaphragm and gasket
Injectors - Bosch III yellows - 0-280-155-700 (19#, I think) - USED
- Unknown history on the Bosch injectors. They came with my TPI setup from a 1991 Corvette. I tested each one with a multimeter, as well as cleaned with carb cleaner while pulsing the injector.

Putting a vacuum gauge on the AFPR, I'm getting a loss of vacuum, so I'll be removing the plenum to check that out today. Have a new diaphragm on the way, in case it is needed.

My next step would be purchasing a set of injectors from SouthBay, but I'm hoping to do all the diagnosis as possible to make sure that will solve the problem before throwing cash at the issue.

Any help will be much appreciated!

 

Increasing and decreasing vacuum will change the fuel pressure.
take the vacuum line off it and plug/cap the port from the plenum. Does it still fluctuate? My guess is no.
More importantly is finding out if you have vacuum leaks and find out what's ticking so bad. It sounds like you need to adjust the rocker arms. Fixing that may fix everything.

 

Great point on the ticking! I found my #1 intake rocker was loose after making the short video. Working on it this morning, the rocker nut comes loose after that valve has been adjusted. Have some jam nuts to cinch it down, but waiting for engine to cool before removing my custom valve cover. I modified an old center bolt with holed to adjust the valves with engine running. Been handy here!

Also, pressure gauge has been fluctuating with line to AFPR disconnected and capped at the plenum.

 

Fuel pressure may just be a symptom, not a cause.
How bad is the fluctuations when capped? Just like the video? Or less. There could be a bit of movement from the injectors actuating. Hard to rule out a stuck injector till you do some more checks.
Could be a problem at the regulator (example, spring) or the pump but they're pretty independent of the engine running other than the vacuum line.
There's no fuel in the vacuum line, correct?
Make sure your pressure is still good with the engine off.
Did you do a smoke check to look for vacuum leaks?
And fix those rockers.
You'll get it. Keep plugging away.

 

Thanks for the tips! Got the driver side rockers all properly loaded. Discovered the BRAND-NEW rocker nut on the #1 exhaust valve would back itself out, throwing it all into tappity-tap mode. Watched it move while working on the #1 Intake. Had planned to put jam nuts on all the studs, but couldn't see a way to get them down and tightened. Fortunately, I'd kept all the valve train from the engine when I'd bought it for rebuilt. Used one of those factory nuts and it is doing the trick. No more movement and running much quieter.

Will do my best to answer in order:
1) Fluctuations the same with it capped, although when the idle smooths out for a bit, the fluctuations ease.
2) Have regulator diaphragm arriving tomorrow, in case the new one is wrecked. Hopefully not, as those little guys are $75+ now. OUCH!
3) No fuel in vacuum line running up from regulator, so hoping diaphragm is ok. However, there is a small vacuum leak in there somewhere I'll have to find. Possibly the housing not tightened down enough, when I put my MityVac on the FPR line, it will slowly leak down. On another one I have with an OEM FPR, it will hold pressure overnight.
4) Pressure stays pretty solid after engine shut off, or when the fuel pump primes. There ends up being leakdown, which I think is the absence of a check ball in the fuel pump. Fuel pressure drops even with return line clamped, leading me to that theory.
5) I've done two smoke checks over the past week, thinking I had to have a huge vacuum leak to be having such trouble with idle. Found a small wisp of smoke at the cruise control servo, but that was it. Unhooked that line and been using it to operate my vacuum gauge. Otherwise, nothing around the intake, runners, plenum, at all.

Really wondering if my fuel and spark tables are just completely out of whack. I'm running a '7427 ECM, modified from TBI to MPFI setup. I've tuned a car from scratch before, but this one is kicking my butt.

I really appreciate the ideas and where to look, please throw any more this way if you think of it. Thanks again!