seems like I occasionally get the flooding when it sits for a while after morning drive-
then I can drive it, stopping and starting no problems.

I realized I never changed temp II
I put in a new Bosch the other day.
Better cold starts, and I have not had the no start since.
fingers crossed-duh me

Correct, this is not my car
It's an 89 (this why posted in the 89 relay post). This is not my first rodeo. I flew out here to Vegas to help owner to just be a nice guy and help after he did all listed below. I posted in the 89 relay post to see if anyone had an "aha" answer that a very specific thing caused their failure but I'm happy to answer this.

It's a rebuilt Lh, owner got it
It's a rebuilt Ezk, owner got it
It's a rebuilt MAF (John speake I believe)
Has a VCB supercharger (problem was prior to this as you'll see below)
New hall, cps sensors from Roger
New Greg brown high output alternator (which as a side note is fabulous)
It is a new to this car CE panel which owner sourced (replacement didn't solve issue)
All the relays are new
Yes I have wsm in both printed and digital form with me and have been referencing them.

Stan (Mr Merlin) and I have been working back and forth on phone (he was going to come out and help but got busy). I don't have my tools as I didn't want to ship everything. So I am limited to what owner has here. I did have a Power Probe shipped to test ports and test downline wiring.
We are checking FP socket today after my wsm research last night points to what you referred to . We have narrowed it down to that. Stan, Victor Edgar and I have come to the point that it is pointing to the LH. I am taking them home with me (new and old) and testing in my car. We believe this due to car running perfectly with FP jumpered. That eliminates the CPS. What we do need to find is why the LH went (if found to be bad). In tank fuel pump seized (there goes a $1000 part since it sat in car for 8 mos before it got here) so Roger sent me a strainer kit. Wondering if that caused an LH failure? Maybe Alan will know. He's the electron wrangler.
Owner told me (he is second owner) that in his discussion with first owner the car had a "gremlin" since new that caused car to die. Dealer couldn't resolve it. I believe this is why current owner threw all the parts at it.
He does also have a complete car harness and was about to pull interior and put in new body and engine harness. I told him to trace every wire with power probe and verify continuity (power probe can also tell you how far down a wire there is a break as well).
Owner has time and resources to do this so it can't hurt and can do this while I have the LH with me testing it.

How's that?

As an update Louie Ott did both computers on the 89

I know a similar issue was diagnosed and fixed following Greg Brown's advice.
Here's what I found: Hope this helps.

Vanster: Yesterday my trusty 86.5 would not start....It always starts! I checked everything then went to the fuel pump relay. By passed it with a jumper and it starts. I have a box of relays tried them all..nada
We do my local Porsche parts house and got a "used" relay...still won't start. Jump it and it fires right up. The fuel pump has about 30k on it.
Any suggestions?

Greg Brown:Lost power or ground to fuel.pump relay. You can put common test light across "85" and "86) of the fuel pump relay socket (while cranking) to confirm this (relay out)..Then test each "85" and "86" individually to ground (while cranking) to see if you have power on either.

This will tell me a bunch.

While people are saying that losing signal from LH to fuel pump relay is a common problem, I've never seen this.....and I've seen a bunch of LH failures. I can send you up a rebuilt JDS computer to test, if necessary. (I'm thinking I would have put a rebuilt in, BTW.)

I'll call in AM.

Vanster: With a little help from GB on the phone we managed to resolve the issue and it runs perfectly again. We ran a wire from #85 on the FP relay to the #21 fuse block ( the brown and white ) wire on the lower right of the panel ( yellow block). All is good. My first thought that it was the LH, but since it wasn't that old ( 35pin) I needed to check all options before sending it out for repair. It could be a loose wire or something behind the big board ( which gives me a headache just looking at the back of it).

FWIW, it's my 89. Jeff is a true friend coming out to Vegas to help me out with this problem.

Dr. Bob wrote this:

The LH doesn't source voltage to close the relay. The relay coil gets power from the 15 bus (hot with key in RUN or START). The LH controller **GROUNDS the other side of the relay coil, causing the relay to close.
The "fix" was to the hot side wiring so power gets to the relay coil. The ground (LH) side of the relay coil wiring was fine.
** the LH actually pulls its side of the relay coil almost but not quite to ground. It ends up floating somewhere around 0.6 Volts above ground, thanks to the silicon transistor used for the switching inside. Probably not important unless you are in there with the DMM trying to figure out why that side of the relay isn't "properly" grounded.

Excellent!

Given "the car had a "gremlin" since new that caused car to die. Dealer couldn't resolve it" my crystal ball says "wiring harness." Dealer techs, working mostly on new cars, hating 928s, knowing mostly about 911s, rarely seem to have developed the wherewithal to dive into a 928 wiring problem even if its suspected.

However, the LH rebuilt or not is still a potential culprit(*) if your relay socket diagnostics indicate that the socket isn't being 'turned on.' If so, then 'skin' the LH multi-pin plug so that you can put a multi-meter probe on the back of connector for the wire that runs to the FP socket. Check for continuity. If the socket doesn't 'turn on' during cranking and you have continuity to the appropriate socket terminal then the LH is dead.

(*) Not knowing who rebuilt the LH you don't know if it's really good. I only trust JDS and Elektronic Repair for LH. I don't trust any other rebuilder and don't trust "Porsche"-rebuilt LHs. Look on the LH's case for a rebuilder's sticker.

Nevermind the LH. Louie is JDS's domestic rep. So, the LH was good when it was installed. You've got lots of good info now on testing the FP relay socket. Hope that's it and the fix is straightforward.

Last, it's great to know that Joe's getting some additional well-trained hands on his 928.

Right! It's important to remember that most everything is ground-switched not power-switched. Test that you have power to the pin (under the correct conditions for the specific power bus) and then chase ground-switching on the other side.