’87 SDL runs absolutely wonderful - other than this. Car at temperature will not restart until cool again.
Will not re-start after bringing the engine up to normal operating temperature – Every single time. It cranks fast, no fuel problem, just no Fire in the hole!
Get the engine up to temp and turn it off. It will re-start if you try right away, but if you wait 10-15 minutes before trying to re-start, it will not restart. It will start up just fine after one hour or more of sitting and cooling down.
The first thing I did was change all the filters even though they had been recently changed.
Then I checked the fuel lines many times and ended up putting a few clear vinyl hoses on the fuel plumbing so I can actually see the fuel moving and verify that it is not leaking, not loosing prime, and No air bubbles in the fuel from any bad fittings. I have a clear vinyl hose from the filter to the in port on the injection pump. Pretty cool, but it only verified that fuel does not seem to be the problem.
I tried to setup better testing for my problem:
6 times I took the car out from cold starts on an 8 mile loop to get it warm and see if it would re-start. Once it gets up to temp and I turn the car off if I waited 10-15 minutes - it would never start – not once.
Twice, On a cold engine I cracked an injector line open on top of #3 injector to see fuel and estimate the pressure squirt. Powerful squirt of fuel squirts up about 5 inches as car begins to start.
Same test on same injector after the engine is up to normal operating temperature and does not re-start showed only a slow puddle of fuel on the head of injector nut - No squirting of fuel at all – no pressure squirting fuel.
Fuel pump – fuel injector – temp sensor – what could it be?
NOTES: recent history; This injector pump is a rebuilt injector pump just installed 4 months ago. After installing it the car ran perfect for about 2000 miles. Then it had a dramatic sudden lost power; I eventually found and adjusted the ALDA to restore power and it ran great again. Since it was running so great I took it in to have the air conditioner serviced. They had to do an electircal diagnosis to find out why the compresser didn't want to spool up. The replaced a coolant temp sensor - charged me $400. and sent me off. The air conditioner runs fine, but now I have discovered this no restart after being warmed up to operating temp.
Other than that, this car runs like a champ. Plenty of power, idles as smooth as silk when cold or hot. The engine never chugs or misses when cold or hot. When cold it starts up on 3 revs. But, after warming the engine to normal operating temp it will not restart until cool again.
Being an SDL I am told there could be 2 coolant temp sensors, but where are they - how do I test the one they replaced and find the second one?

Help

By your own diagnosis the problem is fuel supply.

Disconnect the fuel filter -> IP line at the IP and crank engine when hot to check whether fuel under pressure is reaching the IP.

The following have all caused either hot running or after running at high speed problems for me:

1) leaking fuel pump
2) invisible cracks in flexible fuel lines
3) loose fuel line clamps
4) a partially blocked metal line that with gunk "flapping" inside. If it settled ("cold") enough fuel would pass or under high power/high fuel flow enough would pass. After running on the highway if I stopped the engine it would not start as the gunk was blocking the line.

If your IP is not receiving fuel _under pressure_ (just a gravity feed won't work) when hot then just isolate the problem. Start with virgin line and go from a temp tank -> fuel pump -> IP with clean and filtered fuel. Then add the fuel filter. If everything works fine at this point then your problem is on the line back to the tank or in the tank itself.

Personally I would just replace all of the rubber lines anyway and blow out the metal lines even if you find out the problem is somethink like the fuel pump. You will save headaches in the future for the cost of an hour or so labor and a few dollars in line.

My SDL was sucking air from the fuel temperature exchange unit. It was also leaking fuel. I just bypassed for the time being.

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87 300SDL - 215K Miles !!
99 F-350CC Dually PSD - 190K
86 300SDL - 189K
All on B-100

Thanks for the ideas.
I have inspected the fuel system and verify that there are no leaks. No air getting into fuel system. The fuel pump is pumping uninterupted fuel all the way through the system. (read 1st post).
The problem is not with fuel system but with something affecting the fuel delivery that is related to temperature.
More ideas

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'87 SDL
'96 VW Passat
'82 VW Caddy
'93 1100cc Trike

I believe your car has a vacuum actuated shut-off valve. For the heck of it, next time it is hot and won't start try to pull the vacuum line off the valve and see if it will start then. Maybe there is some fault causing vacuum to leak to the valve when it is hot.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Nowhere in your post does it say that you hooked up an auxilliary tank directly to the fuel pump and then directly from the fuel pump into the IP when the engine is hot. If you haven't done this simple test when the system is failing you have not verified that it is not a supply problem.

GREAT ! Some Ideas to try - Thanks everyone, thanks.
I will set up a little fuel tank and try to draw fuel from it on a Hot restart test, good idea.
Also, I will pull that vacuum hose off the shut off, I think the hose is not directly on the shut off but I'll try pulling one at a time when it is hot and doesn't want to start.
Thanks,
I'll make sure to post what the evenutal fix is - I hope I can post it soooooon!

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'87 SDL
'96 VW Passat
'82 VW Caddy
'93 1100cc Trike