99 XJ with about 136k on the odometer. I replaced the entire fuel pump assembly with a Bosch N67658 about 2.5 years ago (about 30k miles ago). Lately, I was having a hard starting issue again, long start then stumbled to burn off the excess fuel. Then it would run fine. Fuel pressure was fine at idle (49.2) but would drop below 30 psi almost immediately after shutting off the engine. All signs pointed towards leaky injector(s). I just upgraded to 784's this morning then reset the computer. Idle is way smoother than before and it runs great once it starts, but that is all I have noticed so far today. However, my hard starts are still happening, but now without the stumbling once it starts. I pressure checked the fuel again and same issue (49.2 psi at idle then drops immediately below 30 psi after shutting off the engine). I tested the battery to make sure it was at a full charge and it is. I tried the "poor man's prime" on several start-ups today and this seems to be working. I don't have the "special tool 6923" adapter, nor have I been able to figure out a way to build this tool successfully on my own, so I have not been able to conduct a legitimate fuel pressure leak down test. But I definitely have a problem. My gut says I fixed the leaky injector problem, but that I still have a check valve issue with the pump. So here's my two parted question… Does anyone know how to conduct a legitimate fuel pressure leak down test on a 99 without the "special tool 6923" adapter that the service manual insists is needed (clamping the fuel line itself is not an option as far as I can tell because it is all metal from the rail back to the pump) and though I am sure it is possible, is it likely that my Bosch pump assembly (the check valve specifically) could have failed in just 30k?

As always, thanks in advance for any constructive feedback. It's greatly appreciated.

Updating my original post, I have since noticed the hard starting is still occasionally followed by a stumbling idle. However, every time I "poor man's prime" three times prior to starting the engine, she starts right up with no problem. I believe this is pointing back to a faulty check valve in my Bosch fuel pump assembly that is only 30k miles old. Anyone encounter problems with a Bosch pump?

Have you replaced the fuel pressure regulator on the rail?

How did this turn out?

They're usually pretty good, but nobody's parts are 100%. Even the good stuff has a failure here and there. The startup stumble is gone so I'd bet along with you that it's the check valve, not the injectors. Since your XJ is newer than 1995, the FPR is back in the tank, not on the rail.
Might try running a can of Techron or BG44 if you can find it, just in case there some crud holding the check valve open.

Stick a in line check valve on it .

Could be a leaky injector. Mine did the same thing until I installed Neon injectors.

(I didn't read the book you typed in the first post.) ADD & all.

Radi- you are incorrect. There is a fuel pressure regulator on the rail as well. These can go bad and cause the same problems as a bad in tank regulator being faulty. Also leaking fuel injectors are somewhat common as well and can leak fuel pressure down

1999 does not have a fuel pressure regulator on the rail. 2000 model year started a dampener between injectors 3 and 4, but this is just a silicone diaphragm on a spring to help ease the pulsing action. A couple 1999s got this fuel rail ahead of time. But it is certainly not an FPR.

Not after 1995. Starting in '96 they moved the regulator back to the pump assembly and eliminated the fuel return line. I wish the regulator still was on the rail, it's much easier to service!

Thanks for the responses and apologies for my delayed follow up. I have been traveling for work and haven't had a chance to dig any deeper into the issue. Obviously, the problems still exist and I'm trying to determine my next move. Though it is ridiculously pricey for what it is, I may just order the "special tool adapter" needed to isolate the fuel rail from the rest of the system for a proper pressure leak down test. I'll update with results when completed.

Thanks.

Convinced there had to be a way to build the "special tool adapter" I decided to re-measure my fuel line and realized I obviously f'ed up the measurement the first time. Now knowing I had a 5/16" fuel line, I was able to gather all the pieces I needed for under $20 to build that adapter for a proper pressure leak down test. Results… fuel pump assembly is failing, most likely the check valve, and on a Bosch premium pump that is only two years old. Great! A quick call to Napa and discovered it only has a 1 year warranty. Fantastic! Glad I paid the premium price for a POS. Fortunately, the Napa guy agreed that it shouldn't have failed so quickly and suggested I bring it in and speak to a manager. We'll see how that goes. I'll update again with some final results when I drop the tank and replace that pump.