isuzu npr diesel
 

does anyone know where i can find tech info for an isuzu npr? i will try here, maybe someone knows.

i have a 2000 4cyl npr diesel. it is not getting fuel? i cracked the #4 fuel line loose at the injector and started pumping the primer. at first i pulled up on the primer and it seemed like a vacuum was sucking the primer back down, after pulling up and it going back down on its own several times, it finally seemed like it got some fuel in it and i had to press it back down, once that happened, fuel came out of the line, i tightened it back on and the truck started right up. the next day, same thing, no start, like it lost its prime? did the whole process over again but this time the primer never got fuel, i tried for a long time, all that happened is i pulled up on the primer and a vacuum like action pulled it back down, no fuel? what could be the problem, bad primer, should i put a in-line elect. fuel pump, if so which one is recommended?

thanks.

Try here, lots of good info on the Isuzu 3.9L

http://www.4btswaps.com/forum/forumdisplay.php?f=16

Not an NPR but similar--I have a Fuso. On mine, there's a fuel filter just after the tank, the kind with a glass viewing cover. Do you have a filter in a similar location and is it plugged?
There are some Australians familiar with the Isuzu who post at this forum:

http://www.expeditionportal.com/forum/forumdisplay.php?f=72

You may get a better answer there.

They were also sold with the Chevrolet badge as a W4

I've worked on a few of these - no expert but...

Do check for a filter/water separator between the tank and the engine. Usually down on the frame behind the left front wheel. If it's clogged the fuel pump will be sucking really hard trying to pull fuel and create a vacuum. There is also a bleed bolt on top of the injection pump. Should be about a 14 or 15mm bolt head, painted white. When you use the primer pump (after changing the fuel filter, for example) you're supposed to loosen that bolt a bit before working the primer pump.

My guess is - as suggested earlier - that the water separator is clogged. Just a guess. These suckers are a huge pain to prime. I've had mechanics who work on them just roll their eyes and tell me to get the charger out because it was going to kill the batteries before it purged all the air... :)

I will try and change the filters first. there are 2, one water separator on the frame, next to the batteries and another up on the engine at the back of the valve cover.

Thanks.

Yep. The water separator is on the suction side of the lift pump so if it's blocked the lift pump will be working hard to pull fuel through it. The fuel filter up on the back of the engine is on the pressure side of the lift pump before the IP. Probably the first one. Good luck!

I tried to purchase the water separator from car quest today and they dont have a listing, is that a dealer only piece? I also could not get it off? I assume the aluminum ring at the top side is threaded and holds the separator to the housing, I tried with large water pump pliers and could not break it loose? is there a special technique? if all fails, I am going to try an bypass it to see if its plugged.

Check all the associated steel lines and fittings for rust perforation. A clogged filter will give you poor performance, it won't drain down overnight. An air leak will give the symptoms you have. You may want to try to pressurize the fuel system from the tank to the engine and look for leaks that way.

I haven't had mine apart so can't help, but I would like to know how yours comes apart. I'd try NAPA for the filter. You could try blowing through the water separator/filter to see if it is clogged.
I agree that an air leak gives these symptoms. But an air leak could be caused by a vacuum in the lines as a result of the water separator/filter being clogged.

Parts on-line
 

I've got some bits from these guys before. They seem OK...
http://www.isuzutruckparts.com/

Ok, got the truck to start. what i did was change the spin on filter and bypass the water separator, only because i could not find one. I tried pumping the primer and the same vacuum symptom was happening, sucking the primer back down? i ended up just for kicks cranking the engine and it started up. it started up again the next day, so i am thinking the water separator was clogged, i will put a new one in.

another symptom the truck has always had since i have owned it was, when you first start it up, for the first few seconds it runs ruff, like its missing, then it clears right up and runs perfect. only on start up? any ideas?

thanks.

Bad or malfunctioning glow plugs.

Glow plugs are used only for very cold starts on these trucks, they are direct injection. I still vote for an air leak on the water separator.

I bypassed the water separator with a two sided barb fitting though?