I would recommend nissan plugs Part #22401-FU42A they are an updated plug that has the first three threads removed as they had issues with the old plugs coming out of the head hard and taking the threads out with the plug,be VERY careful when changing plugs,do it with the engine cold and work them out easy.
I guess the threads on the old plugs get carbon build up on them and are a bear to get out of the head with out damaging the threads,especially on high hour trucks.
Thanks Radon,
Kevin has coached me on checking/ correcting the regulator pressure which I did today. The main culprit for slow starting had 4.0 psi when I tested. After removing the guard ( hard to do without the correct tool) I increased the pressure to 4.8 which helped tremendously on starting.
I still think new plugs would be a great idea given so many hours. Is there a "best" brand of plug to use?
I'm not sure what year these trucks are but if you cannot connect laptop you can take out pressure sensor and use that port for fuel pressure, that way your sure its getting to injector body. There is a screen in the inlet side of fuel that can become plugged. I would check your plugs weak spark may cause hard starts too, amongst many other things.
Got it! Thanks for the info you sent as well.
top of the regulator(NIKKI) is a 17 mm hex take it out and can screw a 1/8 NPT nipple in it(dont force it in tho,just finger tight) and check the pressure,see what it does also under load(tilt bypass) should hold around 4.5 PSI
Kevin, I didn't. I have a low pressure gauge to check Impco model J's. Where would the test port be?
Possible Vaporizor problem,did you check your fuel Pressure coming from the vaporizor,should be about 4.5 PSI.
Even if you drained the tar could be problems with it causing problems.