Help Upgrade 4jb1t pump head to 12mm

[rabidrabbit001]

After doing the 4jg2t to 4jg1t conversion i have been using a 4jb1t pump. It has a small miss on injector number 2 at idle. I have tested injector pop pressure and is ok. Replaced delivery valve 2 times with no change. Valve lash is correct. Compression is great. Is it possible to have a small piece of debris in the pump head to number 2 before delivery valve?
Any suggestions will help.
If i have to replace head....maybe upgrade to 12mm.
So does anyone know how to do this or can you point me the right direction? I have searched on google and this site with no real help. So far I have seen suggestions on using a stock Cummins 4bd head. Will this interchange?
My pump is a VE4/11F1800LNP2371 purchased 2 used pumps from Alibabba seller.

[Roderunner]

Have you swapped both the injector and delivery valve over with another cylinder to see if the miss changes cylinders?..the injector line could have a restriction too so it wouldn't hurt to sus it out even if it is unlikely.
Assuming that you have, do the injectors have the 2 shot injection phase? If I remember correctly some engines have a small pre-injection fuel delivery to kick start the burn, and some don't. Also you might want to look at which export pump you do have as the manufacturer specifies at least 3 different injector crack pressures for various export engines depending on where in the world they are being sold. From memory (I saw this in an online workshop manual) the recommended crack pressures ranged from 2600 psi, to 3200 psi.
An experienced injection shop will be able to help you with a possible head swap, but they are probably going to charge you an arm and a leg for the information/rebuild because they can. Also, they probably don't have any prior experience with the 4j Isuzu as far as performance mods go, which is complicated by the change in spec by your head/piston swap.
The 4jg2 pump has a bigger head (11 or 12 mil. from memory), I would probably try using the complete pump, but the cam disc which pushes the injection piston (plunger) will probably have a different profile when compared to the 4jb1 pump's cam disc. Possibly the 4jb1 pump body combined with the 4jg2 head might be worth considering.
If you have a spare 4jb pump handy you could attempt to swap the head yourself, it is complicated but not impossible to do, and there are rebuild threads describing how to rebuild the pump on the net if you search for long enough.
Here's a guide, but the poster made a mistake close to the end, so you may have to read it through before attempting to put your pump back together. http://gnarlodious.com/Vanagon/Bosch_Pump/-Rebuild
EDIT.... The mistake has been edited out since I last visited this page. This pump is from a different vehicle, but most of the internal pump parts are the same as far as reassembly goes. I'm not sure how one goes about getting the right clearance between the camplate and a different plunger shaft / head, maybe checking the thickness of the small spacer and checking the length of both of the plungers will tell if a different thickness spacer is needed.

[Roderunner]

I was just browsing through a bosch V.E. injection pump article, and it appears that the delivery valves vary in design depending on wether the injectors used are direct injection or Indirect injection. From what I understand, using the wrong delivery valves can allow the combustion pressure to push combustion gas into the injector tip, which can result in fuel dribbeling and other problems. It's probably easier if I just post a link to the pdf file rather than try to explain it all. http://gnarlodious.com/vanagon/bosch_pu ... _Pumps.pdf
EDIT page 23

[rabidrabbit001]

I am not using the 4jg2t pump, or head. I converted the motor over to 4jg1t (direct injection). Using a 4jg1t or (4jb1) cylender head. I'm using a 4jb1t pump and 4jb1t single spring (single stage 2630 psi pop)injectors. All the hardware is the same on a 4jg1t and the cylender head is a perfect fit.

[Roderunner]

That takes any unmatched injection components out of the possible problems. I am thinking that the no. 2 injection port in the pump head is possibly the most likely to be affected by any air ingestion as air bubbles tend to rise. As you probably know, the fuel does contain a percentage of air, and any restriction in the fuel supply line often results in the vane pump sucking air in through the front shaft seal, which is made more likely as the crankcase pressure builds up as engine load /revs increase, which tends to put positive pressure onto the outside of the shaft seal The throttle shaft and the hand priming pump are also known to leak some air, which may not be apparent at engine speeds above idle.

[geeves]

have you done a compression test? It might not be a fuel issue

[rabidrabbit001]

geeves wrote:have you done a compression test? It might not be a fuel issue
Compression is well in the acceptable range. I did a pop off test on all the "NEW" injectors that I bought online and here are the numbers I found:
#1. 3300 psi
#2. 2650 psi
#3. 2300 psi
#4. 2750 psi
This was the problem
I shimed all to match 2900 psi.
The miss fire is gone and the motor is very smooth now. I did notice a drop in performance....less pep.
Should I now change timing from .55mm lift @ 12° btdc to .55mm lift @ 14° btdc. Or .55mm lift @ 16° btdc?

[Roderunner]

It's good to hear that you solved the misfire. Advancing the injection timing comes down to personal preference, because there is the risk of shortening engine life. I used to run injection advance, but the engine ran hotter during normal operating conditions than what it did before the adjustment so I decided to wind it back to the factory setting.
I did see some damage which was probably from too much advance in a 4jb1T engine , the top rings had dug a deep groove into the top of the sleeves, it seems that the firing stroke peak pressure goes up with too much advance and forces the rings (via gas pressure) onto the walls hard enough to overload the oil film on the cylinder wall, which was probably compounded by the owner not changing the engine oil when due (if at all). Some people prefer to advance the injection timing during the colder months and back it off again for summer, I wouldn't expect 2 or 3 degrees of advance to make a huge difference to engine life myself, but everyone has their own opinion.

[rabidrabbit001]

*****UPDATE****
I have been reading that the duel stage injectors are a better design. So I purchased a set of 4jh1t injectors and swapped them in and HOLY CRAP these things make my engine run sooooo smooth. I do want to increase the fuel to the injectors so I am still on the hunt for a suitable 12mm gear drive direction (spin left) pump head. Can someone point me in the right direction please?
Cheers mates

[rabidrabbit001]

Bump for my last question. And also what should the timing be for this setup. 4jh1t injectors 280 pump on 4jg1t engine. 12°btdc .50mm lift static?