Pump Calibration

[johncarrol]

Hello again. Awesome website! This is what I would like to do with the forum's help. I have 2 engines: 1991 J-model 6.2NA and a mid to late 90s 6.5NA Hummer engine. I have 3 IPs with their respective lines and injectors. I would like to take the 2 best of the 3 to a shop to be gone over and calibrated, to end up with the best ones that will give me the best fuel economy for my 2 engines. Both engines have their origional heads. I understand different heads affect MPGs, but I'm not interested in swapping heads at this time. Can someone inform me the differences in IPs as far as light vs heavy duty, and help me to decide which 2 of the 3, I should use for my engines. My 3rd IP is from a 6.2NA hummer engine. What is the best settings for the IP and injectors I should tell the shop to use? Please correct me if I'm wrong, but I assume there's not enough difference between a 6.2 and a 6.5 to have different IP settings.

[john8662]

6.2 and 6.5 NA engines do have different calibrations.

The 6.5NA pump is likely a DB2831 pump, where the other 6.2 pumps are DB2829. the 31 and 29 are plunger size. for .290" and .310"

Any of them will work fine, no picking to it really, just match your calibration to the engine/year configuration.

If using C-Code cylinder heads from a certain year, ensure you're getting the calibration for that year engine and rating. You could turn it down some.

For injectors, Aim a little higher than the 1800-1900 6.2 Spec, say 1950 pop pressure with correct nozzles.

J

[johncarrol]

OK. My 6.5
Hummer pump is an 831. my 6.2 Hummer pump is an 829. I can't read the numbers on my 1991 6.2 pump except for the last 4 which are: 4875 because they were etched by hand on the plate. Its engine had 312,000 miles on it when I bought the truck ,so I'm guessing it's not the origional. At present I'm running it in the 6.5 in my truck, because the 6.5 Hummer pump's advance is messed up. I put the 6.5 in my 1991 truck until I fix a blown head gasket in its 6.2 The 1991 6.2 pump works great in the 6.5, so after I'm all done, I may keep it as a good working spare. I've learned so far from the forum is: I want to keep an 829 with my 6.2 and an 831 with my 6.5 I do not want more power. What I want is: to have the pumps set up to give me the best fuel milage, but also deliver enough fuel to allow the engines to run smoothly without problems. Is the difference inside between light and heavy duty pumps determine only the amount of fuel delivered or are there other differences? Is it safe to have them calibrated for light duty? Does a "Light Duty" calibrated pump only work correctly with "Light Duty Heads"? Is there any research on this anywhere? Did all Hummer engines Use "Heavy Duty " calibrated pumps? What year should I tell them to calibrate the 6.5 Hummer pump for? Does the shop need to know anything else beside the year, size engine, and pop pressure? If the Pop pressures were raised to 1950, would that affect the timing much?

[john8662]

No physical part difference between light duty pumps and heavy duty pumps, as far as C and J 6.2's are concerned. Same pump, all in calibration.

For the 6.5 pump, you can have it calibrated for a N/A 6.5 years 93-95, like what would be in a G30 Van.

The main differences between the 6.2 pump and your 6.5 pump is different advance piston, larger plungers (831) and the governor stud assembly and parts are different.

J

[DmaxMaverick]

Also note the military pumps will be 24 volts. You'll need to swap some parts between them for civi use.

[johncarrol]

I had the local shop pick up my 6.5 pump, lines and injectors. I told them I wanted the pump calibrated for the best fuel milage and the injector's pop pressures all equalized to 1950 PSI. I made the mistake by not asking them to let me know roughly what it will cost me to have the work done beforehand. they called me a week later telling me the pump will cost $500 to $600 and the injectors would be $50 each. I told them I could send my pump for a complete rebuild and shipping both ways for $255 and buy new injectors for $259. For $100 they gave me back everything, my pump in pieces. I saw a listing on eBay from Diesel Care & Performance to rebuild a 6.2NA pump for $255 total. I called them today asking how much for a 6.5NA. They told me $450-WHY!!! No explanation. I'm ready to send them my converted to 12 volt 6.2 hummer pump to be rebuilt and use it on my 6.5 unless any of you good people can give me a good enough reason not to do so. I've been running the 6.2 pump from my 1991 J engine since the beginning of the year and it runs great. The $195 savings can buy me some more heating oil-oops I mean on road diesel fuel to cruise the streets with.

[johncarrol]

To add a little more here and maybe spark a little more discussion, I know as each year passed there were changes made to pump calibration as well as heads on 6.2s and 6.5s to squeeze more power/fuel milage out of them. It would be nice to have some kind of more specific info or chart available on the different pump calibrations and which engine and year of engine the pump numbers are for, telling us what the calibration changes accomplished. Meanwhile, over this winter, I will fix my 6.2NA and put it back in my 1991. I want to put the origional pump and injectors back on it that I'm running on my 6.5NA now to keep everything matched and origional on my 1991. Before I do that, I think I'll try a 6.2NA pump from a Hummer engine on my 6.5NA Hummer engine to see how it works before I pull it out. I want to eventually sell my 1991 Sierra SLX and use the 6.5NA in a project truck.

[DmaxMaverick]

The "pump calibration", in relation to the 6.2, 6.5 and other engines using similar fuel delivery systems, is essentially overrated. The year to year, and model to model pump updates were more for internal pump performance, stability, durability, maximum volume output, and environmental extremes. The injectors are the big player, as they determine fuel system operating pressure, volume, and atomization efficiency and pattern. The pump only determines when the injectors get to play, and the extreme limits of fuel delivery.