M998A1 6.2 NA injector options

[Humpty]

I have a 94 M998A1 with a 6.2 engine and can’t seem to find a definitive answer regarding injectors. Will injectors from a civi GM 6.2 of the same era work? Coarse threat, fine thread, long or short,… putple bsnd, green band, no band.. lots of options in a google search and all of them say they work on the 6.2 AND the 6.5.

My truck starts and runs fine. Has a bit of fuel burn smoke on acceleration.. 33k on the odometer and no speedometer cable present so mileage unknown. Just wanted to replace the injectors so i knew they were the right ones. It’s definitely getting fuel.. probably a bit too much.

 

[Retiredwarhorses]

The injectors have a Bosch or Delphi part number on them, that’s what you are after, you can’t install purple or orange banded
injectors into your motor, those are for 6.5NA and Turbo motor

 

[87cr250r]

On the civvy engines 88.5 and earlier had long bodies and later had short. Your application likely has shorts. You can tweek the injector lines to fit shorts if you have to.

 

[Humpty]

The injectors have a Bosch or Delphi part number on them, that’s what you are after, you can’t install purple or orange banded
injectors into your motor, those are for 6.5NA and Turbo motor

I guess it's that part number that I'm not having great success in finding. I'm not confident (based on the state of this vehicle) that whatever injectors are in there presently are the correct ones.

 

[Humpty]

On the civvy engines 88.5 and earlier had long bodies and later had short. Your application likely has shorts. You can tweek the injector lines to fit shorts if you have to.

The current installed injectors appear to be shorts (as I compare them to examples of both online) My concern is thread type (I'd read somewhere recently that the civilian engine had different threads to dissuade sticky fingered motor pool personal from liberating injectors for their personal vehicles) and injection volume. I've read that you *can* put turbo injectors in this engine and it'll run, but with lessened fuel economy as the injectors provide more juice per squirt than the NA version resulting in some excess fuel burn off. I've seen MANY listings for injectors that claim to work for both 6.2 and 6.5 turbo or NA so it's not beyond the realm of possibility a previous owner did just that. I just wanna make sure I'm getting the right injector for the 6.2 NA. If a short civvy injector from the same era is the same that would be great because adding "HUMVEE" to the description seems to instantly add $$ to the price.

 

[Mogman]

I'm not sure a little "fuel smoke on acceleration" is a good reason to replace the injectors, this is not a ECM controlled engine and a little smoke on acceleration should be expected.
Why tempt the fates? or Why open Pandora's box or If it ain't broke don't mess with it....

 

[gringeltaube]

My concern is thread type (I'd read somewhere recently that the civilian engine had different threads to dissuade sticky fingered motor pool personal from liberating injectors for their personal vehicles)

Military or civy doesn't matter: only the very early 6.2s had the (coarse) M24x2.0 threaded injectors. From 1983 on, all 6.2L engines have injectors with the M24x1.5 (fine) thread.

 

[Humpty]

I'm not sure a little "fuel smoke on acceleration" is a good reason to replace the injectors, this is not a ECM controlled engine and a little smoke on acceleration should be expected.
Why tempt the fates? or Why open Pandora's box or If it ain't broke don't mess with it....

Well, I’ll tell ya why.. because if i’m going out on the road i’d rather go with known good rather than who knows what. The vehicle is 30 years old and unknown mileage and has undoubtedly sat for many years. In my head, any vehicle that has sat for any length of time with a dubious service history is subject to the basic “tune up” stuff. Coolant flush, thermostat replacement, oil change, and in the case of a diesel, glow plug and injector replacement. A retired war horse should be afforded the same courtesy i’d extend to a lawn mower. That’s just my personal philosophy. Your mileage may vary.

 

[Mogman]

Well, I’ll tell ya why.. because if i’m going out on the road i’d rather go with known good rather than who knows what. The vehicle is 30 years old and unknown mileage and has undoubtedly sat for many years. In my head, any vehicle that has sat for any length of time with a dubious service history is subject to the basic “tune up” stuff. Coolant flush, thermostat replacement, oil change, and in the case of a diesel, glow plug and injector replacement. A retired war horse should be afforded the same courtesy i’d extend to a lawn mower. That’s just my personal philosophy. Your mileage may vary.

Sounds good, do not forget to get the IP rebuilt it is one of the most likely failure points in the injection system, much more so than the injectors themselves

 

[Humpty]

Sounds good, do not forget to get the IP rebuilt it is one of the most likely failure points in the injection system, much more so than the injectors themselves

That was *allegedly* done a few years ago shortly after the previous owner acquired it. I (perhaps mistakenly) attribute a LACK of fuel reaching the cylinders as indicative of faulty or failing injection pump rather than an excess of fuel, which is why I’m working from the cheap (and consumables) stuff back. lol as to Pandoras Box, a strong argument could be made the lid was opened the day I paid cash for this beast.

 

[87cr250r]

The injection pump will cause over fueling and black smoke if it has been turned up or built to a higher output spec which is quite possible to have been done during a rebuild.

 

[Coug]

black smoke under acceleration can also be caused by an air intake restriction, not just faulty injectors or having the fuel system turned up.

If it's not smoking until the acceleration, then it's probably not an injector issue, as a faulty injector with bad spray pattern will give smoke at lower RPMs and no load. They also tend to cause a knocking sound due to the faulty combustion.

With smoke only during heavy load or acceleration, I would say your engine is probably functioning properly.

Have you had an actual diesel tech familiar with these engines look at it, or are you just trying to find things to throw money at?

 

[Humpty]

Have you had an actual diesel tech familiar with these engines look at it, or are you just trying to find things to throw money at?

Well, after having “an actual diesel tech (supposedly) familiar with these engines” tell me it was fine then have a glow plug shoot out of the side of the motor two days later I had an opportunity to pull the corresponding injector out to look around and the injector looked like something dredged up from the bottom of a tar pit I thought i’d replace them. Maybe the smoke situation will lessen, maybe it won’t. Either way, I’ll not likely loose a seconds sleep having replaced the injectors with new ones of the known right type instead of driving around on total mystery injectors.

BTW, for anyone stumbling upon this thread looking to “throw money” at their M998A1 with a 6.2 NA engine for preventative maintenance, the injector part number is 0432217275.

 

[Mogman]

Not sure if that is a valid number or not but the parts TM has two numbers listed depending on what IP you have.
If you have the "correct" IP then it would be the second nozzle, your M998A1 has a UOC of A13