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6.5 Diesel Injector Rebuild

dbrannon79 said:
Please do share, I assume the nozzles are something between the two?

when you order replacements, what are the average cost on them?
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I'm not going to go into too much detail. I've spent alot of time researching injectors so I keep most of the information to myself. Mostly because I plan to start selling pumps and injectors soon.

But I will say this. There is a difference in some of the other style pintle nozzles that I believe will be beneficial. But in order to get them to flow like a marine injector they require some machine work. So im trying to make a "hybrid" nozzle that has the desired flow rate cure im after.

For name brand nozzles (bosch, stanadyne, delphi) they are around $45-50 each from my supplier. Injectors should probably be tested and replaced maybe every 100k.

You need to be extremely clean when working with the 6.5 fuel system. There are no filters in the injectors to catch debris that can fall in just from removing injection lines. Its a good idea to suck out the top of them when removing the lines and also blow out the lines and fittings to prevent junk from getting in the injector during reassembly. Debris can find its way down to the needle and seat causing it to stick open and leak. That's why when you pop test you want to hold pressure just before it pops off and looks for drips. That could be an indication of a bad needle and seat, or a sticking needle in the nozzle. I've disassembled a few injectors where I needed pliers to pull the needle out of the nozzle. They should come out nice and easy.
 
In helping a lot of hummer owners that use it as an occasional toy, sometimes sitting a few years with never being started, I am convinced the ethonal going “varnish” glue.
had a few people pull their injectors and ship to me. Soaked them for days in the classic atf/acetone and they started popping again. Unfortunately Mercedes buddy that had his pop tester moved away. I have the parts to build mine, just another task on the to-do list.
 
other than the different pop pressures marine injectors are set to, what are the advantages or disadvantages to them over stock?

for what ever reason I had the thought cross my mind that if a marine injector was redone and set to pop at the same pressure as a stock injector, what would that achieve? I am only assuming that the marine nozzles have a better atomization spray pattern and with higher pop pressure they would spray more fuel when they release. my theory is probably wrong, but if it was reset to pop at the lower stock pressure it would have a better spray atomization with the normal amount of fuel for a stock engine. Please correct me I know I am probably wrong here!
 
Exactly. You can go higher pop pressure for better atomization without loosing the volume of fuel on marines. doing that means you need to advance timing because the added fuel will take longer to burn, if you don’t have the better misting to help it burn right away.

Two things affect power and mpg more than everything else. Amount of fuel getting injected and timing. The more time fuel is burning in the cylinder increases torque and hp.
So you can have more fuel applied with less throttle and get the required power at lower rpm and improve mpg (if you can keep your foot out of it).

Advance timing for more power. Retard timing for more mpg. This is because you get the greatest torque gains as the top of the piston power stroke. And at the bottom of the stroke burn is more efficiency. So having the ability to use both is a good thing- provided you have enough unrestricted air flow to burn it all, and keep your foot out of it enough to not burn fuel at maximum rate all the time.

But most people that get h.o. injectors and a hig turbo don’t keep their foot out of it! Haha.

I agree 100% that 100,000 mile mark is time to pull injectors. If there is life in them, a good cleaning, and reseting pop pressure brings them back to life. The carbon build up gets eliminated and that helps tremendously. Lapping the nozzle tip is something most should leave to someone who has invested the bigger money into equipment to do it.

The really really hardened german nozzles are the best for recovering and making it to 200,000 miles and beyond without needing new nozzles, But rare as hens teeth unfortunately. They were kind of the Tucker car. by making them be able to last the entire engine life if everything is kept proper- they eliminated their customer base that was willing to pay more for them. Hot rodders and heavy worked trucks wanted them because the slight angle difference of the tip helped the spray mist slightly better. They definitely have a different chirp to them when compared side by side with their counter parts.

I have 2 sets on the magic nozzles on the shelf in sealed protection. But would be happy to loose their theoretical added value to info a new supply of nozzles that can perform the same or even better.
 
The marine DB2 and DB4 are the highest output stock pumps offered for the 6.2/6.5 platform. So the injectors are different to accommodate for the larger fuel volume. The marine pintle design allows for more flow at full needle lift and the higher pop pressure keeps the duration in spec. The whole idea is to to be able to flow the extra fuel volume from the pump in a desired amount of time.

Injectors dont add volume, fuel output is completely controlled by the injection pump. But Injector modifications need to be done when you tune a DS4 or turn up a DB2 to accommodate the additional fuel. Thats why people swap in marine injectors because they are already set up to handle the extra fuel. And if you get into BIG injection pumps then pop pressure might go up to 3000psi along with machine work to gain additional flow.

One thing to keep in mind is a IDI is a two part injection event. The precup actually atomizes fuel when flow is reversed after TDC. So atomization from the injector is less important at that point. Where it is important is just before TDC. A fine mist will help combustion start at the hot prechamber walls (air flow is too fast and pushes all the fuel to the walls). Thats why all IDI injectors use a throttling pintle. They limit fuel at initial opening to get a fine mist. Then increase flow more at full needed lift. The marines are designed to flow the most at full lift because the second stage of the pintle is machined off.
 
so if I am understanding correctly, taking a stock injector nozzle and raising the pop pressure to 2300 where the marine injectors are set at would achieve a finer mist or better atomization on a stock db4 pump where the marine nozzles under the same pop pressure release a higher volume of fuel.

for a stock timing advancement (engine within TDC spec) and the stock IP running a slightly higher pop pressure stock injector would have a better effect on efficiency and possibly better mpg's so long as you have a light foot.

I'm just trying to grasp it in my head.

for a stock IP, I would also assume that raising the pop pressure slightly would make it work harder causing premature failure.
 
When I pulled the marine injectors (sent to dbrannon79) and installed stock injectors, I did notice a small loss in power, but most of the coal smoke disappeared, which is what I was hoping for. I still need to do more driving with it.
 
that's better than what I get! mine seems to only get 13 weather I'm in town or on the highway. of course I have the 4.11 gears but a good while back not long after I got my truck I was getting close to that. the only thing I have different on it now since then is the all terrain tires and a 4" exhaust. I have done some slight tuning but even going to a stock tune I still get the same mileage.

before I replaced the tires, I was running a 235-75 street tire. my speedo was off then too. when I installed the 265-75 all terrains the speedo was corrected just by changing the tire size. this does spark some attention though. I have a set of rims that fit this truck and the old 235 tires. I kept them since they were in good shape except for one was wearing on the inside of the tread. maybe I should mount them and run them for a full tank and see if the mileage comes back. I know just going from a street tire to an al terrain can have worse effects on mileage.
 
dbrannon79 said:
that's better than what I get! mine seems to only get 13 weather I'm in town or on the highway. of course I have the 4.11 gears but a good while back not long after I got my truck I was getting close to that. the only thing I have different on it now since then is the all terrain tires and a 4" exhaust. I have done some slight tuning but even going to a stock tune I still get the same mileage.

before I replaced the tires, I was running a 235-75 street tire. my speedo was off then too. when I installed the 265-75 all terrains the speedo was corrected just by changing the tire size. this does spark some attention though. I have a set of rims that fit this truck and the old 235 tires. I kept them since they were in good shape except for one was wearing on the inside of the tread. maybe I should mount them and run them for a full tank and see if the mileage comes back. I know just going from a street tire to an al terrain can have worse effects on mileage.
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I have 3.73 gears on the ‘99 that had the marine injectors. Cooper A/Ts in 265-75.

My son’s ‘94 has 4.10 gears and same tires and size and sees 17 to 18 mpg Hwy. I don’t think gearing has much of an impact on mileage.
 
All the testing we did with pop pressures- higher pop pressure was better for both power and mpg. We really couldn’t understand why gm didn’t raise it by 200-250 psi more except that they were all so out of balance, if they were as bad with the higher level- they would be way over the top. 250 psi difference from lowest to highest was very normal on brand new trucks.
4 months into testing we started keeping them in stock and swapped out the next time as each truck rolled in for service except for the ones in the “all factory” testing being done.
we figured out same thing most 6.5 folks did- 25psi variations is the most we would allow.
we did a second tester that had a digital gauge set for recording peak like a compression tester. It also was an electric solenoid to drive identical each use so human error of how fast you pump was out of the picture. We got most of them within 10psi of the rest of the set.

We learned the difference of winter fuel vs regular diesel altered the psi.

I am convinced modern fuel will run way different than real diesel and so all the old numbers from gm/ Stanadyne should be a starting point only. Viscosity swings a lot- and since different fuels in different areas- those numbers probably shift a bit for optimum performance

I understand what Rockabillyrat is saying with injectors don’t add fuel. That is correct- the ip is what deliverys a set amount of fuel.

Where the difference comes in is on the pump because at lower rpm the ip puts out max fuel. Top end rpm the ip volume of cc3 fuel becomes less. The better pump builders learn how to get that fueling curve as flat as possible. Ideally you wish for same exact amount of fuel every cycle of the ip. But that just doesn’t happen.

Marine injectors are really for high rpm sustained engines. Think how a boat is used- fast acceleration mean almost nothing. Boats speed up until on plane then maintain that high rpm sustained for a long time. They focus on that volume of fuel and letting in every drop the pump can push spinning that fast. The boats that cruise Lake Mead built by peninsular all run 3900-4000 rpm sustained. My hot rodded ones went over that.

It isn’t a case of the marine injectors putting out more fuel than the normal ones, it is a case of the normal ones not putting out as much fuel at upper rpm as the marines do.
that part is easier to explain than the next one.

The faster rate of acceleration is the other part where the marines helped on hot rodded engines. Picture a torque and hp curve on a graph. When the line goes up sharply at first- very low time from idle to peak rpm and peak hp then maintains a flatter curve..
Instead of a classic “bell curve” getting a “square wave” type of graphing. Thats how the propane and other fuels helped me so much. But the ip being able to supply fuel that quickly was a pain. My fuel amount at 3500 rpm was more if accelerated slowly rather than as fast as possible.

I remember the pump builder saying something about refill rate and a big part of why the incoming pressure was bumped up to around 30psi instead of 3-5 stock.

Definitely I am not a pump or injector guy. My knowledge is from a user place- not a builder place. I rebuilt injectors into the thousands just setting pressure and cleaning up pattern. So keep that in mind when reading my explanation of things. I can easily mis-represent things in my wording.
 
@Will L. in your experience rebuilding them. Is there a significant change in the pop pressure when adding say a .003 shim? I’m just curious how thin of a shim makes a huge pressure change in them. I’m looking into finding some shim stock and a punch set as others seem to be doing as I read further online.

also I’m sure there is a difference in pressures when the injectors are hot and when cold with the internal spring contractions with temperature changes
 
Higher pop pressure isn't hard on these pumps. The AG spec DB2s are calibrated at 3000 psi. The DS4 can easily handle the same higher pop pressure. The only thing that can give you issues is if the Head and Rotor is worn. Higher pop pressure on a worn out pump can cause hot start issues.

If you just running a tuned DS4 or turned up DB2 then marine injectors is all you need. If you getting into anything bigger thats where things get fun.
 
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