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Resetting injector pop pressure

bk95td said:
On several of the 6.5s that I've pulled apart there was actual divets in the tops of the pistons:eek: from the injectors peeing instead of atomizing. Not a good thing.:nonod:
On the mercedes forum that I recently joined[and I don't own one] ,they talk about regular cleaning of the injectors. Take them out ,clean them and reset pop pressure. I haven't caught how often they are recomending doing it ,but every 50,000 miles would be a good guess.:confused: They also mention that the engines being run on wvo should have the injectors cleaned more often than ones run on regular diesel. Merecedes source sells a cleaning kit. It has all the tools needed to clean the nozzles and the rest of the injector.
Click to expand...

Just cuz your hangin with the MB crowd, don't get all snobby on us!!

Are most of these engines IDI Mercedes? Would nozzles be different for DI vs IDI?
 
Good info BK... Do an experiment; compare two known injectors, one COLD and one heat soaked (no torch:)) to about 250*F... See if there is any changes in pop. I'm wondering about spring integrity.

If you get bored.
 
3500GMC said:
Good info BK... Do an experiment; compare two known injectors, one COLD and one heat soaked (no torch:)) to about 250*F... See if there is any changes in pop. I'm wondering about spring integrity.

If you get bored.
Click to expand...

Spring could get softer, shim could expand....???
 
Matt Bachand said:
Just cuz your hangin with the MB crowd, don't get all snobby on us!! Yep, I'm a mb wanna be):h

Are most of these engines IDI Mercedes? Would nozzles be different for DI vs IDI?
Click to expand...
I'm not shure what year mercedes went to direct inject or electronic common rail. Most of their diesel cars are 4 and 5 cylinder and will easily run way past 500,000 miles.:thumbsup: Very few of the diesel models that mercedes produces are imported to the US. I'm not really shure how different direct inject injectors are. My tester said it was good up to 1993 models.
 
3500GMC said:
Good info BK... Do an experiment; compare two known injectors, one COLD and one heat soaked (no torch:)) to about 250*F... See if there is any changes in pop. I'm wondering about spring integrity.

If you get bored.
Click to expand...
That is a interesting question.When the engine is running they are cooled by the fuel running through them. After shut down they would get a good heat soak. I've never read anything about the effect of heat on valve springs either. I was also wondering if the injector springs take a "set" after running for a while. Perhaps the pop needs to be reset after say,10,000 miles to adjust for break-in:confused:.
 
bk95td said:
That is a interesting question.When the engine is running they are cooled by the fuel running through them. After shut down they would get a good heat soak. I've never read anything about the effect of heat on valve springs either. I was also wondering if the injector springs take a "set" after running for a while. Perhaps the pop needs to be reset after say,10,000 miles to adjust for break-in:confused:.
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Cooled by diesel fuel thats been through a heatsoaked, if not HEATED fuel filter, then cooles the IP (supposedly PMD too), then after passing through the V of the engine in the IP, goes to the injectors, 4 of them on the turbo side. I'm not sure how 'cooled' they really get.
 
bk thanks for great write up... when you test do you use a special testing fluid .... if you use diesel what's the temp, its that I read some years ago diesel should be used at 104F (40c) to have the right velocity for the right measurements & Testing Fluid at room temp 70F (21c)
 
I used winter blend diesel fuel at 50f or whatever the temp in my shop was, for the testing.
The tester came with a book. It said to use diesel fuel. I didn't remember any mention of temp. I'll have to check on that. I do remember it saying to not use vegetable oil for testing. The winter blend fuel is thinner[lower viscosity] than straight #2 diesel.
 
I dont think temp and such really matters until you get a tester that measures flow and volume which is not whats happening here. Just observing spray and pop pressure.

If someone was testing various nozzles for flow it would be more complicated.
 
Matt Bachand said:
Cooled by diesel fuel thats been through a heatsoaked, if not HEATED fuel filter, then cooles the IP (supposedly PMD too), then after passing through the V of the engine in the IP, goes to the injectors, 4 of them on the turbo side. I'm not sure how 'cooled' they really get.
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You make it sound like it's almost vaporized before it gets to the injector:eek:. And you forgot how much it heats up from being pumped to high pressure:eek::eek::D
 
Hey,dont ye all get paranoid with all that injection ghost hunting.
if you set the injectors at 2200 psi or close to it,they will settle out slightly below that after a couple hours running and should be good for a 100 k at least.

I have found that purchased new injectors are all over the place for pop pressure and should be tested/reshimmed before install.

BK,maybe you know this,but dont forget to lap the mating surface on both sides of the intermediate washer and the body half to get a leak free connection
 
bison said:
Hey,dont ye all get paranoid with all that injection ghost hunting.
if you set the injectors at 2200 psi or close to it,they will settle out slightly below that after a couple hours running and should be good for a 100 k at least.

I have found that purchased new injectors are all over the place for pop pressure and should be tested/reshimmed before install.

BK,maybe you know this,but dont forget to lap the mating surface on both sides of the intermediate washer and the body half to get a leak free connection
Click to expand...
Do you need to lap "NEW" injectors?:confused: I read about rebuilding and checking in the manual that came with the tester. I didn't think the new injectors should need it because they haven't been heat cycled yet. The book said to use a piece of glass and 3 different grades of wet or dry sandpaper to acheive a almost mirror finish on both halves.
 
bk95td said:
Do you need to lap "NEW" injectors?:confused: I read about rebuilding and checking in the manual that came with the tester. I didn't think the new injectors should need it because they haven't been heat cycled yet. The book said to use a piece of glass and 3 different grades of wet or dry sandpaper to acheive a almost mirror finish on both halves.
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i was actually referring to the used ones you're rebuilding,the new ones should be fine altough it wont hurt to give them a couple of passes,the factory seems a bit sloppy anyway considdering the uneven pop pressures.

I use a sheet of crocus cloth on a piece of glass with some diesel fuel as lub,shines it up nice without scratches
 
BK, thanks for sharing your hard earned efforts with us, i just ordered my set of injectors. Now to find a good injector shop here in the Dallas/Ft Worth area.....
 
I must have missed something here. Where are the injectors from and what was the cost on them? I have a friend that has a tool box lost in his shed with about 50 or so new injectors from his days in the Military Motor pool. Sure wish he'd find it.

John
 
It almost takes all the risk out of the injector purchase because not only do you set the psi yourself, but you visually inspect the entire unit, and the spray pattern.
 
guybb3 said:
BK, would this shim kit work for us? I will only have one set to adjust, so I don't need a ton of shims.

http://cgi.ebay.com/ebaymotors/INJE...mQQptZOther_Vehicle_Parts?hash=item518a53cd6e
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If you have the delphi n/a injectors the most shims you will need are the single or combo to get 1.85,1.90, and 1.95 mm. That is the shim thickness that 23 of 24 I've reset so far have used. I don't know the thickness of the 2 shims that came in each injector. I need to buy a precision caliper or micrometer to measure them. I'm guessing they were at 1.6-1.7 mm at the lower pressure. I would think that the kit you showed would be enough to do 8 if you can reuse some of the original shims. As said before, .05 mm is very close to 50 psi. Be shure to check that the shims are 14.2 mm outside diameter. Hessain imports can make a kit that size for less $. He was at $.85 per shim
 
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