Adjusting injector pressure

[veggie]

Anyone played with the injector pressure on a Listeroid?

When I discussed engine speed and HP with the factory, they advised me to drop the injector pressure if I intend to drop the engine speed from 900rpm to 650rpm.

Here are the instructions I was given:

If you want to reduce the rpm please reduce the injector pressure to 180, (currently set at 220 )
In case you want to reduce the injector pressure follow the steps below.
- Remover overflow pipe from the injector
- Unscrew overflow nipple
- Remove injector cap, (You will find one screw)
- loosen screw slightly by 1/4 turn and the nozzle pressure will drop down.
- With lower nozzle pressure vibration will also reduce.

1] Anyone tried this? and does it result in smoother operation at lower speeds.?
2] Why is this necessary ?

cheers,
veggie

[mobile_bob]

changing the injection pressure will alter the timing a touch, but more importantly it will change the fuel atomization
and by extension the burn rate of the fuel.

it stands to reason if you want to run slower you might also want to slow the burn rate to lower cylinder pressures to a safe
level and also spread the pressure over a larger amount of crankshaft degree's.

that would be my bet anyway.

bob g

[bschwartz]

Oooooooohhh....... I see a turn in the opposite direction for running thicker fuels (ie. WVO) 

[veggie]

Oooooooohhh....... I see a turn in the opposite direction for running thicker fuels (ie. WVO) 

Soooo.... If running slower (turn counter clockwise 1/4 turn).....AND if burning WVO (turn clockwise 1/4 turn)...then I had better leave the screw alone !

veggie

[Horsepoor]

I found an interesting article on how to build your own injector "pop tester" for under $100.

http://www.peachparts.com/shopforum/showthread.php?t=224334

Bruce

[Henry W]

Warning,

Some of the fittings he has used are not rated for high pressure.

Using sub-standard materials for a piece of equipment that see's high pressures is dangerous. If there is air in that pop tester, It could be a bomb waiting to go off.

I am not even going to get into the required list of materials to make a safe pop tester. Just to much to get into. From 1978 to 1984 I was a plumber/pipefitter for a company that built wood pressure treating plants and  high pressure steam generating plants. Lots of the pipe used was Schedule 80 and 160 seamless pipe. Some jobs required all welded joints to be xrayed. I have seen what type of damage been caused by wrong materials and faulty assembly.

I was in a room once and some co-workers did not bleed all the air out of a system that was being hydrostatic tested. Well a pipe cap let loose and went through a cinder block wall.

Also, fuids under high pressure can cause serious injury.
Check out this link: http://biodiesel.infopop.cc/eve/forums/a/tpc/f/159605551/m/6111024582/p/2

Sometimes its be best to purchase equipment already made. Materials that can withstand high pressures are not cheap and you might not save as much as you think you will. I just don't want to see anyone get hurt.

Henry

[Horsepoor]

Wow, what a compelling photograph. Makes me wonder how much I might save by trying to build a $100 pop tester, instead of buying a $300 India version. The medical deductable alone would account for the difference. Thank you for an interesting article post.

[Geno]

I had a tester given to me by a school bus repair facility. They didn't need it any more with the new injectors. I'll bet there's a lot of them laying around in diesel repair shops. Here's how my injector tested.

Pressures from full out (ccw) in turns. YMMV
1 turn CW=500 lbs
1.5=700
2=1100
2.5=1400
3=1700
3.5=2000
4=2300

Thanks, Geno

[carbon-rod]

I just searched up pressure sensor on ebay and I found an electronic one for about 30 bucks, I wonder if it could be plumbed inline with the injector, a max voltage sensor could capture the maximum pressure it sees during normal running or just cranking over the engine saves the mess with trying to pump it up manually, hard part is getting it plumbed inline.

[billswan]

I just searched up pressure sensor on ebay and I found an electronic one for about 30 bucks, I wonder if it could be plumbed inline with the injector, a max voltage sensor could capture the maximum pressure it sees during normal running or just cranking over the engine saves the mess with trying to pump it up manually, hard part is getting it plumbed inline.

You are forgetting part of the testing involves how fast the injector leaks down no way to check that with a running engine. Also a weak pump would through off the test. My advise just buy a used piece of test equipment and skip the cobbled up home made stuff. That is the route I took.

By the way welcome to the forum.

Billswan

[dieselgman]

It is reasonable to sense the injection pressure externally on the injection line, we have used such sensitive devices to set timing. However, this only reads the injection pulse, not the actual pressure. To actually read internal pressure accurately only a bench test rig will do.

dieselgman

[carbon-rod]

Thanks for the welcome billswan!

Ah ok I was unaware that the leakdown time was also a factor that needed to be measured (I am quite new to small engines, my first engine should be on it's way in a few weeks).

dieselgenman, I am not sure how accurate the cheap sensor would be, I doubt it would be as accurate as a proper bench rig though like you suggested. The way I meant to hook it up was as an analogue reading to read the actual pressure not as a digital switch to read a pulse when the injector actually fired. Good idea to set the timing though, the sensor could act as the trigger for a timing light if someone was really keen...

[dieselgman]

That electronic pulse method is standard methodology for John Deere, maybe others.

There are other things that you can determine with a proper bech pop-tester as well. You can observe the actual spray pattern, determine if there are any drips or dribbles, time the leak-down, and adjust to your hearts content with everything in the open. There is no practical replacement that I am aware of. We use these on all builds including testing all new components as a part of the installation process.

dieselgman

[veggie]

I think my "Tiny-Tach" (diesel version) works on the same principle.
It has a small caliper which clamps around the injector line and counts pulses.

veggie

[carbon-rod]

mmm too true dieselgman, definitely no replacement for the proper kit.

That's a great way to detect the RPM veggie, I'm building a device at the moment to monitor the AC frequency and control the speed from that, never thought of harnessing the injector pulse.