Need Pop testing Advice
 

Hi All
I've built a bottle jack pop tester that seems to be working OK.

I have five injectors pulled from the junk yard the five from my '85 300td. Without taking them apart they tested from 1650 psi to 1950 psi. I have six that test at 1900 psi. - but two of those have a less than perfect spray pattern.

I disassembled & cleaned the five from the junk yard. Two of those developed a long single stream from the tip at lower pressure and then pop as usual at higher pressure. What did I do wrong to develop this single stream?

I notice that when I pump the tester fast - I get repeated pops at lower guage pressure. But when I pump slowly I get the pop pressures reported above. The rapid pop may not really be a lower pressure but just that guage doesn't reach the slow pop pressure. Any thoughts on this?

If I end up with five injectors that pop at 1900 psi and a good spray pattern - is that good enough even though I'll be a 131 bar instead of the 135 bar recomended? Or should I try to get them all to 135 bar with shim changes?

The hole at the end spray needle is really tiny and I have nothing small enough to insert and check if they are open. I read somewhere here about using music wire for this. Is that correct and if so - wheere do you buy it? Or - other suggestions?

What about the other holes and passageways - do they also need to be cleaned?

I've read about using Untrasonic cleaning - is that necessary for a good job?

So far I'm soaking the parts in carberator cleaner and then spraying them off with brake cleaner. Is there something better to use?

Of couse it would be easier to just send them off to be rebuilt - but for me the fun of owning my Mercedes is the learning experience. So all help & advice is welcome & appreciated.

Joseph

The MB FSM for the 617.95 engine specifies 120 bar as the minimum acceptable pressure for used nozzles.

I rebuilt mine a while back. You pump slowly until they pop. On my 240D non-turbo they pop around 1600 or 1650 psi - can't remember. They aren't supposed to leak any fuel. You have nothing until it pops and then you're supposed to get a mist. They should all be set within around 50psi of one another. You can buy a shim kit to adjust the pop pressures. Hope this helps.

Scott

The 2 Injector Spray Nozzle parts are a mated set. If any of the parts get mixed with others they most often will stream due to the fact they do not seal in their seating area.
Dirt in the seating area will also cause them to stream.
Rebuilding Injectors is one of the jobs where clean compressed Air is extremely helpful to get loose stuff out of the passages.

If the Gauge you used ins Liquid Filled when you pump fast the Needle will always lag behind because the Gauge is made to dampen pressure Fluctuations.
On Factory Made Pop Tester there is a valve that you close off to protect the Gauge (the Gauges are not liquid filled) when you work the Tester Handle fast and hard. Not closing the valve can sometimes damage the Gauge.

The Factory Service Manual has the info on what size of Music Wire to use. I guess the measurement will be in mm.
You put the short piece of Music wire in a Pin Vice (it has a tiny Cuck to hold the wire). Where I used to work we would grind an Hypodermic Needle type point on the Wire and sort of drill our way through the Carbon with it.
Places like McMasters Karr and Granger sell different thicknesses of Music Wire. However, one box has 100s of feet and it is costly.
Way back 30 years ago some Music Stores used to sell individual Strings; but it would be dumb luck if one matched the size needed.
One of our members has the official Bosch Cleaning kit as show in the Manual. If he reads this perhaps he would loan it out.

a piano tuner may be able to help out with wire.
I have found that if you just give the injector a few good pumps with the pop tester you will remove the gunk.
Be careful poking a wire up the hole. If it jams & breaks of you have a wreaked tip.

A hobby store will often carry the wire required, I work at a hobbytown and we do, it's made by a company called K+S and a 3 foot section sells for a few dollars.

Thanks for the info!

OK the Service Manual does not say what size the wire is. But, it gives the size of the tiny central hole in the Pintel. You will need to use a Wire that is undersized or it will indeed stick in the hole and sometimes break off.

The origional Nozzles had a 0.15mm Central Hole
In Nov of 1981 the hole size was changed to 0.20mm

Also where I worked between 1975-1980 we used Carburator Dip to loosen the Carbon on Injectors and Turbo Chargers. I do not know if the newer less toxic stuff they make now will do the same thing.

A Ultrasonic Tank could also work with some chemical cleaner.

On eBay they have some ads for K&S ENGINEERING wire.

In both cases it would work better if the central Hole was cleaned out with the Wire first so that the Chemicals could actually get inside.

Hi All
Thanks for all the great info. I'll follow up on the K&S wire
Regards,
Joseph

FYI Data.
 

HOW-TO: Rebuild Diesel IDI Injectors
http://vincewaldon.com/index.php?option=com_content&task=view&id=20&Itemid=28

Hi
Thanks. A very interesting DIY. I was quite surprised to learn that lapping the surfaces could take off enough metal to raise the pop pressure so much.
Joseph

Anyone know of a good source for shims?

My experience does not support that theory. I suspect that there are other variables that are not being accounted for.

Call Phil here. He might have them.

Scott

[QUOTE=Diesel911;2410428]OK the Service Manual does not say what size the wire is. But, it gives the size of the tiny central hole in the Pintel. You will need to use a Wire that is undersized or it will indeed stick in the hole and sometimes break off.

The origional Nozzles had a 0.15mm Central Hole
In Nov of 1981 the hole size was changed to 0.20mm
QUOTE]

Hi Diesel911
Thanks for the size. Lots of music wire on e-bay but too thick to fit.

Then I found www.smallparts.com. They carry .0065 dia.(.165mm) wire in 304v stainless steel. $4.74 for 30 inches - plus $4.19 shipping - sold by Amazon.com.
Regards,
Joseph