Cleaning injectors

[cranetruck]

During my trip across the USA I replaced all the injectors in attempts to eliminate a loud knocking from the engine.
Changing the injectors didn't change engine performance, which was good throughout the trip.

Burning some 300 gallons of biodiesel and used veggie oil added to my suspicion that I may be mistreating the engine.


The engine stalled at a traffic light just before arriving at Jason's place in Arkansas, but restarted after a few minutes.
There was a leak around line #3 on top of the hydraulic head at this time.

After my visit at Jason's, the engine stalls at a truck stop in Joplin MO and doesn't restart.
Thanks to Jason, Cabell, David Doyle and others the hydraulic head is replaced along with the #3 injector. The engine starts and runs normally again.
The #3 injector appeared to be blocked by coking.

Question #1: How does a blocked injector cause the hydraulic head to fail?

Question #2: How do I test the removed hydraulic head?

Question #3: How do I clean injectors?

Question #4: How do I test injectors?

Question #5: How does the knocking sound relate to a misbehaving injector?


I have a set of six injectors to return to Jason (among other things) and wish to clean and test them first.

Any info on this would be most helpful. TIA.

 

[Hookin1]

most diesel shops can test the nozzles....we have tester..it uses a manual hand pump like a bottle jack pump assembly..basically you hook a fuel line up to the nozzle and check that it's not seeping fuel...that it only opens at certain pressures...and spray pattern out of the nozzle....

as for the hydraulic head....if a nozzle is sticking open it will allow the compression to get back to the pump........

 

[WillWagner]

Also, if a pintle spring in the inj. is weak/broken, that can cause a knocking sound.

 

[cranetruck]

Thanks, every little bit will help.

The image below shows the apparently clogged injector from #3 cylinder to the left and one similar to the one which replaced it to the right.

 

[DDoyle]

Bjorn,
Some of your questions are addressed in my forthcoming book (hence the copyright notation below),but I will be happy to answer some of them here. And I'll warn all, some of these answers will probably not coincide with preconceived notations, which when I was teaching classes on such subjects always seemed to be the biggest stumbling block. I'll starting with Question #1: How does a blocked injector cause the hydraulic head to fail?

First, we have to understand the basics. All the pump does is to power the volume of liquid, the nozzle office is what generates pressure, and controls the spray pattern - the pump itself is not what generates pressure. An everyday comparison is your garden hose, turn on the spigot, and water flows freely, with very little pressure, place your finger in front of the hose end, and begin closing the gap, and the pressure increases. Your finger is creating an office with respect to the end of the hose. The smaller the office (closer your finger is), the greater the pressure. This is the basic principle of any nozzle, injector or otherwise.

The Bosch IP on the Multifuel has two pumps, the hydraulic head, and the supply pump - which each work completely differently. The supply pump is what is known as a gear pump, two gears run together, and push the fluid (fuel) forward through them - rather like the wringer on an old fashioned washing machine or your wife's pasta machine. How the supply pump works is immaterial to your problem, but is included here for reference.

The hydraulic head is the "high pressure" pump - in fact, the hydraulic head is the true "pump" in the injection pump. In technical terms, it is a positive displacement plunger pump. In fact, the plunger is what is under the hex-shaped plug in the top of the hydraulic head. The bottom end of the IP times the stroke of the plunger properly with respect to the position of the pistons in the engine, and also times the rotation of the plunger sleeve, so that fuel flow is directed to the correct fuel line - rather like the rotor in an older gas engine ignition system. But, for the moment, forget that it we are dealing with an injection pump, or that there are multiple cylinders.

In a positive displacement pump, with each cycle of the pump, a specific amount of fluid POSITIVELY will be moved. In the case of the hydraulic head, with each stroke of the plunger, a fixed amount of fluid (fuel) WILL be moved. The bottom end of the IP varies the stroke, and the fuel flow, and shut off. The fuel is an incompressible fluid. A positive displacement pump that we are all somewhat familiar with is a syringe (although syringes are "cup pumps", it is still a positive displacement pump, so the comparison works). When you depress the plunger of a syringe, the fluid will move. Now, if you plug the outlet, and apply enough force to the plunger of the syringe, something will break, and the fluid will move.

That is exactly what happened to your hydraulic head (and precisely why there are so many fuel filters on these trucks) - the nozzle clogged, and on the next upward stroke of the plunger there was no place for the fluid to go, so something had to break - it could have been something in the bottom end of the pump (and frankly, I'm surprised nothing down there was damaged - and maybe it was), it could have blown the end off of the injector - which would have destroyed the cylinder, it could have split a fuel line, or it could have cracked the hydraulic head. In any event, the fluid HAD to move.

As far as testing the failed head - it truly is a paperweight or a pound or so of scrap metal - but you may want to dismantle it to see how it is made. Starting with a solid cylinder of steel, holes are bored parallel to its axis, this are the bore for the plunger, and the connecting points for the injection lines. Other holes are bored perpendicular to the axis, connecting the central bore to six radial bores. The outer ends of these perpendicular bores are then sealed with Allen-headed plugs. (The only other way to make the head would be through EDM machining, which would be VERY costly). I have simplified this slightly, but this covers the basics. When your nozzle clogged, the fluid found its way out around one of these plugs, likely eroding the threads on the way.

Testing injectors requires specialized equipment, and can be dangerous for the untrained - the nozzle generates considerable force, and is capable of blasting fuel THROUGH your skin, and into the bloodstream, with potentially fatal results. Best bet, read the TM and buy the proper equipment, or let your local diesel shop do this.

I'm out of time for now, but will try to address some of your other questions later today. However, an unusual knock from a compression-ignition engine is often related to a timing issue. Since your engine was nicely running along when suddenly the IP pump tried to stop (when the nozzle clogged), and because the timing gears are slotted, it is possible that the timing changed oh so slightly. Also, if the other nozzles are clogging, this will alter their spray pattern. The Multifuel depends on the precise placement of the bulk of the fuel in the combustion chamber in the top of each piston for its smooth combustion - if the placement is not correct - or if excess carbon deposits alter the air flow inside the combustion chamber, atomization of the fuel won't occur properly. This could cause ignition delay (in effect, changing the timing in the cylinder itself) with a resultant knock.

Note the comments in the last paragraph pertain ONLY to the Multifuel - a conventional diesel relies on the injector nozzles to atomize the fuel - a Multifuel is very different.

Hope this helps,
David Doyle
Copyright 2006

 

[jasonjc]

With useing the bio/WVO you are not getting all the extar stuff they put in to the fuel like the cleaners and stuff(not shure what all is in there).
So I would think that a lager helping injector cleaner/lube would be a must. maybe even more that what the package says to use (it is asumeing that you have some of this in the fuel to start with) OK this is my $0.02 I know we have some on here that know more than me so please tell me if and where I'm wrong. Thank you


David please be shure to tell us more about your books and a link to where to get them.

 

[builder77]

After reading this I have to wonder why the IP does not have a high pressure bi-pass if the injector clogs. It would make alot of sense. Otherwise I guess the only fix is regular injector cleaning if that is possible? Very interesting subject here.

 

[jwaller]

you can keep the inj's clean by running WVO or diodiesel.

 

[houdel]

The hydraulic head does not have a "high pressure bypass" because it would not be practical or cost efficient. The hydraulic head has one piston per cylinder to pump a metered amount of fuel, based on fuel delivery adjustment and throttle postion, to a specific injector. A bypass system as you suggest would require six bypass ports to work, adding greatly to the cost and complexity of the hydraulic head. This may be possible on a common rail system, but not on a rotary hydreaulic head. The best solution is to either ship your injectors out to a competent injector test/rebuilding shop, or get a spare set of injectors, have them tested/rebuilt as needed, install them in your engine and then send the original set out for testing/repair and keep as spares. Cost is around $40-$50 to have your nozzles tested and adjusted to spec.

 

[ken]

I've read a few stories on the net about the fats in the oil clogging injectors. They said that cold starts causes unburt fuel to stick to parts. And they recommed only running B-20 to solve this. They said the exaust valves will coke pretty bad also. If the engine/ambent air is warm this usally doesen't happen. Mabye preheating the engine with a block heater will help?
Did all the injectors look pretty clogged? If they were restricted wouldn't that cause the head pressure to rise too high? I've worried about this with the large amouts of used motor oil that i've ran through mine. Although i haven't had any problems. Since the price of diesel had dropped i have switched back to dino diesel. Mabye i'll putt the injectors too see how they look.

 

[DDoyle]

I have a few more minutes this morning, so I thought I'd take a stab at questions 3 and 4. The nozzle and holder assembly of the Multifuel engine is one of the most precisely made and adjusted components of the entire truck. To go back to the garden hose illustration that I used earlier, if we simply have the hose, with our finger over the end, and turn the flow of water off at the spigot, then the water will gradually come up to "pressure", and when we turn the spigot off, the pressure will gradually drop - and as the pressure rises and falls the hose "dribbles." This may not be problem for our lawn, but it would be in an engine.

Thus, there is a calibrated spring loaded valve in each injection nozzle assembly. This valve does not open until the fuel pressure reaches somewhere around 3100 psi (sorry, don't have my books with me) - which gives one an idea of how much force must have been exerted on the failed hydraulic head, given that 3100 psi is the normal operating pressure. At 3100 psi, the check valve in the nozzle suddenly opens, then instantly closes as the pressure drops. This is rather like using a trigger nozzle in our garden hose illustration - the fast-acting valve of the injector prevents the dribbling as pressure rises and falls as flow to that nozzle stops and starts. This quick fuel cutoff allows smooth, even combustion.

While the nozzle can be dismantled (that's what the "flutes" on its body are for, to accept the points of a boxend wrench) - the parts inside are so precisely made that they are not to be touched with bare hands, as body oils can make them stick. Also, when reassembled, the spring tension needs to be readjusted to the proper opening pressure. Without a nozzle test stand this is impossible, and as cheap and plentiful as surplus nozzles are, for only a few engines its likely not worth the time/money/effort to purchase or construct a test stand.

A nozzle test stand allows the operator to manually pump a test fluid, of a known and constant viscosity, into the nozzle while monitoring the pressure with a gauge. During this time the operator watches for fuel leakage, and also that the nozzle "fires" at the proper pressure. Attention is also paid to the spray pattern produced by the nozzle, which varies from engine model to engine model, even among Multifuels.

Cleaning the nozzle can't be accomplished without dismantling it. Probing the nozzle discharge holes with wire while the nozzle is assembled is likely to scratch the precisely ground valve surfaces inside - and ANY scratch will cause fuel dribble. Some have tried soaking in a carbon removing solvent, by my personal fear is that this would merely break contaminants loose, which would reassert themselves in the future.

I hope that this and my earlier post, as well as the contributions of others, have addressed all the questions raised in your first post.

Hope this helps,
David Doyle

 

[rdixiemiller]

The LDS troubleshooting manual (in the tech section) gives a disassembly and check procedure.

 

[Scrounger]

Just my worth. I have never been one for additives over the years for my vehicles. However, there is one that I have found that actually works. It is called 44K by BG Industries. A friend of mine who turns wrenches for a living recommended it for my K3500. That truck had about 150K on it and was starting to smoke from poor combustion. After two cans in one 34 gal tank the truck stopped smoking and definitely ran and still runs better. I ran three cans in my '68 M54 and it definitely made a difference. From what I understand about 44K is that it is a carbon removing compound that cleans deposits from injectors, heads, pistons and cylinder walls. Unlike injector cleaners that are more volatile this stuff is supposed to be less volatile so it can take its time.

 

[WillWagner]

Bjorn, Check this stuff out. It works great, i've seen it raise HP by 20 to the rear wheels just by using it. It was designed for Cummins PT and STC injectors, but it works good on Bosch type nozzles too.

http://www.cummins.com/sa/pages/en/...ces/toolsandequipment.cfm#Premium_Plus_Flush_

 

[rizzo]

what about Lucas injector cleaner?

 

[builder77]

So can any diesel shop test an injector cleaned and checked, or is the multifuel different enough it should go to a shop that is familiar with them? Any good shops that would be suggested? Houdel is the $40-50 price for cleaning a set of injectors, or each?

 

[DDoyle]

I live in an agricultural and trucking intensive area - and any injection pump service shop in the area can perform these tests - note that many diesel shops don't have this equipment, but injection pump shops all do. It is helpful to take the TM pages regarding the nozzle with you, as the spray pattern is not typical.

Hope this helps,
David Doyle

 

[motorolanut]

I have heard good stuff about Lucas products as well as Sea Foam, anyone else wanna chime in on these two??

 

[24-VOLTS]

Just out curiousity. My engine smokes a bit and more upon start up. Would having my inectors cleaned help reduce the smoke?
Or could it be the pistons are picking up some oil from the crankcase due to her age and use.
Any way to diagnose the smoking issue?
Since I was considering having my injectors cleaned also.

Thanks

Phill

 

[DDoyle]

Phill,
I'd pull an engine oil sample and have it analyzed. Cat, and other similar dealers sell the kit and service to do this. It is relatively inexpensive, and can give you an exellent overview of your engine's wear.

Regards,
David Doyle