Fuel injector leak down

[dcraigk]

Recently there was a thread that mentioned the amount of acceptable psi an injector can leak down after its popped. I searched the forum and the 'net and I can't find out that number.

I'm trying to figure out why my '85 TD stumbles and smokes when I start it up. It runs great for the first few seconds and then starts acting up.

I bought a pop tester from Uncle Ken and I was watching his video on setup. At the end he's pop testing an injector and takes pressure off the lever. Then it's out of the jack entirely. In the background you can see the injector very, very slowly starts to lose pressure. I have new Firad nozzles and they all drop down pretty quickly, some faster than others.

Any help is appreciated.

[DanHoug]

what happens when you hold pressure at about 150psi below the pop pressure? are you getting dribbling out of the nozzle? if not, you're not leaking and the hydraulic pump is just bleeding pressure through its own seals.

did the car run poorly before the nozzle switch?

[dcraigk]

Ahhh, I guess I misunderstood the other thread.

I think it started running poorly during the end of a Diesel Purge. I'll check the injectors to see if they leak just before they are supposed to pop. I pop tested all 5 this morning and one of them occasionally sprayed when it reached pop pressure.

I have a set of Monark nozzles to put in so I'll toss the Firads.

[dcraigk]

Well I changed one injector to a Monark and I have a question. When I pump it up just below firing pressure I don’t see any leaks. When I try to get it to fire it doesn’t pop, I just get a long stroke with a fine mist. No rapid bursts. These are brand new Monark nozzles. What’s happening here?

[Diseasel300]

Internal leakdown would not cause the engine to run fine when initially started, then start running rough. Quite the opposite. Engine would run rough until the injector pumped back up and bled through.

Bleedoff should be pretty slow if everything is lapped and fitted correctly. No more than 500PSI drop in 30 seconds. Internal leakdown is typically due to a poorly lapped face on the internal pieces, inadequate torque of the injector holder, or carbon/rust built up in the lower holder where the nozzle sits causing a misalignment of the nozzle in the holder.

Personal experience: I went through 2 sets of Monark nozzles in my 603 and swore them off forever. People here seem to like them, but I had nothing but trouble with nozzles hanging up after ~5K miles and causing nailing or smoke. I never had a set that did a good job on the "chatter" test when calibrating and popping, I assume their internal tolerances are too tight. Presently I run Firad 314's in my 350SD and have had ZERO issues with them. I didn't expect them to be very good since they're cheap, but they've totally exceeded any expectations I had for them. Success in rebuilding nozzles is down to how clean and thorough you are and how well the mating surfaces are lapped. It's an art more than a science.

[dcraigk]

So you think the bleed down is from the injector and not the jack(pump)?

The Firad I just tested leaked down 500 psi in 15 seconds. The Monark nozzle in installed in one holder over the weekend was twice as fast.

I’m surprised how little information there is on the internet about rebuilding injectors. Nobody has written a comprehensive document on the subject, at least I couldn’t find it.

[Diesel911]

Originally Posted by dcraigk

So you think the bleed down is from the injector and not the jack(pump)?

The Firad I just tested leaked down 500 psi in 15 seconds. The Monark nozzle in installed in one holder over the weekend was twice as fast.

I’m surprised how little information there is on the internet about rebuilding injectors. Nobody has written a comprehensive document on the subject, at least I couldn’t find it.

How to Rebuild Injectors
http://vincewaldon.com/index.php?option=com_content&task=view&id=20&Itemid=28

In the above sit I only disagree with the method of lapping the precision surfaces.
Not lapping the precision surfaces well can also result in the Injector leaking off.
However, the Injector is suppose to some extent leak off as that is what lubricates the Nozzle inside and why you have return lines coming off of your Injectors.

When I worked in a Fuel Injection shop there was no spec for the time an Injector was supposed to hold pressure. It was merely something that you learned by seeing what was normal and what was not.
In any event I have seen new Nozzles leak or pee out of the tip of the nozzle and be bad but I have never seen any that did not hold the pressure sufficiently where the cause was the Nozzle concerning leak by. It was always a lapping issue.

[Diseasel300]

Originally Posted by Diesel911

In any event I have seen new Nozzles leak or pee out of the tip of the nozzle and be bad but I have never seen any that did not hold the pressure sufficiently where the cause was the Nozzle concerning leak by. It was always a lapping issue.

This has pretty well been my experience too. There is no substitution for correctly lapping the mating surfaces and thoroughly cleaning the lower half of the holder where the nozzle sits.

[dcraigk]

I bookmarked that article before and it is helpful. What it doesn't mention is anything on the pop testing procedure. I know what the spray pattern should look like but I don't remember seeing anything about the gauge leaking down, which my injectors do pretty fast.

I didn't lap these holders because they were just rebuilt by someone else. The nozzles weren't leaking or peeing.

I will re-lap and clean them and see what happens.

I'm trying to eliminate the things that are causing this engine to stumble and smoke.

[Diseasel300]

The faster the injector leaks down, the more likely it is to have problems with fuel delivery at idle. As D911 said above, leak down is normal and is important to lubricate the pintle of the injector nozzle, but the leak rate is very small. Quick leak down is usually due to the holder parts being poorly lapped, the nozzle itself needing the mating face lapped, or the holder having carbon or rust on the nozzle seat causing it to sit cocked instead of square in the holder.

Use some 2000 grit sandpaper on a sheet of glass as your lapping surface. Dribble some diesel on the paper to act as a lubricant. Press the part you're lapping down firmly on the paper and move in slow, wide circles. You will know when the part is lapped, suddenly it will smoothly glide across the paper. The upper half of the injector holder and both sides of the "disc" inside the holder need to be lapped. Bonus points if you lap the sealing face of the nozzle.

To test the pop tester, if you have a shim kit, shim an injector to well above the pop pressure you want and see how fast the pump leaks down. If the leak down rate is the same or faster than with the injectors you're trying to calibrate, perhaps the pop tester is leaking to an extent. Try tightening the release valve slightly and see if it slows or stops.

[dcraigk]

I didn’t know you lap a new nozzle.

[Diesel911]

Originally Posted by dcraigk

I didn’t know you lap a new nozzle.

See the attached picture.
Note be sure you get the parts back in the right order and direction or when you torque it you snap off the protruding end if the needle/Pintel.

Also there is 2 types of Injector Bodies. Don't mix the parts of the different Injector Bodies.
You normally don't have to lap New Nozzles unless there is some obvious scaring on the surface. The Needle/Pintel is mated to that one nozzle body. Don't mix parts as they are not interchangeable.

If you do lap the Nozzle be sure to get all of the lapping compound out of the Nozzle.

[Diseasel300]

Originally Posted by dcraigk

I didn’t know you lap a new nozzle.

After all the BS I went through with the Monark nozzles I had, I always lap the nozzle mating face now. The Monark nozzles I got from a certain "Source" were rough on the mating faces and caused my leak down issues. The key is cleanliness. A good solvent wash and dip in fresh clean diesel to get any grit or debris flushed from the lapped pieces goes a long way towards injector happiness.

[Diesel911]

Is there a way to plug off the Jack/Pop-tester to see if the leak down is inside of the Jack?