Injector Leak-off Test

tvacom

New member
Hello All,
I just did the leak down test on my injectors for my 263k miles 2002 170" ex fedex truck. The number one was replaced last month but I started to see Black smoke when I step on it so I did this test. The number 2, 4, and 5 are all over or getting near 1/2. The number 3 isnt even registering (barely) anything(what could that mean). Thanks for the write up on how to do the test it was easy.

The turbo has a little play on the turbine bearing and the vein celenoid makes a buzzing sound under vacuum, Could that be the culprit for the black smoke under load?
(Giving her lots of gas to get up to speed on an on ramp etc)

Thanks
dave
 
Last edited:

flman

Okay wait for it....... Red Herring cop out!
So is this test telling us the tube with fuel in it is going to leak into the cylinder area, or that this injector is not going to get fuel into the cylinder eventually?
 

MillionMileSprinter

Formerly Type2Teach
I'm no expert, but I have figured out a few things about what this test can and can't tell us.
First what it can tell us: if a tube is filled with diesel fuel, it's telling us that the injector is "leaking off" way too much fuel and wearing out. This excessive leak off can allow the fuel rail to not have enough psi, thereby triggering a "no start" or in the case of an 02-03, a complete engine shut down and subsequent "no start" until the injector and fuel cool down enough to not leak off too much and cause low rail pressure.
Here's what the test doesn't tell us:
If the injector is overfueling
If the injector has a bad spray pattern
If the injector is prone to "black death"
If the injector is leaking.
To repeat:
A leak off test (as far as I can tell) is only good for two (very important) things:
1. As preventative maintenance to identify injectors that are wearing out and should be replaced sooner rather than later.
And 2. To help identify the causes of low rail pressure that can trigger a CEL, engine shut down or a "no start" situation.
Hope this is helpful.
Anyone feel free to correct me or add to my incomplete info here.
 

MillionMileSprinter

Formerly Type2Teach
No, you can do it with the engine cold, but the fuel is thinner when it is hot, and therefore "leaks off" even more. So you get a more accurate result with the engine at operating temps. But that's not to say that it won't work with the engine stone cold. I have run the test on vehicles with hot and cold engines.
 

jackbombay

Active member
No, you can do it with the engine cold, but the fuel is thinner when it is hot, and therefore "leaks off" even more.
Thats what I figured, which had me thinking that an injector could pass a "cold test" but fail a "warm test".

I'll see what I get with a warm engine and go from there...

Thanks!
 

jackbombay

Active member
Well, with the engine warmed up about 3/4 of the way I ran the test and had very similar amounts from each injector, 1/2 to 5/8" , the engine did cough a couple times as I was cranking, but certainly didn't run.

My van always cranks briefly when I start it, and a couple of times when it was hot out and I had been running on the highway it took 3-4 seconds of cranking before it fired up so something needs some attention it seems...

If 1.5" of fuel in one line indicates a bad injector which results in long cranking periods when the engine is hot wouldn't 3" combined from all 5 injectors mean result in the same long cranking periods?

Here is a pic from my test, I'm a little puzzled by the different color of the fuel from #2 and #5 as well.

Capture.JPG
 
Last edited by a moderator:

Bajabum

Vi veri veniversum vivus
Thought this might be a simple preventive measure to take since it sounds so simple to do. The question I have is just how difficult is it to get the plastic fittings up off the injectors? I have tried to pull them off while twisting back and forth but they don't want to budge. I realise they have an O ring which makes the seal but is it necessary to use pliers or some other tool in order to get them out. What are the chances of breaking plastic fittings that have been sitting on top of a hot engine for over 200K miles? Hell you would think changing a fuel filter would be a simple task too....................................
 

Aqua Puttana

Poly - Thread Finder
Thought this might be a simple preventive measure to take since it sounds so simple to do. The question I have is just how difficult is it to get the plastic fittings up off the injectors? I have tried to pull them off while twisting back and forth but they don't want to budge. I realise they have an O ring which makes the seal but is it necessary to use pliers or some other tool in order to get them out. What are the chances of breaking plastic fittings that have been sitting on top of a hot engine for over 200K miles? Hell you would think changing a fuel filter would be a simple task too....................................
Once the clips are removed the fitting should pop straight off.

You are correct to be concerned about breaking the fairly fragile plastic fittings. As I recall I was able to get the side of a flat screwdriver blade under the fittings to pry up on it a bit. Be certain to keep the blade in close on the fitting body and go from one side to the other as the fitting begins to rise. Perhaps using 2 blades at once.

Be careful and good luck.

vic
 
Last edited:

MillionMileSprinter

Formerly Type2Teach
I use a needle nosed pliers to remove the clip and then use the same pliers to gently pry the T fitting up. No broken ones yet!
 

Attachments

Bajabum

Vi veri veniversum vivus
The needle nose pliers did the trick without any problems.
The first test I performed with the engine cold resulted in no fuel in the tubes.
Warmed engine to 110 and tried again. Looks like my injectors are OK.
 

Attachments

josh8loop

New member
I have an 2005 E320 CDI 6 cyl Mercedes and performed an injector leakoff test. I did mine at idle with a hot engine and got the following results:

I ran 3 tests and ran the engine until one of the bottles reached the 10mL mark. In my case it took around 6 minutes and 10 seconds at idle to do this. Here are the results:

Cylinder #1: 10mL
#2: 8.5mL
#3: 10mL
#4: 8mL
#5: 8.75mL
#6: 9mL

All three tests came out to within .25mL of each other-close enough to call all 3 tests exactly the same. Supposedly maximum deviation on Bosch injectors is 3x the lowest value recorded. My values seem to be a bit lower than the values you all recorded-then again my engine was running and you all test your with the CPS disconnected. Any thoughts?
 

Sprayfoamjamo

New member
so how much are the injectors, and how difficult is it to replace one? I'm a sprayfoamer, not a mechanic, so is it doable?? replacing an injector that is...typically, how much will the shop cost to do all 5?
 
Last edited:

MillionMileSprinter

Formerly Type2Teach
so how much are the injectors, and how difficult is it to replace one? I'm a sprayfoamer, not a mechanic, so is it doable?? replacing an injector that is...typically, how much will the shop cost to do all 5?
Read the thread entitled "remove, replace, pull injector" in the T1N write up section. That will give you a good idea of what is involved.
 

psychoboy

05&06 Dodge Longs & Talls
just a word of warning...

if you /do/ break one of the plastic nipples, you cannot buy it new from the dealer. they are going to sell you a whole new line with five new nipples, and it ain't cheap.

on the positive side...the new nipples are metal.
 

Aqua Puttana

Poly - Thread Finder
just a word of warning...

if you /do/ break one of the plastic nipples, you cannot buy it new from the dealer. they are going to sell you a whole new line with five new nipples, and it ain't cheap.

on the positive side...the new nipples are metal.
...
 

renchr56

New member
Well now on to my next dilemma. I am doing this leak down test. I have 1 injector pulled completely out. Will I still be able to do this test. Reason I ask is because when I turn the key on I get no fuel flow to the rail and when I crank the engine only a little comes out of the injector line that I have pulled.
 

josh8loop

New member
you need to reread the the directions as how to perform the test, what you did was all wrong.
Maybe I will retest some time with the CPS disconnected. I've got to believe that testing the injector leak off value while the engine is running(more close to normal conditions) should give some useful information. I believe that's how most of the guys testing their vehicles are doing it (with the engine running).
 

Top Bottom