Injector Leak-off Test

MillionMileSprinter

Formerly Type2Teach
Do you think you have a bad injector? Here's a VERY simple test you can do to determine if you have one or more injectors that are already dead or on their way out.
In fact, it's SO simple that while you are doing regular maintenance, it might be a good idea to check the injectors before one leaves you stranded. And from what I've read on the list, it's WAY easier to get injectors out of a hot engine than a stone cold one.

[EDIT - UPDATE: I have learned that doing the test with the engine hot is a more accurate way to test the leak off quantity. https://sprinter-source.com/forums/showpost.php?p=439828&postcount=47]

1. Purchase 3/8" ID clear tube from home depot- 2ft
2. Cut it in 4" lengths.
3. Take injector cover off
4. Pull clips off of each of the return fittings on top of the injectors
5. DON'T LOOSE THEM (I keep a clean peanut butter jar with lid around just for this purpose- they store the cut sections of tubing in them when not holding the clips)
6. Carefully pull the return line plastic fittings up and off the injectors (they can break- I've never broken one, but I have read on the forum that the only source for them is Andy)
7. Unplug the Cam sensor (next to injector #5)
8. Fit one tube over each injector head
9. Using a vice grip and cardboard, pinch the fuel return line BEHIND the "T" for #5 injector- fuel can come backwards out the fittings and you can have a mess on your hands.
10. Crank the engine for a full 10 seconds- it won't start because you have your cam sensor unplugged.
11. Check for one or more tubes that are overly full. Andy told me that 2.5ml or more fuel in the tube meant that it was time to replace the injector. I just measured this and in that 3/8" tube on the injector, that would be right at 1 and 1/2" or 37mm for the rest of the world.
Here's a picture of an obviously bad injector followed by two pictures of the same engine (mine) with the #2 injector replaced and other injectors following suit after about 500 miles.

Added by vic said:
Confirmed same results seen by SneakyAnarchistVanCamper. I performed both tests. Did the one as per the manual first with the fuel rail solenoid unplugged and got ZERO leakage. Not even a drop of fuel appeared above any injectors. However, when I plugged the fuel rail solenoid back in, I got results similar to other posts in the writeup. The picture is after performing the test with solenoid plugged in. Regardless, since both tests appear to have passed (#5 was the worst, but still under 1.5"), I'm deeming my injectors OK as far as this test is concerned. I'm still hoping maybe someone has an answer why the two different methods produce different results and which one should be used for determining when to replace injectors.
The injector leak off test is useful when diagnosing starting issues at cranking speeds.

The fuel rail pressure needs to be above 3000 psi for starting to occur.

For the test to be valid you must have proper feed pressure and the rail solenoid needs to have its electrical connector plugged in.

Rail pressure with solenoid plug disconnected will be limited to approx. 870 psi max.

If you do not have cranking speed rail pressure issues, this unplugged reduced pressure will not be enough to reveal accurate injector leak off.

If you have serious starting issues due to very low rail pressure (and caused by severe injector leak off) the offending injector(s) will likely be revealed at low rail pressure and electrical plug status may not matter.

Doktor A
 

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MillionMileSprinter

Formerly Type2Teach
No problem, Alex. I was surprised that there was no DIY write up on it, and I actually just heard about it from another member when I tried it. I never saw that post you linked to.
It was just so simple and effective and I had photos, so I figured I would take a few minutes to write it up. Good luck and let us know the results of your test.
PS- if you happen to have a bad injector and need to replace it, there's a great write up on it here in the T1N Write-Ups section. I did #2 and my experience was an easy one. I didn't need the special puller. I'm replacing #5 tomorrow, and I'm hoping I won't need the puller for that one, either.
 

surlyoldbill

New member
Thanks for the write up and the pics. Also, you can get a hose clamp at Harbor Freight for about $4-5.
 
thanks for this. andy told me how to do this on the phone the other day and i was a tiny bit confused. this make it all come into focus. should check it this weekend.
 

SewerRatz

Illinois Licensed Plumber
Thank you for sharing a great write up. One question, where did you get the new injectors from and how much should I expect to pay per injector?
 

talkinghorse43

Active member
1/2" is OK.
 

NelsonSprinter

Former Nelson BC Sprinter
.... the leak test and all injectors go up about 1/2" up the tube with fuel and was wondering what that meant. /QUOTE]

Much more than 1/2" of fuel in the tube means a clogged or worn or defective injector, needing replacement.
 

woodgrain

2006--2500--118in.--60kmi
What is the point of disconnecting the cam sensor? Is it just so the engine won't start? Or something else?

thanks
 

Aqua Puttana

Poly - Thread Finder

Sasha2006

New member
this was my first time trying this test. Here are my results
Injector #1 - 1/2 inch
Injector #2 - 3/4 inch
Injector #3 - 5/4 inch
Injector #4 - 1/2 inch
Injector #5 - 5/8 inch
i am wondring what is the amount of fluid; to consider replacing the injectors?
 

jdcaples

Not Suitable w/220v Gen
this was my first time trying this test. Here are my results
Injector #1 - 1/2 inch
Injector #2 - 3/4 inch
Injector #3 - 5/4 inch
Injector #4 - 1/2 inch
Injector #5 - 5/8 inch
i am wondring what is the amount of fluid; to consider replacing the injectors?
I can see how you could miss this the first time

<snip>
10. Crank the engine for a full 10 seconds- it won't start because you have your cam sensor unplugged.
11. Check for one or more tubes that are overly full. Andy told me that 2.5ml or more fuel in the tube meant that it was time to replace the injector. I just measured this and in that 3/8" tube on the injector, That would be right at 1 and 1/2" or 37mm for the rest of the world.
<snip>
More than 2.5 milliliters in the tube, which is about 1.5 inches of fluid depth in a 3/8-inch tubing.....

-Jon
 

Sasha2006

New member
thank you for your reply, I did crank the engine for 10 seconds. And that was my result; but yea I must of missed number 11. looks like my injectors still have some life in them.
 

416cdi

04 LWB 416cdi T1N OM612
Finding a thread like this gives me delusions of being able to do mechanical things to my van :bow:
 

sassmatt72

2006 high top long, Fully converted by me
did you clamp the return line? I can't see it in pic and without that would give mixed results at best.
"using 3/8" tube look for more than 1.5" of fluid (this is too much, less ok)
yours looks low(i.e. O.K.).
but then there are more than one type of injector leak, the injector it self (leaking diesel to the external area), the pressure circuit within the injector leaking pressure into the return circuit (this test), and compression seal leakage past and around the injector (resulting in black death (coke built up under top cover)....
Step right up & roll the dice, which do you have?
 

amrbackup

New member
For my non metric friends that are challenged to measure the amount of diesel in the tube. 2.5 ml = 1/2 tsp. Or you could use google to search to their calculator: ml to tsp conversion
I found it easy to plug the end of the tube and pour in 2.5 ml of water to see the location of the amount, it won't be the exact place on the tube because the tube fits into the injector, but at right around 1 1/2" from the plug point should be the max level talked about. One could always use an eye dropper and suction out the diesel and measure into a 1/2 tsp measuring spoon that you did not:rolleyes: get from the kitchen drawer
 

orson

New member
Thanks for posting this, I've been dreading the diagnostic cost for years after starting to detect a slight miss.
 

load2go

New member
Do you think you have a bad injector? Here's a VERY simple test you can do to determine if you have one or more injectors that are already dead or on their way out.
In fact, it's SO simple that while you are doing regular maintenance, it might be a good idea to check the injectors before one leaves you stranded. And from what I've read on the list, it's WAY easier to get injectors out of a hot engine than a stone cold one.
1. Purchase 3/8" ID clear tube from home depot- 2ft
2. Cut it in 4" lengths.
3. Take injector cover off
4. Pull clips off of each of the return fittings on top of the injectors
5. DON'T LOOSE THEM (I keep a clean peanut butter jar with lid around just for this purpose- they store the cut sections of tubing in them when not holding the clips)
6. Carefully pull the return line plastic fittings up and off the injectors (they can break- I've never broken one, but I have read on the forum that the only source for them is Andy)
7. Unplug the Cam sensor (next to injector #5)
8. Fit one tube over each injector head
9. Using a vice grip and cardboard, pinch the fuel return line BEHIND the "T" for #5 injector- fuel can come backwards out the fittings and you can have a mess on your hands.
10. Crank the engine for a full 10 seconds- it won't start because you have your cam sensor unplugged.
11. Check for one or more tubes that are overly full. Andy told me that 2.5ml or more fuel in the tube meant that it was time to replace the injector. I just measured this and in that 3/8" tube on the injector, that would be right at 1 and 1/2" or 37mm for the rest of the world.
Here's a picture of an obviously bad injector followed by two pictures of the same engine (mine) with the #2 injector replaced and other injecters following suit after about 500 miles.
Will this same process work on a 07reg 311cdi engine?
 

NelsonSprinter

Former Nelson BC Sprinter
Will this same process work on a 07reg 311cdi engine?
Yes all Common Rail Direct Injection systems will work this way
 

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