Injector Leak-off Test

Josh, the test is for when the engine is cranking, not running. If you have the cam sensor wire unplugged, the engine will NOT run. Since I wrote this DIY up, though, I have learned that doing the test with the engine hot is a more accurate way to test the leak off quantity.

Thanks for the write-up Dennis.
I made a PDF from it that I printed out and took with me to the garage to do my test. Posting it here if anyone just wants to print it out.

....broke a clip. Any one have a OEM part number for the clips or the whole fuel line? The Amazon link above looks aftermarket .....

No need to go OEM on these. If you can wait, this kit from the UK is a good deal:
http://www.ebay.com/itm/281466773901

How does the leak line attach to the return fuel rail? The nipple on #5 broke in the injector and I have new leak line ordered. I cannot tell how it attaches at the banjo bolt. Any help much appreciated.

jmblaes said:

How does the leak line attach to the return fuel rail? The nipple on #5 broke in the injector and I have new leak line ordered. I cannot tell how it attaches at the banjo bolt. Any help much appreciated.

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I don't know the specific answer.

If there is no clamp or clip a little help from a heat gun to soften the tubing may allow easy removal from a metal nipple.

A bit of heat often helps with tubing installation too.

I use boiling water for pool and spa tubing. Boiling water water can be used for fuel tubing too. I just give a couple good shakes and blot the end with a paper towel before installation. As a practical matter there just isn't that much moisture left. Some may disagree.

vic

Is there a minimum amount which the test should show? I'm getting between 1/4 inch and 1/2 inch on each injector. Could this indicate my injectors are over fueling? I have had some black smoke ever since my engine was rebuilt.. Thanks in advance.

vanski said:

Is there a minimum amount which the test should show? I'm getting between 1/4 inch and 1/2 inch on each injector. Could this indicate my injectors are over fueling? I have had some black smoke ever since my engine was rebuilt.. Thanks in advance.

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The leak off test won't directly show an overfueling injector. It tells you the internal wear of the injectors mechanical components. A worn injector is more likely to have a problem.


There isn't a minimum, but one injector reading very low would be suspicious.


The leak back is a function of the clearances (wear) in the ball seat and around the needle of the injector, so it will always have some leakback.

Overfueling is usually caused by the injector sticking open, or damage to the seat/seal where the needle sits. Either of these can cause the injector to drip fuel into the engine when closed, or cause excessive fuel to be injected during when its open.

The manual says to disconnect the fuel rail solenoid while doing this test. 14-2 Fuel systems pg 980

The write up does not mention this.

I did this test with the rail solenoid unplugged, and it didn't leak. With it plugged in, it did leak. So I think this is affecting the test, assuming mine is not faulty.

SneakyAnarchistVanCamper said:

The manual says to disconnect the fuel rail solenoid while doing this test. 14-2 Fuel systems pg 980

The write up does not mention this.

I did this test with the rail solenoid unplugged, and it didn't leak. With it plugged in, it did leak. So I think this is affecting the test, assuming mine is not faulty.

Click to expand...

I had the same question on why the manual says to unplug the solenoid, but the writeup doesn't mention it. I'm curious why unplugging it would affect the results, but evidently it did for you. When you had leakage with the solenoid plugged in, was it enough to say the injectors were bad? Or was it just the difference between no leakage and a little bit of leakage between the two tests... but injectors OK in both?

I'm trying to decide if I should follow the writeup or the manual procedure...

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.

doug022984 said:

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.

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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

Excellent guide, thank you. Not too sure about my results though. Injector 1 was just under 1.5 inches. #2 was not too far away either. The other 2 seemed OK for now.

So I'm thinking I need to replace #1 now and buy a spare for #2 in a few months (are reconditioned injectors worth the saving? like this one: http://www.ebay.co.uk/itm/Mercedes-...596713?hash=item3d30bb7569:g:pzEAAOSw9ENZod1e)

My tests came out very slightly under the 1.5 inch limit each time. Does this mean injectors are not the cause of my vans refusal to warm start? (starts and runs fine from a cold start). I've changed the o-ring in the pressure regulator, should i replace the cam shaft sensor too? that seems to be the last thing that ticks the warm start symptoms


Here's a video, would you expect this much leak off to prevent a van warm starting? https://youtu.be/7H97mPHqL_E

I recently blew a hole in my #5 piston after only 50,000 miles and everything I've read indicates that it's probably due to improperly burnt fuel overheating a small part of the piston head.

This stuff is beyond my pay grade so please go easy on me, but could it be related to a bad injector?

cacaw said:

... but could it be related to a bad injector?

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Yes. I believe it *could*.

Now that the bad injector piston failure possibility is highlighted in this Sticky, please take further discussion back to your original thread here:
https://sprinter-source.com/forum/showthread.php?p=594061#post594061

Thanks.
vic

It's beyond my pay grade too.

Based upon my post here:

https://sprinter-source.com/forum/showthread.php?p=587430#post587430

I believe some of the pictures in the provided links convinced me that your failure could have been related to a bad injector.

To answer your question.

cacaw said:

... but could it be related to a bad injector?

Click to expand...

Yes. I believe it *could*.

Now that the bad injector piston failure possibility is highlighted in this Sticky, please take further discussion back to your original thread here:
https://sprinter-source.com/forum/showthread.php?p=594061#post594061

Thanks.
vic

2 each posts related to piston failure are moved to here.

Stuck in the desert - sudden power loss
https://sprinter-source.com/forum/showthread.php?p=594061#post594061

The possibility of bad injectors causing piston failure was highlighted by Cacaw's question. Further piston specific discussion will take this Leak Off Sticky too far of topic.

Please refer input to the other piston damage thread.

vic

Is it safe to unplug an injector with the engine running to check for over-fueling injector?
I am thinking a heavily over-fueling injector may keep the engine running fine when briefly unplugged as its fueling all the time.
I would expect a functioning injector to make the engine note change a lot when unplugged.

Is that a valid test as it would be on a petrol? Is it safe to do briefly? I have no o2 sensors to worry about.

I have 2 that are near the leak-off limit and 2 that barely register in the tubes. Thinking they are now most likely the cause of huge fuel consumption as pretty much everything else has been ruled out. (170K original injectors)
Would the 2 that have high leakoff be suspected as over-fueling due to being "sticky"?

Hi all, my sprinter is 2001 year 413 cdi.
here is my Injector Leak-off Test
are you comments ?

no:1 10 mm
no:2 15 mm
no:3 15 mm
no:4 10 mm

Hey ya'll, is it possible to introduce air into the system if the fuel line isn't clamped well at the last T-connector? We have air in the lines now, after doing this test, and we didn't before. On the first crank, I noticed that fuel was still coming out of the line, not the injectors. (Fuel never came out of the injectors, but that's a different thread...)

Just wondering if it's possible to introduce air into the system from the fuel line not being clamped correctly. 2002 former FedEx van , 158", 903.

Almost nothing from the injectors except number 4. When I took the t connections off I noticed a hissing sound. Any idea why?


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