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Old 09-21-2014, 12:24 AM   #21
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Default Re: Injector Leak-off Test

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 by tvacom; 09-21-2014 at 02:55 PM.
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Old 12-30-2014, 08:06 PM   #22
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Default Re: Injector Leak-off Test

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?
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Old 12-31-2014, 12:55 AM   #23
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Default Re: Injector Leak-off Test

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.
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Old 01-27-2015, 06:12 AM   #24
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Default Re: Injector Leak-off Test

The engine should be up to operating temp for this test, yes?
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Old 01-27-2015, 11:05 AM   #25
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Default Re: Injector Leak-off Test

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.
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Old 01-27-2015, 04:39 PM   #26
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Default Re: Injector Leak-off Test

Quote:
Originally Posted by Type2Teach View Post
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!
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Old 01-27-2015, 09:45 PM   #27
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Default Re: Injector Leak-off Test

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.

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Old 04-02-2015, 03:34 AM   #28
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Default Re: Injector Leak-off Test

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....................................
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Old 04-02-2015, 12:53 PM   #29
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Default Re: Injector Leak-off Test

Quote:
Originally Posted by Bajabum View Post
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
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Last edited by Aqua Puttana; 04-02-2015 at 12:58 PM.
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Old 04-02-2015, 08:15 PM   #30
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Default Re: Injector Leak-off Test

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!
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