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I was able to construct a fuel return flow tester for my LMM. Rough cost about $45. I will try to post the construction details on the DIY forum.

Was able to test the flow rates on the driver side.


Will post results with passenger side bank when completed. Enclosed pix of test aparatus.
Impressive! If you don't mind, how much time did you spend identifying necessary parts, locating and purchasing parts, setting it up, and working out any kinks? And how much time did it actually take to setup and perform the test?

I try to factor the cost of time into any DIY project for cost benefit analysis. (build it or buy it) If not too bad, I may have to give it a try...especially now that you've taken all the hard part out of it when posted to DIY. Plagiarism is the most sincere form of flattery :)

Also, so what's the verdict on the injector returns? It looks like you have 3 bad because there is only one with the lowest volume. I've seen other test results were it was very easy to tell which were bad...two were almost level with each other and were the low mark...the others were all different volumes but all had more fluid.
 

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Discussion Starter · #22 ·
Return test issues

Thanks for the encourgement, I have completed the tests. I am also trying to communicate with the staff to see how I can submit a DIY post. I have written up three: How to make a tester, How to measure API, How to run return test.
I still have some questions to work out on the API calc. I will make some call today and if I come up blank, I will post my questions to this wonderful forum.

Basically, I am doing a manual density test instead of using a special hydrometer to measure the API. Since API is a measure of fuel density and fuel density decreases with heat, the flow rate of each injector will increase with heat. DOes the API pass/fail falues in the manual take that into consideration. I think that they are calibrated to 60F. If I am getting failure as fuel temps over 100 F, should I use a different API value as the threshold?
 

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Discussion Starter · #23 ·
DIY injector return test tool 1

I wanted to do the injector fuel return test on my 2007 LMM Silverado 3500. However, this calls for a special tools J45873 and J45873-30 costing over $100. After looking over the special tool write-up and thinking about it, I felt that I could make one myself a whole lot cheaper using workshop scrap and some inexpensive parts.


This tester seemed to be four graduated cylinders to measure the diesel fuel from the injector return lines. This was coupled with four hoses that connected to four couplings that were inserted into the injector return ports. The test is done one bank of four cylinders at a time.


The four graduated 10ml cylinders cost $2.80 each from Scientific Strategies - Laboratory Products for a Scientific World. p/n 6130-20EA.


The four couplings that insert into the injector return port ( a single Bosh assembly) were $19.30 from HDiesel.com p/n 0928400552.


Also ordered three nozzle plugs for 6.2L at $.72 p/n D14066301 from HDiesel



The four hoses were cut from 25' roll of 1/4" OD X .170" ID Polyethylene tubing for $2.50 available from Home Depot



Total cost about $45 including shipping.
 
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Discussion Starter · #24 ·
DIY injector return test tool 2

The couplings were scrounged from the Bosch replacement return fuel line assay for right side. I just cut off the existing tubing and attached 30" lengths of the polyethylene tubing.

The tubing was later cut to fit once the fixture was mounted in the wheel well.
 

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Discussion Starter · #25 ·
DIY injector return test tool 3

The Return line assay has three "T" couplings and one "L" coupling just like the one on the engine.
 

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Discussion Starter · #26 ·
DIY injector return test tool 4

I used the nozzle plugs to cap the ends of the three "T"s.
 

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Discussion Starter · #27 ·
DIY injector return test tool 5

The other end of the tubing goes into each cylinder.
 

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Discussion Starter · #28 ·
DIY injector return test tool 6

I made a wooden fixture from scrap to hold the contraption together.
 

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Discussion Starter · #29 ·
DIY injector return test tool 7

By mounting it on wires, I could suspend it from the top of the wheel well.
 

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Discussion Starter · #30 ·
DIY injector return test tool 8

I also made it so that I could slide the tubing fixture up the wires and secure them and then rotate the cylinder fixture to dump the fuel.
 

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Discussion Starter · #31 ·
DIY injector return test tool 9 of 9

This has worked pretty well. With the benefit of hindsight, I offer some tips

1. Use polyethylene tubing for testing instead of buying actual fuel return hose, it is much cheaper. Although for repairs to exiting hoses I would get the right stuff available from HDiesel as 6.2 Return fuel hose p/n M-13300 at $.24/foot. The 6.2L hose fit the couplings perfectly.

2. Mount some rubber caps on the part of the coupling that goes into the injector. This protects them from getting grime on them. Swap them onto the existing return line when doing the test to protect them from dirt too.

This took about three hours to make, not including travel times and shopping.
 

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This has worked pretty well. With the benefit of hindsight, I offer some tips

1. Use polyethylene tubing for testing instead of buying actual fuel return hose, it is much cheaper. Although for repairs to exiting hoses I would get the right stuff available from HDiesel as 6.2 Return fuel hose p/n M-13300 at $.24/foot. The 6.2L hose fit the couplings perfectly.

2. Mount some rubber caps on the part of the coupling that goes into the injector. This protects them from getting grime on them. Swap them onto the existing return line when doing the test to protect them from dirt too.

This took about three hours to make, not including travel times and shopping.
Very nice!!! Wow...from $500 to $50 + a few hours...no brainer. Thanks for putting all this together.

How did it turn out? Any bad sprays?
 

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Discussion Starter · #33 ·
I managed to make it happen, but to see what the pass/fail criteria is, I will have to have the API for the Diesel fuel that I was using. Next post to be DIY for measuring API.
 

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Discussion Starter · #34 ·
Diesel Fuel API Calculation 1

Diesel Fuel API Calculation

In order to do the injector return test, you must measure the API of the fuel you are using and use that value to determine what the correct pass/fail threshold is for the test.

As far as I can tell, the API value for your diesel fuel is based on its specific gravity (measure of density) at a particular temperature.
All of the measurements and calculations are done relative to 60 degrees F. You can buy an API tester ($100+), which is similar in operation to the old style hydrometer battery tester, or you can run the test and calculation yourself.

Here are the steps to make the measurement for free

Summary
A. Measure the weight of equal volumes of water and your diesel fuel
B. Measure the temperature of the fuel when you weigh it
C. Calculate the specific gravity (SG) of the fuel using these measurements
D. Normalize the measurement to 60 F temperature using a chart
E. Find the API corresponding to the SG at 60 F


Detailed steps A-C
I used plastic water bottles of about 12 oz.

1. Fill one bottle with the diesel fuel you are measuring about 3/4 full
2. Fill the other bottle with water
3. Make sure both bottles stay together at the same temperature
note: . I went to my local shop for mailing services like UPS etc and used their postal scale
4. Weigh the bottle of diesel fuel
5. Use a black magic marker to mark the level of the fuel
6. Measure the temperature of the fuel when it was weighed
7. Dump out diesel fuel and refill using the bottled water to the level that was marked
8. Weigh the bottle of water
9. Dump out the water and weigh the bottle empty

In my measurement, I had the following values

weight of diesel bottle 11.3 oz
weight of water bottle 13.5 oz
weight of empty bottle 0.4 oz
temp of fuel when weighed 80 F
 

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Discussion Starter · #35 ·
Diesel Fuel API Calculation 2

Subtract the weight of the empty bottle from both the diesel and water weights and then divide the diesel weight by the water weight
Specific gravity = (11.3-.4) / (13.5-.4) = 10.9 / 13.1 = .8317

This gives us the ratio of equal volumes of fuel relative to water at 80 F which is specific gravity at 80 F.

Detailed step D
I found a chart of Specific gravity vs. temperature for Diesel fuel. This chart was plotted for a specific sample of diesel fuel with some API value that is likely different than yours. The assumption here is that generally, your diesel fuel will have a similar temperature vs. SG characteristic .


So looking at the chart of Specific Gravity vs. Temp F for Diesel, the black line is the original plot for their sample of diesel. What we have just measured for our sample of diesel is a SG of .8317 at 80 F. So, for our sample’s plot, it should be a line that is parallel to the black line and has a data point on it of .8371 SG at 80F.

Draw a line up from .8371 and draw a line over from 80 F and then draw a line parallel to the black line which falls on the intersection of the horizontal and vertical lines. This is the Blue line. It represents the temp vs. SG plot for our fuel sample.

Now you must find what the SG would be if the sample was 60 F. Draw a line over from 60 F to the blue line and then drop a line down to the SG axis and read off the value. These are the red lines. The value read at 60 F is .8453.
 

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Discussion Starter · #36 ·
Diesel Fuel API Calculation 3

Detailed step E


Using the API vs SG for Diesel chart, draw a line up from .8453 to the black line and then over to the API axis to 35.9. Now you have the API (35.9) of the fuel you are testing. These are the orange lines.


In my shop manual they indicate that the max reading for the LMM fuel injector return test is from the following table

API v. ml for 15 sec
30-34 -3ml
35-39 - 4ml
40-44 - 5ml

Therefore, you would use the max return rate of 4ml for 15 sec as the threshold for pass/ fail for fuel with API of 35.9.
 

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Discussion Starter · #37 ·
Injector Return Flow Test 1

Fuel Injector Return Flow test for Duramax LMM Engine

Since I was having trouble with a low pressure fault P0087 for the injector fuel pressure, I wanted to measure the return flows of the injectors to see if they may be contributing. This series of steps is my test procedure.

Before I start, I should say that the faults tended to be produced when the truck was pulling a very heavy load and the fuel was hot. Therefore, I was determined to run this test with the engine and fuel hot.

I tested each bank of injectors, first left then right. Each bank took about three hours of setup work. The actual test only takes 15 seconds

Tools needed:
Injector return flow test kit ( see DIY kit Instructions)
API measurement of fuel being tested (see DIY measurement procedure )
12 and 13 mm sockets
Flat blade screwdriver
Thermometer
Stopwatch


In order to get the fuel as hot as possible, I slipped a thin piece of cardboard between the fuel cooler and the screen in front of it to block the air flow during the warm-up.

CAUTION! DO NOT forget to remove the cardboard after the test.

I removed the wheel well liner and removed the cable bolts before going on the warm-up ride so that I didn’t have any cool down time while I took them off.

Took a warm-up ride of 30 minutes to get engine up to temp and fuel hot.


Jack up driver side and place jack stand under for safety.
Remove tire and set aside.
 

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Discussion Starter · #38 ·
Injector Return Flow Test 2

This picture is of the wheel liner that I removed before the warm-up ride. The plastic plugs that hold it in can be removed by gently prying up on both sides at once with a couple of flat blade screwdrivers.
 

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Discussion Starter · #39 ·
Injector Return Flow Test 3

Once the wheel liner is removed, you can see a rats nest of pipes and cables. This is the route you will take to attach most of the injector return hoses. Some injectors are reached more easily from over the fender.
 

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Discussion Starter · #40 ·
Injector Return Flow Test 4

This is the test fixture with the hoses and couplings that go into each injector return port.
 

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