What is the best way to test fuel injectors on our motor?

blackout51

Original poster
Member
Oct 18, 2012
157
I'm still trying to get my idle issue nailed down (only misfire at idle and not so much that the cel flashes or even lights up) and I'm just trying to weigh all my options, coils are all working good, new plugs, new fuel pump, clean throttle body, and checked all bolts on intake manifold. I'm just trying to figure out what's the best way to test for leaking injector.
 

TangoBravo

Member
Dec 5, 2011
208
Did you check the CPAS?
 

jbacklund

Member
Dec 16, 2012
118
There's not really any DIY method to balance test the injectors. You could get a little hint from the spark plugs to see which cylinder is running rich.

Pull them all and send to a shop for balance testing and cleaning. Either way you'll have to do the job if there's a leaking injector.
 

blackout51

Original poster
Member
Oct 18, 2012
157
jbacklund said:
And I forgot. Read a while ago about the possibility to do a balance test with Tech II.

I just really don't want to pull the intake manifold if I'm not 100% sure I have to, where do I test with a tech 2?
 

CaptainXL

Member
Dec 4, 2011
2,445
blackout51 said:
I just really don't want to pull the intake manifold

Whoa there. no need. An injector balance test is done with a Tech2 or equivalent bidirectional scan tool. Some misfires at idle are normal. This is documented in a couple TSB's.

[video=youtube;3CTuRW27n_Q]http://www.youtube.com/watch?v=3CTuRW27n_Q[/video]
 

mrphoenix80

Member
Jan 1, 2013
251
A Tech 2 can do a injector balance test. However GM has a new tool called an Active Fuel Injector Testor(AFIT) that flow tests each injector with no disassembly. Plus it will give you a % of difference in flow rate. I love this thing! It shows the flow rate change in .1% increments. Anytime I have a question about injectors I break this baby out and know in minutes.
 

CaptainXL

Member
Dec 4, 2011
2,445
mrphoenix80 said:
A Tech 2 can do a injector balance test. However GM has a new tool called an Active Fuel Injector Testor(AFIT) that flow tests each injector with no disassembly. Plus it will give you a % of difference in flow rate. I love this thing! It shows the flow rate change in .1% increments. Anytime I have a question about injectors I break this baby out and know in minutes.

Why would someone buy an AFIT? They are like $2000. You can buy a used Tech 2 for under $800. Some on ebay can be had for $500. The MDI's that are replacing the Tech 2 are $800.
 

MAY03LT

Member
Nov 18, 2011
3,412
mrphoenix80 said:
A Tech 2 can do a injector balance test. However GM has a new tool called an Active Fuel Injector Testor(AFIT) that flow tests each injector with no disassembly. Plus it will give you a % of difference in flow rate. I love this thing! It shows the flow rate change in .1% increments. Anytime I have a question about injectors I break this baby out and know in minutes.

That sounds pretty neat. Have you had it catch something that the injector balance test didn't?
 

mrphoenix80

Member
Jan 1, 2013
251
When you do a balance test it shuts the injector off and you see the RPM drop. If you drop the same across the cylinders that is the best you can hope for. With the AFIT it does a flow test that will give you a result like... inj1 +1.2%, inj 2 -2.3%, inj 3 -50.2% and so on. Any thing over 8% is an issue. You may not have a full clog but it will tell you if you are off a bit. I have not caught anthing on the T trucks but on K trucks I have. A lot of the newer stuff even has a code for fuel trim imbalance bank1 to bank2. The AFIT is a huge help in tracking these codes down.

On a side note I still have not figured out how they get the bank1 to bank 2 info on the Uplander vans. I understand on the fullsize trucks with 2 sets of O2's. The Uplander is a V6, but only has 1 up stream and 1 down stream O2. I have asked the engineers and have not got an answer yet. Best guess is a timing thing????
 

CaptainXL

Member
Dec 4, 2011
2,445
Do all dealers have AFIT? How do I request this test? Does it provide a printout like when getting an alignment?
 

mrphoenix80

Member
Jan 1, 2013
251
They should have it. It is an "essential tool" meaning the dealer gets if they want it or not. So then the question is do they know where it is?? And do they have someone that can run it? Honestly running it is the easy part. It hooks to the DLC, and the Schrader valve on the fuel line, and the Battery. Then you build your vehicle like on any scan tool and follow the steps on the screen. Once the test gets going you can walk away for about 10min and it's done.

I can't believe it, but it does not have a printer. With the way GM wants warranty RO's documented, I would have thought it would. The new battery charger even has a printer!(but the charger is a whole other issue:hissyfit:)

EDIT:I don't know how to ask for the test because you have to go through the service writer(and he won't know what the AFIT is). You could ask "Can I have my injectors flow tested?? I hear you have a tool that will give very acurate readings on flow rate."
 

jaguarjoe

Member
Nov 22, 2012
73
I haven't tried this on my TB, but it worked on my Jags-

Assemble a cylinder from an 8" long hunk of 2 or 3" PVC and two end caps with barbed fittings on each cap. Mount this to keep it upright. Attach a small air regulator to the top of it set at 43#. Attach the lower fitting to the inj. inlet. Make an injector holder so that it sprays down into a graduated cylinder or small beaker.
2/ 3 of the Jags had P+H injectors so I made a timer circuit to open the injector hard, then flip to hold for 5 seconds. Fill the PVC cyl. 1/2 full with gasoline, cycle the timer and note the amount in the graduated cylinder and also watch the spray pattern. Compare with the other injectors.

Another way is to add a pressure gauge to the fuel rail and put the key in run without starting the car to keep the FP running. Build or buy a short duration timer (or pulser) and pulse an injector. Note the before and after pressures on the gauge and compare with the other injectors.
 

mrphoenix80

Member
Jan 1, 2013
251
jaguarjoe said:
Another way is to add a pressure gauge to the fuel rail and put the key in run without starting the car to keep the FP running. Build or buy a short duration timer (or pulser) and pulse an injector. Note the before and after pressures on the gauge and compare with the other injectors.

Poor mans AFIT. That is exactly what it does. YOu will need a timer that pulses the injector for you, because the difference in your timing will give you scewed results. There is a harness connector at the top of the engine that has all the wiring in it for the injectors. So you should be able to test it from there.
 

jd8181

Member
Jan 8, 2012
22
Maybe use a temp gun and check the manifold and see if there is any big tempature differences.
 

CaptainXL

Member
Dec 4, 2011
2,445
jd8181 said:
Maybe use a temp gun and check the manifold and see if there is any big tempature differences.

That's exactly what you should do for a quick test. Bruno and Matt do this on the tv show Trucks. They use a laser gun and fire it at the each runner to see if there is any difference.
 

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