I'm looking for some ideas on how to build an injector test harness. I want one to cycle the injector for cleaning. Right now the only thing that I have thought up is an injector lead wired to a switch that is wired to a 12 volt source. But I don't know whether it is safe to leave the injector in the open position for say 5 seconds to shoot cleaner through it, or will that ruin the injector to stay open that long?

Any other ideas, pictures, or things not to do would be helpful. Thanks.

 

That would equate to 100% duty cycle with no limit to how much current is passed through the injectors and that is genarally a great way to burn out the solenoids.. so the answer is no don't do that. What you need is an electronic injector driver like the LM1949 but as mentioned in the text you also need the external driver transistors, 5v and 12v power supplies, and of course an appropriate input signal source(square wave) that mimics the pulse rate the injectors would see in an engine... ex 500hz would be acceptable.

LM1949 - Injector Drive Controller

 

Why not use your truck then you do not have to remove them.
Just disable the fuel pumps and fuel pressure regulator and idle the engine on injector cleaner.
Then run the cylinder balance test to see if they are all working the same.

That is how I do mine.

 

Thanks for the replies, looks like what I thought up is probably not the best thing to do, that is why I asked because I knew somebody would know something I don't. I don't think I am going to go the sophisticated route like Conanski offered, sounds expensive.

Subford, could you expand on how to run it on injector cleaner, and running the cylinder balance test. I have heard about that test but I'm under the impression that you have to have some sort of computer or scanner to do it.

 

As for the Injector cleaner I have two ways I do it.

First you have to disable the fuel pumps so you do not get any fuel to the engine while cleaning the Injectors. You can pull the fuel pump fuse or trip the Fuel shut off switch in the passengers kick panel.

Then you have to remove the vacuum line from the fuel pressure regulator so no Injector cleaner goes back to the fuel tank. With the vacuum line unhooked and plugged the cleaner pressure would have to go above 40-45 PSI to go back to the fuel tank with the engine running.

You have to do the above two items with either type of cleaner tool.

I have a tool that you can screw the 3M Injector cleaner into and the tool has a regulator and a gauge on it and you hook it up to the fuel rail and adjust the pressure to about 38 PSI and start the engine and run it until it dies (out of cleaner).

My other tool has a container on it you poor the injector cleaner into and you hook it to shop air and adjust the air to about 38 PSI and you hook it to the fuel rail also.
Then start the engine and run it until it dies (out of cleaner).
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As for the cylinder balance test with an SFI engine like yours you need no special computer or scanner to run it.
Just ground the STI wire with the engine running and after the KOER test ends you entered the test by depressing and releasing the throttle within two minutes after the Engine Running Self-Test stops out putting codes.

Cylinder Balance DTM - SFI Engines Only

The purpose of the cylinder balance test is to assist the technician in finding a weak or non-contributing cylinder. The test is entered by depressing and releasing the throttle within two minutes after the Engine Running Self-Test DTCs have been output.

Once the test is entered, the IAC duty cycle is fixed and the engine is allowed to stabilize. Engine rpm is measured and stored for later use. Next, the fuel is shut off to one of the cylinders depending on the engine. After a brief stabilization period the engine rpm is again measured and stored. The injector is turned on again and the process is repeated for each of the injectors down to one. At this point, the maximum rpm drop that occurred is selected from the table of rpm drops for each cylinder. This maximum rpm drop is multiplied by a calibratable percentage. The resulting number (rpm) is used as the minimum rpm that each cylinder must have dropped to pass this test.

Example: 150 rpm x 65% = 98 rpm

If all cylinders drop at least this amount, then a code 90 is output indicating a pass. No further testing is necessary. If a cylinder did not drop at least this amount, then the cylinder number would be output. For example, 30 for cylinder number 3. This indicates that cylinder number 3 is either weak or non-contributing.

The test can be repeated a second time if the throttle is depressed and released within two minutes of the last code output. This time the maximum rpm drop that occurs is multiplied by a lower percentage. This number is used as the minimum rpm drop for each cylinder to pass this test.

Example: 150 rpm x 43% = 65 rpm

If all the rpm drops are greater than 65 rpm, then a code 90 is output. If cylinder number 3 had failed the first level and passed the second, then cylinder number 3 is considered to be weak. If cylinder number 3 failed again, the code 30 would be output again.

The test can be repeated a third time by depressing and releasing the throttle within two minutes of the last code output. This time the maximum rpm drop that results is multiplied by a still lower percentage. This number is used as the minimum rpm drop for each cylinder to pass this test.

Example: 150 rpm x 20% = 30 rpm

If all the rpm drops are greater than 30 rpm then a code 90 is output. If cylinder number 3 had failed the first and second level, but passed the third, then it is considered to be a very weak cylinder. If cylinder number 3 failed the third level, then a code 30 would again be output. In this case, cylinder number three would be considered a non-contributing cylinder.

The Cylinder Balance DTM may still be repeated as many times as desired by depressing and releasing the throttle within two minutes of the last code output. All further testing (i.e. 4th, 5th pass) will be done using the third level percentage.



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Thanks Subford, I think I am going to have to try that. A couple questions though. When depressing the throttle to enter the balance test, how far does it need to be depressed, all the way or half throttle? And when it spits out the codes for the weak cylinder how does it put out the 0 in 30, because without a code scanner or anything I just count engine light blinks and it can't blink a 0 so does it just blink 3 lights for number 3?

 

The 10, 20, 30, 40, ...........
is what a code reader will display.
You only see a single flash for a 10 and then nothing or a nine flashes and nothing for a 90.

Number of flashes per code.
* 1 - Number 1 Cylinder Low
* 2 - Number 2 Cylinder Low
* 3 - Number 3 Cylinder Low
* 4 - Number 4 Cylinder Low
* 5 - Number 5 Cylinder Low
* 6 - Number 6 Cylinder Low
* 7 - Number 7 Cylinder Low
* 8 - Number 8 Cylinder Low
* 9 - Passed Cylinder Balance Test


Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a
jumper wire or paper clip to put the computer into test mode. Start
the engine and let it go through the normal diagnostic tests, then
quickly press the throttle to the floor. The engine RPM should exceed
2500 RPM's for a brief second. The engine RPM's will increase to about
1450-1600 RPM and hold steady. The engine will shut off power to each
injector, one at a time. When it has sequenced through all 8 injectors,
it will flash 9 for everything OK, or the number of the failing cylinder
such as 2 for cylinder #2. Quickly pressing the throttle again up to
2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is
weak and isn’t putting out power like it should.

 

Alright, thanks a lot Subford.